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

MATERIALS TRANSACTIONS Vol. 43 (2002), No. 10

  • Low-Temperature Superplasticity in Aluminum Alloys Processed by Equal-Channel Angular Pressing

    pp. 2364-2369

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    DOI:10.2320/matertrans.43.2364

    Equal-channel angular pressing (ECAP) was applied to achieve grain refinement of Al–3 mass%Mg alloys containing 0.2 mass%Sc, 0.2 mass%Fe or 0.1 mass%Zr. The thermal stability of the fine-grained structures was examined by conducting static annealing experiments. The fine grain sizes produced by ECAP were essentially retained up to a temperature of 523 K for the Fe-containing and Zr-containing alloys and up to a temperature as high as 773 K for the Sc-containing alloy. The three alloys with Sc, Fe and Zr additions were pulled to failure in tension at 523 K corresponding to 0.59Tm, where Tm is the absolute melting point of the alloy, and maximum elongations of ∼ 640%, ∼ 370% and ∼ 390% were obtained at an initial strain rate of 3.3×10−4 s−1, respectively. Such elongations resulted in more than three times or approximately twice the elongation achieved in a binary Al–3%Mg alloy. It is shown that either Fe or Zr may be used as an alternative element in place of Sc to attain low temperature superplasticity. Tensile testing was also conducted on the Sc-containing ternary alloy at a temperature as low as 473 K corresponding to 0.54Tm. A maximum elongation of ∼ 420% was attained at an initial strain rate of 3.3×10−4 s−1. This appears to be the lowest homologous temperature reported to date for superplasticty of Al-based alloys.
  • High Strain Rate Superplasticity in an Al-Li-Mg Alloy Subjected to Equal-Channel Angular Extrusion

    pp. 2370-2377

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    DOI:10.2320/matertrans.43.2370

    The superplastic behavior of an Al–4.1%Mg–2.0%Li–0.16%Sc–0.07%Zr alloy (1421 Al) subjected to intense plastic straining by equal-channel angular extrusion (ECAE) was studied in the temperature interval 250–450°C at strain rates ranging from 1.4×10−5 to 1.4 s−1. The grain size after ECAE was about 0.8 \\micron and the fraction of high angle boundaries was about 80 pct. The highest elongation of 1850% without failure appeared at a temperature of 400°C and initial strain rate of 1.4×10−2 s−1 with corresponding coefficient of the strain rate sensitivity of 0.6. It was shown that the ECAE processed 1421 Al exhibits superior superplastic properties in the temperature range 300–450°C with the strain rate sensitivity higher than 0.4. Microstructural evolution and cavitation during high strain rate superplastic deformation were examined.
  • Deformation and Fracture at High Temperatures in an Al-Mg-Mn Alloy Sheet Consisting of Coarse- and Fine-Grained Layers

    pp. 2378-2384

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    DOI:10.2320/matertrans.43.2378

    High temperature deformation and fracture of the Al–Mg–Mn sheet consisting with the coarse-grained surface and the fine-grained center layers have been investigated. Such a microstructure was produced by the continuous cyclic bending (CCB) and the subsequent annealing. The elongation to failure has a peak value at 713 K at initial strain rates of 5.6×10−4 s−1 and 5.6×10−3 s−1 in both of as-received sample (0P) with fine grains and CCBent and annealed one (20P_A) with the coarse and the fine grains in spite of different microstructures. The m value decreases for 20P_A and increases for 0P with increasing temperature. However, the increase of the m value is not correspondent to the change in the elongation. Deformation mechanism is discussed with activation energy. The SEM micrographs of original surfaces of tensile specimen deformed to failure reveal that at the relatively high temperatures many cracks are formed inside the coarse grains. The features of fractured surface for the 20P_A sample reflect the coarse- and the fine-grained layers faithfully.
  • Effects of Flow Stress and Grain Size on the Evolution of Grain Boundary Microstructure in Superplastic 5083 Aluminum Alloy

    pp. 2385-2391

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    DOI:10.2320/matertrans.43.2385

    The effects of flow stress and grain size on the evolution of grain boundary character distribution (GBCD) at elevated temperatures were investigated using a superplastic aluminum 5083 alloy. In the superplastic region, the percentage of random boundaries was high and was almost unchanged during deformation. In addition, stress and grain-size dependencies on the variation of GBCD were not observed during superplastic deformation. On the other hand, in the dislocation creep region, the percentage of low-angle boundaries gradually increased with increasing strain. Stress and grain-size dependencies on the variation of GBCD were observed and the degree of increase in low-angle boundaries increased with increases in both stress and grain size. This microstructural change could be considered to be influenced by grain boundary sliding (GBS). The degree of increase in low-angle boundaries increased with a decrease in the contribution of GBS.
  • Effect of Cu and Zr Additions on the Superplastic Behavior of 6061 Aluminum Alloy

    pp. 2392-2399

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    DOI:10.2320/matertrans.43.2392

    Experiments were conducted to evaluate the influence of zirconium and copper additions on superplastic behavior of a 6061 aluminum alloy. Fine grains were produced in a commercial grade of 6061 Al and a 0.15%Zr+0.7%Cu-modified 6061 alloy by two-step thermomechanical processing. The superplastic properties and microstructure evolution of both alloys were examined in tension at temperatures ranging from 475 to 620°C and strain rates ranging from 7×10−6 to 2.8×10−2 s−1. It was shown using differential thermal analysis that both alloys exhibit the highest superplastic characteristics in a partially melted state. The 0.15%Zr+0.7%Cu-modified 6061 aluminum alloy exhibits a maximum elongation-to-failure of 1300% at 590°C and an initial strain rate of 2.8×10−4 s−1. In contrast, the highest total elongation of 350% (m∼0.6) was achieved in the commercial grade 6061 alloy at 600°C and a strain rate of 1.4×10−4 s−1. The results suggest the addition of Zr provides high stability of the fine-grained structure under superplastic deformation at high temperatures by precipitation of Al3Zr dispersoids. Apparently, the increased amount of liquid phase caused by the copper addition can enhance the superplastic properties of the 6061 alloy.
  • Continuous Dynamic Recrystallization in a Superplastic 7075 Aluminum Alloy

    pp. 2400-2407

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    DOI:10.2320/matertrans.43.2400

    New grain evolution taking place during superplasticity was studied by means of tensile tests as well as metallographic observation for a unrecrystallized coarse-grained 7075 aluminum alloy. Grain boundary sliding (GBS) frequently takes place even on the layered high angle boundaries (HABs) parallel to the tensile axis and brings about rotation of subgrains near the HABs and subsequently in grain interiors. The misorientations of (sub)grain boundaries evolved in the pancaked grains increase accompanied by a randomization of the initial texture, followed by development of new grains with HABs. This indicates that unrecrystallized and pancaked grain structure developed by cold rolling is an important prerequisite not only for the appearance of superplasticity, but also for the dynamic evolution of new fine grains. It is concluded that the mechanism of new grain evolution can be a deformation-induced continuous reaction, that is continuous dynamic recrystallization (CDRX). A model for CDRX is discussed in detail comparing with previous several models.
  • The Role of Grain Boundary Sliding in Microstructural Evolution during Superplastic Deformation of a 7055 Aluminum Alloy

    pp. 2408-2414

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    DOI:10.2320/matertrans.43.2408

    The microstructure evolution in a 7055 aluminum alloy subjected to thermomechanical processing (TMP) was studied at 450°C and \\dotε=1.7×10−3 s−1 at which the material exhibits superplastic behavior with a total elongation of 720% and the coefficient m=0.58. Partially recrystallized initial structure of the as-processed 7055 Al consisted of bands of recrystallized grains with a mean size of 11 \\micron alternating with bands of recovered subgrains with a mean size of 2 \\micron. The true stress–true strain curve exhibits a well-defined peak stress, followed by gradual strain softening. The coefficient of strain rate sensitivity, m, remains unchanged at ε≤1 and tends to decrease with strain at ε>1. The initial microstructure persists near the peak strain. Following strain leads to evolution of initial partially recrystallized structure into uniform fully recrystallized structure due to occurrence of continuous dynamic reactions, i.e. continuous dynamic recrystallization (CDRX). The data of microstructural observation and misorientation analysis show that low-angle boundaries (LAB) gradually convert to high-angle boundaries (HAB) resulting in an extensive flow softening. It was shown that grain boundary sliding (GBS) provides superplastic flow at all strains. Concurrently, GBS plays an important role in the dynamic evolution of new grains facilitating conversion of LABs to HABs.
  • The Critical Stress at the Interface for Cavity Nucleation in Superplastic Aluminum Matrix Composites Reinforced with Si3N4 Particles

    pp. 2415-2418

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    DOI:10.2320/matertrans.43.2415

    The minimum particle size for cavity nucleation was experimentally investigated for superplastic 2124Al and 6061Al composites reinforced with 20 vol% Si3N4 particles. From the minimum particle size for cavity nucleation, the critical stress at the interface for cavity nucleation was estimated to be about 5 MPa. The local stresses at the interface for the particles of average size where large elongation above 200% is attained in a temperature range below the partial melting temperature are lower than the critical stress. It may be therefore suggested that large elongation is attained without the accommodation helper process of liquid under the conditions that the local stress at the interface is lower than the critical stress at the interface for cavity nucleation.
  • Low Temperature Superplasticity of ECAE Processed Mg-10%Li-1%Zn Alloy

    pp. 2419-2423

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    DOI:10.2320/matertrans.43.2419

    In order to achieve low temperature superplasticity at relatively high strain rate in magnesium alloys, Mg–10 mass%Li–1 mass%Zn (LZ101) α+β two phase alloy was subjected to ECAE (Equal Channel Angular Extrusion) processing and tensile tests of the obtained specimens of the alloy were carried out to investigate the superplastic properties. In a specimen of the LZ101 alloy, which has improved microstructure through repetitive ECAE processing at 323 K, superplasticity occurs at 423 K, which is below Tm⁄2 (Tm: melting point of the alloy), under a relatively high strain rate of 1×10−3 s−1 with fracture elongation of 391%. Such a specimen after tensile test contains fine grains due to dynamic recrystallization and the precipitation of β phase along the grain boundaries and at triple points in recrystallized α phase. This microstructural change enhances grain boundary sliding, resulting in the occurrence of low temperature superplasticity at relatively high strain rate.
  • High Strain Rate and/or Low Temperature Superplasticity in AZ31 Mg Alloys Processed by Simple High-Ratio Extrusion Methods

    pp. 2424-2432

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    DOI:10.2320/matertrans.43.2424

    There have been numerous efforts in processing metallic alloys into fine-grained materials, so as to exhibit high strain rate superplasticity (HSRSP) and/or low temperature superplasticity (LTSP). The current study applied the most simple and feasible one-step extrusion method on the commercial AZ31 magnesium ingot to result in HSR&LTSP . The one-step extrusion was undertaken using a high extrusion ratio at 250–350°C, and the grain size after one-step extrusion became ∼ 1–4 \\micron. The processed AZ31 plate exhibited satisfactory room temperature tensile elongation of 30–50%; 200°C elongations of 600% at 1×10−4 s−1 and 425% at 1×10−3 s−1; and 300°C elongations of 900% at 1×10−4 s−1, 520% at 8×10−3 s−1, 300% at 2×10−2 s−1, and 210% at 1×10−1 s−1. This suggests that the current AZ31 Mg alloy has possessed HSRSP at relatively low temperatures of 280–300°C, as well as LTSP at 200°C. The low flow stress of 15–30 MPa and the true strain rate sensitivity of 0.3–0.4 both suggest that grain boundary sliding and solute drag creep have operated under these loading conditions. The current results imply that the simple high-ratio extrusion method might be a feasible processing mean for industry applications.
  • Superplastic Behavior and Microstructural Evolution in a Commercial Mg-3Al-1Zn Magnesium Alloy

    pp. 2433-2436

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    DOI:10.2320/matertrans.43.2433

    Superplastic behavior and microstructural evolution in a commercial Mg–3Al–1Zn magnesium alloy were investigated at temperatures between 623 K and 723 K and strain rates between 10−5 and 10−3 s−1. Grain refinement was obtained in the test alloy due to the dynamic recrystallization during an initial stage of tensile test. As a result, the alloy exhibited good superplasticity at all strain rates and temperatures, and a maximum elongation of 314% was obtained. The results of optical microscopy and SEM revealed that the dominant deformation mechanism was grain boundary sliding, and the dynamic recrystallization was the accommodated mechanism for the deformation.
  • Superplasticity and Cavitation of Recycled AZ31 Magnesium Alloy Fabricated by Solid Recycling Process

    pp. 2437-2442

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    DOI:10.2320/matertrans.43.2437

    Superplastic behavior and cavitation have been investigated for the solid recycled AZ31 magnesium alloy made of machined chips. The elongation to failure of the solid recycled specimen was lower than that for the extruded specimen from a virgin block (virgin extruded specimen) at elevated temperature, although the strain rate sensitivity for the solid recycled specimen was the same as that for the virgin extruded specimen. The volume fraction of cavities and the total number of cavities for the solid recycled specimen were larger than those for the virgin extruded specimen. Moreover, cavity nucleation occurred not only at grain boundaries, but also in the grains for the solid recycled specimen. It is suggested that contamination of oxide particles at grain boundaries and in grains promotes cavity nucleation in the solid recycled specimen and adversely affects the elongation to failure.
  • Superplastic Forming of AZ31 Magnesium Alloy Sheet into a Rectangular Pan

    pp. 2443-2448

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    DOI:10.2320/matertrans.43.2443

    Superplastic behaviour of Mg-alloy AZ31 was investigated to clarify the possibility of its use for superplastic forming (SPF) and to accurately evaluate material characteristics under a biaxial stress by utilizing a multi-dome test. The material characteristics were evaluated under three different superplastic temperatures, 643, 673, and 703 K in order to determine the most suitable superplastic temperature. Finite Element Method (FEM) simulation of rectangular pan forming was carried out to predict the formability of the material into a complex shape. The superplastic material properties are used for the simulation of a rectangular pan. Finally, the simulation results are compared with the experimental results to determine the accuracy of the superplastic material characteristics. The experimental results revealed that the m values are greater than 0.3 under the three superplastic temperatures, which is indicative of superplasticity. The optimum superplastic temperature is 673 K, at which a maximum m value and no grain growth were observed. The results of the FEM simulation revealed that certain localized thinning occurred at the die entrance of the deformed rectangular pan due to the insufficient ductility of the material. The simulation results also showed that the optimum superplastic temperature of AZ31 is 673 K.
  • Room Temperature Deformation Behavior of Zn-22 mass%Al Alloy with Nanocrystalline Structure

    pp. 2449-2454

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    DOI:10.2320/matertrans.43.2449

    The deformation behavior near room temperature in Zn-22 mass%Al alloy including nanocrystalline structure produced with Thermo Mechanical Controlling Process (TMCP) technology has been characterized over a wide range of strain rates from 10−6 to 10−1 s−1 at temperatures from 273 to 473 K . The microstructure of TMCP produced Zn-22 mass%Al alloy had both a random distribution of equiaxed Al-rich and Zn-rich phases with grain size of 1.3 \\micron and many nanocrystalline Zn particles in Al-rich phases. Since the flow stress in the deformation near room temperature was much larger than that in superplastic deformation and a maximum m value is only 0.3 (n=3) at low strain rates below 10−5 s−1, the pure superplastic behavior may not be observed near room temperature. However it is noted that the large elongation of ∼ 200% was observed at 10−5 s−1. From microstructural observations of the specimens tested in the condition with the m value of 0.3 near room temperature, furthermore, it is considered that grain boundary sliding (GBS) is the dominant deformation process, and the specimen may be fractured by cavitation as well as the conventional superplastic materials. Therefore, it seems that the various factors contribute to the deformation flow at room temperature.
  • Grain Boundary Character and Superplasticity of Fine-Grained Ultra-High Carbon Steel

    pp. 2455-2462

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    DOI:10.2320/matertrans.43.2455

    The characteristics and superplasticity of the (α+θ) microduplex structures formed by various thermomechanical processings were studied in an ultra-high carbon steel (Fe–1.4Cr–1.0C). After heavy warm rolling of pearlite, an (α+θ) microduplex structure with equi-axed α grains of 0.4 \\micron in diameter and spheroidized θ particles of 0.2 \\micron in diameter is obtained. The α matrix exhibits a recovered structure in which most of α grain boundaries are low-angle boundaries, resulting in rather smaller elongation at 973 K . Heavy cold rolling and annealing of pearlite produces an (α+θ) microduplex structure which consists of the coarse-grain region (dα∼0.4 \\micron) with high-angle α boundaries and the fine-grain region (dα∼0.2 \\micron) with low-angle α boundaries. Superplasticity in this specimen is slightly better than the warm-rolled specimen. When pearlite was austenitized in the (γ+θ) region, quenched and tempered at the temperature below A1, an (α+θ) microduplex structure in which α and θ grain sizes are nearly the same as in the warm-rolled specimen and most of α boundaries are of high-angle one is formed. Such ultra-fine α grains are formed through the recovery of the fine (α lath martensite+θ) mixture during tempering. This microduplex structure exhibits superior superplasticity. Heavy warm rolling prior to the quenching and tempering improves total elongation further because the distribution of prior γ grain size is more uniform. When cold-rolled pearlite was austenitized and air-cooled, an (α+θ) microduplex structure with high-angle α boundary is formed. However, since the α grain size was relatively large (ca. 2 \\micron), its superplastic performance is poor. Finally, more simplification of processing for superplasticity was attempted. Further improvement of superplasticity was achieved by omitting the tempering in the quenching and tempering treatment.
  • Deformation Behavior of Pt-based Metallic Glass at Elevated Temperatures

    pp. 2463-2467

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    DOI:10.2320/matertrans.43.2463

    Pt60Ni15P25 metallic glass ribbons prepared by a single-roll melt-spinning method were deformed in tension at a strain rate of 2×10−2 s−1 in the supercooled liquid region. In-situ observations of the deformation behavior of the metallic glass ribbons were carried out using an optical microscope. It was found that a homogeneous deformation of more than 200% elongation took place by a viscous flow of the supercooled liquid of Pt60Ni15P25 metallic glass at 523 K, an intermediate temperature in the supercooled liquid region. In the case of the tensile tests after partial crystallization at 543 K, it was found that the residual supercooled liquid deformed preferentially without deformation of the crystalline solid, and therefore inhomogeneous deformation occurred.
  • Local Bonding States of Titanium and Germanium-doped Tetragonal Zirconia Polycrystal and Their Correlation to High Temperature Ductility

    pp. 2468-2472

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    DOI:10.2320/matertrans.43.2468

    The chemical bonding states of GeO2 and/or TiO2-doped tetragonal zirconia polycrystal (TZP) are calculated by a first principle molecular orbital method using model clusters. It is clarified that Ge4+ and Ti4+ ions, which are substituted into a lattice of TZP, have a high covalent bond with oxygen ions rather than Zr–O bond. Covalency of TZP is more increased by solution of germanium ions than that of titanium ones. In superplastic deformation of TZP, an addition of GeO2 or TiO2 enhances tensile ductility of TZP . Germanium ion is more effective to improve ductility than titanium. The increment of covalency is in a good agreement with the improvement of elongation to failure in doped TZP . Dopant cations segregate at grain boundaries and form no secondary phase. Assuming that a dopant effect on chemical bonding states in grain boundaries is similar to that in grain interior, segregation of germanium or titanium ion increases covalent bonding strength nearby grain boundaries. Such increasing of covalency is likely to enhance cohesion of grain boundaries. The enhancement of grain boundary cohesion suppresses intergranular failure during tensile deformation at elevated temperatures. This must be the reason why an addition of GeO2 and TiO2 is effective to improve the high temperature ductility of TZP . Our calculation suggests that the covalency nearby grain boundaries have a critical role in the tensile ductility of TZP.
  • Thermal Conductivity of Superplastically Deformed 3Y-TZP

    pp. 2473-2479

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    DOI:10.2320/matertrans.43.2473

    The thermal diffusivity and specific heat of superplastically deformed 3Y-TZP specimens were measured in a temperature range from 298 to 1273 K . From these data, the thermal conductivity has been evaluated and discussed. A weak temperature dependence of the thermal conductivity was observed. The thermal conductivity showed almost no dependence on the grain size and grain aspect ratio of the 3Y-TZP specimens. On the other hand, the thermal conductivity was considerably sensitive to the deformation-induced cavities. The influence of the cavities on the thermal conductivity is related with temperature. An expression was proposed for predicting the relationship between the effective thermal conductivity and deformation-induced cavities within the present experimental range.
  • Characterization of Cavities in Superplastically Deformed Tetragonal Zirconia Polycrystals by Means of Small Angle Neutron Scattering

    pp. 2480-2486

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    DOI:10.2320/matertrans.43.2480

    Small angle neutron scattering (SANS) method was applied to investigate morphology of cavities in superplastically deformed 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP). The 3Y-TZP specimens were deformed in tension at 1723 K with an initial strain rate of 3.3×10−4 s−1 in the air to pre-determined nominal strains ranging from 0.0 to 200%. Three kinds of SANS instruments having individually different scattering vector ranges were used. Results obtained from a pinhole SANS instrument revealed that initially fine and equi-axed cavities evolved, with the progress of the deformation, into the anisotropic ones with their longest diameters parallel to the tensile direction. Results obtained from a double bent-crystal and a Bonse-Hart SANS instruments showed that the average radius of all cavities existing in the specimens decreased initially with increasing nominal strain, but subsequently this trend was reversed when the nominal strain exceeded about 100%. Specific surface of cavities began to increase at a nominal strain of approximately 20%. Size distributions obtained from the SANS data showed that highest peaks appeared at a cavity radius of around 200 nm for each of the specimens deformed to different strains, which indicated that the cavities with radius of around 200 nm accounted for the largest in number among all the cavities existed.
  • Microstructures and Mechanical Properties of Al3Fe Reinforced Aluminum Matrix Composites Fabricated by a Plasma Synthesis Method

    pp. 2487-2493

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    DOI:10.2320/matertrans.43.2487

    The MMCs of Al/Al3Fe and A2218/Al3Fe composites were fabricated by injection of Fe particles into the Al melt through a plasma synthesis method. The elastic modulus and yield strength of the fabricated composites were evaluated through the measurement of ultrasonic velocity and room temperature compression test. The measured values were compared with the predicted ones based on the continuum mechanics approach for the elastic modulus and the micromechanics approach for the yield strength. The properties of Al/Al3Fe were well consistent with the predicted models, while the properties of A2218/Al3Fe exhibited lower values than the predicted ones. The deviations of the properties for A2218/Al3Fe were examined in terms of the matrix microstructures.
  • Bio-Functionalization of Titanium Surfaces for Dental Implants

    pp. 2494-2501

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    DOI:10.2320/matertrans.43.2494

    Since dental implants are used in contact with many different tissues, it is necessary to have optimum surface compatibility with the host bone tissues and soft tissues. Furthermore, dental implant surfaces exposed to the oral cavity must remain plaque-free. Such materials can be created under well-controlled conditions by modifying the surfaces of metals that contact those tissues. “Tissue-compatible implants,” which are compatible with all host tissues, must integrate with bone tissue, easily form hemidesmosomes, and prevent bacterial adhesion. This research was aimed at developing such tissue-compatible implants by modifying titanium surfaces using a dry process for closely adhering to the titanium substrate and ensuring good wear resistance. The process includes ion beam dynamic mixing (thin calcium phosphates), ion implantation, titania spraying, ion plating and ion beam mixing. At the bone tissue/implant interface, a thin calcium phosphate coating and rapid heating with infrared radiation was effective in controlling the dissolution without cracking the coating. This thin calcium phosphate coating may directly promote osteogenisis, but also enable immobilization of functional proteins or drugs such as bisphosphonate for dug delivery system. At the oral fluid/implant interface, an alumina coating and F+-implantation were responsible for inhibiting the adhesion of microbial plaque. In conclusion, dry-process surface modification is useful in controlling the physicochemical nature of surfaces, including the surface energy and the surface electrical charge, and in developing tissue-compatible implants.
  • Prediction of Glass-Forming Composition Ranges in Zr-Ni-Al Alloys

    pp. 2502-2508

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    DOI:10.2320/matertrans.43.2502

    Glass-forming composition ranges in the alloy system Zr–Ni–Al are predicted by applying Miedema’s semi-empirical method. The compositional dependence of the formation enthalpies of amorphous ΔH(\\mathitAmo), solid solution ΔH(\\mathitSS), and intermetallic compound phases ΔH(\\mathitComp) is calculated. We propose that the enthalpy difference parameters of ΔH(\\mathitSS)-ΔH(\\mathitAmo), ΔH(\\mathitAmo)-ΔH(\\mathitComp) and simple criteria, including electronegativities, can be used to predict the glass-forming composition ranges (GFR) and the dominant factors determining the glass-forming ability (GFA). The wide GFR in the system, apart from the Al-rich region, and the tendency of the intermetallic compounds to form and constrain any extension of the GFR, are clearly predicted by a combining evaluation of these parameters and the simple criteria. The large negative heat of mixing, the atomic size difference among the constituent elements, and the short-range order stabilize the glassy phase leading to a high GFA of the alloy system. Furthermore, the composition dependence of crystallization temperatures Tx and the glass transition temperatures Tg can be estimated on the basis of the enthalpy values. Results compare well with the experimental data.
  • Electron Beam Welding of Zr50Cu30Ni10Al10 Bulk Glassy Alloys

    pp. 2509-2515

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    DOI:10.2320/matertrans.43.2509

    By using a conventional electron beam welding machine, an electron beam welding of Zr50Cu30Ni10Al10 bulk glassy plates has been achieved in the welding condition leading to the suppression of heat affected zone (HAZ). In order to obtain the cooling rate, which is sufficient for glass formation, the welding speed was controlled to be higher than 100 mm/s and the beam-radiated area should be limited to be smaller than 0.8 mm in diameter. Joint strength of the welded bulk glassy plate is about 1400 MPa, which is lower by 15% than the tensile strength (1650 MPa) of the glassy alloy. The fracture of the welded alloy plate occurs along shear slip plane across the welded area, reflecting good ductility in the welded area of the Zr50Cu30Ni10Al10 bulk glassy alloy.
  • Technology for Recycling Magnesium Alloy Housings of Notebook Computers

    pp. 2516-2522

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    DOI:10.2320/matertrans.43.2516

    Magnesium housings, which are lightweight, strong, and have high heat radiation characteristics, are in widespread use for portable personal computers and similar devices. Another characteristic of magnesium alloy is that it is a metal that can be melted for recycling. There are two ways of recycling magnesium alloy housings, one for recycling excess material generated during the molding process and one for recycling collected magnesium alloy housings that have been painted. Whether the molding method is die casting or thixomolding, the housing weight accounts for only about 30% to 50% of the Mg alloy that is injected. The remaining 50% to 70% is sprue and runner, which are excess after molding. It is important to establish a method of recycling for the excess material by as cost reduction. However, the data available for the material that was recycled repeatedly was not adequate. This was an issue to resolve in promoting the recycling of Mg alloy housings. Notebook PCs collected from the market are encased in painted MG alloy housings. Now, painted Mg alloy housings is rarely recycled. In the former process, adjusting the composition of the magnesium alloy in the remelting process restores the same strength and corrosion resistance characteristics as the virgin material despite repeated recycling. In the latter process, soaking in a solution causes the paint to flake off the magnesium alloy housings. The remaining alloy that is then remelted and the adjusted composition can produce a recycled material having the same performance characteristics as the virgin material without generating much gas or dust in the remelting process. The technology for recycling excess material was first applied to the production of the Fujitsu PC FMV-BIBLO notebook that was marketed in 1999. The technology for recycling painted magnesium alloy housings will be applied in full starting in fiscal 2002.
  • Surface Segregation of Chromium in a Copper-Chromium Alloy and its Effect on Formation of a Native Oxide Layer

    pp. 2523-2526

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    DOI:10.2320/matertrans.43.2523

    Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) has been used for studying the surface segregation of chromium in a copper-0.4 mass% chromium alloy. The influence of the chromium segregation on native oxide layers formed on the surface in this alloy has also been studied. According to a simple layered model assuming thin homogeneous layers, the average surface concentration chromium was found to increase up to about 15 at% on the alloy surface by annealing up to about 1000 K under ultra high vacuum. The AR-XPS results for the alloy surface with chromium segregation, which was exposed to air, showed that the growth of the native oxide layer of copper was not significantly suppressed by segregated chromium. This small influence of chromium segregation on the native oxide layer is considered to result from the relatively high oxidation rate of copper and the microscopic heterogeneity of chromium segregation on the alloy surface.
  • High Temperature Oxidation of Ti-(45, 47)%Al-2%Mn-2%Nb-0.8 vol%TiB2 Alloys

    pp. 2527-2530

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    DOI:10.2320/matertrans.43.2527

    The oxidation behavior of XD45 (Ti45Al2Mn2Nb–0.8 vol%TiB2) and XD47 (Ti47Al2Mn2Nb-0.8 vol%TiB2) alloys that were thermomechanically treated to have (γ+α2) duplex microstructures was studied between 1073 and 1273 K in air. XD47 displayed a little slower oxidation rate and better scale adherence than XD45. The oxide scales consisted primarily of an outer TiO2 layer, an intermediate Al2O3-rich layer, and an inner (TiO2+Al2O3) mixed layer. Mn and Nb tended to segregate at the outer TiO2 layer and the inner (TiO2+Al2O3) mixed layer, respectively. The outer layer grew primarily by the outward diffusion of Ti and Mn, and the inner mixed layer by the inward transport of oxygen. Dispersoids of TiB2 oxidized to semiprotective TiO2 and highly volatile B2O3 which evaporated. A small amount of TiN and Ti2AlN formed during oxidation.
  • High Temperature Oxidation of Ti-47%Al-1%Mn Alloy

    pp. 2531-2535

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    DOI:10.2320/matertrans.43.2531

    The thermomechanically treated Ti–47%Al–1%Mn alloy was oxidized in air at 1073, 1173, and 1273 K . When compared to Ti–47%Al, the oxidation resistance of Ti–47%Al–1%Mn was better at 1073 K, slightly better at 1173 K, but poorer at 1273 K . The scale adherence was improved by the addition of Mn to a certain degree. The oxidation products were TiO2 and α-Al2O3, together with a very small amount of MnTiO3, Mn2O3, TiN and Ti2AlN . Within the (TiO2, Al2O3) oxide grains, some dissolution of Mn was noticed. The oxidation progressed via the outward diffusion of Ti ions to form the outer TiO2 layer, and the inward transport of oxygen to form the inner (TiO2+Al2O3) mixed layer, between which an intermediate Al2O3 layer existed. Subsurface zone within the metal phase was depleted in Al.
  • Formation and Annealing Behavior of Nanocrystalline Steels Produced by Ball Drop Test

    pp. 2536-2542

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    DOI:10.2320/matertrans.43.2536

    Nanocrystallization by a ball drop test in an eutectoid steel with either pearlite or spheroidite structure has been studied. By a ball drop test, nanocrystalline layer has been formed along the surface (near the edge of the impact crater) and interior of specimen (near the bottom of the impact crater). Prior deformation of specimens has been found to reduce the number of ball drops to produce nanocrystalline layer. When the prior deformation was severe enough, one time of ball drop could produce a nanocrystalline layer. Severe shear deformation was observed at the nanocrystalline layer. This suggests that strain localization under a high strain rate deformation promotes nanocrystallization. For the samples with pearlite structure, cementite dissolved completely in the nanocrystalline layer. For the samples with spheroidite structure, most of cementite particles also dissolved by a ball drop test. A mechanism account for dissolution of spherical cementite is proposed. After annealing at 873 K for 3.6 ks, grain growth took place in the nanocrystalline region in contrast to recrystallization in work-hardened region like observed in ball milled powders. Fine cementite particles re-precipitated at nanocrystalline ferrite grain and then inhibited the grain growth effectively.
  • Effects of Hydrogen on the Mechanical Properties of Ti50Ni25Cu25 Metallic Glass

    pp. 2543-2547

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    DOI:10.2320/matertrans.43.2543

    A number of studies on the internal friction of hydrogenated amorphous alloys have been recently performed in order to develop new high damping materials with mechanical strength higher than that of crystalline ones. In this work, effects of hydrogen on the mechanical properties such as fracture strength and internal friction have been investigated in a Ti50Ni25Cu25 metallic glass. It is found that the Ti50Ni25Cu25 metallic glass has high fracture strength even after absorbing hydrogen up to 24.7 at%, while the fracture strength decreases significantly in the high hydrogen content up to about 40 at%. It is also found that the internal friction peak Q−1 is about 5.0×10−2 at 185 K in the case of 40.2 at% hydrogen content. It should be noted that the peak temperature is observed between room temperature and 185 K and decreases with increasing hydrogen content while the peak height increases gradually with increasing hydrogen content.
  • Effect of Cell Size on the Dynamic Compressive Properties of Open-Celled Aluminum Foams

    pp. 2548-2553

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    DOI:10.2320/matertrans.43.2548

    In the present paper, open-celled AA6101–T6 aluminum foams, Duocel, with virtually the same relative density of 0.09 were tested at both a dynamic strain rate of 1.2×103 s−1 and quasi-static strain rate of 1×10−3 s−1 in compression at room temperature. These Duocel foams have different cell sizes (10, 20, and 40 ppi) but similar cell morphology and microstructure. The mechanical strength and energy absorption of these foams were characterized as a function of strain rate and cell morphology. Experimental results indicated that the mechanical responses of Duocel foams were independent of the cell size and strain rate. Similar tests were also conducted with fully dense AA6101–T6 aluminum alloy and the results were compared with those obtained from the foam materials.
  • Mechanical Properties and Press Formability at Room Temperature of AZ31 Mg Alloy Processed by Single Roller Drive Rolling

    pp. 2554-2560

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    DOI:10.2320/matertrans.43.2554

    Mechanical properties and press formability at room temperature of AZ31 Mg alloy processed by single roller drive rolling were compared with those of the one processed by normal rolling. The single roller drive rolled specimens showed the weaker intensity of (0002) texture. As a result of tensile tests, there was no difference in unidirectional elongation between them. However, results of conical cup tests show that the press formability of the single roller drive rolled specimen was rather better. The planar anisotropy was lower and twins were observed for the single roller drive rolled specimen, indicating that the weaker intensity of texture leads to twining, resulting in the lower planar anisotropy.
  • Corrosion Resistance of Alumina-Chromia Ceramic Materials Against Molten Slag

    pp. 2561-2567

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    DOI:10.2320/matertrans.43.2561

    Improvement of the corrosion resistance of refractories is required critically, since Al2O3 based conventional refractories used for incineration at the power generation plants are seriously corroded by the molten oxide mixture. In this study, the effect of the addition of Cr2O3 to Al2O3 on the corrosion resistance, and the corrosion behavior of Cr2O3–Al2O3 system are investigated in the molten oxide. Cr2O3–Al2O3 ceramic materials with TiO2 as a sintering additive were used for the corrosion tests. Specimens were soaked into the SiO2–CaO–Al2O3 based molten oxide and rotated. The corrosion rate of the material is controlled by the diffusion of components of Cr2O3–Al2O3 through the boundary layer. The corrosion resistance was improved by addition of Cr2O3. The largest improvement was achieved when the addition of Cr2O3 was 81.6 mol%. It can be explained by the difference of diffusion rate of Cr3+ and Al3+.
  • Hi-NicalonTM Fiber-Reinforced CVI-SiC Matrix Composites: I Effects of PyC and PyC-SiC Multilayers on the Fracture Behaviors and Flexural Properties

    pp. 2568-2573

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    DOI:10.2320/matertrans.43.2568

    The flexural properties of 2D plain-woven Hi-NicalonTM fiber reinforced SiC/SiC composites with various PyC and PyC-SiC multilayers were studied at ambient temperature. The composites were fabricated by chemical vapor infiltration process (CVI). The interlayers were deposited by isothermal CVI process from methane for PyC layer and CH3SiCl3 (MTS) for SiC layer. The effects of the various interlayers on the fracture behaviors and flexural properties were investigated. The PyC layer thickness showed significant influence on the flexural strength and an optimum PyC layer thickness was defined to be ∼ 150 nm. Fiber/matrix interfacial debonding occurred at the very fiber surface for single PyC layered composites while several interfacial debonding and cracking behaviors were observed with the PyC-SiC multilayered composites.
  • Hi-NicalonTM Fiber-Reinforced CVI-SiC Matrix Composites: II Interfacial Shear Strength and Its Effects on the Flexural Properties

    pp. 2574-2577

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    DOI:10.2320/matertrans.43.2574

    The interfacial shear strengths (ISSs) of a series of 2D Hi-Nicalon/SiC composites with various pyrolitic carbon (PyC) or PyC-SiC multiple fiber/matrix interlayers were investigated using the single fiber pushout tests. The influence of the obtained ISS on the proportional limit stress (PLS) of the materials upon bending was discussed based on the experimental results and a thoretical model calculation. The ISS showed close PyC layer thickness dependence. The ISS decreased quickly from 505 MPa to ∼ 100 MPa with increasing the PyC layer thickness up to ∼ 200 nm, beyond which slight decrease of the ISS occurred till 760 nm of the PyC layer. The ISS showed significant influence on the PLS. Good agreement between the model calculations and the experimental results was obtained, when correlating the PLS to the ISS. The comparison between the model calculation and the experimental results may be indicative on further efforts on further improvement of the mechanical performance of SiC/SiC composites.
  • Formation and Thermal Stability of Ca-Mg-Ag-Cu Bulk Glassy Alloys

    pp. 2578-2581

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    DOI:10.2320/matertrans.43.2578

    Calcium-based bulk glassy alloys in Ca–Mg–Ag and Ca–Mg–Ag–Cu systems were produced by a metallic mold casting method. The maximum rod diameter (dmax) for the formation of a glassy phase was 4 mm for Ca60Mg20Ag20 and 7 mm for Ca60Mg20Ag10Cu10. The glass transition temperature (Tg), crystallization temperature (Tx), temperature interval of supercooled liquid region (ΔTx=TxTg) and melting temperature (Tm) were 401 K, 435 K, 35 K and 654 K, respectively, for the former alloy and 398 K, 428 K, 30 K and 624 K, respectively, for the latter alloy. The simultaneous addition of Ag and Cu in the Ca–Mg–(Ag, Cu) system causes a steep decrease in Tm and an increase in the reduced glass transition temperature (TgTm), leading to an increase in the glass-forming ability.
  • Formation of Pores during Unidirectional Solidification of Water Containing Carbon Dioxide

    pp. 2582-2588

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    DOI:10.2320/matertrans.43.2582

    Water-carbon dioxide solutions of various concentrations of carbon dioxide are unidirectionally solidified upwards in a glass cell at various growth rates, and the formation of the pores of carbon dioxide is in-situ observed. Columnar pores are formed at low growth rates. The length of the columnar pores becomes shorter as the growth rate increases or as the carbon dioxide concentration increases. The distribution of the pores is not uniform but periodic along the solidification direction, except under the conditions of high growth rate and high concentration. The change in the length of the columnar pores and the periodic formation of the pores are explained in terms of the rate of supply of carbon dioxide to the growing pores from the surrounding liquid.
  • Synthesis of TiAl(Cr)/Ti2AlC Composites by Reactive Arc-Melting

    pp. 2589-2592

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    DOI:10.2320/matertrans.43.2589

    TiAl(Cr)/Ti2AlC composites have been prepared by a reactive arc-melting technique using elemental powders of Ti, Al, Cr and C . Resulting composites have been reinforced using 3.5, 10 and 18 vol% Ti2AlC in a matrix of TiAl with and without addition of Cr. The axial ratio of γ-phase has been lowered through the complete solid solution of chromium. The grain size of the matrix has been found to decrease whereas its distribution converges along the content of Ti2AlC . The lamella grains in the matrix have been changed both into TiAl and very fine Ti2AlC particles by a homogenizing treatment. Compared to TiAl single-phase alloy, studied composite materials have revealed superior mechanical properties, such as bending strength, compressive strength and fracture toughness. This improvement is caused by the formation of Cr solid-solution for hardening, dispersion of the Ti2AlC particles and the fine grain of the TiAl matrix.
  • Phase Transformations in Al87Ni7Ce6 and Al87Ni7Nd6 Amorphous Alloys

    pp. 2593-2599

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    DOI:10.2320/matertrans.43.2593

    This paper reports on studies of the effect of different rare earth (RE) elements on the devitrification behaviour of alloys of general composition Al87Ni7RE6 (here RE=Ce, Nd). We have evidenced two crystallisation mechanisms as a function of the type of rare earth element. When RE=Ce the transformation proceeds in two steps as shown by Differential Scanning Calorimetry (DSC) traces. When RE=Nd the transformation sequence has an additional step. There is also evidence of a calorimetric continuous background for all alloys which is attributed to diffusional homogenisation of the matrix. The glass transition becomes manifest for both alloys when fast enough rates are used in DSC (higher than 10 K/min and 40 K/min, respectively for Al87Ni7Ce6 and Al87Ni7Nd6). The first crystallisation step implies the precipitation of nanocrystalline Al. The kinetics of this process is influenced by the simultaneous occurrence of the glass transition. In Al87Ni7Ce6 when it takes place above Tg (i.e. at high heating rates) it also implies the formation of an intermetallic compound. Kissinger plots for the first transformation display a kink at temperatures corresponding to the glass transition range marking the change in mechanism for the transformation. In Al87Ni7Nd6 the glass transition remain visible after partial crystallisation showing that the matrix is readily homogenised. Therefore the molten state of these alloys appears rather fragile.
  • Interface Stability in Diffusion Couple of L10 type TiAl and L12 type (Al, Mn)3Ti Alloys at 1273-1473 K

    pp. 2600-2603

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    DOI:10.2320/matertrans.43.2600

    Titanium trialuminide coating on L10-type titanium aluminide alloys represents a valuable mean to improve oxidation resistance. Selection of L12-type titanium trialuminide alloys containing Mn as a coating material is particularly attractive because of its good ductility at room temperature and good oxidation resistance at high temperature of 1273 K . However, stability of the coated titanium trialuminide at high temperature and adhesion to the substrate are not established. Two kinds of diffusion couples composed of L10 and L12 single phase alloys with or without vanadium were applied to diffusion experiments in a temperature range of 1273–1473 K for 2.5–20 h. During the diffusion process, L10 and L12 phases coexisted without any inter-phase, irrespective of diffusion temperature and vanadium addition. The diffusion couples composed of the alloys without vanadium exhibited cracked region at the interface between the L10 and L12 phases, while the diffusion couples composed of the alloys with vanadium exhibited no cracked region. The L12-type alloy with vanadium was shown to be an appropriate coating material on the L10 alloy.
  • Laser Brazing of Diamond Grits Using a Cu-15Ti-10Sn Brazing Alloy

    pp. 2604-2608

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    DOI:10.2320/matertrans.43.2604

    Brazing of diamond grits onto a steel substrate, using a Cu–Ti–Sn brazing alloy, was carried out via laser brazing in an argon atmosphere. The laser power was maintained at either 400, 450, or 500 W, while the laser irradiation time was 10 seconds. For a brazed layer of about 7 mm in diameter and 90 \\micron in thickness, a power input of 450 W was found to yield the optimal result. Due to the short irradiation time at high temperatures, discrete TiC grains of about 100 nm in size developed, instead of a continuous TiC layer formed at higher and longer process conditions, on the diamond surface. These TiC grains still effectively reduced the stress associated with the mismatch between the diamond grit and Cu in the aspects of lattice constant and thermal expansion coefficient. Accordingly, only a low percentage (about 5%) of diamond grits was pulled out of the brazed layer after a grinding test.
  • Structure of Thermoelectric Material CoSb3 Formed by Reactive Diffusion

    pp. 2609-2616

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    DOI:10.2320/matertrans.43.2609

    Thermoelectric material, CoSb3, has been formed in solid Co/solid Sb, solid Co/liquid Sb and solid Co/vapor Sb reactive diffusion couples in the temperature range between 723 K and 1123 K . The solid Co/vapor Sb diffusion couples were annealed in a furnace having two homogeneity temperature zones keeping Co side and Sb side temperatures independently. CoSb3 phase formed in these Sb diffusion couples showed various structures such as granular grains, large size polygonal grains with sharp edge and a flat diffusion layer with many small voids or with Sb phase depending on the kind of diffusion couples and temperature. The formation kinetics of such structures and growth of CoSb3 have been studied and discussed.
  • On The Characterization of Plastic Flow in Zr-based Metallic Glass Through Micro-indentation: an Atomic Force Microscopy Analysis

    pp. 2617-2621

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    DOI:10.2320/matertrans.43.2617

    We report an atomic force microscopy analysis of multiple shear bands emerged under multiaxial deformation through micro-indentations of Zr60Ni10Cu20Al10 metallic glass forming system. Both relative variations of normal and lateral force components as a result of contact between a Si3N4 tip mounted on a cantilever beam and incomplete circular pattern features developed around indentation are recorded at the nano and micro-length scales. Accurate three-dimensional measurements of shear offset as function of position along the shear band and the loading charge in the range of 0.5 to 5 N are determined. Evidence for propagation of discrete displacement increments is shown. Numerical calculations based on the well defined strain localization model including hydrostatic pressure effect on elastic variation of the average free volume are developed to explain the incomplete circular patterns of shear bands observed under constrained deformation.
  • The role of Silicon on Microstructure and High Temperature Performance of Aluminide Coating on Superalloy In-738LC

    pp. 2622-2628

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    DOI:10.2320/matertrans.43.2622

    The microstructures of slurry Si-modified aluminide coatings on Ni-base superalloy In-738LC have been investigated using SEM, TEM, EDS and XRD . The corrosion performance of the coatings has been also investigated by hot corrosion and cyclic oxidation tests. In order to evaluate the hot corrosion performance, the anodic polarization curves were measured in Na2SO4–25 mol%NaVO3–5 mol%NaCl at 1053 K . The cyclic oxidation test was carried out by exposure to alternate conditions of air atmosphere at 1373 K and room temperature. The analyses of SEM, EDS and XRD were also used to characterize attack morphologies of the coatings exposed to the test conditions. The results showed that the heat-treated slurry Si-modified aluminide coating was composed of β-NiAl phase including fine precipitates, which were found to be complex silicides. The results of hot corrosion tests indicated that at least 10–13 mass%Si in the coating layer is needed to improve the corrosion resistance of the aluminide coating. The coatings that met this criterion also showed a good cyclic oxidation resistance.
  • Microstructure Control of Particle Reinforced Metal Matrix Composites Fabricated by Low-Pressure Infiltration Process

    pp. 2629-2634

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    DOI:10.2320/matertrans.43.2629

    Process parameters to control the microstructure of particle reinforced MMC in the low pressure infiltration process (LPI process), have been investigated. The mixed powder of reinforcement particle and pure aluminum particle in various volume fraction was employed to control the volume fraction of the reinforcement particles in PRMMC . The Al–12 mass%Cu alloy melt was forced to infiltrate into the mixed powder layer by applying a certain pressure of argon gas on the melt surface. The pressure required to infiltrate remarkably increased from 0.05 to 0.5 MPa with a decrease in the particle size from 100 to 20 \\micron, indicating that the pressure at the advancing melt surface decreased due to the resistance based on a capillary force and a friction force between melt and particle. In the microstructure of PRMMC obtained, the reinforcement particles were homogeneously distributed and a linear relationship was obtained between the volume fraction of reinforcement particle in the mixed powder and the observed area fraction. It was found that a homogeneous particle distribution and accurate control of the volume fraction of reinforcement particles could be attained in the LPI process.
  • Effects of Mn Contents on the Microstructure and Mechanical Properties of the Fe-10Al-xMn-1.0C Alloy

    pp. 2635-2642

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    DOI:10.2320/matertrans.43.2635

    The microstructures and mechanical properties of the Fe–10 mass%Al–(5–40)mass%Mn–1.0 mass%C alloys sheet castings have been investigated by using optical microscope (OM), transmission electron microscope (TEM), scanning electron microscope (SEM), experimental model analysis, tensile test and hardness test. Based on the present studies, the macroscopic microstructure of the present alloys are a mixture of austenite (γ) and ferrite (α) duplex phases, and the α phase would decrease with the Mn content increased. In the meantime, according to the examination of TEM, the macroscopic γ phase is a mixture of the γ+fine(Fe, Mn)3AlCx(κ)+(Fe, Mn)3AlCx) phases and the macroscopic α phase is a mixture of the D03+coarse(Fe, Mn)3AlCx′′) phases. The mechanical properties such as the ultimate tensile strength (UTS), yield strength (Y.S.), elongation of these alloys were in the range of 646–887 MPa, 575–824 MPa, and 16.3–29.2%, respectively. The hardness of these alloys were in the range of HRC 31–44. Moreover, the relationship between hardness and ultimate strength is UTS\\fallingdotseq20.93HRC. In addition, the damping ratios and Young’s modulus of the present alloys were in the range of 0.0603–0.0417, and 139–165 GPa, respectively. It is noted here that the results have never observed by other research workers in the Fe–Al–Mn–C alloy system.
  • Tensile Properties from Room Temperature to 673 K of Mg-0.9 mass%Ca Alloy Containing Lamella Mg2Ca

    pp. 2643-2646

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    DOI:10.2320/matertrans.43.2643

    Tensile properties were investigated from room temperature to 673 K of a binary Mg–0.9 mass%Ca alloy where Mg2Ca phase was dispersed as lamella. The 0.2% proof stress significantly increased by the Mg2Ca phase in the temperature range investigated. It was suggested that strengthening by stable lamella Mg2Ca in the grains and limitation of deformation related to grain boundaries by Mg2Ca phase at grain boundaries contribute to improvement of high temperature strength for the Mg–Ca alloy.
  • Microstructure Feature of Bulk Glassy Cu60Zr30Ti10 Alloy in As-cast and Annealed States

    pp. 2647-2650

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    DOI:10.2320/matertrans.43.2647

    The microstructures of a bulk glassy Cu60Zr30Ti10 alloy in as-cast state and annealed at glass transition temperature (Tg), i.e., 440°C, have been studied using an electron transmission microscope (TEM) and a high-resolution transmission electron microscope (HRTEM). Nanocrystals with a size of 4 nm were observed in the cast rod with a diameter of 4 mm. The nanocrystal was determined to be CuZr, which is primitive cubic structure with a lattice parameter of a=0.3262 nm by analyzing its nano-beam electron diffraction pattern, suggesting that such nanocrystals have a positive effect on mechanical properties. Obviously distinguished interval dark and bright regions were observed in the glassy Cu60Zr30Ti10 alloy annealed for 10 min at Tg. Nanocrystalline phase with a size of ∼10 nm was recognized after the annealing treatment. The concentration distribution of Cu, Zr and Ti in the alloy annealed for 10 min at Tg was examined with a three-dimensional atom probe field ion microscopy (3DAP-FIM). It was found that the Cu and Zr elements fluctuated along depth direction while the Ti element remained almost unchanged. It is therefore interpreted that the annealing-induced nanocrystalline phase results from nucleation and growth at the sites of the Cu-rich and/or Zr-rich regions as well as from growth of the cast-in nanocrystals.

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