Microstructure And Properties Of The New Third Generation Powder Metallurgy Superalloy Prepared By Spray Forming Processing

We adopt spray forming(SF)technology to prepare a new 3rd generation PM superalloy,that is a rapid solidification technology of near-net forming.Compared with traditional Cast&Wrought and PM process,it has unique advantages.In this paper,FGH100L for aircraft engine turbine disc was prepared through SF+ hot isostatic pressing(HIP)+ isothermal forging(IF)+ heat treatment(HT)process.The microstructure and properties of FGH100L alloy under these three processes(SF,SF+HIP+HT and SF+HIP+IF+HT)were investigated.SF deposit billet,HIP alloy and IF alloy below represent FGH100L alloy in three process states respectively.The grain sizes of these three alloys increased first and then decreased,and the grain shapes changed from near spherical to polygonal and then to near spherical;The room/high temperature tensile strength increased gradually,and the plasticity decreased slightly,and the SF deposit billet had the best plasticity.The room/high temperature tensile yield strength,fracture strength and elongation of FGH100L alloy were 165MPa/2.3MPa,82MPa/63.1MPa and 6.5%/8.5%higher than that of LSHR alloy respectively.The low cycle fatigue life of FGH100L alloy was 4.4 times that of LSHR alloy.The effect of solution temperature on the structure and properties of FGH100L alloy was studied.The results show that after different solution temperature+two-stage aging heat treatment,with the increase in solution temperature(1110-1170?),the grain size of HIP alloy and IF alloy was gradually increasing.When the solution temperature was 1130?,three kinds of ?'precipitates with reasonable size/quantity balance matching were obtained in HIP FGH100L alloy:the primary ?' phase distributed in chain shape at the grain boundary,with the size range of 0.73-3.55?m and irregular shapes;most of the secondary ?' phase was splitting and distributed in cubic shape within the crystal,with the size range of 0.27-0.92?m;a large number of spherical tertiary ?' phase distributed between the secondary ?' phase and tertiary ?' phase,with the size range of less than 0.17?m;When the solution treatment was 1170?,only was obtained tertiary ?' phase with single mode distribution in the alloy.At the solution temperature of 1130?,the room/high temperature tensile yield strength,ultimate strength and elongation of IF FGH100L alloy are the best.The effect of long-term aging on the stability of microstructure and properties of Sub-solvus/Super-solvus HIP and IF alloy was studied.It was found that at 760?,with the increase in aging time(500-2000h),the grain sizes in HIP and IF alloy changed little.At 2000h of aging,compared with the alloy before aging,the room/high temperature tensile yield strength and fracture strength of Sub-solvus IF alloy decreased by 229MPa/228MPa,198MPa/30MPa,and the elongation decreased by 12.9%/4.35%respectively.At 1000h of aging,the high temperature tensile properties of Sub-solvus IF alloy were better than that of Super-solvus IF alloy.There were a large number of dislocations piling up between y' phases both in Sub-solvus and Super-solvus IF alloy.Another deformation mechanism of the Sub-solvus IF alloy was that stacking faults cut y'precipitates and forming continuous stacking faults.However,in Sub-solvus IF alloy,there was no stacking fault cutting ?' phase,and only a small amount of super dislocations cut into ?' phase.The creep properties of FGH100L alloy under different processes and the effects of temperature and stress on the creep behavior of alloy were studied.The results show that:At 705?/897MPa,the creep fracture time and strain of HIP and IF FGH100L alloy are 56.96h/81.54h,and 16%/21.9%,respectively.The creep deformation mechanism of HIP and IF FGH100L alloys is that dislocations and stacking faults pass through the ?' phase by cutting,which makes the total dislocations more easily to decompose.There are continuous wide stacking faults throughout the ?' matrix and ?' phase in the alloy.In the later stage of creep,more and more dislocations generated,which are piling up near serrated grain boundaries and carbides,hindering dislocation movement.At 897MPa and 650-750?,the orientation difference of IF FGH100L alloy decreased gradually with the increase in temperature,which indicated that the higher the temperature,the less the strain concentration in the alloy.At 750? and 450-897MPa,the orientation difference of IF FGH100L alloy decreased gradually with the increase in stress.The strain in the alloy was mainly distributed near the grain boundary,which was the weak position.