Microstructural evolution and mechanical properties of Nimonic 105 alloy aged at 750 °C

Abstract

The microstructural evolution and mechanical properties of Nimonic 105 alloy aged at 750 °C for times up to 10000 h were investigated. It is shown that the grain size increased slightly, while no significant variation was found in the morphology, size and distribution of MC carbides during long-term aging. In contrast, the M23C6 carbides displayed obvious coarsening during the aging and formed nearly continuous networks after aging for 5000 h, which was the main reason for the remarkable drop in toughness. The weight fractions of M23C6 carbide and γ′ phase increased gradually with increasing aging time up to 600 h and after that did not significantly change. During long-term aging, the γ′ precipitates coarsened significantly and showed a transform from spherical to cuboidal morphology. The γ′ precipitates exhibited an uni-modal size distribution and the coarsening kinetics of γ′ precipitates follows the t1/3 law. In the first 2000 h aging, the γ′ precipitates were largely cut by strongly coupled dislocation (SCD) pairs and the occurrence of peak strength after aging for 600 h resulted mainly from the increased amount of γ′ precipitates. After aging for 5000 h and above, the strengthening mechanism changed from SCD cutting to Orowan looping, thus the yield strength decreased gradually with prolonging aging time.