Heat treatment of Ti-6Al-7Nb components produced by selective laser melting

The purpose of this paper is to describe a preliminary investigation into the heat treatment of Ti-6Al-7Nb components that had been produced via selective laser melting (SLM). Bars of Ti-6Al-7Nb were produced using SLM by MCP-HEK Tooling GmbH in Lubeck, Germany. These bars were then subjected to a range of heat treatments and the resultant microstructure evaluated with respect to its likely effect on fatigue. It was found that the as received material consisted of an α[variant prime] martensitic structure in a metastable ß matrix. Evidence of the layer-wise thermal history was present, as were large (up to ∼500 μm) pores. Solution treatment at 955°C (below the ß transus) did not completely disrupt this layered structure and is therefore not recommended. When solution treatment was performed at 1,055°C (above the ß transus) a homogeneous structure was produced, with a morphology that depended on the post-solution treatment cooling rate. It was concluded that the most promising heat treatment consisted of a moderate cooling rate after solution treatment at 1,055°C. The study had only limited material and therefore it was not possible to perform any mechanical property testing. The paper presents the initial findings of a project which is aimed at optimising the mechanical properties of Ti-6Al-7Nb components produced using SLM. Currently, little is known about the heat treatment and subsequent mechanical properties of this Ti-6Al-7Nb alloy when produced using rapid manufacturing techniques. Such lack of knowledge limits the potential applications, especially in the biomedical field where the consequences of implant failure are high. The paper presents the first step in developing this understanding.