In-situ remelting induced healing of cracks and strength-ductility synergy in additively manufactured Haynes 230 alloy

Hot-cracking hinders the application of nickel-based superalloys fabricated by laser powder bed fusion (LPBF) in the aerospace industry. In this work, an innovative in-situ remelting process was utilized to heal cracks. Nearly crack-free LPBF-prepared Haynes 230 specimens were obtained. More specifically, hot-cracking mainly occurred in the center of the deep and large molten pool. By controlling the remelting depth to 70-80 % of the original layer depth, most of the original cracks were remelted, while the remaining cracks were backfilled by the liquid metal in the molten pool, and the cracks were healed. This enabled the significant alleviation of W, Cr, Mo, C solute elements and O impurity element segregation at the grain boundaries (GBs), and also promoted the precipitation of high melting point M23C6. In addition, the remelting process melted the oblique growth dendrites on the sides and the coarse dendrites in the middle and top of the molten pool, which resulted in the cracksensitive GBs reduction and GB serration, relieving increased residual stresses caused by remelting. Furthermore, the higher dislocation density and more random grain orientation of the remelted specimens led to an enhanced contribution of dislocation strengthening with a great plasticity, reaching the properties of Haynes 230 reinforced by ceramic particles. This study broadens the application of crack-prone LPBF-prepared superalloys by proposing a novel crack healing mechanism that bypasses the technical hurdles of effectively inhibiting cracking with changes in alloy composition.