Flow behavior and microstructure evolution of Ti-6Al-4V titanium alloy produced by selective laser melting compared to wrought

Abstract

Nowadays, selective laser melting (SLM) represents an option for manufacturing parts from titanium alloys, especially from Ti-6Al-4V alloy. However, mechanical properties of parts made of SLM-produced Ti-6Al-4V, such as ductility and fatigue resistance, are significantly lower than that of wrought ones. The promising way to improve mechanical properties of SLM parts without expensive hot isostatic pressing can be combination SLM and deformation post-processing. Therefore, the goal of the present study is to investigate the flow stress behavior and microstructure evolution of Ti-6Al-4V fabricated by SLM in a wide temperature range in comparison with conventional manufactured material. In contrast to wrought material, SLM-produced Ti-6Al-4V shows high plastic flow instability at test temperatures of 20–900 °С, which was demonstrated via temperature sensitivity and softening rate. FEM-simulation of hot isothermal compression of samples was conducted in order to compare the deformation inhomogeneity between SLM-produced and wrought materials, namely, local strains e in the severe plastic deformation and dead metal zones. The microstructure in these characteristic zones of both materials deformed in (α + β)-field was examined by means of optical microscopy. The type of microstructure and grain size of the SLM-produced and wrought material were studied. It turned out that the deformation of SLM-produced Ti-6Al-4V at a lower temperature (800 °C) and a higher strain rate (1 s−1) makes it possible to obtain ultrafine-grained microstructure. This, in turn, opens the door to the production of Ti-6Al-4V parts with high mechanical properties via processing route SLM + metal forming.