Heat-treatment induced microstructural evolution and enhanced mechanical property of selective laser melted near beta Ti-5Al-5Mo-5 V-3Cr-1Zr alloy

摘要

The unique solidification character of selective laser melting (SLM) can result in non-equilibrium microstructure and correspondingly unreliable mechanical properties in as-built Ti-alloy components. As a classical microstructure optimization method, heat treatment is promising in tailoring the microstructure and enhancing the mechanical properties of SLM-built Ti-alloys. This study aimed to increase the strength of metastable beta structure of SLM-fabricated near beta Ti-5Al-5Mo-5 V-3Cr-1Zr (Ti55531) alloy via heat treatment. Three conventional heat treatments, including solution in beta phase region and aging (beta-STA), triplex heat treatment, and solution in alpha+beta phase region and aging (alpha beta-STA) were carried out to tailor the metastable beta structure, and the transformed beta, bi-lamellar and bimodal structures were formed respectively. Tensile tests were performed on horizontal and vertical planes in order to evaluate the anisotropy and the relationship between microstructures and mechanical properties. It was found that the strength and ductility were influenced by the intragranular a precipitates and the intergranular alpha continuity along grain boundary, respectively. The anisotropic tensile behavior in these heat treated samples was affected by the beta grain morphology. This work demonstrated that SLM-fabricated metastable beta Ti-alloy had a strong heat treatability, which can provide different heat treated microstructures and mechanical property. (C) 2020 Elsevier B.V. All rights reserved.