Impact Toughness of As‐Built and Heat‐Treated Near‐β Ti–5Al–5Mo–5V–3Cr–1Zr Alloys Fabricated by Selective Laser Melting and Electron Beam Melting

Abstract

Herein, the effects of heat treatment on the microstructure evolution and impact toughness of selective laser‐melted (SLM) and electron beam‐melted (EBM) near‐β Ti–5Al–5Mo–5V–3Cr–1Zr (Ti55531) alloy specimens are systematically investigated. As fabricated SLM and EBM Ti55531 alloys contain metastable β and α + β microstructure, respectively. The metastable β microstructure of SLM‐fabricated Ti55531 is transformed to bilamellar, lamellar, and bimodal structure after supertransus triplex heat treatment, hot isostatic pressing and α/β solution and aging treatments, respectively. In the EBM‐fabricated Ti55531 specimens, the defects are effectively eliminated after hot isostatic pressing. The correlation between microstructure and impact toughness of as‐built and heat‐treated specimens are elucidated. Both SLM and EBM specimens with lamellar microstructure show a high impact toughness due to the deflecting effect on crack propagation of α lamella. In addition, hot isostatic pressing further enhance the impact toughness of EBM‐fabricated Ti55531 via eliminating the defects formed during the fabrication process. This work demonstrates that heat treatment is a potential way to tailor the microstructure and enhanced the impact toughness of additive manufactured near‐β Ti alloys.