| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1987: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1986: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
The <gamma> (disordered fcc) and <gamma>' (ordered Ll_2 structure) phases constitute the major part of Ni-base superalloys for high temperature use. Inspite of its practical importance, the <gamma>/<gamma>' phase equilibrium has not been well established because the equilibrium is difficult to be studied due to the very fine dispersion of the <gamma>' phase. In order to clarify the effect of alloying elements on the relative stability of <gamma>' phase, the phase equilibria between <gamma>,<gamma>' and <eta>(Ni_3Ti) phases are studied by diffusion couple method. The results obtained are as follows. 1. Phase equilibria in the Ni-Al, Ni-Ti and Ni-Al-Ti systems.
The phase boundaries of Ni-Al, Ni-Ti and Ni-Al-Ti systems were accurately determined. It was shown that a considerable amount of Ti dissolves in the <gamma>' phase while the solubility of Al in the <eta> phase is small.
2. Partition of alloying elements between <gamma> and <gamm>' phases. The partition behavior of the alloying elements between <gamma> and <gamma>' phases was classified into three groups; (1) the elements of Nb,V,Si,T, and Ta distribute to the <gamma>'phase rather than <gamma> phase, (2) Cu,Co,Cr,Fe and Mn distribute to <gamma> phase and act as <gamma> stabilizer, (3) Mo and W change from <gamma>' to <gamma> former with increasing alloying content.
3. Partition of allying elements between <gamma> and <eta> phases. All the elements except for Ta distribute to the <gamma> phase rather than <eta> phase. These results suggest that Nb,V,Si,W and Mo are the useful elements to supress the <gamma>' <eta> transformation.
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