Investigations on the high temperature properties of a superalloy after microstructure engineering

•Fractions of Ti(C, N) precipitates were increased during GBE process.•Fraction of twins appeared to affect the formation of non-twin type Σ3.•The internal oxidation was interrupted by special boundaries.•A model has been developed to relate creep behaviour to special boundary. Special boundaries have the potential to improve high temperature properties of metal alloys, and a type of microstructure engineerings called grain boundary engineering (GBE) can increase fractions of special boundaries and optimize their distribution in the microstructure. The present study has found that unavoidable microstructure changes associated with the formation of titanium carbonitride (Ti(C, N)) could occur during the process of GBE in a solid solution strengthen Incoloy800H superalloy. Experimental results indicate that although fraction of non-twin type Σ3 special boundaries could be increased by multiple-cycles of thermomechanical processes, the presence of Ti(C, N) hindered the migration of grain boundary, and affected both grain size and special boundary formation. Although formation of non-twin type Σ3 special boundaries in the superalloy had lead to improvements in oxidation resistances, its creep resistance was degraded in present study; to elucidate the underlying mechanisms, correlations between minimum creep strain rate, grain size, and the fractions of special boundaries have been determined.