The Research On Microstructure And Properties Of Weldable Cast Superalloy K487

The microstructure and properties of weldable cast superalloy K487 and the effect of heat treatment on it have been investigated. K487 is a superalloy developed for a new missile engine, it is still in developing, the result of this research is important for the develop and application of K487.The temperature of solution treatment of K487 is studied by differential thermal analysis and the microstructure and properties of K487 in different solution treatment is studied in this paper. The results show that after the solution treatment of 1120℃×4h, γ' phase of K487 has been dissolved into matrix, the plastic property of K487 has been increased compared with it in as-cast.Based on the research on the temperature of solution treatment, the microstructure and properties in as-cast, as-solution and as-solution and aging treatment have been investigated by metallographic analysis and energy spectrum analysis. The results show that the microstructure of K487 mainly includes γ matrix, γ' phase, MC, μ phase and M₆C. γ' phase is cube in as-cast, massive MC and granular μ phase and M₆C precipitates on grain boundary and between dendrites. After solution and aging treatment, γ' phase is changed into spherical particle, dimension of MC decrease and μ phase and M₆C are mainly granular and massive . Compared with alloy in as-cast, the properties is obviously raised after heat treatment.The effect of aging temperature and aging time on microstructure and properties of K487 have also been investigated in this paper. The results show that as the processing of aging treatment, γ' phase and μ. phase of K487 is ripening by the rule of Ostwald ripening, this process is accelerate as the raise of aging temperature and the prolonging of aging time. As this process, diameter of γ' phase increase and the shape of μ phase converted from needle and thin particle to granule with the diameter of 2-5 μm and massive, tensile properties of alloy decrease and the plastic properties raise. The result show that in the first 5 hour of aging treatment, the transfer of μ phase is obviously and during when the aging time last from 5 hour to 25 hour, there is little change of μ phase. When the aging temperature below 900℃, although aging time lasted to 25h, there are many μ phase with the shape of needle and thin particle exist. According to the date of experiments, comprehensive properties of K487 is good after the treatment of 1120℃ ×4h+900℃ ×5h.