Study On Tensile Properties And Damage Mechanism Of GH3536 Alloy Prepared By SLM

The GH3536 alloy formed by selective laser melting(SLM)has the advantages of high strength and high density,but the GH3536 formed directly has poor plasticity and low elongation after fracture,and these two indexes are lower than forgings,severely limiting the processing and application of the alloy.As a result,in this paper,hot isostatic pressing(HIP)and hot isostatic pressing and heat treatment(HIP+HT)were performed on GH3536 alloy formed by SLM,and the microstructure and mechanical properties of the material were optimized.The damage and deformation mechanism of samples were studied from three perspectives: grain deformation,surface damage and failure mode,and the root cause of the effect of post-treatment on the properties of alloys was discussed.The tensile test at room temperature reveals that the deposited specimens have the highest ultimate tensile strength,exceeding 900 MPa,with only a 23% elongation.The alloy’s elongation increases to 67% after HIP+HT treatment,but its strength decreases slightly.Using tensile strength*elongation(MPa*%)as the material’s comprehensive mechanical properties,the comprehensive properties of the samples after post-treatments are significantly improved,especially those after HIP+HT treatment reach the best comprehensive properties.Damaged samples with different deformation degrees were prepared by loading-unloading test based on the average fracture strains of the alloys obtained by tensile test.The micromorphology,porosity,and mechanical properties of the damaged samples were used to characterize the damage process.After HIP treatment,the internal defects are reduced and the density is increased.The microstructure changes from coarse columnar grain to equiaxed grain.Special morphology such as molten pool boundary and “fish-scale” structure vanished.After HIP+HT treatment,the microstructure transformed into equiaxed grains,and a large number of recrystallized grains with sizes less than 50μm appeared at the grain boundaries,while the average grain size of the alloy decreased.The porosity characterization results of damaged samples showed that the porosity of deposited samples increased by 12.3% from undeformed to fractured,1.4% after HIP treatment,and 5.4% after HIP+HT treatment.Nanoindentation tests were used to characterize the mechanical properties of damaged samples.Hardness and porosity changes in deposited samples were concentrated primarily in two deformation stages of 0-25% and 75%-100%.Hardness and porosity changes in HIP and HIP+HT samples were concentrated in the 50%-75% stage and tended to be stable later in deformation.Grain statistics,EBSD,and TEM were used to characterize the deformation mechanism.According to the EBSD characterization results,the grain deformation of the deposited and HIP+HT samples were mainly occurred in the middle and early stage of tensile deformation.The grain deformation of HIP sample was concentrated in the late deformation after 50% of the sample deformation degree.The proportion of deformed grains in deposited damaged samples after fracture is only 78%,which is significantly lower than the proportion in post-treated samples(more than 95%).According to TEM characterization,different types of precipitated phases were detected in three different state samples.According to the grain statistics,the main grains of GH3536 alloy formed by SLM have the same deformation mechanism,which is not affected by the post-treatment.Deposited samples contain three characteristic grains,among which the fine dendrites are easy to transform into the priority failure zone.HIP treated samples have the best deformation capacity.With the coordination of small equiaxed grains,the deformation coordination ability of HIP+HT treated samples is the best.The fracture modes of the samples in three states are all ductile fracture,but the section morphology is different.HIP+HT treated specimens have the best toughness,the largest number and average size of dimples,and almost no large holes and long cracks.The toughness of the deposited samples is the worst,the neck shrinkage is not obvious,and the main characteristics of the fracture surface are long cracks and holes.