Quantitative and qualitative characterization of the damage, deformation mechanisms, and failure modes of a nickel-based GH3536 alloy prepared via laser powder bed fusion after various heat treatments

Abstract

Nickel-based alloys prepared via laser powder bed fusion (LPBF) exhibit high strength and low elongation during tensile testing at room temperature. To optimize the performance, hot isostatic pressing (HIP) and HIP with heat treatment (HT), that is, HIP + HT were applied to the deposited GH3536 samples. The plasticity and elongation of the post-treated Ni-based alloy are clearly improved; this can be attributed to the change in micromorphology from columnar grains to equiaxed grains, as well as to the reduction in defects and internal stresses. It is experimentally confirmed that the characteristic grains and defects formed during the LPBF process caused the porosity of the deposited samples to change considerably during tensile testing. The increment is up to 12.3%, and the grain deformation rate of the deposited samples is minimal. The porosity increased by 1.4% for the HIP-ed GH3536 (i.e., after hot isostatic treatment) samples and by 5.4% for the (HIP + HT)-ed GH3536 (i.e., after hot isostatic pressing and heat treatment) samples during tensile testing. The results of electron backscatter diffraction characterization and grain statistics revealed that the average grain diameter of the HIP-treated samples increased the most (>25 μm) during the tensile process, and the samples exhibited the best deformation ability. Microstructural characterization showed that the (HIP + HT)-ed samples contained a large number of “small equiaxed grains” (i.e., grains with the grain size are always less than 50 μm in the whole process of deformation). According to the grain deformation behavior analysis, these small equiaxed grains coordinated the deformation process, resulting in the (HIP + HT)-ed samples exhibiting the best deformation coordination ability and deformation mechanism.