| Abstract Scope |
In-situ subsurface grain refinement of Ni-Cr-based alloys facilitates the formation of the protective superficial layer during high-temperature treatments, leading to an enhancement of the lifetime of component at elevated temperatures. This can be explained by rapid diffusion mediated by high densities of grain boundaries and dislocations. However, the immediate recovery may decelerate their contributions during the long-term heat treatment at elevated temperatures. To elucidate the occurrence of diffusion-induced grain boundary migration (DIGM) and its effect on the carburization, a pre-oxidized Ni-Cr-Fe alloy is subjected to a post-carburization at 1100 °C. The superficial layer is composed of dense Cr2O3, MnO2 and SiO2. Beside the continuously thickening of the Cr2O3 layer, the upward Cr diffusion results in DIGM followed by recrystallization in the Cr-depletion area. Further heat treatment results in the thickening of either the oxide layer or the Cr-depletion area, and the recovery and grain growth in the recrystallized zone. |