Microstructural change and stress rupture property of Nimonic 105 superalloy for advanced ultra-supercritical power plants

Abstract

Microstructural change, stress rupture property, deformation and fracture mechanisms of Nimonic 105 superalloy at 750 °C have been studied. Experimental results showed that the stress rupture strength of the alloy at 750 °C for 105 h is about 200 MPa. γ′ precipitates and M23C6 carbides grew gradually with prolonging the rupture time, while no significant change was observed in MC carbide morphology. After stress rupture test at 750 °C and 250 MPa for 23,341 h, a transition from spherical to cuboidal morphology of γ′ precipitates was found, and nearly continuous chains of M23C6 carbides formed on the grain boundary. Orowan looping and strongly coupled dislocation pairs cutting and microtwinning were the dominant deformation mechanisms at 750 °C and 350–450 MPa, while the main deformation mode was Orowan looping at 750 °C and 250 MPa. The failure of the alloy was mainly attributed to the nucleation, growth and interlinkage of voids.