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

Abstract

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 β structure of SLM-fabricated near β Ti-5Al-5Mo-5 V-3Cr-1Zr (Ti55531) alloy via heat treatment. Three conventional heat treatments, including solution in β phase region and aging (β-STA), triplex heat treatment, and solution in α + β phase region and aging (αβ-STA) were carried out to tailor the metastable β structure, and the transformed β, 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 α precipitates and the intergranular α continuity along β grain boundary, respectively. The anisotropic tensile behavior in these heat treated samples was affected by the β grain morphology. This work demonstrated that SLM-fabricated metastable β Ti-alloy had a strong heat treatability, which can provide different heat treated microstructures and mechanical property.