Novel eutectoid Ti-5Ni alloy fabricated via direct energy deposition

Abstract

Direct energy deposited (DED) Ti-5Ni (wt.%) alloys promote significant grain refinement with fine equiaxed grains (similar to 30-50 mu m); they have discontinuous grain boundary a, fine eutectoid a laths (similar to 1 mu m width), and alpha + Ti2Ni phases. Post-heat treatment below beta transus for 24 h stimulates the formation of near equiaxed alpha, and the temperature significantly influenced the microstructural constituents, which included pre-eutectoid alpha + retained beta + Ti2Ni (760 degrees C), pre-eutectoid alpha + alpha' + Ti2Ni (8000C), and fully a' + Ti2Ni (850 degrees C) phases. The tensile properties of the as-fabricated and the heat-treated alloy remarkably improved compared with the other conventionally processed eutectoid Ti-Ni binary alloys. Thus, the proposed approach opens up new opportunities and possibilities for fabricating other eutectoid-forming alloy systems with improved manufacturing efficiency, which can overcome limitations in the other manufacturing processes. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.