The use of β-tricalcium phosphate (β-TCP) as osteoconductive and bone morphogenetic protein-2 (BMP-2) as osteoinductive bone graft substitutes has recently gained considerable research interest in spine surgery. However, whether the combination can be extrapolated to a successful interbody spinal arthrodesis remains uncertain. In this study, β-TCP combined with recombinant human BMP-2 was examined in the canine lumbar spine model as a substitute for autograft used for packing interbody fusion cages. The discectomy and interbody cage fusion were performed at three disc spaces in 8 dogs. The examination of microradiographs and histological sections of the lumbar spine at 16 weeks post-surgery revealed three fusions in autograft group (A), three β-TCP group (B), and five in β-TCP-BMP-2 (C). The mean percentage of trabecular bone area in the cages was 51.9% in group A, 48.8% in group B and 65.6% in group C. Statistical analyses of the results could not give significance. The young animal model used in this study might suppress difference between the groups. As mentioned, however, actual data of mean percentage of trabecular bone formation and of mechanical stiffness were largest in the cages filled with β-TCP and BMP-2. In clinical settings, we expect that a cage filled with β-TCP and BMP gives beneficial effects especially for patients with poor fusion statuses.

We attempted to fabricate α-tricalcium phosphate (α-TCP) ceramic porous body with interconnected continuous pores through conventional sintering process. Porous bodies were obtained by sintering the bodies prepared from slurry composed of β-TCP, potato starch and ultra-pure water. Distribution in pore size was uniform ranging between 10-100 μm in diameter. The pore size was mainly due to similarity of distribution in particle size of the potato starch. The porous body (CP-50), that is prepared from the slurry containing 50 mass% of starch, has 73.8% of porosity, and is able to be easy in secondary machining with surgical knife. Porosity of porous body increased with increasing the amount of potato starch added to the slurry. Compressive strength of porous bodies remarkably decreased with increasing the porosity of the porous body. Dissolution behavior was evaluated by released amounts of calcium and phosphate ions from the porous body in buffered solutions. Higher porosity of the ceramic body resulted in higher dissolution rate in the buffered solution. In vivo evaluation by peripheral quantitative computed tomography (pQCT) shows higher density of regenerated bone after the implantation of CP-50 than that of no specimen at defect in rabbit tibia, at four weeks postoperatively. α-TCP ceramic porous body was almost completely absorbed within four weeks after implantation. Consequently, we successfully fabricated α-TCP ceramic porous body with uniform pore distribution through a process with a direct casting method of slurry containing potato starch. This microstructure of the porous body gives high machinablity as well as bioresorbability.

A novel sponge, coated with bonelike apatite (b-HA) on its skeleton surface, was prepared using a particle-leaching technique combined with a biomimetic processing. A powder mixture consisting of calcium carbonate/poly(lactic acid) composite (CCPC) and sucrose was hot-pressed and then the resulting compact was soaked in the simulated body fluid at 37°C. Within the first hour, the sucrose was completely dissolved out, resulting in the formation of large-sized pores in the compact, and subsequently, after 3 hours of soaking, b-HA formed on the skeleton consisting of CCPC. On the other hand, on a pore-free CCPC, the apatite started to form after 12∼18 hours. The induction period for b-HA formation on the skeleton of the CCPC sponge prepared using a particle-leaching technique is significantly shorter than that of the pore-free CCPC. The short period is suggested to originate from that a large amount of Ca²⁺ ion is rapidly supplied into the compartment space (pore) from the CCPC skeleton. The formed sponge has numerous, large pores of 450∼580 μm in diameter, which are connected with channels having a diameter in the range of 70∼120 μm, as well as a high porosity of 75%. Animal test using rats showed that the sponge has osteoconduction. The sponge is expected to be one of the promising candidates for osteoconducting fillers or tissue-engineering scaffolds.

Natural bone is a kind of nanocomposites composed of orientated hydroxyapatite (HAp) along c-axis and fibrous collagen. Therefore, composites exhibiting composition and structure analogous to those of natural bone have been expected to be useful bone substitute materials. Organic polymer-HAp composites have been attracted much attention since they have interesting features such as bone-bonding ability, i.e. bioactivity and flexibility. In the present study, chitosan-HAp nanocomposites were prepared through mechanochemical reaction using conventional ball mill and subsequent aging. The obtained composites contained carbonate-containing HAp, and HAp nanocrystals in the composites aged at 25°C for 24 h showed a needle-like structure. They can form bone-like HAp on their surfaces after soaking in simulated body fluid (SBF), indicating potential for bioactivity in living body. The prepared chitosan-HAp composites are expected to be one of the useful bone substitute materials.

The microstructure and orientation distribution of aragonite crystals in the nacreous layer of cultured Pteria penguin are investigated in this paper. Helical patterns formed by growth forefronts of the nacreous layer for good-quality shells are observed using a laser microscope, whereas no clear pattern is observed on the nacreous layer surfaces of bad-quality shells. The observed aragonite crystals are plate-shaped and hexagonal for both the good and bad-quality shells, in which the top and bottom faces are parallel to the (001) plane and the side faces are parallel to the {110} and (010) planes. The aragonite crystals in the nacreous layer of good-quality shells seem to be harmonically oriented along a crystallographic direction. These orientation distributions basically indicate that the (001) basal planes are parallel to the inner shell surface, and the [100] and [010] axes are oriented in almost the same direction, respectively. Some of the aragonite crystals are rotated about the c axis by approximately ±60° from the basic orientation distribution. On the other hand, the aragonite crystals of bad-quality shells seem to be randomly oriented in the nacreous layer. These orientation distributions indicate that the (001) basal planes are parallel to the inner shell surface in a similar manner as those of good-quality shells, but their [100] and [010] axes are randomly oriented about the c axis. Therefore, it is considered that such different orientation distributions result in different qualities of pearls that are developed in the shells.

The aim of this study is to develop a functionally graded material (FGM) of biodegradable poly (L-lactic acid) (PLLA) with a hardness gradient. For this purpose, the PLLA was extruded at elevated temperatures to introduce molecular orientation. Two types of extrusion, direct extrusion and equal channel angular (ECA) extrusion, were carried out. Heat treatment without extrusion was also carried out at 50°C, 60°C and 70°C. For the mechanical property characterization, the hardness distributions were investigated using a Vickers microhardness tester. Biodegradability of PLLA FGM was measured by evaluating the mass decreasing ratio after incubation in a physiological saline solution at 37°C. It was found that the PLLA FGMs with symmetric and asymmetric hardness gradients could be fabricated by direct extrusion and ECA extrusion at elevated temperature, respectively. Although in the initial state the mass of PLLA gradually increased with the softening of the FGM, it started to decrease after two weeks.

The differentiation of porcelain from tooh using fluorescence emission was investigated as a basic research for the visual detection of porcelain-restored teeth in mass dental health examinations. The fluorescence spectra were taken from the extracted human maxillary central incisors and five types of porcelain by excitation using the light 380-470 nm. There was a clear difference in fluorescence intensity between tooth and porcelain using excitation longer than 400 nm. Tooth and porcelain could be successfully distinguished on an image photographed by fluorescent light.

A time-resolved evanescent wave absorption technique is employed in studying the adsorption of a mammalian protein (cytochrome c) from an electrolyte-free solution on a hydrophilic glass surface. The method combines the sensitivity of a fast-scan spectral analyzer and surface specificity of slab optical waveguide (SOWG) technique. While proteins are viewed to undergo an overall irreversible adsorption process brought about by structural changes that occur after the initial adsorption phase, we have used an SOWG technique to investigate the first stage of the adsorption process while no noticeable changes have taken place. Absorbance data within the first two seconds after contact fit well into the reversible adsorption model characteristic of Langmuir-type adsorption but the goodness-of-fit diminishes as the protein molecules spend more time on the surface.

This paper describes a quantitative evaluation method for metal surface texture. We used surface roughness and glossiness as parameters to describe surface texture. Specimen surface roughness was evaluated based on geometrical product specification data taken from japanese industrial standards. The effects of surface roughness on glossiness were investigated by aluminum alloys. The relationship between the glossiness and the roughness height, the period of the roughness profile and the slope for the surface roughness processed by a vertical milling machine were studied for determining if the topography of the surface roughness affects the glossiness. The surface of the specimens were polished using abrasive paper and blasted, so that the arithmetical mean deviation, Ra, was less than 1.00 μm. The effects of roughness on glossiness were investigated on polished surfaces and blasted surfaces. The results show that the surface roughness shape and the glossiness prove to be effective indices for evaluating the surface textures of aluminum alloys.

This paper describes the establishment of an evaluation method for metal surface texture. The evaluation parameters used for surface texture were roughness, glossiness and color. Seven sample materials were studied: aluminum alloys (A2017, A5052), stainless steel (SUS304) and copper alloys (tough pitch copper C1100, brass C2801, phosphor bronze C5191 and nickel silver C7541). The surfaces of all specimens were polished using waterproof abrasive papers. The correlation of the surface texture parameters for all specimens was investigated experimentally. The surface roughness of specimens was evaluated using the arithmetical mean roughness “Ra”. The method for evaluating surface color was assessed by using CIELAB color space. The CIELAB color space is one of a uniform color space defined by CIE (Commission Internationale de l'Eclairage) in 1976. The results indicated that as surface roughness value “Ra” decreased, as the glossiness value “Gs(60°)” increased exponentially. The lightness value “L^*” of the CIELAB color space decreased, as surface roughness value “Ra” decreased. Thus, the relationship between the lightness value “L^*” and surface roughness value “Ra” showed an inverse correlation with the glossiness value “Gs(60°)” and surface roughness value “Ra”. Moreover, the surface color showed that the blue hue increased, as the surface roughness value “Ra” decreased for all seven types of materials.

A newly developed scanning electron microscope (SEM) installed with a 3D analyzer and a confocal laser scanning microscope (CLSM) were used to evaluate the images and surface profiles of enamel and dentin after CO₂ laser irradiation. The surface roughness (Ra) was measured and the results were correlated with a stylus profilometer. Raman analysis was done and the laser irradiation effect after acid etching was also examined. Human intact extracted teeth were vertically sectioned. The laser was applied perpendicularly to non-etched and 35% phosphoric acid-etched teeth. The enamel resulted in a crater-like surface. The material was removed in the places where hydroxyapatite crystallites ran parallel to the irradiated surface. Non-etched dentin showed little change after irradiation, with some cracks mostly in the peritubular dentin; whereas in acid-etched dentin there was evaporation of collagen and melting of hydroxyapatite. The SEM and CLSM showed similar profiles and different image contrast. Ra levels obtained by the SEM and CLSM were similar to that obtained with the stylus profilometer. Raman analysis showed that bands of organic collagen matrix on dentin were lost and broad peaks due to carbon were observed. Both the SEM and CLSM provided non-contact evaluation of structural changes of teeth by laser irradiation through surface analysis in selected microareas, which was not possible using the stylus profilometer. Dentin showed more structural changes on the acid-etched surface by irradiation than on the non-etched one.

Frictional behavior of stainless steel cup against polyethylene head coated with dimethylacrylamide (DMAA) hydrogel was studied using a pendulum type friction tester. The friction coefficient of the pairs lubricated with Hyaluronic acid aq (HA) was as about 0.01, which is similar to that of living human hip or knee joint. The friction of the pair increased with loading time. When the coated head was immersed in the HA lubricant during an interval of repeated swing motions of the pendulum, the friction coefficient was above low value. The friction coefficient of the pair lubricated with a hydrophobic liquid (silicone oil) was as a high value of 0.4, close to the value without any lubricant. The friction coefficients of pairs lubricated with HA were not dependent on the load. The coefficients of friction lubricated with the biological factor (albumin, phospholipid) additive HA showed a little increase. Especially with albumin, the coefficient of friction increased with load. This behavior may be caused by the attachment albumin to hydrophilic high molecular chain by chemical adsorption. From these experimental observations, it is surmised that the low friction shown in coated PE head is caused by the formation of highly viscous zone through hydration of DMAA at the solid/liquid interface.

Sealing treatment for the porous titanium layers was performed in attempt to prevent cytotoxic nickel ions releasing from porous titanium plasma-sprayed Ni-Ti alloys due to the existence of chloride ions in the body liquid. Two types of sealants were used for this purpose, one was a group of biocompatible polymer resins and the other was metallic titanium. As polymer sealants, 4 kinds of resins (silicone, cyanoacryl resin, epoxy resin and polyamide resin) were used. The first three sealants were soaked into the porous coating layers after dilution by organic solvents, while the thermoplastic polyamide resin was melted and then penetrated into them. On the other hand, physical evaporation deposition (PVD) technique was employed for sealing with titanium metal. The effect of combination of the thickness of the plasma-sprayed layers and the amount of titanium deposited by PVD was investigated. The effectiveness of the sealants was evaluated by electrochemical polarization measurement. The adhesion test of the coating layer to the alloy substrate was also carried out. Among the polymer sealants, the polyamide resin showed excellent performance. As for the titanium PVD sealing, optimum combinations of the thickness of the coating layers and the amount of titanium PVD existed for both corrosion resistance and adhesion strength.

Domain patterns in several classes of ferroelastics are studied using a Landau expansion in the strains and their derivatives. Examination of the local rotation, the non-order-parameter strains and the local energy density reveals the wedge and other disclinations responsible for the complexity of the patterns in (1) tetragonal-orthorhombic materials, and (2) hexagonal-orthorhombic and related materials. At temperatures where the parent phase is unstable and so has negative stiffness, simulations of hexagonal-orthorhombic systems yield pockets where the order parameter is much reduced; if the parent phase exists experimentally under these conditions, it might give rise to extreme damping. For cubic-tetragonal materials, perturbing the parent phase at a temperature well below its stability limit gives an inhomogeneous noncompact product.

For many years, many researchers had taken it for granted that the martensitic phase of Ni₂MnGa was the tetragonal structure. The common knowledge as regads the magnetic moment of the Heusler alloys including Mn was around 4.0 μ_B per formula unit (f.u.). However, Brown et al. newly observed the super-cell structure as the martensitic phase and reported the small magnetic moments on Mn in Ni₂MnGa. In this paper, the electronic structures are calculated and magnetic moments are estimated for Ni₂MnGa in the L2₁ and martensitic super-cell structures. In our calculation, we obtained a variety of magnetic moments on Mn in the martensitic structure and that values are largely different each other.

To theoretically examine the existence of half-metals in Co-Cr-Fe-Al alloys, band calculations were carried out for these alloys. Seeing energy dispersion curves E(k) of Co₂CrAl with the Heusler structure, we find that the Fermi level intersects the E(k) curves in the majority-spin state but is located at the energy gap in the minority-spin state, that is, it is predicted that this stoichiometric Co₂CrAl alloy is half-metallic. On the other hand, the half-metallic properties are not observed in the electronic structures of Co₂FeAl. The composition dependence of electronic structures of Co₂(Cr_1−xFe_x)Al (x = 1/8—7/8) indicates that the alloys have the tendency to become half-metallic in the range of x < 5/8.

In order to investigate the applicability of laser micro welding to the fabrication of medical devices, Ti-Ni shape memory alloy wires with pseudo-elasticity were micro spot melted by using YAG laser. By changing the melting parameters, such as laser power or pulse duration, the evolution in microstructure, tensile strength and pseudo-elasticity was investigated. Melted metal width decreased with decreasing the input energy and pulse duration. The microstructure of melted areas was cellular dendrite structures and that of heat affected areas was grown cell structure with a cell size of about 3∼10 μm. Tensile strength of spot melted wires was 30% lower than that of base metal, and the fracture occurred in melted areas with a brittle fracture surface. Although melted areas and heat affected areas did not show a pseudo-elasticity due to the larger grain size, minimizing the width of melted metal improved the overall pseudo-elasticity of spot melted samples. For the sample wires that were prepared by spot melting of cold rolled wires and by the subsequent heat treatment for shape memorizing, the pseudo-elasticity was improved because heat affected zone recrystallized to form fine grains.

Ni-free Ti-base shape memory alloys (SMA) have been systematically developed by our group for biomedical applications in order to replace Ti-Ni SMAs which posses the possibility of Ni-hypersensitivity. In this study, superelastic behavior of solution-treated Ti-24 mol%Nb-3 mol%Al alloy was investigated by means of tensile tests at room temperature (RT) as well as microstructural observation. The alloy was fabricated by Ar arc-melting followed by a homogenization at 1273 K and then cold-rolled with the reduction of 99% in thickness without intermediate annealing. The cold-rolled sheets were solution treated at 1273 K for 1.8 ks in vacuum. Then, cyclic loading-unloading tensile tests were performed at RT. In the tensile tests, the tensile direction was systematically changed from rolling direction (RD) to transverse direction (TD) in the plane of the cold-rolled sheets. It was found by the tensile tests that the superelastic behavior strongly depends on the tensile direction and the number of deformation cycles. The solution-treated alloy after 99% cold rolling exhibits the best superelasticity when loaded along RD. The nature of the anisotropy in the superelastic behavior is discussed related with the texture developed during the fabrication process. It is concluded that the thermo-mechanical treatment performed in this study is quite useful as a superelastic treatment for the Ti-base SMAs, and that this alloy should be used industrially by taking into account such anisotropy of superelasticity.

Textures of severely cold-rolled Ti-24 mol%Nb-3 mol%Al superelastic alloy were examined by X-ray pole figure measurements for the bcc parent phase (β) and the relationship between transformation strain and loading direction was evaluated on the basis of the lattice correspondence and change in the potential energy of an external stress. A well-developed recrystallization texture of ‹110›_β{112}_β type was confirmed by X-ray pole figure measurements for the material which was 99% cold-rolled followed by a solution-treatment at 1273 K. Crystallographic analysis showed that the maximum dilatation component of the martensitic transformation from β to α″ is ‹110›_β parallel to the rolling direction (RD). An energy consideration revealed that only one α″-variant (lattice-correspondence variant) can be induced by the tensile stress along RD when the recrystallization texture appears. The transformation strain generated under the RD tension was about three times larger than that generated under the tension along transverse direction (TD). These calculations were in good agreement with experimental evidences.

Mechanical properties and shape memory behavior of Ti-Mo-Ga alloys were investigated in order to develop Ni-free biomedical shape memory alloys. The Ti-Mo-Ga alloys were fabricated by arc melting method. The ingots were cold-rolled up to 95% reduction in thickness. The cold-rolled specimens were heat treated in the temperature range 673—1273 K for 60 s—3.6 ks. The martensitic transformation temperature decreased with increase in Mo and Ga content. The maximum shape recovery strain was obtained in a solution treated Ti-6 at%Mo-3 at%Ga alloy. Mechanical properties and shape memory behavior strongly depend on heat treatment condition in the Ti-6 at%Mo-3 at%Ga. Premature failure was observed in specimens heat treated in the temperature range 673—773 K. Ultimate tensile strength decreased and fracture strain increased with increasing heat treatment temperature. Shape memory effect was obtained in specimens heat treated in the temperature range 1073—1273 K. The shape memory effect was due to the stress induced martensitic transformation yielding tensile deformation and the reverse transformation upon heating after unloading. The martensitic transformation start temperature increased and the yield stress decreased with increasing heat treatment temperature and time. Stable superelastic behavior was obtained in a Ti-7 at%Mo-4 at%Ga alloy at room temperature by cyclic tensile tests. The recovery strain exceeding 4% was achieved in the pre-strained Ti-7 at%Mo-4 at%Ga alloy.

Shape memory properties of Ti-Mo-Ag and Ti-Mo-Sn alloys consisting of biocompatible elements were investigated. The alloys with appropriate combination of Mo and Ag or Sn showed nearly perfect shape memory effect in convenient bending and heating tests. Recoverable tensile strain is more than 3% in some of Ti-Mo-Ag and Ti-Mo-Sn alloys. Microstructure observations and X-ray diffraction measurements before and after tensile test revealed that stress induced β to α″ martensitic transformation was origin of the shape memory effect.

Ni-free Ti-Sc-Mo shape memory alloys are designed as a substitute for Ti-Ni alloys in the biomedical field. From results of bending and recovery test with heating, Ti-Sc-Mo alloys were found to have superior shape memory effect. The optimum composition for the shape memory effect was Ti-4.0 to 6.0Sc-6.0Mo alloys. The maximum shape recovery strain in the Ti-5.0Sc-6.0Mo alloy was 5.3% measured through cyclic tensile deformation. Vickers hardness and 0.2% proof stress were remarkably decreased and elongation was increased with Sc content. The marked grain refining was also achieved. The relationship between microstructure and mechanical properties was briefly discussed. Microstructure observations and XRD measurements before and after tensile deformation showed that the shape memory effect was associated with the stress induced β to α″ transformation.

Using Ti-50Ta, Ti-50Ta-Sn and Ti-50Ta-Zr alloys, the effects of Sn and Zr additions on phase constitution in the solution treated and quenched state and aging behavior were 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 aged at temperatures up to 1323 K in Ti-50Ta-Sn alloys and 1173 K in Ti-50Ta-Zr alloys. Shape recovery test was also performed in bent Ti-50Ta, Ti-50Ta-Sn and Ti-50Ta-Zr alloy specimens. In the STQed state, only reflections of orthorhombic α″ martensite were observed by XRD in Ti-50Ta and Ti-50Ta-4Sn alloys. In STQed Ti-50Ta-10Zr alloy, coexistence of α″ and β (bcc) phases were found by XRD. In STQed Ti-50Ta-8Sn and Ti-50Ta-20Zr alloys, only β phase was identified. In Ti-50Ta, Ti-50Ta-4Sn and Ti-50Ta-10Zr alloys, resistivity at liquid nitrogen temperature and resistivity ratio increased with isochronal aging up to a certain temperature. It is considered that these increases are due to reverse-transformation of α″ into metastable β phase. Shape-recovery test confirmed the shape memory effect of Ti-50Ta, 50Ta-4Sn and 50Ta-10Zr alloys.

The composition of Ti-30Nb-10Ta-5Zr, which is simplified that of the Ti-29Nb-13Ta-4.6Zr alloy developed for biomedical applications, was selected, and then Nb content in the basic composition was varied from 20 to 35%. The deformation mechanisms of such Ti-Nb-Ta-Zr system alloys were investigated by loading-unloading tensile tests and characterizing deformed microstructures. The behavior of unloading and reloading of the stress-strain curves up to strain about 2% of Ti-20Nb-10Ta-5Zr and Ti-25Nb-10Ta-5Zr alloys is similar to that obtained in metastable β type titanium alloys where the stress induced martensite transformation occurs. This indicates that the stress and strain induced martensite transformation occurred in these alloys. Furthermore, the elastic deformation of Ti-30Nb-10Ta-5Zr alloy disobeys Hooke's law. However, the behavior of stress or strain-induced martensite transformation does not recognized in the stress-strain curve up to strain about 2% of this alloy. The main deformation mechanism up to fracture of Ti-20Nb-10Ta-5Zr alloy, Ti-25Nb-10Ta-5Zr alloy and Ti-35Nb-10Ta-5Zr alloy is identified as the deformation - induced martensite transformation of β phase to α″ phase, deformation-induced martensite transformation of β phase to α″ phase and deformation twin, and slip, respectively. The deformation mechanisms for Ti-30Nb-10Ta-5Zr alloy are not explained by slip, deformation twining and deformation-induced martensite transformation. However, the super elastic behavior observed in this alloy is expected to occur without deformation-induced martensite transformation.

A group of multicomponent Ti-Cu-Ni(Cr, Fe, Co)-Sn-Ta(Nb) alloys were investigated in terms of the microstructure and the mechanical properties. A composite microstructure with a micrometer-sized dendritic bcc-β-Ti(RM) (RM = Nb, Ta) phase dispersed in a matrix was obtained. The TEM observation on the Ti₆₀Cu₁₄Ni₁₂Sn₄Ta₁₀ alloy shows that the matrix is composed of a nano/ultrafine bcc-phase with the size of 50—100 nm which is isolated by a tetragonal-phase. The designed Ti alloy exhibit very high yield strength (1050—1472 MPa) and relative lower Young's modulus (67—105 GPa). Such combined properties, not easily achievable in previous Ti alloys, make these new designed Ti alloys promising candidates as biomedical materials.

Successful bone formation which leads to functional osseointegration is determined by the local mechanical environment around bone-interfacing implants. In this work, a novel porous titanium material is developed and tested and then impact of porosity on mechanical properties as a function of bone ingrowth is studied numerically. A superplastic foaming technique is used to produce CP-Ti material with rounded, interconnected pores of 50% porosity; the pore size and morphology is particularly suitable for bone ingrowth. In order to understand the structure-property relations for this new material, a numerical simulation is performed to study the effect of the porous microstructure and bone ingrowth on the mechanical properties. Using ABAQUS, we create two-dimensional representative microstructures for fully porous samples, as well as samples with partial and full bone ingrowth. We then use the finite element method to predict the macroscopic mechanical properties of the foam, e.g., overall Young's modulus and yield stress, as well as the local stress and strain pattern of both the titanium foam and bone inclusions. The strain-stress curve, stress concentrations and stress shielding caused by the bone-implant modulus mismatch are examined for different microstructures in both elastic and plastic region. The results are compared with experimental data from the porous titanium samples. Based on the finite element predictions, bone ingrowth is predicted to dramatically reduce stress concentrations around the pores. It is shown that the morphology of the implants will influence both macroscopic properties (such as modulus) and localized behavior (such as stress concentrations). Therefore, these studies provide a methodology for the optimal design of porous titanium as an implant material.

The feasibility of using slip casting of titanium powder as a method for manufacturing dental prosthetic appliances was examined. Slips with water-powder (W/P) ratios, 0.318, 0.354 and 0.391, and with minimum viscosities were cast in plaster molds. Castings were sintered in an argon atmosphere at 1373, 1473 and 1573 K for 3.6, 7.2 and 10.8 ks, respectively. Green densities and strengths of castings were 2.20 kg/m³ and 2.31—3.82 MPa, respectively. Linear shrinkages and relative densities of sintered castings varied from 17.6 to 20.8% and 0.82 to 0.97 of the theoretical density of titanium, respectively. Tensile strengths and Vickars hardness of the sintered castings were 199.5—315.4 MPa and 233.0—247.7, respectively. There was almost no elongation. Decreasing porosity and crystal grain growth were found in the microstructures of sintered castings and rod-like precipitates of TiC with α-titanium were also observed. Concentrations of carbon and oxygen in the microstructures of sintered castings were higher than those in wrought titanium. Fractured surfaces showed ridge patterns typical of brittle fracture. Further modification of the sintering atmosphere and the additives for the slip is needed to improve the microstructure of slip-cast sintered titanium.

The performance of laser welding of Ti and two dental precious alloys (Ag-Pd-Au, Au-Pt-Ag) was investigated by mechanical testing and microscopic observation, using butt joint as design. The laser irradiation was done using a commercial Nd:YAG dental laser-welding device in a single pulse mode with output currents 150, 200, 250, 300 A, spot diameters 0.6, 0.9, 1.2 mm, and pulse duration 10 ms. The average welding fracture strength of the dissimilar metals were 108.9 and 137.2 MPa for Ti and Ag-Pd-Au alloy, and Au-Pt-Ag alloy, respectively. The average welding fracture strength of the same metals were 594.9, 648.8 and 312.9 MPa for Ti, Ag-Pd-Au alloy and Au-Pt-Ag alloy. The hardness increased in weld zone, compared with the base metals. Penetration depths were affected by the welding conditions such as the output currents and spot diameters. The welding cracks and porosity were observed in microstructures of the welds. Mapping by EPMA showed the remarkable heterogeneity of the component metals concerned. The welding cracks, porosities and granular precipitates similar to metallic compounds in the weld zones were suggested as the cause for lower welding fracture strength in the dissimilar welds, compared with the similar metals.

Silicate glass coatings on Vitallium^®, a Co-Cr alloy were prepared using a simple enameling technique. The composition of the glasses in the SiO₂-Na₂O-K₂O-MgO-CaO-P₂O₅ system has been tailored to match the thermal expansion of the alloys. The optimum glass composition and firing conditions (temperature and time) needed to fabricate homogeneous coatings with good adhesion to the alloy were determined. The final coating thickness ranged between 40 and 60 μm. Coatings fired under the optimum conditions do not delaminate during indentation tests of adhesion. Excellent adhesion to the alloy has been achieved through the formation of 150 nm thick interfacial layers (CrOx). The silicate glass can be successfully coated to Co-Cr alloy and formed hydroxyapatite on the glass surface when immersed in a simulated body fluid (SBF) for 30 days.

A glassy phase containing cubic phase particles with a size of 3—5 nm was formed in cast Cu₆₀Zr₃₀Ti₁₀ and Cu₆₀Hf₃₀Ti₁₀ bulk alloys. The cubic phase is in a metastable state and its lattice parameter (a₀) is 0.45 nm for the former alloy and 0.51 nm for the latter. These bulk alloys exhibit good mechanical properties of 2000—2130 MPa for tensile strength (σ_t,f), 2060—2160 MPa for compressive strength (σ_c,f) and 0.008—0.017 for compressive plastic strain (ε_c,p). The temperature interval of the supercooled liquid (SL) region prior to crystallization is 37 K for Cu₆₀Zr₃₀Ti₁₀ and 67 K for Cu₆₀Hf₃₀Ti₁₀. The primary crystallization occurred by precipitation of cubic CuZr (a₀ = 0.35 nm) in a diffusion-controlled growth mode of nuclei and an orthorhombic Cu₈Hf₃ phase in an interface diffusion-controlled growth of nuclei with decreasing nucleation rate. The difference in the precipitation modes is interpreted to be the origin of the difference in the SL region. Furthermore, the addition of Al to Cu-Zr and Cu-Hf alloys caused the formation of a glassy single phase in the rod form with diameters up to at least 3 mm, though bulk glassy alloy rods with critical diameters up to 1.5 mm and σ_c,f of 1920—2260 MPa were formed in Cu-Zr and Cu-Hf binary systems. The ternary bulk glassy alloys exhibited high σ_c,f of 2100—2370 MPa with ε_c,p of 0.002—0.006. The addition of Pd, Pt, Ag or Au increased ΔT_x and a large ΔT_x of 102—110 K was obtained for the Cu-Hf-Al-M (M=Pd or Ag) glassy alloys. The synthesis of Cu-based bulk glassy alloys with good mechanical properties and large ΔT_x in glassy single, and mixed glassy and cubic phase states, is important for future applications of bulk glassy alloys.

Criteria for estimating the glass-forming ability accessible by the molecular dynamics simulations are proposed. The enthalpy of the glassy phases and the density of the supercooled liquid phases can be the criteria, the former reflects the energetics and the latter reflects the dynamics. The relaxation behavior of the glassy phases suggests that the cooling rate dependence of the glass transition temperature also could be the criterion as to explore the ‘energy landscape’ and the phase stability for both supercooled liquid and glassy phases.

Local electronic structures of Zr-based metallic glasses have been calculated using the discrete variational Xα cluster molecular orbital method. The cluster models are constructed for Zr-Cu, Zr-Ni and Zr-Pd metallic glasses on the base of local structure parameters determined by extended X-ray absorption fine structure analysis. The valence-band X-ray photoelectron spectra computed from the local electronic structures agree well with experimental spectra. Based on the feature of chemical bonds in those glasses evaluated from the electronic structures, we discuss the relationship between the chemical bond and the stability of supercooled liquid state. The strength of the Zr-Ni bond is larger than that of Zr-Cu bond, while the Cu-Cu bond strength is nearly equal to the Ni-Ni bond. Moreover, the Zr-Zr bond strength is larger in Zr-Cu glass than in Zr-Ni glass. This indicates that the formation of primary crystalline phase is more difficult in Zr-Cu glass than in Zr-Ni glass. The difficulty contributes to the relative stabilization of supercooled liquid state in Zr-Cu glass compared with that in Zr-Ni glass. It is also shown that local atomic structures of Zr-Pd glass are well described by the icosahedral atomic configuration.

In this paper, we will discuss and apply the formation rules for bulk metallic glasses, originated from quasicrystals composition rules, by combining two most common factors, atomic size factor and electron concentration (e/a) factor. According to literature survey, to our experience on quasicrystal formation, and to our own experimental verification, we propose two criteria, based on atomic size and electron concentration e/a respectively. The first criterion is quantified as the R_av-constant criterion, R_av being the average atomic radius, and the second one the e/a-constant criterion. In a given alloy system the optimum BMGs and their crystalline counter parts tend to share the same R_av and e/a values. These criteria have been applied to determine the ideal BMGs in Zr-Al-Cu-Ni system.

Composition optimization for the largest glass-forming ability has been performed in the Zr-Al-Ni(Co) systems in this investigation. Two guiding criteria, termed respectively the e/a-constant criterion and the e/a-variant criterion, are applied. They are incarnated into the e/a = 1.5 composition line and the Zr₉Ni(Co)₄-Al composition line. Bulk metallic glasses are obtained by suction casting alloy melts of compositions within an e/a span of 1.3∼1.5, with their thermal stabilities and glass forming abilities being increased with increasing e/a. The intersecting point of the two lines gives the composition Zr₅₃Al_23.5Ni(Co)_23.5 with the largest glass-forming ability.

The structural relaxation process was investigated for a Pd_42.5Cu₃₀Ni_7.5P₂₀ metallic glass (bulk and ribbon samples) isothermally annealed at 566 and 573 K just below glass transition temperature T_g = 576 K. The relaxation process was examined by differential scanning calorimetry (DSC) and electrical resistmetry. Then, the resistivity of bulk glass was exactly estimated from the resistance and the geometry of the sample. Although the DSC absorption peak appeared just after glass transition became larger with the progress of the relaxation, the growth was terminated after annealing for 6 × 10³ s at 566 K or 6 × 10² s at 573 K, meaning that the free volume content reached a constant value and a fully relaxed state was attained. The corresponding change was also seen in the room temperature residual resistivity ρ(300) during relaxing at 566 K. Then, the ρ(300) increased with time for initial 6 × 10³ s and was constant during further 6 × 10⁴ s.

We have studied the elastic and anelastic behavior of fully structural-relaxed Pd₄₀Ni₄₀P₂₀ and Zr₅₅Al₁₀Ni₅Cu₃₀ bulk metallic glasses using high-frequency ultrasound vibrations at elevated temperature, and found that the structural anomaly is induced by ultrasound vibrations in a supercooled liquid region. The electromagnetic acoustic resonance and resonant ultrasound spectroscopy methods were employed to measure the resonant spectra and ultrasonic attenuation coefficients. When the glassy samples are subjected to sub/low-MHz ultrasound vibrations during heating process, the crystallization is accelerated around their glass transition temperatures, and with this abrupt structural change, irregular Λ-shaped internal friction peaks appear. From the standpoint of ultrasonic echography, the glass transition and crystallization temperatures are considerably lowered by ultrasound vibrations in the present measurements.

Advanced techniques of electron microscopy were employed for analyzing a local structure of an as-formed Fe₇₀Nb₁₀B₂₀ metallic glass. From nano-diffraction with an electron probe size of 1 nm, diffraction patterns of bcc-Fe and Fe-boride were observed which indicated an occurrence of nano scale phase separation in the glass. Atomic pair distribution function (PDF) analysis of the glass was also performed by means of precise electron diffraction intensity analysis taking advantage of energy-filter and imaging plate techniques. An atomic structure model was constructed using reverse Monte-Carlo calculation followed by Voronoi polyhedral analysis in order to know local atomic arrangements in the glass structure. The Voronoi analysis revealed atomic arrangements with bcc-Fe-like and B-centered trigonal prism polyhedral structures in this glass, which is consistent with the local structural study by nano-diffraction.

Structures of amorphous Fe₈₄Nb₇B₉ (FN7) and Fe₈₅Nb₆B₉ (FN6) alloys were investigated by high-energy X-ray diffraction. The structures of FN6 and FN7 contain a relatively large amount of bcc-Fe like clusters. This cluster size seems to grow larger for FN6 than for FN7. From the lattice parameters of αFe precipitates, the crystallization behavior of both alloys were discussed. The αFe precipitates contain supersaturated Nb and B. These solute atoms are removed from αFe by annealing at elevated temperature and stabilize the amorphous matrix. This appears to prevent the growth of αFe to maintain nano-scale αFe particles.

Glassy type Al-based alloys, with a distinct glass transition and a supercooled liquid region before crystallization, were formed in (Al_0.84Ni_0.1Ce_0.06)_100−xB_x (x = 0 to 10 at%) and (Al_0.84Ni_0.05Y_0.09Co_0.02)_100−xB_x (x = 0 to 3 at%) systems by melt spinning. The addition of an optimum amount of B was found to increase the temperature interval of supercooled liquid region from 18 K to 23 K at 6%B for the former system and from 28 K to 31 K at 1.5 and 2%B for the latter system. The similar increase with B content was also recognized for Vickers hardness (H_v) and tensile fracture strength (σ_f) and the highest values of H_v and σ_f are 400 and 1060 MPa, respectively, at 6%B and 375 and 1140 MPa, respectively, at 1.5%B. The maximum phenomena of temperature interval of supercooled liquid region (ΔT_x = T_x — T_g), H_v and σ_f at optimum B contents can be interpreted in the framework of the three empirical component rules for the stabilization of supercooled liquid and the formation of bulk glassy alloys. The crystallization occurs through two stages of glass → Al + metastable phase → Al + Al₃Ni + Al₄Ce for the Al-Ni-Ce-6%B alloy and through three stages of glass → Al + glass → Al + metastable phase + glass → Al + Al₉Co₂ + Al₃Y + Al₄NiY + Al-Y-Ni-Co quaternary compound for the Al-Ni-Y-Co-2%B alloy. The finding of Al-based glassy alloys with large ΔT_x values above 30 K is encouraging for future development of Al-based alloys as a high strength material with light weight.

High-strength Cu-based bulk glassy alloys with a large supercooled liquid region in Cu-TM-Al (TM=Zr, Hf) ternary and quaternary systems were synthesized by copper mold casting. The maximum diameter was 3.0 mm for the Cu₅₀Zr₄₅Al₅, Cu_52.5Hf₄₀Al_7.5, Cu₅₀Hf_42.5Al_7.5 and Cu₅₀Hf_22.5Zr_22.5Al₅ alloys. The glass transition temperature (T_g), temperature interval of supercooled liquid region ΔT_x(=T_x — T_g) and reduced glass transition temperature (T_g/T_l) are in the range from 701—781 K, 54—91 K and 0.61—0.63, respectively. The Cu-based bulk glassy alloys exhibit good mechanical properties, i.e., 102—128 GPa for Young's modulus, 1885—2370 MPa for compressive fracture strength, up to about 0.6% for compressive plastic elongation, and 550—670 for Vickers hardness. The finding of the new Cu-based bulk glassy alloys with large supercooled liquid region above 54 K, high reduced glass transition temperature above 0.60, and high fracture strength above 1885 MPa is encouraging for future development as a new type of bulk alloys which can be used as structural materials.

The glass-forming ability and mechanical properties of Fe-B-Si-Nb glassy alloys have been investigated. The Fe₇₂B₂₀Si₄Nb₄ glassy alloy was prepared in a cylindrical form with a diameter of 2 mm. Young's modulus, compressive fracture strength and plastic elongation of the bulk metallic glass were 200 GPa, 4200 MPa and 1.9%, respectively. Many shear bands were observed along the shear plane, which was declined by about 43 degrees to the direction of applied load, and the fracture occurred along the shear plane. The local-ordered regions were recognized in the high-resolution TEM image of the Fe₇₂B₂₀Si₄Nb₄ bulk metallic glass with a diameter of 2 mm. The good mechanical properties are attributed to the suppression effect of the local-ordered regions on the propagation of shear bands.

The density and the magnetization process of the melt-spun glassy Fe-(Al, Ga)-(P, C, B, Si) alloys are investigated to clarify the origin of low coercivity of the glassy alloys. The differences of the density (Δρ_c) between the crystalline and the amorphous phases of glassy Fe-(Al, Ga)-(P, C, B, Si) alloys are much smaller than those of the ordinary amorphous Fe-B(-Si) alloys. The H⁻¹-power law behavior of ΔJ (= J_s — J, where J_s is the saturation magnetization) is observed for both the glassy and ordinary amorphous systems in the magnetic field (H) range of 20—25 < μ₀H ≤ 50 mT. In the high magnetic field range of 50 ≤ μ₀H < 70 mT, ΔJ of both the alloy systems obeys the H⁻²-power law. The length of the effective Burgers vector and width of quasi-dislocation dipole (QDD) type defects are nearly independent of the alloy system. This means that the local volume contraction is independent of the alloy system, but the density of QDDs in the glassy alloys is much smaller than the ordinary amorphous alloys because the glassy alloys exhibit much smaller Δρ_c than the ordinary amorphous alloys. Since the coercivity originates from elastic stress of QDDs is proportional to (Δρ_c)^1/2, the origin of low coercivity of the Fe-(Al, Ga)-(P, C, B, Si) glassy alloys is the low density of QDDs which corresponds to low density of the domain-wall pinning centers.

Microforming can be a good application for bulk metallic glasses. It is important to simulate the deformation behaviour of the bulk metallic glasses in a supercooled liquid region for manufacturing micromachine parts. For these purposes, a correct constitutive model which can reproduce viscosity results is essential for good predicting capability. In this paper, we studied deformation behaviour of the bulk metallic glasses using the finite element method in conjunction with the fictive stress constitutive model which can describe non-Newtonian as well as Newtonian behaviour. A combination of kinetic equation which describes the mechanical response of the bulk metallic glasses at a given temperature and evolution equations for internal variables provide the constitutive equation of the fictive stress model. The internal variables are associated with fictive stress and relation time. The model has a modular structure and can be adjusted to describe a particular type of microforming process. Implementation of the model into the MARC software has shown its versatility and good predictive capability.

A fretting fatigue test was carried out with commercially available Zr-based amorphous alloy (7.6Ni-12.3Cu-3.5Al-76.6Zr in mass%) in air and in a pseudo-body fluid, PBS(-). The fracture behaviors were investigated. The fretting fatigue test was performed under load control using a sinusoidal wave with a stress ratio of 0.1, a frequency of 20 Hz in air or 2 Hz in PBS(-) and a fretting contact pressure of 30 MPa. The 10⁷-cycle fretting fatigue strength in air was one-third the 10⁷-cycle plain fatigue strength. On the other hand, the 2 × 10⁶-cycle fretting fatigue strength in PBS(-) was approximately two times the fretting fatigue strength in air. However, there was little difference between the friction coefficients in air and PBS(-). SEM observations showed that the actual contact area damaged by fretting in air due to the roughness of the surfaces became smaller than that in PBS(-). Thus, it can be considered that the fretting fatigue strength was decreased since in air the actual contact pressure caused by the roughness became higher than the apparent contact pressure. Also, based on the observation that film-forming elements in PBS(-) were different from those in air, it is believed that the surface film can affect the frictional wear characteristics and contribute to the suppression of fretting fatigue crack initiation.

The fillability and imprintability of a Ni-based bulk metallic glass (BMG) prepared by the precision die-casting was investigated. A three-dimensional microgear made of Ni-based BMG is successfully prepared by the precision die-casting technique. The cast Ni-based BMG has excellent fillability against a microindentation formed by Vickers indentation, and the filling area obtained using a confocal scanning microscope reaches 99%. In addition, the cast Ni-based BMG exhibits excellent imprintability of the die surface even on a nanometer scale. It is therefore concluded that the Ni-based BMG is suitable as a material for micromachines due to its superior fillability and imprintability.

By use of excellent properties of bulk metallic glasses, some industrial products were practically prepared and their performances were investigated. Ni-based BMG microgear prepared by injection casting exhibits nano-imprintability against the surface roughness of mold. Linear actuator constructed by a set of Fe-based BMG yokes generates relatively large driving force due to the Lorentz force. The newly developed alloy with a nominal atomic composition of Ti₅₂Cu₂₃Ni₁₁Mo₇Fe₇ exhibits high yield strength of 1250 MPa, high fracture strength of 2740 MPa and large plastic elongation of over 20%. These results for the industrial products made of BMGs are promising for future developments as industrial materials with high performance.

The Nd doping effect on the room temperature magnetoresistance in manganites (La_1−xNd_x)_0.67Sr_0.33MnO₃ was investigated. With increasing Nd doping content in manganites (La_1−xNd_x)_0.67Sr_0.33MnO₃ the room temperature magnetoresistance ΔR/R₀ decreases for low Nd content x < 0.1, which may be mainly due to the sharp reduction of the room temperature saturation magnetization M_S. For x > 0.1, an enhancement of the room temperature magnetoresistance can be obtained. Such enhancement of the room temperature magnetoresistance is correlated with the shift of the Curie temperature to near room temperature and the slow change of the room temperature saturation magnetization M_S induced by the appropriate Nd doping. The ΔR/R₀ become small again at large Nd doping contents. The drop of ΔR/R₀ may be attributed to their lower metal-insulator transition temperature T_MI far from the room temperature and the smaller M_S value at room temperature. Values of the room temperature magnetoresistance ΔR/R₀ for manganites (La_1−xNd_x)_0.67Sr_0.33MnO₃ depend not only on the Curie temperature T_C but also on the metal-insulator transition temperature T_MI and the room temperature saturation magnetization M_S.

Peak broadening and peak shifts of Bragg reflections were studied with the synchrotron single-crystal X-ray diffraction method for an Al_72.7Ni_8.5Co_18.8 decagonal quasicrystal classified as the 5f state. From the Q_⊥ and Q_|| dependences of the full width of half maximum (FWHM) of the Bragg reflections along the longitudinal direction, the coexistence of random phason strains with phonon strains was observed. High-resolution synchrotron X-ray measurements could present quantitative estimations of these strains. The value of the random phason strain component is 0.0054 ∼ τ⁻¹¹. The asymmetrical broadening due to the phonon strain shows that the single crystal may be constructed with two kinds of grains that have A_5D values of 0.6273 and 0.6265 nm.

Equal-Channel-Angular extrusion (ECAE) has been conducted at room temperature in order to develop an ultrafine-grained structure in a Zn-22 mass% Al eutectoid alloy. The microstructures had an equiaxed and homogeneously distributed Al-rich and Zn-rich duplex-phase and its average grain size was about 0.35 μm. This alloy exhibited a large elongation of 240% albeit at room temperature and a high strain rate of 10⁻² s⁻¹. A grain-size-dependent phenomenon was also observed at lower strain rates. The activation energy was close to that for grain boundary diffusion. It was apparent that the deformation behavior at room temperature is consistent with that observed in conventional superplasticity. From the results, it was concluded that the dominant deformation mechanism was grain boundary sliding accommodated by dislocation movement controlled by grain boundary diffusion.

Creep deformation behavior of coarse-grained Mg-Al based solid solution alloy (AZ31) was studied in a wide strain rate range of 2 × 10⁻⁵∼7 × 10⁻² s⁻¹ at temperature range of 573∼673 K. Viscous glide controlled creep (VGC), dislocation climb creep (DCC) and power law breakdown (PLB) showed up in order with increasing stress as the flow rate-controlling process. From the former results for Mg-Al and Mg-Al-Zn alloys, the creep mechanisms of VGC and DCC in Mg and Mg alloys are confirmed. Moreover, several theories presented for DCC and VGC are applied to convey the creep mechanisms in Mg and Mg alloys by analytical way. Transitions in Mg alloys are analyzed also by comparing experimental results and theories. Alloying effects on creep strength and transitions of deformation mechanism are analyzed.

Effects of yttrium addition on the formation of oxide scales and the oxidation resistance of elemental powder metallurgy (EPM) processed TiAl-Mn-Mo-C alloys were studied. The Y-containing TiAl-based alloys (0.1∼0.6 at%Y) showed better oxidation resistance than Y-free alloy oxidized in air at 800°C for 350 h. The Y-containing alloys showed a significantly reduced weight gain, especially for 0.6 at%Y-added alloy. In the Y-free alloy, the scale formed during extended air-exposure at 800°C consisted of TiO₂ and α-Al₂O₃. For 0.6 at%Y-added alloy, however, the oxide scale was composed of a complex mixture of TiO₂, α-Al₂O₃, Y₂O₃ and Al₅Y₃O₁₂. The formation of multi-phase (Y, Al) O-type oxides layer in a transitional Y-rich subscale close to the substrate and an increase of the amount of α-Al₂O₃ in the mixture oxide layer in the Y-added alloys were the main contributor to improving the oxidation resistance of the alloys. The reduction of oxygen content in the substrate also had a beneficial effect on the oxidation resistance of the Y-containing TiAl-based alloys.

The lead-free soldering technology has been devoloped all over the world while IEEE ReHS prohibits the use of lead contained solder in 2006. Sn-Ag-Cu solder of which melting point is 219°C has the highest solder joints reliability of leadfree solder materials. This melting point is much higher than that of the conventional solder of 183°C. So reflow process for low heat-resistant components on Print Circuit Board needs lower melting point solder. Sn-Zn-Bi solder with low melting point of 197°C has a high barrier to apply to electric products due to lower reliability at high tempereture, in high humidity and after reheating a joint comparing to conventional solder. Adding both bismuth and indium into Sn-Ag solder alloy is effective especially for decrease of melting point of Sn-Ag solder and Sn-Ag-Bi-In solder which had a melting point of 206°C was devoloped. In this paper, we mentioned design of the solder alloy and soldering properties of Sn-Ag-Bi-In to the point of apearance and microsructure of solder joints concerning about the influences of temperature, humidity and heat story of joint surface after 1000 cycles at −40°C/125°C and after 1000 hours of 85°C/85%RH. But the solder joint strength of Sn-Ag-Bi-In in comparable to that of Sn-Pb eutectic solder in each test. And no significant deterioration of Sn-Ag-Bi-In solder had the same reliability as conventional solder and could be useful to expand the practical use of lead-free solder for a lot kinds of products.

Interreactions of diffusion couples of TiAl₃ film on bulk γ-TiAl and TiAl₃ film on bulk α₂-Ti₃Al are investigated at high temperature. Experimental results show that TiAl₂ layer and TiAl₂/γ-TiAl mixed layers are observed at the interfaces of TiAl₃ film/bulk γ-TiAl and TiAl₃ film/bulk α₂-Ti₃Al diffusion couples, respectively, at 700∼1000°C. In addition, the growth rates of TiAl₂ and γ-TiAl product layers comply well with a parabolic law. The growth activation energy, Q_k, of the TiAl₂ phase in the TiAl₃ film/bulk γ-TiAl system is calculated as 158.9 kJ/mol, and Q_k values of γ-TiAl and TiAl₂ phases in TiAl₃ film/bulk α₂-Ti₃Al system are 163.4 kJ/mol and 147.9 kJ/mol, respectively. These Q_k values are similar in magnitude with those of TiAl₃ phase formation in Ti-Al thin film diffusion systems. In this study, TiAl₂ formation is suggested to have been nucleated at the interface during the heating prior to reaching the set temperature.

Steam oxidation resistance of 50Ni-50Cr coatings sprayed by a high velocity oxyfuel process on modified 9Cr-1Mo steel substrate was evaluated in the temperature range of 873-1023 K. The present study focuses on the microstructural changes during the oxidation tests. The coated samples showed the formation of chromium carbide at the coating/substrate interface during the steam oxidation. The magnitude of the chromium carbide formation was increased with increase in the temperature and the duration. Microstructural examination of the etched cross sections showed that beneath the chromium carbide layer the substrate microstructure transformed from tempered martensite to higher grain-width ferrite microstructure. The carbon depletion in this region resulted into longer ferrite grain formation. Micro hardness studies showed that at the coating/substrate interface the micro hardness values increased with increasing the test temperature and the duration. The substrate layer just beneath the coating showed the decreased hardness values compared to the core substrate region.

The boron and nitrogen contents of GaAs and InP melts equilibrated with B₂O₃ flux were examined at 1523 and 1373 K, respectively, using a chemical equilibrium technique. GaAs or InP was melted with B₂O₃ flux in a silica ampoule with and without a BN crucible. The boron content decreased with increasing nitrogen content in both of the melts equilibrated with B₂O₃ flux and BN. The solubility product of BN in the melts was expressed as a function of nitrogen content. The relationship between the boron and nitrogen contents of a GaAs melt coexisted with BN agreed well with that in the residue after LEC crystal growth of GaAs. The boron content of the GaAs melt coexisted with silica was much larger than that of the GaAs melt with BN. It was suggested that the reduction of B₂O₃ by silicon introduced into the melt from silica led the increase of boron content.

Nickel/ultra-dispersed PTFE composite films with various PTFE content are electrochemically prepared from a Watt's nickel plating bath in which the PTFE particles (mean diameter 0.3 μm) are suspended using a cationic fluorocarbon surfactant. The microstructures of Ni-PTFE composite films are analyzed by means of XRD, SEM and TEM, and their water-repellencies are also measured. The results indicate that the PTFE particles take a homogeneous distribution within all the composite films. The PTFE particle content in the composite films is dependent upon the particle concentration in the plating bath and the plating parameters, and strongly influence the physical properties of Ni-PTFE composite films such as water-repellency. The contact angle of a water drop on the surface of composite film with maximum PTFE content of about 47.4 vol% reaches 154.9°, showing a superior water-repellency.

We developed a chemical model to analyze ionic equilibria in a cobalt chloride solution at 298 K. The chemical model consisted of chemical equilibria, mass and charge balance equations. The activity coefficients of solutes and water activity were calculated with Bromley equation. Values of the equilibrium constants for the formation of cobalt chloride complexes at zero ionic strength and of the interaction parameters were estimated by applying Bromley equation to the reported equilibrium constants at different ionic strength. The effect of CoCl₂ and HCl concentrations on the distribution of cobalt species was obtained. The predicted pH values for CoCl₂-HCl-NaOH-H₂O system agreed well with those measured at 298 K.