Effects of Initial Grain Morphology on Anisotropy of Microstructure and Mechanical Property in LPBF-Inconel 738 Alloy by Hot Isostatic Pressing

Abstract:

Effects of initial grain morphology on anisotropy of microstructure and mechanical property in Inconel 738 alloy prepared by laser powder bed fusion (LPBF) under different scanning strategies after hot isostatic pressing (HIP) treatment were studied. The results show that the initial grain morphology is highly heritable. The initial grain morphology of Inconel 738 alloy formed by scanning strategy 90° (As-built 90 alloy) presents elongated columnar grains and irregular fine grains. After HIP treatment, the recrystallized grain morphology of HIP 90 alloy presents elongated columnar grains and a few equiaxed grains. The As-built Inconel 738 alloy formed by scanning strategy 67° (As-built 67 alloy) initially has short columnar and equiaxed grains, and the recrystallized grain morphology of HIP 67 samples shows similarly equiaxed and equiaxed grain morphology. The main reason is that the initial grain morphology determines the strain distribution. The strain distribution of As-built 90 samples is in the shape of “bar”, while that of As-built 67 samples is in the shape of “net”, and the strain distribution is more uniform. During HIP treatment, the strain concentration region preferentially provides nucleation location for recrystallized grains, which determines the morphology of recrystallized grains in HIP samples. The mechanical anisotropy of HIP 90 alloy is larger than that of HIP 67 alloy, which is mainly related to the grain morphology of HIP 90 alloy. The equiaxed grain morphology of LPBF-Inconel 738 alloy after HIP treatment requires appropriate LPBF process parameters.