Effect Of Post-treatment On Microstructure Evolution And Mechanical Properties Of GH3230 Superalloy Fabricated By Selective Laser Melting

GH3230 superalloy has high thermal strength,excellent oxidation resistance and high temperature creep resistance,making it widely used in the aerospace field,especially in the fabrication of hot end components such as the combustion chamber and flame tube of aircraft engines.However,traditional manufacturing processes such as casting and forging are difficult to complete the manufacturing of complex components,greatly limiting the transformation of superalloys to large-scale industrial applications.Selective laser melting（SLM）technology not only can achieve the integrated forming of parts from design to fabrication,but also has many advantages such as high utilization of raw materials and design freedom,thus SLM technology providing a good solution for the development of superalloys.However,parts made using SLM often have defects such as pores and cracks,which can have a negative impact on the service life and performance of materials.Therefore,this paper aims to improve the microstructure of GH3230 superalloy fabricated by SLM through different post-treatment processes,and summarize the optimal post-treatment process parameters to achieve the goal of optimizing the comprehensive properties of the material.In this work,the effects of heat treatment processes at different temperatures on the microstructure and mechanical properties of GH3230 alloy produced by SLM were investigated.The effect of heat treatment on the microstructure of the deposited was explored by characterizing the evolution of the elemental distribution and size of the precipitated phase,as well as the grain orientation and size,with the increase of heat-treated temperature.At the same time,the mechanical properties of the deposited and heat-treated samples were tested through various characterization methods.It is found that the vertical direction of the deposited consists of columnar crystals epitaxially grown through several molten pools with fine dendrites.After heat treatment,the molten pool disappeared and particles/needle like precipitates were precipitated inside the matrix.With the increase of heat treatment temperature,the carbide undergoes a process of"uniform precipitation first,then aggregative growth,then dissolution matrix".Combined with the type of precipitated phase calculated by JMat Pro software,EDS element distribution test and XRD qualitative analysis,it is shown that the precipitated phase is W-rich M₆C carbide.After heat treatment at 1250℃/30 min,the grain size of the alloy significantly increased.As the heat treatment temperature increases,the hardness of the material also significantly decreases.The tensile strength,yield strength,and elongation of the deposited were 913 MPa,591 MPa,and 31%,respectively.The fracture mode was plastic fracture,and there were pore defects left in the fracture surface during the manufacturing process;After heat-treated at 1200℃/30 min,the optimized values were 898 MPa,389 MPa,and 41%,respectively.The fracture mode was microporous-aggregation ductile fracture,and there were many tear edges distributed on the fracture surface.It was found that after heat treatment,although the ductility of the material was improved,it also affected the tensile strength.Therefore,in order to further improve the mechanical properties of materials,hot isostatic pressing（HIP）and HIP+heat treatment processes are used to conduct heat treatment processes at different temperatures on HIP specimens to explore the relationship between microstructure evolution and mechanical properties.After HIP,the melt pool disappeared,the microstructure consists of irregular columnar crystals and fine dendrites,and precipitated the second phase;After HIP+heat treatment,the microstructure did not change significantly.The EDS surface scanning and XRD test results confirmed that the precipitated phase was a W-rich M₆C carbide.The average grain size after HIP is 22.25μm.Reduced to19.71μm after HIP+1250℃/30 min.The tensile strength,yield strength,and elongation reached 800 MPa,454 MPa,and 28%after HIP,and they improved to 1015 MPa,556 MPa,and 49%after HIP+1250℃/30 min.The fracture mode of the HIP specimen is intergranular-dimple fracture,and there is no significant change after HIP+heat treatment.