The Effect of Oxygen Content on the Tensile Properties of SLMed Ti6Al4V alloy

The Selective Laser Melting (SLM) is a novel technique to produce net shape part directly from pre-alloyed powders. Ti6Al4V alloy, which consists of the α+β phase, is studied in the present work. During the SLM process some degree of oxygen is usually picked up because titanium has high affinity with oxygen atoms. Oxygen is an interstitial alloying element, it has strengthening effect on various Ti alloys, and it also increases the temperature of the beta transus. The commercial standard limits oxygen content below 0.2 wt% in Ti6Al4V.
   Oxygen concentration has influence on the microstructure and mechanical properties of Ti6Al4V alloy but it should not lead to the formation of texture. However, it has been observed in the SLMed Ti6Al4V under different oxygen contents, tensile properties along vertical build direction and horizontal direction vary differently with the change in oxygen concentration. It appears that oxygen content in SLMed Ti6Al4V affects the texture of the SLMed microstructure. This study is to understand the underlining mechanism for the above effects. SLMed Ti6Al4V samples with oxygen content ranging from 1000 ppm to 1900 ppm have been characterized in terms of tensile properties, microstructure, lattice parameters, texture, and ordering of α phase.
   Microstructure analysis shows that the difference between yield stress from vertical and horizontal samples are accounted by the prior β grain size not the α Lath size. Lattice parameters calculated from XRD (X-Ray Diffraction) spectra indicates that the change in c/a ratio is negligible with changing oxygen content. Pole figures calculated from XRD shows similar weak texture on samples with different oxygen levels. TEM (Transmission electron microscopy) results reveals the presence of α₂ phase in all tested samples.