Effect Of Heat Treatment On Microstructures And Fatigue And Creep Properties Of Inconel 718 Manufactured By Selective Laser Melting

Selective laser melting(SLM)has become an important additive manufacturing(AM)techniques due to its advantages,such as excellent geometrical complexity and high density comparing with the other additive manufacture techniques for metal materials.Inconel 718(IN718),a precipitation strengthening nickel-based superalloy,possesses high strength,good oxidation resistance,and excellent fatigue and creep resistance at elevated temperature due to its containing of a lot of alloy elements.The precipitation of strengthening phases is normally inhibited due to the cooling rate of the SLM process,resulting in the precipitation of Laves phase.Therefore,it is necessary to conduct appropriate heat treatment to modulate the microstructures and corresponding mechanical properties of SLM-manufactured IN718.In this work,the microstructures of SLM-manufactured IN718 in as-built and heattreated statuses were characterized.Microhardness,tensile properties,fatigue properties and creep properties of the as-built and heat-treated samples were investigated,respectively.Effects of the heat treatment on microstructures and mechanical properties of the SLM-fabricated IN718 were investigated systematically.The typical microstructure of the as-fabricated IN718 was columnar grains on YZ plane and equiaxed grains on XY plane.The as-fabricated sample mainly consists of matrix phase,carbides and Laves phase,and there was no strengthening phase.The density of as-fabricated sample was 99.995%.After homogenization+aging heat treatment,recrystallization occured,the Laves phases were almost dissolved completely,and ?'/?" strengthening phases were precipitated and uniformly dispersed in the matrix.After 1065? homogenization treatment,partially recrystallized occured,a small amount of ? phase distributed on the grain boundaries,and the grain size was slightly increased.After 1150? homogenization treatment,both the degree of recrystallization and the grain size increased.After 1200? homogenization treatment,almost all of the columnar grains were transformed into equiaxed grains,and the grain size increased evidently.With the increase of homogenization temperature,the size of ?"phase increased.After homogenization+aging heat treatment,the microhardness of the samples was obviously improved.When the homogenization temperature was 1065?,the tensile strength of SLM-manufactured IN718 samples was superior to that of the wrought IN718.The tensile strength at 650? was comparable to the strength at room temperature.With increasing the homogenization temperature from 1065?to 1200?,the microhardness and tensile strength of the SLM-manufactured IN718 samples gradually decreased.The fracture mode of tensile samples was characterized by ductile transgranular fracture.The fatigue limit of 1065?,1150? and 1200? homogenization treated IN718 samples was 319.5 MPa,274.5 MPa and 252 MPa,respectively.However,the 1200? homogenization treated samples exhibited potential low cycle fatigue properties.When the homogenization temperature was 1150?,the steady state creep rate of heat treated samples was the lowest and the creep life was the highest.When the homogenization temperature was 1065?,the steady state creep rate heat treated samples was the highest and the creep life was the lowest.