Additive manufacturing of Ni-based superalloys : Residual stress, mechanisms of crack formation and strategies for crack inhibition

The additive manufacturing (AM) of Ni-based superalloys has attracted extensive interest from both academia and industry due to its unique capabilities to fabricate complex and high-performance components for use in high-end industrial systems. However, the intense temperature gradient induced by the rapid heating and cooling processes of AM can generate high levels of residual stress and metastable chemical and structural states, inevitably leading to severe metallurgical defects in Ni-based superalloys. Cracks are the greatest threat to these materials’ integrity as they can rapidly propagate and thereby cause sudden and non-predictable failure. Consequently, there is a need for a deeper understanding of residual stress and cracking mechanisms in additively manufactured Ni-based superalloys and ways to potentially prevent cracking, as this knowledge will enable the wider application of these unique materials. To this end, this paper comprehensively reviews the residual stress and the various mechanisms of crack formation in Ni-based superalloys during AM. In addition, several common methods for inhibiting crack formation are presented to assist the research community to develop methods for the fabrication of crack-free additively manufactured components.