Choosing a Suitable Heat Treatment Regime for Stress-Relief and Microstructure Stabilization of Ti6Al4V Alloy 3D-printed by SLM Method

Abstract

During the processing of Ti6Al4V alloy by a 3D printing method SLM (selective laser melting), high internal stresses are developed in the material as a result of high temperature gradients between microvolumes of the powder melted at a given time and the already solidified material. Cooling rates thus reach up to the order of 108 °C·s-1. At such rates, a diffusionless martensitic transformation occurs, which also contributes to internal stresses in the material. High internal stresses can be a problem already during production; they can manifest themselves by cracking of products, deformations of thin parts, etc. Even in defectless products, internal stresses negatively affect their properties; in particular, they reduce ductility. Therefore, it is desirable to include a heat treatment after the 3D printing, which would reduce the stresses and transform the metastable martensitic structure into a stable one. As a result of the heat treatment, the ductility increases at the expense of strength. The subject of this paper is to find such heat treatment regime that provides the best combination of mechanical properties.