Defect-induced interfacial delamination and transgranular fracture in laser-cladded stellite alloys under thermal cycling

This study reveals a dual-mode fracture behavior in laser cladding Stellite alloy coatings under quasi-in-situ thermal cycling. Intergranular fracture dominates (78.99 %), occurring primarily along eutectic phase boundaries, accompanied by secondary transgranular fracture within eutectic carbides. Cross-scale microstructural analysis identifies critical interfacial features: stacking faults, Lomer-Cottrell locks, and incoherent phase boundaries, that govern stress localization. Multiscale stress field analysis demonstrates a synergistic interaction between thermal stress (σ th ), dislocation-induced stress (σ disl ), and lattice mismatch stress (σ misfit ), with dislocation-mediated stress identified as the primary contributor. Nanoindentation measurements reveal that reductions in reduced elastic modulus and hardness are closely associated with transgranular cracking and the accumulation of residual stress during thermal cycling. These findings highlight the pivotal role of atomic-scale defects in governing fracture mechanisms in complex eutectic microstructures. • A dual-mode fracture mechanism is revealed in laser-cladded Stellite alloy coatings under quasi-in-situ thermal shock. • The critical atomic-scale defects, stacking faults, Lomer-Cottrell locks, and incoherent phase boundaries, are qualitatively identified and analyzed. • Multiscale stress fields, including thermal, dislocation-induced, and lattice mismatch stresses, are quantified and correlated with fracture evolution. • Residual tensile stress promotes mechanical degradation and transgranular fracture of the brittle carbide phase.