| Project/Area Number |
62850133
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| Research Category |
Grant-in-Aid for Developmental Scientific Research
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| Allocation Type | Single-year Grants |
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| Research Field |
金属材料(含表面処理・腐食防食)
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| Research Institution | TOKYO INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
KIKUCHI Makoto (1988-1989) Tokyo Institute of Technology, Faculty of engineering Professor, 工学部・金属工学科, 教授 (30089817)
菊池 実 (1987) 東京工業大学, 工学部, 教授
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| Co-Investigator(Kenkyū-buntansha) |
MATSUO Takashi Tokyo Institute of Technology, Faculty of engineering Associate Professor, 工学部・金属工学科, 助教授 (10089823)
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| Project Period (FY) |
1987 – 1989
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| Project Status |
Completed (Fiscal Year 1989)
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| Budget Amount *help |
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1988: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1987: ¥5,700,000 (Direct Cost: ¥5,700,000)
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| Keywords | Creep / High Temperature Strength / Strengthening / Subgrain / Superalloy / Intermetallic compound / クリープ / クリープ抵抗 / 固溶強化 |
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| Research Abstract |
Creep properties and microstructure of Ni-2OCr-Nb-W alloys containing variable amounts of niobium and tungsten were investigated at 900 and 1,000ﾟC, focusing on a role of grain boundary precipitates. The alloys with higher niobium content. In which the Widmanstatten type beta-Ni_3Nb phase precipitates after its precipitation at grain boundaries, showed a relatively small minimum creep rate at 900ﾟC, accompanied by the degradation of rupture elongation. The effect of time lag between the in-grain and grain boundary precipitations of the beta-phase on creep resistance of the alloy was evaluated by observing their creep rate-time curves. When the tungsten content of a Ni-2OCr-3Nb-l3W alloy increased up to 17 wt%, marked improvement of creep properties was found under lower stress levels and it is strongly correlated to the grain boundary precipitation of the alpha_2 W-phase which occurs after that of the beta-phase. It is concluded that the grain boundary precipitation strengthening effect due to such dual phases as beta and alpha_2, is one of the most effective methods for improving the creep strength.
In order to make the high temperature creep strength of Ni-Cr-Nb-W type alloys higher, the effects of boron and zirconium on creep properties in high-purity Ni-2OCr alloys were investigated. By the boron and zirconium addition, creep resistance, rupture life and rupture elongation of a Ni-20Cr alloy were improved. The longer rupture life and larger rupture elongation with the addition of boron or zirconium would be caused by the formation of subgrains and dynamic recrystallization which retard the initiation and propagation of grain boundary aracks.
The possibility of the development of a new alloy for nuclear heat exchanger with far higher creep rupture strength than several candidate alloys ( Ni-Cr-W type alloys ) was suggested.
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