Creep damage failure mechanism of nickel-based superalloy IN738LC

This study investigates the creep damage failure mechanisms of as-cast IN738LC, a γ'-strengthened nickel-based superalloy, under 850°C/300 MPa conditions using creep rupture and interrupted creep tests. Microstructural characterization via scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) reveals that tertiary creep (Stage III) is dominated by grain boundary (GB) sliding-induced void nucleation and MC carbide decomposition. Creep interruption at 1.2% strain demonstrates the formation of interconnected micro-voids at GBs and cracking of MC carbides due to lattice misfit with the matrix. The bimodal γ' phase distribution undergoes significant coarsening, with primary cuboidal γ' transforming into spherical shapes and secondary γ' particles growing in size, reducing their effectiveness in hindering dislocation motion. EBSD analysis further confirms localized recrystallization and increased kernel average misorientation (KAM) at GBs, indicating stress concentration and plastic deformation accumulation. These findings highlight that GB damage, γ' phase coarsening, and MC carbide degradation collectively drive the transition to accelerated creep and final fracture, providing critical insights for improving creep resistance in nickel-based superalloys.