Effect of specimen geometry and orientation on tensile properties of Ti-6Al-4V manufactured by electron beam powder bed fusion

Abstract

Tensile testing is often proposed as the preferred methodology to qualify builds and materials produced through additive manufacturing. While there is already work demonstrating the difference in measured properties between tensile specimens produced in different build orientations, this does not extend to different specimen geometries. In addition, the body of knowledge in this domain is typically made up of studies that utilize custom combinations of specimen geometries, part finishing, and post-processing, making it challenging to compare results. To study the impact of geometry of tensile specimens on tensile testing results, a selection of standard specimen types provided in ASTM E8/E8M was prepared in Ti-6Al-4V using an electron beam powder bed fusion additive manufacturing machine. These specimens were characterized to observe any porosity defects, dimensional deviations, and surface topography that could impact performance. It was found that changes in specimen geometry, specimen size, build orientation, and the internal porous defects; have significant effects on the tensile properties of the specimens. The horizontally built specimens had higher yield and tensile strengths, but lower elongation compared to vertically built specimens. With an increase in cross-sectional area, an increase in the yield, tensile strength, and elastic modulus was observed. With an increase in surface area to volume ratio, there was a decrease in the yield and tensile strength. The average solid fraction of the specimens had no influence on any measured tensile properties. Furthermore, with an increase in maximum pore size, the elongation of the specimen decreased.