Crack reduction in Inconel 939 with Si addition processed by laser powder bed fusion additive manufacturing

Inconel 939 (IN939) suffers from cracking in the laser powder bed fusion based additive manufacturing (LPBF-AM) process. Previous studies attempted to minimize the crack density by reducing the Si content. In contrast, this paper demonstrates that Si addition can substantially lower the crack density in LPBF-AM IN939 alloy parts. Si addition into IN939 shows a moderate impact on the crystallographic orientation and grain size of LPBF-AM parts, and promotes the formation of precipitates. Mechanical tests show that Si addition increases tensile strength and indentation hardness but decreases ductility. This work suggests that the dominant cracking mode in LPBF-AM IN939 alloy parts is solidification cracking, the suppression of which by Si addition can be qualitatively rationalized using Clyne's model and Kou's model. The present findings provide a different perspective on designing defect-free LPBF-AM Ni-based superalloy parts with balanced mechanical properties, one which can be extended to other alloy systems.