Study On Microstructure And Property Of Powder Metallurgy Superalloys Prepared By Hot Oscillatory Pressing

Powder metallurgy superalloy prepared by hot isostatic pressing(HIP)is perfered material for the preparation of advanced aeroengine turbine disk.But the materials are prone to prior particle boundary(PPB),abnormal grain growth and other microstructural defects in the preparation process.To overcome these defects,additional hot working process,such as hot extrusion and isothermal forging,is often required,resulting in a significant increase in preparation costs.Hot oscillatory pressing(HOP)technology has been shown to promote powder deformation and inhibit grain growth,so it is expected to overcome the above problems.In addition,the service temperatures of turbine disk rim and disk core are different,so it is necessary to carry out room temperature and high temperature tensile behavior of powder metallurgy superalloy.On this basis,the hot oscillatory pressing technology was used to prepare powder metallurgy superalloy in this paper.The microstructure evolution and room temperature/700 ℃ high temperature tensile behavior of the samples were investigated,and compared with the alloy prepared by hot pressing(HP)and HIPing.The main research contents and conclusions are as follows:(1)The microstructure evolution and room temperature tensile behavior of the samples prepared by HOPing and HPing were investigated.The results show that HOPing samples have higher density,higher recrystallization degree and lower PPBs defect scale than HP samples at the same sintering temperature.In particular,when the HOPing temperature is 1160 ℃,the samples show fine grains and low PPBs scale,and the best tensile properities.Its ultimate tensile strength and elongation are 1403±2 MPa and 35.1±2.5 %,respectively.While it is difficult to cooperatively control the PPBs defects and grain structure in the HPing samples.The best tensile properties of HPing sample are obtained at 1080 ℃,and its ultimate tensile strength and elongation are1414±19 MPa and 31.0±3.5 %,respectively.(2)The tensile behavior at 700 ℃ of samples prepared by HOPing,HPing and HIPing was investigated.The results show that HOP samples exhibit excellent tensile properties at 700 ℃,and its ultimate tensile strength and elongation are 1094±13 MPa and 20.0±1.1 %,respectively.The cracks initiate from the coarse borides,and propagate along the grain boundary or transgranular.The fracture surface present intergranular predominately,and the inter-particle fracture are small in account.The tensile properties at 700 ℃ of HOP samples are better than those of HP samples(1012±15 MPa and14.7±1.6 %),and are similar to those of HIP samples(1085±7 MPa and 23.6±0.8 %).Low preparation cost and high performance powder metallurgy superalloys can be prepared by HOPing,The HOPing pressure and time of 70±10 MPa and 2 h,and HIPing pressure and time of 150 MPa and 4 h.(3)In order to prepare powder metallurgy superalloys with high recrystallization degree and low PPBs scale,a new two-step HOP process was proposed.The microstructure and tensile behavior of the sample prepared by this process were investigated and compared with the single-step HOP process.The results show that the PPBs defects of the samples prepared by the new process are lighter,and the elongation and performance stability of the samples are higher than that of the single step process.The tensile fracture shows intergranular and transgranular fracture.The lighter PPBs scale of the two-step HOPed sample result in coarsening of the grain structure and reduce the yield strength of the sample.In addition,the fine and uniform γ’ phases in the two-step HOPed samples offset the damage of grain coarsening against ultimate tensile strength.