Fuxing YIN
,
Jianxin ZHANG and Nanju GU(Hebei Institute of Technology
,
Tianjin
,
300132
,
China)Tsukio Tadaki(Institute of Science and Industrial Research
,
Osaka University
,
Japan)Ken
,
ichi Shimizu(Kanazawa Institute of Technology
,
Ishigawa 921
,
Japan)
材料科学技术（英文）
With electron microscopy the investigation on isothermal martensite transformation in an Fe20.5Ni-4.8Mn alloy has been carried out to clarify the effect of austenite state on the transformation, by applying pre-deformation to austenite before isothermal holding. Under the condition without pre-deformation, the isothermal martensite products are lath martensite with {111}fhabit planes. Dislocations in austenite seem to contribute to nucleation of martensite, and in this nascent Stage austenite substructure has no obvious effect on martensite growth. The consequent thickening of martensite laths is apparently influenced by local austenite states, resulting in the changes in orientation, morphology as well as substructure of martensite lath. The kinetics of isothermal martensite transformation is controlled by intedece dislocation determined nucleation of martensite in primary stage, but to a larger extent, by the austenite accommodation for the shape strain of martensite in the thickening Stage
关键词:
Fuxing YIN
,
Y. Ohsawa and A.Sato (National Research Institute for Metals
,
Tsukuba
,
Ibaraki 305-0047
,
Japan)K.Aawahara(B.B.Materia Co. Ltd.
,
Chiba-Shi
,
Chiba 267-0066
,
Japan)
材料科学技术（英文）
A high damping condition is easily obtained in Mn-(16~24)Cu-(4~6)Ni-2Fe (at. pct) alloys,when cooling rate is controlled after the solid solution treatment at 1173 K. It is observed that the temperature dependent changes of Iogarithmic decrement in 10 h cooled samples are sensitive to the alloy composition. As compared with water quenching treatment, controlled 10 h cooling improves TN temperature of the alloys extensively by producing a Mn-enriched matrix portion in the alloys. Calcuiations suggest that the relative decreases of Cu and Ni content in the matrix portion be dominated by the Ni content in the original alloys, and therefore, the volume fraction of the Cu, Ni-enriched precipitates is estimated to be about 20% and 10% in the 4Ni and 6Ni alloys, respectively. As a result, the TN temperature fOr each alloy, corresponding to the rising temperature of logarithmic decrement, has been related to the Cu, and Ni content in the Mnenriched matrix. The existence of {110} twinning boundaries is confirmed in the microstructure of both 4Ni and 6Ni alloys. However, the relative lattice strains, which the twinning boundaries act to accommodate, are found largely different in the two alloys. It is considered that boundaries with smaller orientation deviation could coordinate the external Stresses easily by cyclic moving, and therefore, the broader damping peak which occurs in the 10 h cooled 6Ni alloy becomes feasible. Electron diffraction results also indicate possible for mation of many sub-crystals in the matrix phase, which are relatively rotated on some invariant planes. Those sub-crystal boundaries might play some attenuation roles in the temperature range between TN and room temperature.
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