Assessment of solidification cracking susceptibility and mechanisms in 316L stainless steel repaired by laser-deposited CoCrFeNi high entropy alloy

Although laser-deposited CoCrFeNi high entropy alloy (HEA) promises to repair 316L stainless steel damaged under complex service conditions, its application is limited by solidification cracking compromising reliability. This study adopted the trans-varestraint test (TVRT) to evaluate the solidification cracking susceptibility of repaired 316L samples and investigated crack initiation/propagation and their correlations with microstructure. Results show repaired samples have coarse epitaxial columnar grains. TVRT results show maximum crack distance increases in an S-shape with strain, and critical strain threshold is 1%–2%. The repaired samples (cracking susceptibility index, CSI : 1838; solidification cracking temperature range, SCTR : 228 °C) have much higher solidification cracking susceptibility than 316L substrate and is comparable to Ni-based superalloys. Notably, the SCTR index characterizes laser-deposition repair cracking tendency more accurately than conventional CSI . Solidification crack modes vary with constraint strain. At low strain (∼2%), cracks initiate at columnar/equiaxed grain interfaces. At medium-high strain (∼3%), cracks initiate at columnar grain junctions and propagate along high-angle grain boundaries (HAGBs). At ultra-high strain (∼5%), transgranular initiation occurs at cellular subgrain boundaries, driven by mechanical forces. Furthermore, intragranular regions with significant orientation gradient (>5°) and abundant low-angle grain boundaries (LAGBs) have high solidification cracking susceptibility. HAGBs can act as crack propagation paths but are not sufficient for cracking. Instead, their geometric morphology and connectivity play a critical role. Straight and interconnected grain boundary pathways promote crack propagation, while a tortuous and interlocked grain boundary network formed by staggered grains can effectively inhibit crack propagation.