Liquation cracking facilitated by stray-grain chains in a high-γ'-content nickel-based alloy K4002 produced via electron beam powder bed fusion

Abstract

Cracking significantly hinders the development of additive manufactured high-γ’-content nickel-based alloys. This study investigates the microstructure and cracking behavior of a high-γ'-content nickel-based alloy K4002 produced via electron beam powder bed fusion (EBPBF). The results suggest that liquation cracking is the predominant cracking mechanism observed. Stray-grain chains were found to promote liquation cracking due to several factors: i) The presence of high angle grain boundaries (HAGBs) between the stray grains and adjacent columnar grains; ii) the higher density of geometrically necessary dislocations (GND) within stray grains; iii) Cr₂₃C₆ carbides, at the stray grain boundaries, hinder dislocation motion and promote strain accumulation; and iv) the formation of low-melting-point regions around the Cr₂₃C₆ within the stray grain chains. Furthermore, the origin of stray-grain chains was analyzed using the Rayleigh number and the columnar-to-equiaxed transition (CET) criterion, revealing that the stray-grain chains originate from the CET. As a result, through optimizing the solidification rate to inhibit CET, stray-grain chains were effectively eliminated, leading to a 55 % reduction in crack incidence. The findings in this work provide guidance for mitigating liquation cracking induced by stray-grain chains during additive manufacturing.