| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1999: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1998: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
In the first year of this program, I investigated a relation between the volume fraction and micro structural morphology of each phase in Nb-Al multiphase alloys controlled by MG/MA. The mechanical property of niobium solid solution (NbィイD2ssィエD2 as ductile phase was also studied. In the investigation, it was found that the modification of the mechanical property of NbィイD2ssィエD2 was very important for the harmony of a fracture toughness and high temperature strength to a high degree.
Then, I studied Nb-Si-Al alloys. Nb-Si-Al alloys compose in-situ composites, which are stable to high temperature. The mechanical properties of NbィイD2ssィエD2 as a component of multiphase alloy in Nb-Si-Al system can be changed by an amount of Si and Al in NbィイD2ssィエD2. I investigated the fracture toughness and the high temperature strength of two- or three-phase alloy consisted of NbィイD2ssィエD2 NbィイD23ィエD2Al and NbィイD25ィエD2SiィイD23ィエD2. The ductility of NbィイD2ssィエD2 as a component of multiphase alloy increases
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and then elastic-plastic fracture toughness of multiphase alloys increases, if the amount of Si and Al of Nb-Si-Al multiphase alloy decreases. However, plain strain fracture toughness of Nb-Si-Al three phases alloy with higher amounts of Si and Al than Nb-Si alloy is higher than Nb-Si or Nb-Al alloys, because the strength of NbィイD2ssィエD2 decreases as decreasing the amounts of Si and Al. The high temperature strength of Nb-Si-Al three phases alloy is also higher than Nb-Si or Nb-Al alloys, because the high temperature strength of NbィイD2ssィエD2 of NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 alloy is the highest by solid solution hardening.
The effect of the addition of titanium on the toughness, high temperature strength and the oxidation resistance of NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three phases alloy in Nb-Si-Al-Ti system was investigated. Results are as follows. (1) NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three-phase region exists to about 20 mol% of titanium in Nb-Si-Al-Ti system. (2) The fracture toughness of NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three phases alloy in Nb-Si-Al-Ti system is higher than the alloy in Nb-Si-Al system. The KィイD2ICィエD2 of the plain strain fracture toughness is about 12 MPa【square root】m. The high temperature strength of NbィイD2ss'ィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three phases alloy is higher than the conventional Ni based super alloy. Thus, NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three phases alloy in Nb-Si-Al-Ti system show harmony of fracture toughness and high temperature strength. (3) The oxidation resistance of NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three phases alloy is extremely improved by the addition of titanium. However, the oxidation resistance of NbィイD2ssィエD2+NbィイD23ィエD2Al+NbィイD25ィエD2SiィイD23ィエD2 three phases alloy with the addition of titanium is inferior to Ni based super alloy. Less
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