Microstructure And Mechanical Properties Of Sc,Y Microalloyed René104 Superalloy Prepared By Selective Laser Melting

Powder metallurgy superalloy is the preferred material for hot section components,such as turbine disk of aerospace engine,due to its excellent high-temperature mechanical properties,creep resistance,corrosion resistance and fatigue resistance.And René104 nickel-based superalloy with high Al+Ti content is a typical third-generation powder metallurgy superalloy.However,those parts with complex morphologies cannot be integrally formed by traditional powder metallurgy methods..Therefore,selective laser melting(SLM)technology has attracted extensive attention.For René104 alloy with high Al+Ti content,the cracking of SLMed parts needs to be solved urgently.Facing the challenge,this paper aims to reduce the cracking sensitivity of René104 nickel-based superalloy and eliminate the cracks in the alloy through Sc and Y microalloying,so as to broaden the process window,as well as improve microstructure and mechanical properties.The main contents and conclusions are as follows:(1)Through Sc and Y microalloying,the flowability of powder is improved,the loose density and tap density are increased,the cracking sensitivity is improved,and the SLM process window for preparing crack-free parts is widened to 30～55 J/mm~3.Under the optimal parameters,namely,the laser power of 263 W,exposure time of 60μs,volume energy density of 49.5 J/mm~3,the crack-free René104 nickel-based superalloy with a relative density of 99.47%is prepared.When volume energy density is low,irregular pores were observed in the SLMed parts.With the increase of volume energy density,the pores gradually disappear.When volume energy density is too high,lots of keyholes and cracks are formed in the SLMed parts.(2)The microstructure of the Sc,Y microalloyed René104 alloy prepared by the optimal process parameters is mainly composed of fine columnar,in which there are fine dendrites and cellular substructures with an average width of about 660 nm.A lot of dislocations at the boundary of dendrite and cellular substructure are observed,which indicates a large residual stress in the as-printed alloy.Through Sc,Y microalloying,the mechanical properties of René104 superalloy prepared by SLM were significantly improved.The yield strength,tensile strength and elongation are 1021±35.8 MPa,1362±7.5 MPa and 20.2±1.4%,respectively,which has increased by 44.2%,50.2%and 462.1%compared with René104superalloy,respectively.(3)In order to further improve the performance of the alloy,the effects of direct aging and solid solution aging at three different temperatures on the microstructure and mechanical properties were studied.The alloy after direct aging still maintains the grain morphology of as-printed alloy,and the elongated tertiaryγ′phase with an average width of about 40 nm is uniformly precipitated in the grains..It shows the highest tensile strength and yield strength as well as the lowest elongation,which are 1492±7 MPa and 1391±9 MPa,5.1±0.7%,respectively.While the recovery and recrystallization actuated in the alloy at 1180℃solid solution temperature cause the alloy grain tend to be equiaxed and annealing twins appear.The square tertiaryγ′phase with an average width of about 150 nm is uniformly precipitated in the grains.And the dendrites and cellular substructures merge and grow,with an average width of about1940 nm.After 1180℃solution aging treatment,the alloy has better comprehensive properties,and its tensile strength,yield strength and elongation are 1412±1 MPa.1259±7 MPa and 6.8±0.2%,respectively.