Enhanced mechanical properties of the additively manufactured IN738LC superalloy through thermal history management during the laser powder bed fusion process

Abstract

IN738LC superalloy, as one of the hard-to-weld Ni-based superalloys, is relatively difficult to be produced by laser powder bed fusion (LPBF) due to its high cracking susceptibility. In this study, local heat accumulation based on substrate preheating and chessboard scanning strategy modification was proposed to reduce the thermal stress and promote the dynamic precipitation of IN738LC superalloy during LPBF process, which contributes to the crack inhibition and mechanical property enhancement. The as-built IN738LC superalloy exhibited superior room temperature tensile yield strength (YS) of 1011 ± 7 MPa, ultimate tensile strength (UTS) of 1400 ± 12 MPa, and good ductility of 17.4 ± 2.9 %. The superior mechanical performance was achieved mainly due to the successful elimination of micro-cracks, the formation of hierarchical microstructure composed of columnar γ grains, cellular dislocation network, especially in-situ formation of carbide precipitates. The formation of micro-cracks was fully eliminated due to the reduced temperature gradient and residual stress. In-situ formation of carbide precipitates was enabled by well-controlling the thermal history during the LPBF process. The use of a chessboard scanning strategy and substrate preheating was found to be beneficial for achieving a larger melting pool size, coarser dendrite/cellular arm spacing, and a larger volume of carbide precipitates due to enhanced heat accumulation during the LPBF process, which was verified by finite element analysis. This work provides insights into the effects of thermal profiles inherent to LPBF processes on the performance of LPBF-processed IN738LC superalloy.