Achieving bimodal grain structure in Incoloy 945 nickel-based alloy through precipitation control

Abstract

The Incoloy 945 nickel-based corrosion-resistant alloy was subjected to a low-temperature solid solution with a two-step aging process to fabricate a bimodal grain structure. The study investigated the mechanism behind the formation of the bimodal grain structure and its impact on mechanical properties. The results show that numerous clusters of fine grains, with an average size of 4 μm, were formed among the normal grains, which had an average size of 23 μm. The precipitation behavior in fine-grain clusters differs from that in normal grains. A high density of rod-like δ phases tends to precipitate inside refined grains. The inhomogeneous precipitation of δ phases is the main reason for the formation of fine-grain clusters because they have a strong ability to pin the grain boundaries for the growth of new recrystallized nuclei. The morphology of γ’ varies from short rod-like particles to spherical particles depending on their location in fine-grain clusters or normal grains. The difference in precipitation and grain structure leads to different deformation mechanisms in the two regions. The bimodal grain structure results in higher strength and work hardening rate during tension. The quasi-in-situ tensile test indicates that slip transfer is more easily induced in fine-grain clusters. Fine grains had an advantage in accumulating necessary geometric dislocations during deformation, resulting in a high work hardening rate for this bimodal grain structure sample.