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Volume 74, Issue 6
Displaying 1-8 of 8 articles from this issue
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Toshikazu Akahori, Mitsuo Niinomi, Masaaki Nakai, Harumi Tsutsumi, Tor ...2010 Volume 74 Issue 6 Pages 337-344
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSThe purpose in this study is to investigate the effect of microstructure on the unique hardening behavior of dental silver alloy, Ag-20Pd-14.5Cu-12Au (mass%), fabricated by hot rolling process (AS material), which is in as-received condition, and liquid rapid solidification (LRS) process (LRS material). The following results were obtained.
The microstructure of AS material is consisted of α1, α, and β phases. The microstructure of AS material changes to α, β, and β′ phases through a solution treatment (ST). The microstructure of LRS material is consisted of α, α1, and α2 phases without β phase. The microstructure of LRS material becomes single α phase through ST. Relatively large β phases with the diameter of tens of μm on AS material coarsen according to increasing the ST time, while the small those with the diameter of a few μm are solid-soluted into the matrix. On the other hand, the coherent participation of β′ phases with long and short axes of around 100 nm and 10 nm, respectively, also occurs during ST although the amount of β′ phase decreases with increasing the ST time. The hardness and tensile strength of LRS material and LRS material subjected to ST are relatively smaller than those of AS material and AS material subjected to the same treatment. From this results, the effect of solid solution hardening of α, α1, and α2 phases is lower than that of precipitation hardening of β′ phases. In a case of the unique hardening seems to occur because the precipitation of β′ phases are enhanced during ST.
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Nana Fukamachi, Nobuki Tezuka, Satoshi Sugimoto2010 Volume 74 Issue 6 Pages 345-350
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSRecently, materials composed of both soft and hard magnetic phases have been attracting a lot of attention. This paper describes the preparation of composite nanoparticles by the reduction and oxidation of cobalt ferrite (CoFe2O4) nanoparticles. Neither the composite nanoparticles of hard ferrites and soft magnetic materials nor the hydrogen reduction of ferrite nanoparticles has been reported. Therefore, investigation of the relationship between their microstructure and magnetic properties is needed. Our study revealed the cobalt ferrite powders prepared by the coprecipitation method showed the highest coercivity Hc=750 kA•m−1 in the case of ternary cobalt ferrite. After the cobalt ferrite powders were reduced by heat treatment at 450°C for 15 min in hydrogen, the reduced powders were shown to consist of a Fe-Co (bcc) phase and XRD analysis of the lattice parameter suggests the composition was around Fe67Co33. After oxidization of the reduced powder by heat treatment at 300°C for 15 min in air, the powders consisted of a Fe-Co(bcc) phase and a spinel-type phase. TEM analysis revealed that the oxidized particles had a core-shell structure and the shell was shown to have a spinel-type phase, with some amorphous structures. Therefore the magnetic properties of the core-shell powders were shown to exhibit low coercivity Hc=120.4 kA•m−1 and low saturation magnetization σs=80.2 Am2•kg−1.
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Masatoshi Takahashi, Masafumi Kikuchi, Osamu Okuno2010 Volume 74 Issue 6 Pages 351-355
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSThe purpose of this study was to improve the grindability of titanium by alloying with zirconium. The grindability of dental cast Ti-Zr binary alloys (10, 20, 30, 40 and 50 mass%Zr) was evaluated using a carborundum wheel. The Ti-Zr alloys up to 30 mass%Zr formed an α structure, and the 40 mass%Zr and 50 mass%Zr alloys formed an α′ structure. The Ti-40 mass%Zr alloy at up to 1000 m•min−1 and the Ti-50 mass%Zr alloy at up to 1250 m•min−1 exhibited significantly higher grindability than titanium. More than twice the volume of metal was removed from the alloys than from titanium per minute. The improved grindability could be attributed to the α′ structure in addition to the decrease in elongation. The Ti-Zr alloys, which formed an α′ phase structure, are candidates for use as machinable biomaterial in dental applications.
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Shinji Tanaka, Mamoru Mizusawa, Yoshiharu Miyabe, Takehito Hagisawa, K ...2010 Volume 74 Issue 6 Pages 356-364
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSThe influence of cooling rate on the solidification structure and mass of eutectic compounds in Cu-Cr and Cu-Cr-Zr alloys was investigated. Small-size ingots as well as large-size electro-slag remelting (ESR) ingots were produced. ESR was applied so as to get ingots that were solidified over a wide range of cooling rates. The dendrite arm spacing in Cu-0.52 mass%Cr varied directly with a minus one-third power of cooling rate. The mass of eutectic compounds in Cu-0.52~0.66 mass%Cr was reduced with the addition of Zr. The mass of eutectic compounds in Cu-0.52~0.66 mass%Cr-0~0.09 mass%Zr alloys did not depend on the cooling rate.
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Jung Eun Choi, Masahiro Kitada2010 Volume 74 Issue 6 Pages 365-369
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSThe microstructure and impurities in a Korai (10~14c) Bronze Mirror illustrated with four boys with musical instruments has been investigated. Transmission electron microscope, X-ray diffractometer, scanning electron microscope, and electron dispersive X-ray analyses are used to determine the structure of the specimen. The composition of the specimen is Cu-9.7 mass%Pb-10 mass%Sn-0.6 mass%S, and Ag and Si are detected as trace elements. The microstructure of the Korai bronze mirror consists of αCu, αCu41Sn11, Pb, and a phase containing S. It is clarified that the phase containing S is Cu2S (JSPDS 33-0490) by electron diffraction pattern analysis. It is thought that Cu2S is a residue of the intermediate product, Cu2S, in the refining of the copper ore, chalcopyrite (CuFeS2). Therefore, the copper ore has not been completely refined. Fine Pb particles are observed in the Cu2S grains, and fine PbS crystals also exist between Pb and Cu2S.
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Akiko Inoue, Takahiro Sekigawa, Kazuyuki Oguri, Tetsuya Tagawa, Takash ...2010 Volume 74 Issue 6 Pages 370-377
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSShot peening is widely used in the aerospace industry in order to improve fatigue property of structural high strength aluminum alloy. However, the optimum shot peening condition has not been revealed, considering the effect of the shot peened surface roughness and the residual stress profile on fatigue life. In this study, fatigue life improvement of 7050-T7451 due to the shot peening with the fine particles whose diameter was less than 0.1 mm was studied and compared with the fatigue life of the shot peened material with the conventional steel shot of 0.6 mm in diameter. The fine particle shot peened (FPSP) specimens endured about ten times longer fatigue life than the virgin specimens and several times longer than the conventional shot peened specimens. The fatigue crack in FPSP specimens initiated at the subsurface layer or the inside of the specimen, while the fatigue crack initiation site in the conventional shot peened specimen or the virgin specimen located on the specimen surface. It was revealed that the fatigue improvement effect of FPSP mainly resulted from the transition of the crack initiation site due to the shallow compressive residual stress layer near the specimen surface, considering the arrested small cracks detected on the fractured specimen side surface K analysis based on the compressive residual stress profiles.
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Masaru Kanmera, Takuya Fujima, Ken-ichi Takagi, Yöhei Nakagomi, S ...2010 Volume 74 Issue 6 Pages 378-383
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSTo study effects of Cu addition on the sintering behavior of SUS304L stainless steel powders and mechanical properties of their sintered compacts, SUS304L, 4 mass% Cu pre-alloyed SUS304L stainless steel powders and 2 mass% Cu mixed these two powders were sintered at 1323~1523 K in vacuum after compacted at the pressure of 490 MPa. In addition to density measurement, micro structural observation and tensile test for each sintered compacts, differential scanning calorimetry and thermomechanical analysis for each powder were conducted.
As a result, the sintered compact of 4 mass% Cu pre-alloyed stainless powder showed higher density and strength than those of other powders due to the formation of small amount of liquid phase. Alloying elements of silicon and manganese in the powders considered to react with copper during sintering and resulted to form liquid phase at relatively low temperature. Moreover, pre-alloyed copper more than solubility limit also generated small amount of liquid phase which enhanced the densification and strengthening of the sintered compacts. The sintered compact of 2 mass% Cu mixed 4 mass% Cu pre-alloyed powder showed little lower tensile strength than that of the 4 mass% Cu pre-alloyed powder because copper over the solubility limit preferentially existed at the grain boundary which played the fracture path at the tensile test.
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Yoshihiro Ohno, Junichi Inotani, Yoshihisa Kaneko, Satoshi Hashimoto2010 Volume 74 Issue 6 Pages 384-391
Published: 2010
Released on J-STAGE: June 01, 2010
JOURNAL FREE ACCESSSliding wear tests were conducted on copper single crystals having (110) and (111) surface, and polycrystalline copper. Evolution of high-angle grain boundaries during the sliding wear was investigated by the electron backscatter diffraction (EBSD) technique. The high-angle grain boundaries, which were formed in the vicinity of the worn surface, could be classified into two kinds from their morphology: one is parallel to the worn surface (Type A high-angle boundary) and the other is a grain boundary surrounding an equiaxed fine grain (Type B high-angle boundary). At Type A high-angle boundaries, a rotational axis between adjoining grains was almost parallel to z-axis which is defined as the direction perpendicular to both wear direction and worn surface normal. Grain boundary character distribution of Type A boundaries was sensitive to crystallographic orientation of the z-axis. When the z-axis was <110>, orientation relationship of Σ33a had high frequency. On the other hand, high Σ31a frequency was obtained at the sliding wear occurring under <111> z-axis condition. It is concluded that the evolution of Type A boundaries was caused by lattice rotation induced by sliding wear. For Type B high-angle boundaries, fractions of low-Σ coincident site lattice (CSL) boundaries were high, and the frequency distribution of CSL boundaries was almost independent of wear direction and worn surface orientation. Unlike Type A boundaries, rotational axes at Type B boundaries showed no preferred orientation. These crystallographic features suggest that recrystallization is the most plausible origin for Type B boundary evolution. Consequently, the high-angle boundaries were produced probably by two different processes during sliding wear.
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