Effects of cerium addition on the microstructure and stress rupture properties of a new nickel-based cast superalloy

Abstract

The microstructure and stress rupture properties of a new nickel-based cast superalloy were investigated with the cerium (Ce) additions of 0, 19, 50, 96, 150, and 300 ppm, respectively. The results indicated that Ce was mainly found in MC and M23C6 carbides, and it was also found to exist in the form of cerium-rich phases or inclusions. According to the microstructure evidence, Ce promoted the formation of MC carbides and aggravated the inhomogeneity of M23C6 carbides along grain boundaries. It was also identified that the average sizes of primary and secondary γ' phases all decreased with the rising Ce content. The acceleration of Ti, Nb, and C segregations during solidification was attributed to the influence of cerium on the variation of carbides along grain boundaries. The stress rupture life experienced a significant drop as the Ce content increased from 19 to 300 ppm. Explorations showed that the degradation was mainly attributed to the severe degradation of MC carbides and the easily forming micro-voids around them caused by the Ce addition. In addition to that, the increments in the inhomogeneous distribution of M23C6 carbides at grain boundaries and the accelerated coarsening rate of γ' phases both induced the fracture under complex stress conditions.