Effect of aging on the strength of corrosion-resistant incoloy alloys 945 and 945X: A microstructural perspective

The results of this study show that Incoloy 945X is 19.36% harder and 10.91% stronger than Incoloy 945. Of particular interest is the morphology of precipitates responsible for precipitation hardening in both alloys. To identify and understand the physical mechanisms that lead to these results, this study undertook an extensive microstructural study in which γ’ size, shape and elemental constitution was investigated and correlated to the aging conditions. The main strengthening phase for both alloys is identified by transmission electron microscopy to be the main population of γ’ precipitates, which are between 10 and 25 nm in size. Scanning transmission electron microscopy line scans across the γ’ precipitate reveal more Nb and Ti deflection in Incoloy 945X than in Incoloy 945. This is further supported by the results of transmission electron microscopy, in which γ’ in 945X appear bright (because of Nb) with faceted growth, resulting in a higher value of 0.2% yield strength (1100 MPa) and hardness (430 HV5) than Incoloy 945.