| Nickel-based powder metallurgy(PM)superalloy is the preferred material for hot end components such as turbine disk of aeroengine,but it is difficult to solve the problem of coarsened grain structure and original particle boundary(PPBs)defects during the process of hot isostatic pressing.When the hot isostatic pressing temperature is higher than the γ’ phase dissolution temperature,PPBs can be inhibited obviously,but the grain is easy to coarsen,and vice versa.The new powder sintering technology-Hot Oscillatory Pressure(HOP)technology can effectively promote the plastic deformation of powder and improve the tensile behavior of metal and ceramic materials by applying dynamic longitudinal oscillatory pressure to powder during powder consolidation.However,the effect of oscillatory pressure on the microstructure,precipitated phase and tensile behavior of powder superalloy forming has not been reported.Therefore,plasma rotating electrode method(PREP)was used to prepare superalloy FGH4096 powder,and the effects of hot oscillatory pressing temperature and the oscillatory pressure on the microstructure and mechanical properties of the alloy were studied.The effect of heat treatment on the microstructure and tensile behavior of the HOPed alloy was also investigated.The main research results are as follows:(1)The effect of oscillatory pressure on the microstructure and properties of PM superalloy at super-solvus temperatures was studied.PM superalloys were prepared at 1150℃,1180℃ and 1210℃by hot oscillating pressing sintering,and were compared with the hot pressing samples prepared at1210℃.Results showed that prior particle boundaries(PPBs)defects were prevalent in HOPed samples and HPed samples,the application of oscillatory pressure and HOP temperature had obvious effects on PPBs scale.Compared with the HPed samples,HOPed samples exhibited larger degree of plastic deformation and lower PPBs scale due to the application of oscillatory pressure,and remarkedly enhanced tensile property.The increase of 52.3% was achieved in tensile elongation.With the increase of HOPing temperature,the PPBs scale reduced,grain size increased,tensile property tended towards stability,the yield strength of samples gradually decreased,the ultimate tensile strength and tensile elongation increased firstly and then decreased.(2)The effect of oscillating pressure on the microstructure and properties of PM superalloy at sub-solvus temperatures was investigated.The prior particle boundaries(PPBs)exist in the samples prepared at subsolution sintering temperature,which affects the plasticity of the materials.This experimental study aims to improve this problem.The samples were prepared by oscillating hot pressing and hot pressing respectively at sub-solid sintering temperature.The results showed that:Compared with hot pressing,the oscillatory pressure was beneficial to the increase of alloy density,the refinement of grain,the inhibition of PPBs,and the improvement of plasticity at room temperature.In addition,when the sintering temperature was close to the dissolution temperature ofγ’ phase,the tensile behavior at room temperature of the HOPed sample was higher,and the ultimate tensile strength and elongation were 1397 MPa and 28.9 %,respectively.(3)The effects of different heat treatment processes on the microstructure and tensile behavior of the HOPed samples were studied.The results showed that,compared with the HOPed samples,the yield strength of the PM superalloy was significantly increased about 45% by solution + aging heat treatment,and the elongation was decreased.The heat treatment could effectively dissolve the coarse primary γ’ phase on the grain boundary and secondary γ’ phase in the grain,and precipitate the smaller and uniform tertiary γ’ phase in the grain.However,the higher solution temperature and longer aging holding time leaded to the increase of the size and number of the carbides on the PPBs and their continuous distribution was in sheets.Meanwhile,the grain size of the sample increases. |
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