Defect Formation Analysis And Heat Treatment Process Of Inconel 625 Fabricated By Selective Laser Melting

Incone625 alloy is one of the main materials for preparing high-temperature parts in aerospace,chemical and other fields.However,it is difficult to manufacture Incone625alloy parts with complex structures by traditional processes such as casting and forging.Selective Laser Melting?SLM?technology can realize the rapid and accurate forming of Incone625 alloy,which becomes an effective method for preparing Inconel625 alloy parts with complex structures.At present,domestic and foreign researches on SLM-ed nickel-based superalloys focus on optimization of manufacturing process and performance testing.However,systematic research on the formation defects and post-treatment regulation is insufficient.Therefore,this subject systematically studied the effects of preparation parameters on the pores,cracks,and spheroidization defects of the SLM-ed Inconel625 alloy,and analyzed the formation process and formation rules of these defects.Meanwhile,the microstructure,mechanical properties and corrosion properties of the SLM-ed Inconel625 alloy were analyzed.In addition,the effects of stress relief,recrystallization and decarburization heat treatment on the microstructure,mechanical and corrosion properties of SLM formed Inconel625 alloy were also investigated.The results show that the SLM-ed Inconel625 samples exhibit high density?higher than 99.5%?and few defects?pores,etc.?with bulk energy density of the laser inputted form 55J·mm^-3to 78J·mm^-3.When the bulk energy density of the laser inputted is lower than 55J·mm^-3,the powder un-melting phenomenon occurs in the forming process,resulting in the generation of irregular pores.Besides,under a large temperature gradient,the surface tension is too large and cracks are formed.When the bulk energy density of the laser inputted is higher than 78J·mm^-3,the bubbles vaporized by the protective atmosphere or low-melting-point elements are blocked at the bottom of the molten pool by the Marangoni effect,thereby forming circular pores.In addition,when the line energy density of the laser inputted is insufficient or excess,the spheroidization of the SLM-ed Inconel625 alloy is obvious.As the laser line energy density increases,the larger the unfused powder bonded particles and spheroidized particles of the SLM-shaped Inconel625 sample.SLM-ed Inconel625 alloy is mainly composed of small cellular grains,rough honeycomb grains and columnar grains.The average grain size is about 30?m.Additionally,the number of high-angle grain boundaries is significantly greater than that of low-angle grain boundaries.There is a small amount of<001>texture.Besides,there are a certain number of Nb-rich and Mo-rich precipitates around the grains.In addition,the tensile strength,yield strength,and elongation of SLM-ed Inconel625 alloy are 930±5 MPa,700±5 MPa and 29.5%,respectively.And it shows a good corrosion resistance in HCL solution.Stress-relief annealing promote the precipitation of fine granular carbides at the grain boundaries of SLM-ed Inconel625 alloy.Moreover,the tensile strength,yield strength,and elongation are increased by 19%,20%and 8%,respectively.The recrystallization temperature directly affects the precipitated carbides shapes and compositions of SLM-ed Inconel625 alloy,leading to the changes of corrosion resistance and mechanical properties.At 730?,micron-level Cr-rich and Mo-rich M₂₃C₆ and M₆C carbides precipitate at the grain boundary after the recrystallized heat treatment.Elongation are increased,while tensile strength and yield strength are decreased.SLM-ed Inconel625 alloy crystals recrystallized heat treatment at 830?,the needle-like?phases appear.Irregular and band-shaped Cr-rich and Mo-rich M₂₃C₆ and M₆C carbides precipitate at the grain boundaries and intragranular,which results in the increased elongation,tensile and yield reduced strength.Large Cr-rich,Mo-rich,and Nb-rich M₂₃C₆,M₆C,and MC carbides appear in the intragranular and grain boundaries of the recrystallized SLM-ed Inconel625 alloy at 930?.Elongation increase,while tensile strength,yield strength decrease and corrosion decreased.Decarburization annealing can dissolve some carbides formed at 930?recrystallized heat treatment of SLM-ed Inconel625 alloy.In addition,rice grain-like Mo-rich and Nb-rich M₆C and MC carbides precipitate at the intragranular and grain boundaries.Moreover,the elongation increases,the tensile strength and yield strength decrease.