Intermediate temperature embrittlement of a solution treated Nimonic 105 superalloy

The tensile properties of Nimonic 105 alloy after solution treatment at 1150 °C was studied by tensile tests at temperatures between room temperature and 900 °C, and the intermediate temperature embrittlement mechanism of the alloy was investigated through microstructure observation utilizing scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that the ultimate tensile strength of the alloy dropped with increasing temperature, while the yield strength remained basically unchanged below 800 °C, above which it reduced sharply. The elongation decreased markedly above 600 °C, and then enhanced gradually with further increasing temperature after reaching a minimum at temperatures of 750–800 °C. TEM examination showed that the primary deformation mechanism was shearing of γ′ precipitates by coupled dislocation pairs below 800 °C, and it changed to Orowan bowing combined with climb and cross-slip of dislocations above this temperature. The ductility minimum of the alloy at 750–800 °C resulted mainly from the precipitation of M₂₃C₆ carbides at the grain boundaries and grain boundary segregation of S.