| The superalloys GH4586A and GH4586B on the base of the GH4586 used in spaceflight were developed in order to promote the national aviation industry. Not only the time used is requested to extend, but also the more complicated environments of stress and corrosion are endured, which lead to the request for its strict performance. That is well known that the mechanical property is determined by microstructure of the alloy. The changes of microstructure of superalloy GH4586B in long-term aging are observed and contrasted to GH4586A so that the influence of composition changes to microstructure can be found out, that can be helpful to material composition design.In the research, the microstructure changes of GH4586B have been observed and analyzed by means of optical microscope, TEM and SEM. The changes of y'phase, carbides precipitate and TCP phase are mainly studied. The fracture behavior under room temperature is also observed after long-term ageing by metallography and SEM, which could provide a theoretical base for improving of the alloy.The conclusions are as follows:(1) The average of EVN Nv of alloy GH4586Aby phacomp calculatio is 2.372, which exceeds the critical value ofμphase's precipitation which is 2.30, So the alloy GH4586A has the tendency of precipitating TCP phase. However, the Nv of GH4586B which the components is adjusted from GH4586A is 2.243, which is lower than the critical value 2.30 ofμphase's precipitation.(2) TCP needle-like phase is unprecipitated in GH4586A aged at 750℃for 500h, but When the aging time is prolonged to 1500h, a few of short and thin TCP needle-like phases are precipitated around grain boundary, and with the prolonging of aging time to 2000h, a lot of long needle-like TCP phases are precipitated. But there is not TCP needle-like phase precipitated in GH4586B aged at same temperature for 500h, and with the prolonging of the aging time, there are only the growing bigger grain boundary carbides, the needle-like or flake-like TCP phase is still unprecipitated.(3) The research reveals y'phases of GH4586A coarsening uniformly during long-term aging, following the lattice-diffusion-controlled growth rule(Ostwald ripening).While y'phases precipitated in GH4586B are appeared two kinds of sizes different each other which the big one shows as square and irregular distribution and the small one shows as round and dispersion distribution after long-term aging, which is beneficial to the matching between strength and toughness of the alloy.(4) There are three types of carbides MC,M6C and M23C6 in GH4586A and GH4586B. With the prolonging of the aging time, the carbides of GH4586A gradually congregation at the grain boundary to form flake-like discontinous strengthening phase. When the aging time is prolonged to 2000h, the quantity of the carbide reduces. The carbides of GH4586B congregation around the grain boundary after aged for 2000h and form a continous chain-like shape to strengthen the grain boundary.(5) Impact property of GH4586B aged at 750℃decreases rapidly with aging time increasing. From the comparison of experimental results, at the same condition of aging treatment, the impact toughness of GH4586B is higher than that of GH4586A.(6) The tensile intensity at 20℃and 750℃of GH4586B is lowered a little as contrasted to GH4586A, because the strength elements in GH4586B are reduced after its chemical components are adjusted from GH4586A.
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