Investigation of cracking mechanism and yield strength associated with scanning strategy for an additively manufactured nickel-based superalloy

Abstract

Laser powder bed fusion (LPBF) is considered as a promising technique to fabricate the high W-content nickel-based superalloys, which have excellent mechanical properties and oxidation resistance. However, there still exist some challenges in the LPBF nickel-based superalloys, such as crack elimination and crystallographic optimization. In this work, three scanning strategies are used to investigate the cracking behavior, crystallographic microstructure and tensile properties of a nickel-based superalloy. For the scanning strategy without rotation between the successive layers, the coarse-grained microstructure with a preferred {011}< 111 > texture occurs. After 90° rotation, the grain size decreases and the {001}< 110 > component develops. A fine-grained microstructure with random grain orientation occurs in the samples with 67° rotation. As for the defects, the samples without rotation have the highest susceptibility to solidification cracking and solid-state cracking. After 90° rotation, the cracking tendency significantly decreases. No crack can be found in the 67°-rotation samples. The residual stress and the liquid feeding resistance induced by the grain size effect is the main reason for the scanning strategy-dependent cracking tendency in different samples. Furthermore, the samples with 67° rotation have the lowest yield strength, while the samples without rotation have the highest yield resistance. The difference in yield strength is mainly attributed to the Taylor factor resulting from the grain orientation effect.