| Co-Investigator(Kenkyū-buntansha) |
KUGITA Tsuyoshi The Nishi-Tokyo University, Department of Science and Engineering, Assistant, 理工学部, 助手 (80225127)
KOJIMA Yo Nagaoka University of Technology, Department of Engineering, Professor, 工学部, 教授 (60016368)
|
|---|
| Research Abstract |
The present work was carried out to clarify the influence of the element addition on the microstructures, mechanical properties and oxidation resistance in the (beta+gamma')-two phase intermetallic alloys with the composition of Ni-33.9mo1%Al-0.1mo%B. On the basis of the ternary phase diagrams, Fe and Co were selected as the candidates for additives for the base alloy. It is recognized that these elements substitute for Ni site of beta or gamma' phase and have the relatively large solubility limit than other elements. Alloys with 2 and 4 mo1% of Fe and Co were prepared using arc-melting method and then subjected to homogenizing heat treatment followed by heat refining treatment. Subsequently, observation of microstructures, compressive and tensile tests at high temperatures were attempted for these specimens. Also, the oxidation tests were conducted at 137** in air. For both Fe and Co added alloys stresses showed the maximum and then decreased gradually, namely high temperature yieldin
… More
g phenomena were observed. The maximum stresses tend to decrease with the contents of additives. The steady state deformation stress, however, increased with Fe addition, suggesting solid solution hardening. On the other hand, it was found that Co addition has little contribution to solid solution hardening. Apparent activation energies for high temperature deformation were estimated at 224 KJ/mol for base alloy, 251 KJ/mol for 2Fe, 262 KJ/mol for 4Fe alloys and also 236 KJ/mol for 2 and 4 Co alloys. Since these values are considerably less then those for bulk diffusion, it is inferred that grain boundary sliding controlles the high temperature deformation. The strain rate sensitivity exponent, m value, is assessed at 0.4 for the base alloy. While for Fe added alloys m value was about 0.28, Co added alloys showed above 0.35. Fe added alloys fractured by brittle manner with lower elongation than base alloy, when they were tested at 1073K and strain rate of 8.3 chi 10^<-5> s^<-1>. But the Co added alloys exhibited larger elongation compared with the base alloy, indicating that Co addition promotes the superplasticity of the two phase alloy. Whereas Fe addition decreases the oxidation resistance, Co addition seldom change that properties. Less
|
