Understanding the microstructural stability in a γ′-strengthened Ni-Fe-Cr-Al-Ti alloy

[摘要] Ni-Fe-Cr-Al-Ti alloys, with Ni levels of about 45 at% have the potential to develop a microstructure consisting of a face-centered cubic (gamma) matrix with homogeneously precipitated, nanoscale ordered gamma' precipitates similar to that found in traditional Ni-based superalloys with a significantly greater Ni content. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and CALPHAD-based thermodynamic modeling were employed to determine the phase stabilities and microstructural evolution in an age-hardenable 44.56Ni-26.6Fe-19.2Cr-1.0Co-3.4A1-4.4Ti-0.7Mo-0.14 C (at%) alloy. The primary heat treatment of solution annealing at 1121 degrees C for 4 h followed by age-hardening at 760 degrees C for 16 h resulted in a microstructure consisting of fine gamma' precipitates in an austenitic matrix along with grain boundary precipitates of carbides and other minor phases. Long-term aging at 900 degrees C for 250 h resulted in the coarsening of gamma' precipitates along with a change in the morphology from an initial spherical to a more cuboidal shape. In addition, the formation of plate-like eta phase precipitates was observed, concomitant with the partial dissolution of the gamma' phase. The ability of computational thermodynamic models to predict microstructural characteristics is discussed. (C) 2021 Published by Elsevier B.V.

[发布日期] 2021-12-15

[关键词] gamma&PRIME precipitate;Fe-Ni-Cr-based superalloys;Atom probe tomography;CALPHAD