MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 43 (2002), No. 12

  • Application of Vanadium-Free Titanium Alloys to Artificial Hip Joints

    pp. 2936-2942

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    DOI:10.2320/matertrans.43.2936

    The application of titanium and its alloys to surgical implants has created much interest recently. Ti–6Al–4V has been used for numerous applications that require high mechanical properties, however this alloy contains vanadium, which has been proven to be cytotoxic. Two types of vanadium-free titanium alloys were developed and applied to artificial hip joints. As for the cemented type, Ti–15Mo–5Zr–3Al alloy was adopted because of its high fatigue strength, and its low elastic modulus, which approaches bone elasticity. As for the non-cemented type, Ti–6Al–2Nb–1Ta–0.8Mo alloy was adopted because of its less decrease of fatigue strength through heat treatments up to 1270 K, which is necessary to create the porous surface to activate the reaction between the implant and the bone. In addition, new coatings and bioactive methods were applied to the newly developed non-cemented type of prostheses. These hip joints are now successfully being used with excellent clinical results.
  • Implant Applications of Highly Corrosion-Resistant Ti-15Zr-4Nb-4Ta Alloy

    pp. 2943-2948

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    DOI:10.2320/matertrans.43.2943

    The release of metal ions from the Ti–15Zr–4Nb–4Ta alloy in pseudo body fluids was compared with those from Ti–6Al–4V and vanadium-free Ti–6Al–7Nb alloys widely used as implantable titanium alloys throughout the world, in order to choose an optimum acceleration solution for immersion testing. Bone plates, artificial hip joints of the cementless type and artificial tooth implants were experimentally fabricated using the Ti–15Zr–4Nb–4Ta alloy. The quantities of titanium ions released from the titanium alloys into phosphate-buffered saline, α-medium and fetal bovine serum were very small, and much lower than those released into 1.2 mass% L-cysteine, 0.05 mass%HCl and 1 mass% lactic acid solutions with lower pH values than the phosphate-buffered saline and α-medium. It was suggested that 1 mass% lactic acid solution was promising as an acceleration solution for immersion test. The quantities of titanium ions released from the Ti–15Zr–4Nb–4Ta alloy into fetal bovine serum, 1.2 mass% L-cysteine, 0.05 mass%HCl and 1 mass% lactic acid solutions were approximately 30% of those of titanium ions released from the Ti–6Al–4V alloy. The total quantity of zirconium, niobium and tantalum ions released from the Ti–15Zr–4Nb–4Ta alloy was much smaller than that of elements released from the Ti–6Al–4V and Ti–6Al–7Nb alloys. Bone plates, artificial hip joints and artificial tooth implants were successfully fabricated with the Ti–15Zr–4Nb–4Ta alloy using conventional manufacturing processes. The Ti–15Zr–4Nb–4Ta alloy with its excellent corrosion resistance is expected to become the preferential titanium alloy for implant applications in the future.
  • Corrosion Fatigue Properties of Metallic Biomaterials in Eagle’s Medium

    pp. 2949-2955

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    DOI:10.2320/matertrans.43.2949

    The corrosion fatigue properties under sine wave loading in Eagle’s medium were compared among various metallic biomaterials: SUS-316L stainless steel, Co–Cr–Mo cast alloy and three types of vanadium-free titanium alloy, namely α+β type Ti–6Al–7Nb, Ti–6Al–2Nb–1Ta and a variety of newly developed Ti–15Zr–4Ta–4Nb alloys. The number of cycles to failure for the SUS-316L stainless steel and Co–Cr–Mo cast alloy increased as the maximum stress decreased. The fatigue strengths of the SUS-316L stainless steel and Co–Cr–Mo cast alloy at 1×108 cycles were much lower than those of the titanium alloys. The fatigue strengths of the vanadium-free Ti–6Al–7Nb and Ti–6Al–2Nb–1Ta alloys at 1×108 cycles were approximately 600 and 720 MPa, respectively. The fatigue strengths of the Ti–15Zr–4Nb–4Ta alloys annealed at 700°C for 2 h were about 700 MPa at 1×108 cycles, and were not significantly affected by varying the frequency from 2 to 10 Hz. Aging of the Ti–15Zr–4Nb–4Ta alloy containing 0.2%O and 0.05%N after solution treatment increased its ultimate tensile strength to 1150 MPa, and the total elongation and reduction in the area were 15 and 50%, respectively. The fatigue strength of the Ti–15Zr–4Ta–4Nb alloy treated in this way was 880 MPa under sine wave loading of 10 Hz at 1×108 cycles. This strength proved to be nearly identical to that estimated for the human hip joint, following an analysis of its movements and the forces acting upon it in vivo. The fatigue strength ratios at 1×108 cycles to ultimate tensile strength of the SUS-316L stainless steel and Co–Cr–Mo cast alloy were about 50%. The fatigue strength ratio at 1×108 cycles to ultimate tensile strength of the Ti–6Al–2Nb–1Ta alloy was high at 75%. In the case of the Ti–15Zr–4Nb–4Ta alloy annealed or aged after solution treatment, the fatigue strength ratio to ultimate tensile strength was about 75%. Many striations and cracks caused by fatigue were visible on the fatigue-fractured surfaces of the SUS-316L stainless steel and Co–Cr–Mo cast alloy. Micro-cracks in dimples were also apparent on the fatigue-fractured surface of the titanium alloys.
  • Phase Decomposition in a Ti-13Nb-13Zr Alloy during Aging at 600°C

    pp. 2956-2963

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    DOI:10.2320/matertrans.43.2956

    Phase decomposition in a Ti–13 mass%Nb–13 mass%Zr alloy during isothermal aging at 600°C has been investigated by means of transmission electron microscopy and Vickers hardness measurements. Specimens solution-treated at 1000°C in β phase field were quenched and aged at 600°C in (α+β) region. Beta phase was fully transformed into martensitic α laths by quenching from 1000°C. Formation of β phase on tempered α lath interfaces occurred during aging. Early in the stage of aging, β phase transformed into α′′ martensite completely by quenching. As increasing in aging time, athermal ω phase was formed in β phase by quenching. Beta phase was stabilized by prolonged aging. Enrichment of Nb content into β phase occurred with increasing in aging time, resulting in the formations of athermal ω phase and (α+β) two-phase structure. The hardness increased with the ω phase formation in β phase, followed by the decrease of hardness due to suppression of ω phase formation induced by enrichment of Nb in β phase.
  • Effect of Nb on Microstructural Characteristics of Ti-Nb-Ta-Zr Alloy for Biomedical Applications

    pp. 2964-2969

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    DOI:10.2320/matertrans.43.2964

    The effects of several commonly used heat treatment schemes on the microstructures of two Ti–Nb–Ta–Zr alloys aimed at biomedical applications were studied in this work using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specimens were water quenched from 790°C and then aged at temperatures between 300°C and 600°C. The experimental results showed that α and ω phase precipitated from the metastable β matrix in Ti–29Nb–13Ta–4.6Zr alloy during isothermal ageing. But for Ti–39Nb–13Ta–4.6Zr, the precipitation reaction was more sluggish than that in Ti–29Nb–13Ta–4.6Zr because of high amount of β stabilizing elements in the former alloy. As a result the α phase was unable to precipitate during short time ageing treatment. After longer time (12 days) ageing treatment at 500°C or 400°C, recognizable α precipitates were observed in the aged samples. It is concluded that Ti–29Nb–13Ta–4.6Zr can be heat treated to obtain different microstructures and is better than Ti–39Nb–13Ta–4.6Zr in terms of age hardenability.
  • Development of Low Rigidity β-type Titanium Alloy for Biomedical Applications

    pp. 2970-2977

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    DOI:10.2320/matertrans.43.2970

    The low rigidity type titanium alloy, Ti–29Nb–13Ta–4.6Zr was designed, and then the practical level ingot of the alloy was successfully fabricated by Levicast method. The mechanical and biological compatibilities of the alloys were investigated in this study. The following results were obtained. The mechanical performance of tensile properties and fatigue strength of the alloy are equal to or greater than those of conventional biomedical Ti–6Al–4V ELI . Young’s modulus of the alloy is much lower than that of Ti–6Al–4V ELI, and increases with the precipitation of α phase or ω phase in the β matrix phase. The compatibility of the alloy with bone of the alloy is excellent. Low rigidity of the alloy is effective to enhance the healing of bone fracture and remodeling of bone. The bioactive coating layer of hydroxyapatite can be formed on the alloy.
  • Effect of Heat Treatment and Sn Content on Superelasticity in Biocompatible TiNbSn Alloys

    pp. 2978-2983

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    DOI:10.2320/matertrans.43.2978

    Martensitic transformation and tensile properties of 4 to 5 mol%Sn-doped Ti–16 mol%Nb alloys consisting of biocompatible elements were investigated to provide superelasticity for biomedical applications as a function of heat treatment and Sn content. Martensitic transformation (bcc to orthorhombic structure) is accelerated at such quenching conditions that the bcc parent phase is slightly decomposed. Martensitic transformation temperature decreases rapidly with increasing Sn content. In-situ optical microscopic observation on cooling and heating indicates that the martensite is thermoelastic, corresponding to small temperature hysteresis between the martensitic and the reverse transformations, which is determined by differential scanning calorimetry. By controlling the heat treatment condition and Sn content, large superelastic strain is obtained at room temperature.
  • The Effect of Ta Content on Phase Constitution and Aging Behavior of Ti-Ta Binary Alloys

    pp. 2984-2990

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    DOI:10.2320/matertrans.43.2984

    Using Ti–Ta alloy to which Ta was added systematically, i.e. Ti–5 mass%Ta, 10 mass%Ta, 20 mass%Ta, 30 mass%Ta, 40 mass%Ta and 50 mass%Ta alloys, the effect of Ta concentration on phase constitution in the solution treated and quenched state and aging behavior is studied by electrical resistivity and Vickers hardness measurements and X-ray diffactometry. All alloys were solution treated at 1173 K for 3.6 ks and then quenched into ice water (STQ). STQed specimens were isochronally heat treated from 323 to 1173 K . STQed specimens of Ti–50 mass%Ta alloy were isothermally aging at five different temperatures, 573 K, 623 K, 673 K, 723 K and 773 K. In the solution treated and quenched state, only reflections of hexagonal martensite, α were obserevd by XRD in Ti–5Ta to 30Ta alloys, whereas only orthorhombic martensite, α′′, was identified by XRD in Ti–40Ta and 50Ta alloys. α′′ in Ti–50Ta alloy is reversely transformed into β upon isochronal heat treatment: the starting temperature is situated at a temperature between 623 K and 673 K . Isothermal aging of this alloy shows that α′′ directly decomposes to α and β phases without reverse transformation of α′′ at 573 K and 623 K aging. On isothermal aging above 673 K, α′′ reversely transforms into β and then isothermal ω phase precipitates in the reversed β.
  • In Vitro Biocompatibility Studies of Fibroblast Cells on Ti-Ta Alloys

    pp. 2991-2994

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    DOI:10.2320/matertrans.43.2991

    Medical science has enabled the substitution and reinforcement of body organs and tissue through the evolution of better materials. Metallic implants have been utilized to aid in injury wound healing as bone replacements, endoprosthesis, and percutaneous devices. Of concern with metallic devices is the prolonged effects and service life of the implant. It is known that metallic dissolution and premature failure can occur in the body leading to complications for the host. In an effort to provide more corrosion resistant materials with adequate strength for better resistance against high cycle fatigue, Ti–Ta alloys are presented to compete with current, popular materials such as Ti6Al4V . This research focuses on the binary alloy systems of Ti40Ta and Ti50Ta alloys for implant consideration. Three heat-treated versions of the Ti–Ta system that demonstrated high strength properties were also assessed. Cell culture testing of NIH-3T3 fibroblast cells was conducted to perform biocompatibility testing on these metal substrates. MTT cytotoxicity assays were performed to evaluate cellular behavior on the metal substrates. Flow cytometry assays were conducted to analyze rates of cell growth and cycling to determine best surface conditions among these metals. Results indicate very similar cellular activity on the Ti alloys and to a lesser degree on the commercially pure titanium and tantalum. Flow cytometry tests showed similar cellular growth rates on the different materials and on the control plastic. MTT assays indicate a higher degree of proliferation on the Ti–Ta alloys and on the Ti6Al4V . Although the Ti and Ta elemental materials supported slightly fewer cells on their surface, differences were minimal. Ti–Ta alloys appear to be comparable if not slightly more compatible than the standard Ti6Al4V.
  • Tensile Property, Corrosion Resistance and Cytocompatibility of Tungsten Short Fiber Reinforced Ti-6Al-4V Alloy

    pp. 2995-2999

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    DOI:10.2320/matertrans.43.2995

    Tungsten short fiber reinforced Ti–6Al–4V alloy has been investigated in terms of its tensile properties, corrosion resistance and cytocompatibility. This composite material was fabricated by a hot isostatic pressing process. The room temperature tensile strength and the 0.2% proof stress were very high, approximately 1300 MPa and 1200 MPa, respectively. These strengths are excellent compared to those of the existing biomaterial of titanium-base. The cytocompatibility of this composite material was evaluated using the anodic polarization test and the cytocompatibility test to clarify the possibility of its application as a structural biomaterial. Anodic polarization tests in Eagle’s minimum essential medium and in 1 mass% lactic acid were carried out to investigate the corrosion resistance of the composite material in vivo. The current density at the entrance to the passive region of the composite material tended to increase more than that of Ti–6Al–4V alloy. However, the passive region was retained at a potential of about 2 V, which is sufficiently high compared to the potential in vivo. In addition, the cytocompatibility was evaluated by investigating the relative growth ratio of fibroblast L929 cells after four days incubation on the test material. The relative growth ratio is obtained as follows: number of cells on the test material/number of cells on the reference material (control). The relative growth ratio of the composite material in making Ti–6Al–4V alloy into a control was 0.9032. According to the result of ICP-MS analysis, the concentration of tungsten in the medium after four days of incubation on the composite material was high compared to that of titanium, aluminum and vanadium.
  • Surface Oxide Films on Titanium Alloys Regenerated in Hanks’ Solution

    pp. 3000-3004

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    DOI:10.2320/matertrans.43.3000

    Titanium and some of its alloys are successfully used for biomaterials. The surface oxide films on these materials play important roles in maintaining corrosion resistance and biocompatibility. In this study, Ti–6Al–4V, Ti–56Ni, and Ti–xZr (x=0, 25, 50, 60, 75, 100) alloys in mass% were abraded and kept for 300 s in water and Hanks’ solution. The regenerated surface oxide film in Hanks’ solution was characterized using X-ray photoelectron spectroscopy. As a result, phosphate ions were preferentially taken up in the surface oxide film during regeneration. Ions constituting Hanks’ solution other than calcium and phosphate were absent from the surface oxide film. In the case of titanium and Ti–6Al–4V, calcium phosphate was formed on/in the surface oxide film regenerated in Hanks’ solution. However, Ti–56Ni, Ti–Zr, and zirconium did not form calcium phosphate on themselves but formed phosphate without calcium. These results are in good agreement with those for titanium alloys immersed in Hanks’ solution.
  • Surface Modification of Titanium Utilizing a Repassivation Reaction in Aqueous Solutions

    pp. 3005-3009

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    DOI:10.2320/matertrans.43.3005

    The surface modification of titanium utilizing repassivation reaction was attempted. The original surface oxide film on titanium plates were mechanically removed under immersion in water and Hanks’ solutions with pH 5.0 and 7.4 followed by repassivation or regeneration of surface oxide film in the same solutions. Then the surface-modified titanium plates were immersed in Hanks’ solution (pH 7.4) up to 604.8 ks. Their surface was analyzed with scanning electron microscopy with energy dispesive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffractometry, and the mass gain was measured using a microbalance, to confirm the performance of the modification. It was found that more calcium phosphate was precipitated on specimens modified in Hanks’ solutions in comparison with that in water. Calcium and phosphate ions contained in the surface oxides modified in Hanks’ solutions had effect for the titanium surface to adsorb more calcium and phosphate ions than specimens repassivated in water. In addition, more calcium phosphate was precipitated on titanium modified in pH 5.0 solution than that in pH 7.4 solution because more H2PO4 and/or HPO42− ions exist in the surface oxide regenerated in pH 5.0 Hanks’ solution than in pH 7.4 Hanks’ solution. It is suggested that a solution with proper pH and ion concentration for the modification should give higher efficiency for the modification of titanium surface.
  • Evaluation of the Hydroxyapatite Film Coating on Titanium Cathode by QCM

    pp. 3010-3014

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    DOI:10.2320/matertrans.43.3010

    A titanium substrate was coated with a hydroxyapatite (HA) film under a cathodic potential in aqueous solutions containing calcium and phosphate ions and hydrogen peroxide at pH 5.5 and a temperature of 309.5 K . The deposition process was monitored using the current density change, and the mass change was measured using the electrochemical quartz crystal microbalance (QCM) technique at cathodic potentials, and compared with deposition on a gold substrate. The deposits were analyzed using X-ray diffraction and scanning electron microscopy. HA films were obtained at different cathodic potentials, and the film morphology changed with the potential. With electrolysis at −557 mV, HA was deposited and accumulated after 800 s, when the mass gain increased significantly, as determined using QCM. After 800 s, the cathodic current increased and then decreased with HA growth. The HA film was porous, with pores several hundred nanometers in size, and formed a network of aggregates with walls about 50 nm thick. The filling factor was about 59 vol%, as evaluated from the mass gain using QCM and microscopic observation.
  • Preparation of Calcium Phosphate Coatings on Titanium Using the Thermal Substrate Method and Their in vitro Evaluation

    pp. 3015-3019

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    DOI:10.2320/matertrans.43.3015

    Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) and dicalcium phosphate anhydrous (Ca(H2PO4)2, DCPA) were coated onto titanium substrates using the thermal substrate method in an aqueous solution containing calcium and phosphate ions at 150°C with pH values in the range 4–8. Specimens with the HAp and DCPA layer were immersed in a simulated body fluid (SBF) to examine the dissolution and induced HAp growth behaviour of the coated layers in the SBF . No precipitation occurred on the coated DCPA layer after 7 days immersion in the SBF, and also the DCPA did not dissolve in the SBF . On the other hand, a new precipitate, which was identified as HAp, nucleated after 1 day and grew in a spherical manner on soaking the HAp substrate specimens in the SBF . The influence of small quantities of DCPA in the HAp layer on the coating’s bioactive property in the SBF was negligible as the DCPA was not on the surface of the coated layer.
  • Effects of Magnesia Particle Addition on Mechanical and Bioactive Properties of Magnesia/Titanium Composite

    pp. 3020-3024

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    DOI:10.2320/matertrans.43.3020

    In order to develop new titanium matrix composite for surface-coating titanium used in biomedical field, magnesia particles were added into pure titanium through hot press sintering method. Samples fabricated at the temperature of 973 K and at the pressure of 55 MPa were used to investigate the effects of magnesia addition on the properties of the new composite. In the fabricated samples, uniform dispersion of magnesia particles in titanium matrix was successfully obtained and no reaction layer was observed at interface between magnesia particles and titanium matrix. The volume fraction (Vf) and the size of magnesia particles mainly influenced tensile strength of the samples. When the size of magnesia particles was in the range of 25–90 \\micron, tensile strength of the composite was increased with increase of Vf till 5%. With respect to biocompatible property, the results of simulated body fluid immersion test showed that an apatite surface layer was formed on the fabricated magnesia/titanium composite samples, which would be benefit to bonding of the material to surrounding bone when it would be implanted into human body.
  • Titanium Coating of Scaffold Carbon Foam by ECR Sputtering

    pp. 3025-3027

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    DOI:10.2320/matertrans.43.3025

    Titanium films, of 5 \\micron in thickness were deposited uniformly on three-dimensional structures of scaffold carbon foam substrates using a hybrid electron cyclotron resonance-direct current (ECR-DC) sputtering system. A cylindrical hollow cathode with internal diameter of 80 mm and external diameter of 90 mm and length of 60 mm, negatively biased, was used as titanium atoms supplier. The DC sputtering voltage applied to the target controlled the feeding with excited titanium atoms. The Vickers micro-hardness of the films was found to be in the range of 250–300 HV. The film surfaces were smooth and showing pure titanium, preferentially grown on the Ti (100) crystallographic phase. Flexural strength and elastic modulus of the carbon foam were improved by a factor of 1.5 and 2.6 respectively.
  • First Principles Estimation of Bulk Modulus and Theoretical Strength of Titanium Alloys

    pp. 3028-3031

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    DOI:10.2320/matertrans.43.3028

    Titanium alloys are favorable implant materials for medical applications, due to their desirable mechanical properties and biochemical compatibility. However, current bio-titanium alloys were formulated principally by trial and error, which by no means represents the optimum. Here a theoretical investigation of the influence of alloying elements and interstitial elements on the bulk modulus and theoretical strength of α-titanium was presented. The bulk modulus and theoretical strength were estimated from the binding energy against the unit cell volume curves calculated by means of first principles discrete variational cluster method. The results of the calculation suggested that the 3d elements Cr, Mn, Fe, and Co, as well as all the interstitial elements considered in this study (H, B, C, N and O), are capable of enhancing the relative admissible strain of α-titanium.
  • Continuous Cruciate Ligament Measurement Using Surface Mounted Transducers

    pp. 3032-3035

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    DOI:10.2320/matertrans.43.3032

    Cruciate ligament and Achilles tendon graft elongation were studied using two methods of posterior cruciate ligament (PCL) reconstruction, a “Tibial Tunnel” and a “Tibial Inlay”. Under cyclic loading simulating an anterior drawer technique, elongations were recorded using an radially deflecting displacement transducer. The resulting periodic data was subjected to a Fourier analysis and comparisons between the anterior cruciate ligament and Achilles tendon graft elongations were examined for each surgical reconstruction. Spectral signatures revealed a more anatomic reconstruction resulted from the Tibial Inlay reconstruction as compared to the Tibial Tunnel reconstruction.
  • Three-Dimensional Surface Pattern and Chemical Composition of Mucosal Titanium Implant Compartments

    pp. 3036-3042

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    DOI:10.2320/matertrans.43.3036

    Surface topography and chemical composition of mucosal-implant interfaces is thougt to be critical to their clinical success. The aim of our study was to investigate the topography and chemical composition of titanium mucosal-implant interfaces using surface analytical techniques. The mucosal surface compartments of 10 different implant systems were utilized as a test area. The ultramorphological analysis were carried out using Confocal Laser Scanning Microscopy (CLSM), X-ray photoelectron spectroscopy (XPS), Metastable Induced Electron Spectroscopy (MIES), Scanning Electron Microscopy (SEM) and Scanning Force Microscopy (SFM). The surfaces of samples showed different fracturing of metal chips and pitting attack. From the CLSM- and SEM analysis in comparison to the Developed Surface Area (DSA) as ratio of microroughnesses it appears that the diameter of the pits varied in the range of 0,1 to 10 \\micron. MIES showed the presence of Ti, O and C . Several peaks pertaining to titanium and oxygen can be found. The Ti-surface is covered by a 3–5 nm thick TiO2 layer. Only titanium in the oxidic, not in the metallic state is found within the observation depth of 1 nm. We find clear evidence from MIES that saturated hydrocarbon chains form the outermost molecular layer. Virtually no signal from TiO2 is found at the very surface. The results suggest a two-layer structure for the passive film formed on titanium after exposition to the sulcus crevicular fluid. The inner layer has a structure close to TiO2, while the outlayer is dominated by CH2-groups with a few –C=O groups inside the hydrocarbon overlayer. The granular structure observed on mucosal-implant surfaces seems to indicate that the dissolution occurs at localized defects in the passive film influencing the barrier function of implanto-gingival tissues. This was confirmed by the DSA as a hybrid parameter including both spatial and amplitude aspects of the surfaces.
  • Mechanical Properties of Surface Nitrided Titanium for Abrasion Resistant Implant Materials

    pp. 3043-3051

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    DOI:10.2320/matertrans.43.3043

    In order to verify its application for abrasion-resistant implant materials such as abutment in dental implants and artificial joints, mechanical properties of surface nitrided titanium were evaluated by three different tests, the Vickers hardness test, Martens scratch test and ultrasonic scaler abrasion test. The Vickers hardness of a nitrided layer of 2 \\micron in the thickness was 1300, about ten times higher than that of pure titanium. The Martens scratch test showed high bonding strength for the nitrided layer with matrix titanium. The abrasion test using an ultrasonic scaler showed very small scratch depth and width, demonstrating extremely high abrasion resistance. The results show that a surface-nitrided titanium has sufficient abrasion resistance if it is used under clinical conditions.
  • Effects of Particle Size on Cell Function and Morphology in Titanium and Nickel

    pp. 3052-3057

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    DOI:10.2320/matertrans.43.3052

    The dependence of cytotoxicity on particles size in titanium (Ti) and nickel (Ni) was investigated by biochemical functional analysis and by microscopic observation of cellular morphology, in vitro using human neutrophils as probes and in vivo in animal implantation test. The biochemical analyses of cell survival rate, LDH, superoxide anion, cytokines of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and observation by scanning electron microscopy (SEM) showed that Ti fine particles (2 \\micron) stimulate neutrophils and increases the quantity of released superoxide anions, whereas Ni particles deform or disrupt the cell membrane of neutrophils. The 2 \\micron Ti particles, smaller than neutrophils of about 5–10 \\micron, were phagocytized by cells in vivo and the results were similar in vitro, which lead to the remarkable release of TNF-α. These results showed that there is the size-dependent cytotoxic effect in Ti fine particles and the effect is the most pronounced when they are smaller than cells. On the other hand, Ni particles caused the disruption of neutrophils in vitro and necrosis of tissue in vivo mainly through ions produced by their dissolution.
  • A Method to Monitor Corrosion of Chromium-iron Alloys by Monitoring the Chromium Ion Concentration in Urine

    pp. 3058-3064

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    DOI:10.2320/matertrans.43.3058

    Binary alloys of chromium-iron (Cr–Fe) are no longer used in dental and orthopaedic applications, and were used only for comparative purposes in the present study. Four kinds of Cr–Fe binary alloys, namely, 10 mass%, 15 mass%, 20 mass% and 30 mass%Cr in Fe, and 100%Cr and SUS316L were prepared. These metals were subcutaneously implanted into rats for four months. There was no significant difference in body weights and organ weights among control (sham-operation) and implant-groups, and no significant accumulation of Cr and Fe in the blood, liver or kidney of the alloy implant groups. To clarify the usefulness of urinary monitoring, the Cr and Fe concentrations in rat urine after implantation were analyzed. Alloy implant groups, including the SUS316L group, intended to excrete higher urinary Cr amounts than the control group during the 3 weeks after implantation. Urinary Cr and Fe amounts of the 15%Cr-alloy group showed especially high values in comparison not only with the control level but also the other alloy groups. The visual corrosion extents of the retrieved implants showed the following order: 10%Cr>15%Cr>20%Cr>30%Cr>100%Cr, SUS316L, and did not always correlate with the levels of the urinary amounts of Cr and Fe. From these findings, monitoring of urinary metal amounts is considered to be useful to monitor the in vivo elution property non-invasively.
  • Tissue Reactions and Sensitivity to Iron-Chromium Alloys

    pp. 3065-3071

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    DOI:10.2320/matertrans.43.3065

    The aim of the study is to see whether corrosion of metallic implants in a living body is related to metal sensitivity reactions. As model materials, we prepared iron (Fe)-chromium (Cr) binary alloys containing various amounts of Cr, having different corrosion resistance. As a comparison, 316L type stainless steel (SUS316L) was used. These specimens were subcutaneously implanted into rats, and the tissue reactions around the implants and the sensitivity to Cr were evaluated by histological examination, patch testing and lymphocyte proliferation tests. After 4 months implantation, there was rust on the surface of all 10%Cr–Fe alloys, three 15%Cr–Fe alloys and one 20%Cr–Fe alloys out of 4 specimens per each group. There were no significant toxicological sign in any of the animals. Tissue responses, such as extent of hemorrhage and frequency of inflammatory cells in or around the fibrous capsule, were scored and the sum total score was determined. With regard to total score of tissue response, no significant difference was found among the groups. Concerning the thickness of fibrous capsule, 10% and 20%Cr–Fe alloy group was somewhat higher than other Cr–Fe alloys and SUS316L, but there was not significant difference. In the histological examination of tissue responses, the sign of metal sensitivity could not be obtained. Although there was no significant difference in the lymphocyte proliferation activity by addition of potassium dichromate (K2Cr2O7)-solution among the implanted groups, two animals exhibited positive skin reactions by topical challenge with K2Cr2O7 in 10%Cr–Fe alloy-implanted group. In 15% and 20%Cr–Fe alloy groups, each one showed a skin response. The skin reaction observed was mainly edema that is characteristic of metal allergy. This suggests that some animals were sensitized to Cr by the implantation of easily corroded Cr–Fe alloy, and the corrosion products of metallic devices in body fluid is likely responsible for development of metal hypersensitivity.
  • Effects of Heat Treatment Conditions on the Mechanical Properties of Orthodontic Stainless Steel Wires

    pp. 3072-3077

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    DOI:10.2320/matertrans.43.3072

    The purpose of this study was to evaluate mechanical properties of the orthodontic wires according to heat treatment environments and cooling methods. Four types of wires were heat-treated in air, argon and vacuum at 500°C, for 6 min, and were then either cooled in the furnace or a water bath. Increases in microhardness, maximal strength, yield strength and Young’s modulus of the orthodontic wires after heat treatment were approximately 0.4–22.9%, 2.9–14.8%, 3.7–14.4% and 2.5–9.0%, respectively. This was considered to be because of mainly precipitation hardening and additionally subgrain formation by the heat treatment. Yield strength and microhardness of the heat-treated wires were also significantly dependent upon the cooling methods. The microhardness and yield strength of the water-cooled wires were lower than those of the furnace cooled wires. This was attributed to the precipitation degree of chromium carbides dependent on cooling rate. Heat treatment in an air oxidized the surface of the wires, and the mechanical properties and surface cleanness of the water-cooled wires were poorer than those of the furnace-cooled wires. Conclusively, orthodontic wires should be heat-treated in vacuum conditions or an inert gas environment after plastic deformation and should be cooled in a furnace in order to inhibit surface oxidation, maximize corrosion resistance and improve the mechanical properties.
  • Corrosion of Orthodontic Wires According to Heat Treatment Conditions

    pp. 3078-3082

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    DOI:10.2320/matertrans.43.3078

    Heat treatments are applied to orthodontic wires in order to relieve the stresses arising during orthodontic work. Four types of wires were heated in air, argon or vacuum environments, and cooled in the furnace or in a water bath. The susceptibility to corrosion and mechanical properties of the heat-treated wires were investigated. Heat treatment marginally increased the yield strength and elastic modulus of all wires. After heat treatment in air, both water- and furnace-cooled wires had similar low corrosion resistances. Corrosion resistances of wires heated under vacuum differed significantly according to cooling methods, such that furnace-cooled wires had higher corrosion resistances than water-cooled wires. Water-cooled wires consistently showed low corrosion resistance whether heated in vacuum, argon, or air environments. After heat treatment under vacuum, furnace-cooled wires had low current densities and high pitting potentials similar to control wires, but other heat-treated wires generally exhibited high current densities and low pitting potentials. Wires heat-treated under vacuum or argon and then cooled in the furnace were the least susceptible to surface oxidation and corrosion, and showed a marginal improvement in mechanical properties. Therefore, we conclude that wires treated in these way can reduce metal ion release and wire fracture, which can minimize adverse effects arising from orthodontic practices.
  • Microstructure and Tensile Strength of Stainless Steel Wires Micro Spot Melted by YAG Laser

    pp. 3083-3087

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    DOI:10.2320/matertrans.43.3083

    SUS304 stainless steel wire was micro spot melted by using YAG laser to investigate the applicabilty to the fabrication of biomedical devices. Effects of laser conditions such as laser power input or pulse duration were investigated on the microstructure and tensile strength of spot melted wires. Width of the melted metal decreased by laser irradiation with a shorter pulse duration and was about 0.3 mm for the 0.35 mm diameter wires. On the contrary, laser spot melting with a shorter pulse duration needed more precise control of laser conditions to achieve the sound melting free from burn out of the samples. Similarly, melting of thinner wire needed more precise control of laser conditions. Melted metal exhibited a rapidly quenched austenite cell microstructure with a cell size of less than about 5 \\micron. Tensile strength of the spot melted wires was 660 MPa, which was almost the same as that of annealed base materials. Besides, corrosion resistance in a quasi biological environment was hardly degraded by spot melting. Crosswise joints was also successfully prepared by laser spot welding of wires, suggesting the laser micro welding is applicable to the fabrication of biomedical devices.
  • XPS Characterization of the Surface Oxide Film of 316L Stainless Steel Samples that were Located in Quasi-Biological Environments

    pp. 3088-3092

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    DOI:10.2320/matertrans.43.3088

    The purpose of this study was to characterize the surface oxide films on 316L austenitic stainless steel located in various environments to estimate the reconstruction of the film in human body. Five kinds of specimens were prepared according to the following methods: polished in deionized water, autoclaved, immersed in Hanks’ solution, immersed in cell culture medium, and incubated with cultured cells. X-ray photoelectron spectroscopy (XPS) was performed to estimate the compositions of the surface oxide film and substrate and the thickness of the film. Surface oxide film on 316L steel after polished in water consists of iron and chromium oxides containing small amount of nickel, molybdenum, and manganese oxides. The surface oxide contained a large amount of OH. Calcium phosphate was formed on/in the film after immersion in the Hanks’ solution and medium and incubated with the cells. Sulfate is adsorbed by the surface oxide film and reduced to sulfite and/or sulfate in cell culture medium and with culturing cells. The results in this study suggest that nickel and manganese are depleted in the oxide film and the surface oxide changes into iron and chromium oxides containing a small amount of molybdenum oxide in human body.
  • Characterization of the Surface Oxide Film of Nickel-free Austenitic Stainless Steel Located in Simulated Body Environments

    pp. 3093-3099

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    DOI:10.2320/matertrans.43.3093

    The surface oxide film on the nickel-free austenitic stainless steel located in various environments was characterized to estimate the reconstruction of the film in the human body. The specimens were polished, autoclaved, immersed in Hanks’ solution, immersed in Eagle’s minimum essential medium containing fetal bovine serum, and incubated with cultured cells. X-ray photoelectron spectroscopy was performed to determine the composition of the surface oxide film and substrate and thickness of the film. The depth profiles of elements in the surface region were also characterized using Auger electron spectroscopy in combination with argon-ion-sputtering. The surface oxide film on the nickel-free austenitic stainless steel, Fe–24.0Cr–1.1Mo–5.1N (at%), polished mechanically in deionized water consists of oxidic species of iron, chromium, and molybdenum, thickness of the surface oxide was about 4 nm and contained a large amount of OH. Large amount of carbon, nitrogen, oxygen, and sulfur originating from amino acids and proteins were detected after immersion in the MEM+FBS and incubation with L929. Sulfur existed as sulfite or sulfide. Nitrogen as alloy component was enriched in the substrate just under the film. Calcium phosphate was formed on the film after immersion in the Hanks and MEM+FBS and incubation with L929.
  • Corrosion Behavior of Nickel-Free High Nitrogen Austenitic Stainless Steel in Simulated Biological Environments

    pp. 3100-3104

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    DOI:10.2320/matertrans.43.3100

    The corrosion resistance of the nickel-free high nitrogen austenitic stainless steel without manganese, Fe–23Cr–2Mo–1.5N (mass%) (HNS) as biomaterials, was evaluated by the polarization test in various electrolytes: 0.9%NaCl solution (saline), phosphate buffered saline (PBS(-)), Hanks’ solution (Hanks) and Eagle’s minimum essential medium (E-MEM). Conventional austenitic stainless steel, 316L, was also polarized for comparison. The both alloys were spontaneously passivated in all electrolytes. The HNS didn’t show pitting corrosion in the polarization range in all electrolytes although the 316L showed pitting corrosion. Passive current densities of the HNS in all electrolytes were lower than those of 316L . Therefore, the HNS shows higher passivity and resistance to pitting corrosion than 316L . The passive current density in Hanks of HNS was lower than that in saline, indicating that the protectiveness of surface oxide film increased with the existence of inorganic ions such as phosphate and calcium ions. On the other hand, the passive current density in E-MEM was higher than that in Hanks, but was lower than that in saline. Consequently, the HNS must show high corrosion resistance in vivo and be a promising biomaterials.
  • Change in Microstructure and Solubility Improvement of HAp Ceramics by Heat-Treatment in a Vacuum

    pp. 3105-3111

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    DOI:10.2320/matertrans.43.3105

    HAp and the related calcium phosphates have been of great interest as biological materials for regenerating hard tissues, but their solubility should be improved to fit the remodeling cycle of hard tissues in vivo before their practical use for bone grafts. Control of the grain size of hydroxyapatite (HAp) matrix and change in constituent phase of the surface layer were examined to improve the dissolution rate in HAp ceramics. Surface and boundary layers composed of calcium phosphate phases with high solubility were formed by annealing at 1350°C in a vacuum, and the apparent mass transfer coefficient in the initial stage of the solubility experiment remarkably increased in an acetate buffer solution at pH of 4.0. The soluble surface and boundary layers are composed of tetracalcium diphosphate monoxide (TTCP), α-tricalcium phosphates (α-TCP) and amorphous calcium oxide (CaO) with high solubility, and their formation mechanism was discussed. Refinement of the grain size of HAp matrix also contributed to a slight increase in the apparent solubility.
  • Polarization Behavior of Bulk Zr-Base Amorphous Alloy Immersed in Cell Culture Medium

    pp. 3112-3117

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    DOI:10.2320/matertrans.43.3112

    Effects of amino acids and proteins on polarization behavior of Zr-base amorphous alloy were examined using Hanks’ solution, minimum essential medium (MEM), and cell culture medium (MEM+FBS) consisting with MEM and fetal bovine serum (FBS), respectively. Amorphous powder consolidated Zr55Al10Ni10Cu15 alloy was cathodically and anodically polarized at the beginning of (after 1.8 ks) immersion and after a long-term (605 ks) immersion in each solution. Parameters on the anodic polarization curve; open-circuit potential (Eopen), polarization resistance (Rp), and pitting potential (Epit), were obtained for the examination of corrosion resistance. In the presence of amino acids and proteins, Rp and Epit increased, indicating that resistance to both general and pitting corrosion was raised with those biomolecules. Thus, the adsorbed biomolecules probably work as a diffusion barrier to molecules and ions such as dissolved oxygen and phosphate and chloride ions. During immersion, the surface oxide film grew, leading to the increase in Eopen, average Epit, and Rp although the parameters showed wide variance of deviation probably caused by the defects in alloy structure. The lowest values of Epit after the long-term immersion were not lower than those at the beginning of immersion, indicating that the sensitivity of defects to chloride ion was not enhanced during immersion. However, the pitting corrosion resistance decreased during immersion because the potential difference between Eopen and Epit decreased.
  • Fatigue Properties of Zr-Based Bulk Amorphous Alloy in Phosphate Buffered Saline Solution

    pp. 3118-3121

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    DOI:10.2320/matertrans.43.3118

    Plain fatigue properties of commercially available Zr-based bulk amorphous alloy (7.6Ni–12.3Cu–3.5Al–76.6Zr in mass%) in a phosphate buffered saline (PBS(−)) were studied and compared with those in air. Fatigue tests were carried out under load control using a sinusoidal waveform at a stress ratio of 0.1 at a frequency of 20 Hz in air or 2 Hz in PBS(−). There was no difference between S–N curve of plain fatigue in air and that in PBS(−). Fatigue limits were detected in both environments and their fatigue strengths at ten million cycles were approximately 150 MPa. The ratio of the fatigue strength to the ultimate tensile strength was 0.12. Fatigue fracture surface in PBS(−) was the same as that in air. Plain fatigue crack initiated at inner defects or impurity particles near the specimen surface except for the specimen in which the cracks were initiated at the square corner of the parallel gauge section.
  • Biocompatibility of Various Kinds of Polymer Microspheres Estimated from Their Effect on Gap Junctional Intercellular Communication of Fibroblasts

    pp. 3122-3127

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    DOI:10.2320/matertrans.43.3122

    Gap junctional intercellular communication is a function that plays an important role in maintaining cell and tissue homeostasis and in regulating cell growth, development and differentiation. Change in this function when contacting fibroblasts with various polymer microspheres was estimated using the fluorescence recovery after photobleaching (FRAP) assay system. When the cells were in contact on test dishes, the inhibition level increased as the diameters of polystyrene microspheres decreased, except for a microsphere with 0.5 \\micron diameter. The function was inclined to be recovered with the increase of the incubation time, while it was not recovered when the cells were cultured with pre-coated polystyrene microspheres. As well as inhibitory activities of the function, cytotoxicity potentials of tested microspheres depended on their diameter and their composition. These findings suggest that the size and the physico-chemical character of polymer microspheres, and how cells recognize them plays important roles in causing influences of the microspheres on both gap junctional intercellular communication and their cytotoxicity. Therefore, estimating the inhibitory effect of biomaterials on the gap junctional intercellular communication will provide valuable information about the biocompatibility of materials even in the form of particles.
  • Tumor-Promoting Activity of 48 kDa Molecular Mass Hyaluronic Acid

    pp. 3128-3130

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    DOI:10.2320/matertrans.43.3128

    Hyaluronic acid (HA), glycosaminoglycan, has long been implicated in malignant transformation and tumor-promoting activity. We found that 48 kDa molecular mass HA in vitro promotes tumor cell growth and tumorigenesis. The increase of cell growth rate in human hepatoma cells (HepG2 cells, cancer cells) and normal human dermal fibroblasts (NHDF cells, normal cells) treated with 48 kDa HA at 2×10−4 kg/L concentration were 110±0.9% and 103±0.5%, respectively. Colony formation activity of 4.8 kDa HA in cultured Balb/3T3 clone A3111 cells was higher than that of 48 kDa HA . However, transforming activity of HA was significantly showed in 48 kDa HA but not in 4.8 kDa HA . These findings suggest that 48 kDa HA has a tumor-promoting activity stronger than 4.8 kDa HA, because the former increase the cell growth of cancer cells than the latter. The increase of cell growth rate in HepG2 cells (cancer cells) and NHDF cells (normal cells) were compared among various molecular masses of HA.
  • Dental Titanium Casting Researches in China

    pp. 3131-3133

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    DOI:10.2320/matertrans.43.3131

    Titanium is an ideal material for use in prosthodontics because of its biocompatibility, corrosion resistance, and mechanical strength combined with its lightweight. Recently the use of titanium and titanium alloys for fixed restorations has increased substantially, mainly due to the improvement of techniques for the casting titanium and its alloys. This article reviewed the studies on titanium casting techniques in China. The rapid developments of the Chinese titanium industry make a good condition for doing researches on dental titanium castings. Now researches on dental titanium casting in China are very active and fast. In 1995 the first titanium casting machine was developed and worked well, by use of which titanium denture frameworks, titanium denture bases, titanium crowns and bridges and titanium-porcelain restorations could be made successfully. To expand the applications of titanium alloys as dental prosthodontic materials, TiZr alloy and TAMZ alloy for dental uses were also developed. Their physical and mechanical properties are better than pure titanium and their biocompatibilities are excellent. In order to solve problems of polishing and finishing of titanium castings, a series of surface treatment techniques and procedures were developed recently, including sandblasting, chemical dipping, mechanical polishing, chemical polishing, electrochemical polishing, and anodizing of titanium castings, which make the surface treatments of the titanium castings more easy and more efficient and have improved the surface qualities of the dental titanium castings.
  • Dental Casting Properties of Ti-15Zr-4Nb-4Ta Alloy

    pp. 3134-3141

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    DOI:10.2320/matertrans.43.3134

    The dental casting properties of the Ti–15Zr–4Nb–4Ta alloy were compared with those of commercial pure Ti grade 2 and Ti–6Al–V alloy. Ti–15Zr–4Nb–4Ta dental castings were also surface-coated by TiN ion plating. Metal plates for complete and partial dentures, crowns and bridges were experimentally fabricated using the Ti–15Zr–4Nb–4Ta alloy. The cast surface down to a depth of about 200 \\micron had a high-hardness layer due to the reaction with the dental investment. Also, there was no sharp increase in the current density caused by the breakdown of the passive film starting from the layer that reacted with the dental investment. The 0.2% proof strength, ultimate tensile strength, total elongation and Young’s modulus of the Ti–15Zr–4Nb–4Ta castings, which were chemically polished by acid treatment after sandblasting, were 761±33 MPa, 970±31 MPa, 6±4% and 90±2 GPa, respectively. The micro-Vickers hardness of the TiN coated-surface was 740. The effect of TiN surface coating on the mechanical properties of the Ti–15Zr–4Nb–4Ta castings was negligible. The Ti–15Zr–4Nb–4Ta alloy exhibited a lower release of metal ions into the artificial saliva and 1% lactic acid solution than the Ti–6Al–4V alloy, and the quantity of metal ions released was less than 20% of that of titanium ions released from the Ti–6Al–4V alloy. The quantities of the titanium, zirconium and niobium ions released from TiN-coated Ti–15Zr–4Nb–4Ta casting into the artificial saliva were smaller than those released from the Ti–15Zr–4Nb–4Ta casting that was only chemically polished. Metal plates for complete and partial dentures, crowns and bridges were successfully fabricated using the Ti–15Zr–4Nb–4Ta alloy. A TiN-coated partial denture was also successfully fabricated using this alloy. The Ti–15Zr–4Nb–4Ta alloy with its excellent corrosion resistance and mechanical properties is expected to be used for dental prostheses in the future.
  • Influences of Electrolyzing Voltage on Chromatics of Anodized Titanium Dentures

    pp. 3142-3145

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    DOI:10.2320/matertrans.43.3142

    The change of colors of anodized titanium and effects of applied electrolytic voltages on chromatics of anodized titanium were investigated. The titanium specimens were anodized in 0.5 mol/L sulfuric acid and 0.2 mol/L phosphate acid electrolyte by use of different voltages. The colors of anodized titanium were measured with a spectrophotometer, and then evaluated in the CIE1976Lab uniform color scale and Mussell notation. It is found that one given volt produces a specific color. The chromatic values expressed in Lab fluctuate widely in different voltage conditions. The hues in Mussell’s notations are distributed widely, which show as red, yellow, green and purple in its five basic colors and yellow-red, green-yellow, blue-green and purple-blue in its five in-between colors in the range of 5 to 80 V . Anodizing with 10 V and 45 V respectively, the titanium plates appear two brilliant goldish yellow colors, but the former color is on the reddish side slightly while the latter color shows greenish a little. The spectrums of the two colors are in the range of wavelengths of yellow to red. It can be concluded that the colors of the anodized titanium are dependent upon the applied voltages. The goldish yellow may be used to improve the esthetics of titanium dentures.
  • Galvanic Corrosion of Dental Amalgams in Contact with Titanium in Terms of Released Ions

    pp. 3146-3154

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    DOI:10.2320/matertrans.43.3146

    Galvanic corrosion between dental amalgams and titanium was examined in terms of released ions. The ions released from the dental amalgams in contact with titanium at surface area ratios of titanium/amalgam in a range of 1/10–10/1 were quantitatively analyzed after being immersed in 0.9 mass% sodium chloride solution at 310 K for 6.05×105 s. The potentials and the anodic polarization curves were also measured under the same conditions. Furthermore, the amalgam surfaces after immersion were analyzed using WDS . Each potential of the conventional amalgams was always lower than that of titanium, though each potential of the high-copper amalgam was reversed in the early stage of immersion and was also lower. When the surface area ratio did not increase to over 1/1, each total amount of ions released from the amalgams in contact with titanium was a little larger or smaller than that released from amalgams not in contact with titanium. However, tin and copper ions released from the conventional amalgams and the high-copper amalgam, respectively, increased greatly when the ratio grew to 10/1. Each amount of released ions with titanium, except mercury ions, was approximated by the equation Wwith=a×(Wwithout)b, where the coefficients “a” and “b” are constant and Wwith and Wwithout mean each amount of the released ions with and without titanium, respectively. The coefficient “b” probably relied on the surface area ratio and immersion time. When the ratio grew to 10/1, the amount of released ions with titanium, except mercury ions, could be shown by the equation Wwith=a×(Wwithout) at a=4.202–9.982. Since the contact with titanium seemed to drastically make the amount of mercury ions decrease, the mercury ions did not fit this equation. These results indicated a risk of galvanic corrosion between dental amalgams and titanium with a large surface area ratio.
  • Proliferation and Differentiation of Normal Human Osteoblasts on Dental Au-Ag-Pd Casting Alloy: Comparison with Cytotoxicity to Fibroblast L929 and V79 Cells

    pp. 3155-3159

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    DOI:10.2320/matertrans.43.3155

    Normal human osteoblast NHOst cells were cultured on the dental Au–Ag–Pd casting alloy using the micromass culture, and the proliferation and differentiation of NHOst cells were determined. 13Au–58Ag–21Pd which met JIS T 6106 and 10Au–62Ag–13Pd which did not meet JIS T 6106 were used in this experiment. 10Au–62Ag–13Pd contained Cu more than 13Au–58Ag–21Pd. The proliferation and differentiation of NHOst cells cultured on 10Au–62Ag–13Pd were significantly decreased more than those on 13Au–58Ag–21Pd, respectively. It was suggested that the content of Cu caused the difference in the proliferation and differentiation between NHOst cells cultured on 13Au–58Ag–21Pd and that on 10Au–62Ag–13Pd. Moreover, the cytotoxicity of the Au–Ag–Pd alloy was evaluated by the MEM elution assay and the colony assay using fibroblast L929 and V79 cells, in order to compare with the cytological effects of the alloy on NHOst cells. 13Au–58Ag–21Pd showed no cytotoxicity to L929 and V79 cells in the MEM elution assay and the colony assay. However, 10Au–62Ag–13Pd showed extremely weak cytotoxicity to L929 cells and weak cytotoxicity to V79 cells in the colony assay, though 10Au–62Ag–13Pd showed no cytotoxicity to L929 cells in the MEM elution assay. NHOst cells expressed the toxicity to the proliferation and differentiation on 10Au–62Ag–13Pd clearly. The in vitro toxicity test based on the proliferation and differentiation of NHOst cells was useful to evaluate the toxicity of medical materials.
  • Fatigue Properties of Cast Ag-Pd-Cu-Au-Zn Alloy for Dental Applications in the Relation with Casting Defects

    pp. 3160-3166

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    DOI:10.2320/matertrans.43.3160

    Ag–Pd–Cu–Au–Zn type alloys have been widely used as dental prosthetic materials. In general, the dental prosthetic products are fabricated by a dental casting method. The dental castings contain the casting defects such as micro shrinkages, pores, surface roughness, etc. Cyclic stress, that is, fatigue stress due to the mastification is applied to the dental prosthesis in the practical use. Therefore, the effects of the casting defects such as micro shrinkages, pores and surface roughness on the fatigue properties of the cast Ag–Pd–Cu–Au–Zn type alloy were investigated in the comparison with the fatigue properties of the drawn Ag–Pd–Cu–Au–Zn alloy in this study. Fatigue tests of Ag–Pd–Cu–Au–Zn alloy cast using a dental casting machine were carried out, and then the fatigue properties of the cast alloy were investigated in the relation with casting defects. The fatigue strength of the cast Ag–Pd–Cu–Au–Zn alloy is considerably smaller than that of the drawn Ag–Pd–Cu–Au–Zn alloy. The fatigue crack of the cast alloy initiates preferentially at the shrinkage near the specimen surface. The scatter of the fatigue strength of the cast alloy becomes to be small by relating the fatigue life with the maximum stress intensity factor calculated assuming the shrinkage that becomes to be a fatigue crack initiation site as a initial crack. This means that the size of the shrinkage affects the fatigue strength of this cast alloy strongly. The tolerant size of the shrinkage that satisfies the target value of the fatigue limit (230 MPa) of this cast alloy is calculated to be below 80 \\micron using the equation derived in this study, which describes the relationship between the maximum stress intensity factor and the number of the cycles to failure.
  • Thermal Conductivity of Intermetallic Compounds with Metallic Bonding

    pp. 3167-3176

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    DOI:10.2320/matertrans.43.3167

    Thermal conductivity is one of the key parameters required for high-temperature structural applications of metallic materials. In this overview, the thermal conductivity of intermetallic compounds are extensively described based mainly on our past works, since there had been less works in this research field. Emphasis is placed on the B2 and the L12 compounds with metallic bonding such as NiAl, Ni3Al, etc., which have been attracting attention for engineering applications at higher temperatures. The thermal conductivity data have been accumulated for the intermetallic compounds, and the phenomenological aspects are reviewed in detail as a function of alloy composition, constituent and temperature. The Wiedemann-Franz law is applicable to the intermetallic compounds, indicating that the carrier of thermal conduction is an electron rather than a phonon. The thermal conductivity of an intermetallic compound with the ordered crystal structure is characterized as an enhancement due to ordering with reference to the basic contribution of solid solution with the disordered crystal structure. It is demonstrated that the thermal conductivity of intermetallic compounds is reduced by the addition of a third element, and this subject is also covered.
  • Microstructure and Corrosion Resistance of HVOF Sprayed 316L Stainless Steel and Hastelloy C Coatings

    pp. 3177-3183

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    DOI:10.2320/matertrans.43.3177

    In order to develop dense corrosion resistant coatings by thermal spraying, 316L stainless steel and Hastelloy C alloy powders were sprayed by an HVOF thermal spraying apparatus onto a mild steel substrate. The microstructure, pore size distribution, composition and corrosion resistance of the obtained coatings were evaluated experimentally. Corrosion resistance in seawater was examined by monitoring the impedance and corrosion potential of samples immersed in artificial seawater at 300 K over a period of more than 3 months and also by polarization measurement. It was found that the stainless steel coatings composed mainly of plastically deformed particles and some splats that were molten at the impact. By increasing the combustion pressure, the porosity measured by a mercury porosimeter was reduced to below 1%. In comparison, Hastelloy C deposits sprayed under a standard condition were so dense that their porosity could not be measured by the porosimeter. The polarization curves and the results of impedance monitoring exemplified that the Hastelloy C coatings possess much superior corrosion resistance to the stainless steel coatings in seawater, which was attributed mainly to the higher density and better adhesion of the Ni-base alloy coatings.
  • Temperature and Strain Rate Dependence of Mechanical Properties and Square Shell Deep Drawability of Al-Mg Alloy Sheets in Warm Working Condition

    pp. 3184-3188

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    DOI:10.2320/matertrans.43.3184

    Uniaxial tensile tests and square shell deep drawing tests on 5000 series aluminum alloy sheets were carried out at temperatures ranging from room temperature (RT) to 300°C in order to investigate temperature and strain rate dependence of tensile properties and deep drawability. At these warm working temperatures, tensile strength (TS) decreases with the increase in testing temperature, and this decrease in TS becomes smaller at high strain rate. Elongation (El) is nearly constant in the range from RT to 100°C, but increases largely with the increase in temperature more than 100°C, and this increase in El becomes larger at low strain rate. This change in El mainly depends on local elongation (LEl). Limiting drawing ratio (LDR) of square shell deep drawing in high speed forming becomes slightly bigger than in low speed forming. The change in LDR is small in the temperature range from RT to 150°C. Above 150°C, the LDR value becomes larger, but it becomes smaller in high speed forming. The difference between the LDR value at elevated temperature and that at RT is designated as ΔLDR value, and this ΔLDR shows the effect of warm deep drawing. The correlation between ΔLDR and mechanical properties (TS, El, LEl) was investigated and the effective experimental equation was derived.
  • Analysis of Heavy Metals in a Tailing Impoundment of Abandoned Mn Mine by Using Two Sequential Extractions

    pp. 3189-3194

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    DOI:10.2320/matertrans.43.3189

    The tailing impoundment was investigated for vertical distribution of minerals by X-ray fluorescence analysis (XRF), powder X-ray diffraction (XRD), and two sequential extraction methods. It was found that Si, Mn, and Fe occupied over 80% in mass balance of XRF, and present as constituents of clay minerals, oxides, and pyrite, respectively. Therefore, the sampling site was regarded as chemically stable. Two sequential extraction methods were complementary to each other, therefore, the combination of two methods is useful for further analysis of sediments including variable minerals.
  • Production of High-Purity Indium and Gallium Metals by Vacuum Refining

    pp. 3195-3198

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    DOI:10.2320/matertrans.43.3195

    Vacuum refining experiments of indium and gallium metals have been performed. When indium metal of 99.97% purity was refined at 1273 K and 1.3×10−3 Pa for one hour, Pb and Bi were effectively removed from indium metal. After refining 99.9% Ga at 1373 K and 1.3×10−3 Pa for six hours, removal of Bi, Pb, Zn, Mg, Ca and Fe were confirmed. The difference of temperature between indium and gallium at which the recovery percentage was abruptly decreased was related to the difference of boiling temperatures of both metals at the pressure of 1.3×10−3 Pa. The vaporization rate of solvent metals obtained from experiments were compared with those calculated by Langmuir equation.
  • Cold-Rolled Zr50Cu30Ni10Al10 Bulk Amorphous Alloys with Tensile Plastic Elongation at Room Temperature

    pp. 3199-3205

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    DOI:10.2320/matertrans.43.3199

    Controlling the cold-rolled structure of the shear-band network in Zr50Cu30Ni10Al10 bulk amorphous alloys can enhance the tensile plastic deformability at room temperature Cold-rolling is useful for controlling the shear band network structure in bulk amorphous alloys. The cold-rolled structure in a bulk amorphous alloy is classified into two regions, the deformed shear-band region and non-deformed block region. Since the pre-deformed shear-band region moves more easily than the non-deformed region, the pre-deformed shear-band network movement is able to release applied tensile strain. Consequently, plastic tensile strain can be obtained in a cold-rolled bulk amorphous alloy by systematical movement of the shear-band network. In this study, we obtained a maximum tensile plastic strain of about 0.25% in 10% cold-rolled Zr50Cu30Ni10Al10 bulk amorphous alloy. The tensile fracture surface was composed of many step marks leading to the pre-introduced shear band movement.
  • Influence of Low Oxygen Contents and Alloy Refinement on the Glass Forming Ability of Zr52.5Cu17.9Ni14.6Al10Ti5

    pp. 3206-3210

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    DOI:10.2320/matertrans.43.3206

    The effect of additions of C, Si, Ca, Sc and La at levels of 0.1, 0.3 and 1.0 atomic percent on the glass forming ability of the alloy Zr52.5Cu17.9Ni14.6Al10Ti5 has been investigated by means of metallography, X-ray diffraction and oxygen analysis using wedge shaped castings. In the original alloy, a very marked influence of oxygen on the glass forming ability is observed even at low concentrations. Low amounts of additional elements were found to influence the glass forming ability significantly. Adding Sc to alloys containing 100–120 ppm oxygen increases the glass forming ability from 4.5 to 10 mm in terms of amorphous ingot thickness. These results were confirmed with additional samples, and best glass forming ability was found with additions of 0.03% to 0.06%Sc. The maximum amorphous thickness in the wedges as measured by metallography correlates within an accuracy of about 1 mm with that measured by X-ray diffraction over a wide range of modified alloys. A possible mechanism for the enhancement of glass formation through these dopants, and reasons for their effectiveness over only a limited concentration range, are discussed using results from differential scanning calorimetry and differential thermal analysis on a series of samples with different Sc concentrations.
  • Effect of the Third Elements on High Temperature Oxidation Resistance of TiAl3 Intermetallic Compounds

    pp. 3211-3216

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    DOI:10.2320/matertrans.43.3211

    The brittleness of TiAl3 is improved by the addition of third elements such as manganese, silver, chromium and so on. The effects of the third elements on oxidation resistance of TiAl3 have been investigated in the point of view of the microstructure and products of oxidation layer. The oxidation test was carried out at 1000°C for 25 h or 30 d in air. For the copper-substituted alloy, Ti(Al, Cu)3, the oxidation layer consisted of TiO2, whose microstructure was porous. Thus Ti(Al, Cu)3 showed very low oxidation resistance. While, for the manganese, silver, iron or chromium-substituted alloys, these oxidation layers consisted of only Al2O3. These alloys showed the oxidation resistance. It is not expected that the iron- or chromium-substituted alloys show the oxidation resistance of long duration, because oxygen atom was detected by EDS analysis in Al-depleted layer after the oxidation test for 30 d. In the oxidation test at 1000°C, the oxidation layer of the iron- or chromium-substituted alloys was constituted of α-Al2O3 and θ-Al2O3. On the other hand, that of the manganese- or silver-substituted alloys was constituted of only α-Al2O3 and their oxidation layer is dense. From these results, it was understood that the substitution elements would influence on the temperature of θ→α transformation. That is, Fe and Cr would solute to θ-Al2O3, and then θ→α transformation temperature would increase. While, Mn and Ag would scarcely solute to θ-Al2O3, and then θ→α transformation temperature would be almost the same as that of pure θ-Al2O3. In the oxidation test at 1000°C, the residence of θ-Al2O3 decides oxidation resistance of Ti(Al, X)3 materials. The choice of the substitution element promoting the transformation from θ-Al2O3 to α-Al2O3 during heating process is important for improving in the oxidation resistance.
  • Conductivity Mapping with Resolution of 140 nm in Diameter by Eddy Current Method Using Small Solenoid Coil

    pp. 3217-3221

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    DOI:10.2320/matertrans.43.3217

    We propose and investigate a conductivity microscope made possible by improving the eddy current method. The scanning eddy current method using a small probe with a small gap between the probe and sample surface was tried; it could make a map distinguishing fine regions with different electrical conductivity related to electron-defect scattering. A copper–aluminum cold-pressure-welded junction specimen was selected, because it is considered to be a good conductor of electrons and is a commonly used interconnection for large-scale integrated circuits. At the bimetallic joint interface, two stages of 300-nm-thick and 600-nm-thick poor-conductivity layers were detected. These poor-conductivity layers of aluminum are considered to include numerous defects and dislocations that were produced by large plastic flow during the welding process. This conductivity microscope can image a terrace layer of about 3.5 \\micron in width at the welded interface after the layer is annealed for one hour at 470 K, which is comparable to that in the case of scanning electron microscope. The electrical resistivity of this layer was indicated to be lower than that of the aluminum bulk by the estimation of the electrical resistivity. The layer is considered to be an α-copper solid solution one. This instrument is available to detect defects and solid solution.
  • Formation, Thermal Stability and Mechanical Properties of (Cu0.6Zr0.3Ti0.1)100-xMx (M=Fe, Co, Ni) Bulk Glassy Alloys

    pp. 3222-3226

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    DOI:10.2320/matertrans.43.3222

    New Cu-based bulk glassy alloys exhibiting a large supercooled liquid region and good mechanical properties were formed in Cu–Zr–Ti–M (M=Fe, Co or Ni) systems by copper mold casting. The maximum diameter for glass formation was up to 4 mm for the Cu–Zr–Ti–Ni alloys. The addition of Co or Ni element caused an extension of a supercooled liquid region (ΔTx=TxTg) from 38 K for Cu60Zr30Ti10 to 54 K for (Cu0.6Zr0.3Ti0.1)95Co5 and 60 K for (Cu0.6Zr0.3Ti0.1)95Ni5, accompanying the change in the crystallization mode from two stages to a single stage. The crystallization of the 5%Ni alloy occurs through the direct precipitation of a metastable (Cu, Ni)10(Zr, Ti)7 phase from the supercooled liquid. The compressive fracture strength (σc,f) and plastic strain (εp) are in the range of 1830 to 2030 MPa and 0.3 to 1.7%, respectively, for the 1 to 4%Fe alloys, 1900 to 1920 MPa and 1.0 to 1.2%, respectively, for the 1 to 5%Co alloys and 1900 to 1960 MPa and 0.6 to 1.9%, respectively, for the 1 to 6%Ni alloys. The best combination of σc,f and εp was 2030 MPa and 1.7%, respectively, for the 2.5%Fe alloy. These favorable properties of the Cu–Zr–Ti–M (M=Fe, Co or Ni) bulk glassy alloys are promising for future practical use as a high-strength engineering material.
  • Activity Measurement of the Constituents in Molten Sn-Mg-Zn Ternary Lead Free Solder Alloys by Mass Spectrometry

    pp. 3227-3233

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    DOI:10.2320/matertrans.43.3227

    Activities of the constituents in an alloy proposed for the Pb-free solder, Sn–Mg–Zn, were studied experimentally using a mass spectrometer. The ion current ratios of Mg to Zn were measured in the temperature range 700–800 K . From the experimental results and the assessed thermodynamic properties of molten Sn–Mg, Sn–Zn, and Mg–Zn binary alloys, the excess Gibbs free energy of liquid Sn–Mg–Zn ternary alloy was determined. Also, phase diagram of Sn–Mg–Zn ternary system was determined.
  • Aging Treatment Characteristics of Shear Strength in Micro Solder Bump

    pp. 3234-3238

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    DOI:10.2320/matertrans.43.3234

    The shear strength of the Cr/Cr–Cu/Cu UBM structure in both the high-melting solder bump and low-melting solder bump after aging were evaluated. SEM and TEM were examined in the intermetallic compounds and bump joint profiles at the interface between solder and UBM . The shear load concentrated on the bump was analyzed by finite element method. In 900-hour aging experiments, the maximum shear strength of Sn–97 mass%Pb and Sn–37 mass%Pb decreased by 25% and 20%, respectively. The growth of Cu6Sn5 and Cu3Sn was ascertained by the aging treatment. The crack path changes from the interior of a solder to the intermetallic compound interface was evaluated. Compared with the Cu–Sn IMC, the amount of Ni–Sn IMC was small. The Ni layer is considered as the diffusion barrier.
  • Preparation of N-type Silicon Carbide-Based Thermoelectric Materials by Spark Plasma Sintering

    pp. 3239-3241

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    DOI:10.2320/matertrans.43.3239

    The SiC/Si3N4 sintered materials were prepared by Spark Plasma Sintering at 2000°C. The crystal structure of sintered materials is cubic β-SiC type with relative density higher than 80%. All sintered materials show n-type conduction and the carrier concentration increases with increasing Si3N4 concentration. Seebeck coefficient α and electrical conductivity σ increased with increasing temperature indicating suitable for high temperature thermoelectric conversion. Thermoelectric properties are improved by addition of Si3N4 and the power factor α2σ takes a maximum value at SiC–7 mass%Si3N4.
  • Color and Tarnishing of CuMn15Zn15Al1 Alloy

    pp. 3242-3246

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    DOI:10.2320/matertrans.43.3242

    This paper reports the color and the tarnishing behavior of CuMn15Zn15Al1 alloy in a synthetic sweat medium quantitatively. German silver BZn15–20–0.3 was selected for comparison. The results indicated that CuMn15Zn15Al1 has a silvery color similar to BZn15–20–0.3 but the tarnishing resistance of CuMn15Zn15Al1 in sweat is not as good as that of BZn15–20–0.3. For CuMn15Zn15Al1, tarnishing in sweat results in the decrease of L values and increase of a values, when both L and a are parameters in the CIE system to express the color. In other words, the color gets darker and redder after the sweat test. The corrosion layers were analyzed by means of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The tarnishing products primarily consist of Cu2O, ZnO and Mn oxides. Some chlorides and hydroxides are detected on the outmost surface.
  • Photocatalytic Preparation of Cuprous Oxide Crystals Using a TiO2 Catalyst

    pp. 3247-3253

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    DOI:10.2320/matertrans.43.3247

    Reddish cuprous oxide crystals can be readily formed by irradiating an aqueous alkaline Cu(II) solution containing suitable complexing agents with UV or sunlight in the presence of a photocatalyst such as TiO2 or ZnO . Various factors, including the Cu(II) concentration, pH of the Cu(II) solution, amount of TiO2 catalyst, method used to agitate the test suspension, concentration of potassium sodium tartarate, and intensity of UV radiation, affecting cuprous oxide preparations were investigated. Concentrations of Cu(II) and potassium sodium tartarate have no significant effect on reaction rates, while pH, and amount of TiO2, play important roles in the reaction. The dispersion of TiO2 in Cu(II) solution is another important factor. Cu(II) reduction rate is not affected as far as the amount of reduced Cu(II) plotted against the cumulative intensity of UV radiation is concerned. It is necessary to stop the cuprous oxide formation before the complete reduction of Cu(II), since metallic copper is formed on cuprous oxide.
  • Effect of Cr Addition on Microstructure and Mechanical Properties in Nb-Si-Mo Base Multiphase Alloys

    pp. 3254-3261

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    DOI:10.2320/matertrans.43.3254

    The effects of Cr addition to Nb–22Si–5Mo alloy on phase equilibria, microstructures and mechanical properties are investigated by metallography, X-ray diffraction, scanning electron microscopy equipped with wavelength dispersive X-ray fluorescence spectroscopy and compression test at temperatures from room temperature to 1773 K . With increasing Cr content a duplex microstructure consisting of Nb5Si3 and Nbss (niobium solid solution) is changed to three-phase microstructure consisting of Nb5Si3, Nbss and NbCr2. Chromium addition does not change the volume fraction of constituent phases in the two-phase alloys, whereas it increases the volume fraction of NbCr2, C14 Laves phase, at the expense of mostly Nbss in the three-phase alloys. The ca axis ratio of α-Nb5Si3 phase increases with increasing (Cr+Mo) content. It is found that Cr alloying in Nbss increases the room temperature strength due to atomic size misfit and decreases high temperature strength due to accelerated diffusion. The existence of C14 Laves phase increases high temperature strength, but degrades room temperature deformability. High temperature strength is found to be sensitive to the volume fraction and crystal structure of constituent phases as well as microstructure.
  • Preparation and Fracture Behavior of Alumina Platelet Reinforced Alumina-Monazite Composites

    pp. 3262-3265

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    DOI:10.2320/matertrans.43.3262

    Fracture behaviors were investigated in the laminated alumina composite ceramics. To improve the mechanical properties of alumina ceramics, templated grain growth (TGG) technique of α-Al2O3 platelet and LaPO4 as a second phase were introduced. Textured samples were made by the lamination of green tapes through the tape-casting method, while random samples were made through the conventional powder processing method. Green compacts were sintered at 1600°C for 2 h in air. Fracture toughness was tested using indentation strength bending (ISB) method. Indentation on the sample surface was produced by Vickers indent at various loads. From the bending test, enhanced fracture toughness was found in the textured composite, compared to the random composite.
  • Deformation and Fracture Behaviors of Pd-Cu-Ni-P Glassy Alloys

    pp. 3266-3272

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    DOI:10.2320/matertrans.43.3266

    Thermal behavior and mechanical properties of Pd-based glassy alloys with compositions of Pd35+xCu30Ni15−xP20 (x=0, 5, 7.5 at%, group-I) and Pd40+xCu20Ni20−xP20 (x=0, 5, 10 at%, group-II) have been studied. Group-I alloys lie in an invariant eutectic reaction region of the quaternary system. The invariant eutectic reaction of L→Cu3Pd+Ni2Pd2P+Cu3Pd5P2+quaternary phosphide exists at a composition of approximately Pd42.5Cu30Ni7.5P20 and at a temperature of about 800 K . Both group glasses possess a large supercooled liquid region of over 80 K before crystallization. The compressive strength, Young’s modulus and Vickers hardness in each group increase with increasing Ni content. The compressive fracture strength and Young’s modulus are in the range of 1610 to 1740 MPa and 100 to 110 GPa, respectively. Under a uniaxial compression mode, these glassy alloys deformed inhomogeneously and fractured adiabatically. No distinct plastic deformation was observed for group-I alloys, while group-II alloys exhibited serrated flow with a maximum plastic strain of about 1.3%.
  • Effects of the WC Grain Size on the Surface Roughness of WC-10%Co Cemented Carbide Micro-Die Machined by FIB

    pp. 3273-3275

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    DOI:10.2320/matertrans.43.3273

    Micro-dies with five steps were fabricated by machining with the focused ion beam (FIB) process using two types of WC–10%Co cemented carbide with a WC grain size of 5 \\micron and 0.5 \\micron. The surface roughness of the dies was investigated by atomic force microscopy (AFM). In the coarse-grained cemented carbide, the surfaces of the WC phase were very smooth. However, those of the Co phase were rough, particularly near the interface. In the fine-grained cemented carbide, the surfaces were smoother on the whole and the irregularities of roughness were smaller compared with the coarse-grained cemented carbide, but some voids of about 0.5 \\micron, almost the same size as the WC grain, were observed.

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