Effect of solution treatment on microstructure and tensile properties of a U720LI Ni-based superalloy

The effect of solution treatment in a range from 1130 °C to 1150 °C on the microstructure and tensile properties of an as-forged U720LI superalloy was investigated under various temperatures between room temperature and 750 °C of tensile tests. It was revealed that a high solution treatment temperature leads to coarsening of grains and secondary gamma prime precipitates, and thus decreases of room temperature and 400 °C strength and ductility. A combination of ductile and brittle mode characterized by dimples and quasi-cleavage facets feature was observed for 1130 °C and 1140 °C solution treatment. The initiation and coalescence of microvoids at the interface of matrix and precipitates as well as the planar-slip process promoted the formation of quasi-cleavage fracture. In addition, a mixed intergranular and transgranular quasi-cleavage fracture with some dimples features for 1150 °C solution treatment was also identified under 750 °C tensile test.