Microstructures And Properties Of The Nickel-Based Powder Metallurgy Superalloy Prepared By Selective Laser Melting

The Selective Laser Melting(SLM)technology has a high near-net forming capability for parts with complex shapes.The application of SLM technology to the preparation of nickel-based powder metallurgy superalloy parts can simplify the structure,reduce the weight,and improving the thrust-to-weight ratio of aeroengines.However,the research on SLM of nickel-based powder superalloy is still in the early stage,and relevant experimental datas are relatively few.Based on this,the paper took FGH4096 nickel-base powder superalloy as the research object,carried out research work.The main content and conclusion of the paper are as follows:In this article,the effects of laser power,scanning speed and remelting rate on SLM FGH4096 alloy were studied,and the optimum processing parameters were obtained with laser power 95W,scanning speed 1200mm/s and remelting rate 30%.The optimal input line energy was 2.64J/mm2 and the optimal input unit volume energy was 105.56J/mm3.Later,the microstructures and properties of the as-build alloy were characterized.It is mainly composed of austenite matrix ?phase,and a small amount of fine ?' phases and carbides with size below 100nm distribute in the alloy.So the as-build alloy has a high elongation up to 25.9%at the forming direction,while the strength of the alloy is relatively low,1204.13MPa.In the alloy,columnar grains were dominant,in which fine dendrites and equiaxed structures with an average width about 0.5?m were arranged regularly.There were a lot of dislocations at the boundaries of dendrites and equiaxed structures,indicating larger strains in the as-build alloy.In the study about heat treatment(HT)for as-build alloy,the alloy after direct ageing has high tensile strength with ultimate strength 1595.56MPa and yield strength 1459.46MPa at room temperature in the forming direction.The alloy after direct ageing remains the grain morphology of as-build alloy.The columnar grain structures are maintained,and the secondary ?' phases in the alloy precipitate regularly along the growth direction of the dendrites at solid solution temperature from 1010? to 1090?.While the recovery and recrystallization actuated in the alloy at 1110? solid solution temperature caused the dendrite and equiaxed structure disappeared,and the alloy grains tended to be equiaxed.When the solid solution temperature was above 1100?,the alloy was in a state of supersaturation or close to supersaturation,so the tertiary ?' phases precipitated uniformly during subsequent aging process.Meanwhile the higher the solid solution temperature was,the more random the grain orientation tended to be.In order to obtain equiaxed grains,reduce the internal textures and form a multi-dimensional distribution of ?‘phases,the double solid solution+aging treatment was adopted to optimize the microstructure of the alloy and enhance the strength of the grain boundaries.During this process,the growth mechanism of the ?' phases that the large-size ?' phases absorbed the small-size ?' phases and the similar size y' phases merged were observed.In order to further improve the performance of the alloy,the influence of hot isothermal pressing(HIP)with three different temperatures and subsequent HT systems on the microstructures and properties were studied.The results show that SLM+HIP(1130?)+HT(1130?)alloy obtained better performance:at room temperature,the ultimate strength,yield strength and the elongation are 1523MPa,1073MPa and 17.34%respectively;at high temperature,the ultimate strength,yield strength and the elongation are 1420MPa,1098MPa and 16.92%respectively.After HIP and HT,the grains with sizes decreased in the forming direction tend to be equiaxed and irregularly shaped,and the dendrite structures and equiaxed structures basically disappeared.The creep properties of SLM+HIP(1130?)+HT(1130?)alloy were studied.At 650?/690MPa,the creep life reached 900h,and the elongation after fracture is 22%.At the same time,the creep behaviors of the alloy at different creep stages were studied.The creep deformation mechanism is that the dislocations propagate in the initial stage to cut the ?' phase,and later a large number of stacking faults cut the y' phase.The creep activation energy of the alloy was calculated to be 330.90kJ/mol and the failure mechanism of the alloy is the initiation and propagation of intergranular cracks.