Measuring the tensile properties of Ti6Al4V fabricated by laser powder bed fusion: Influence of specimen dimensions

This study presents the mechanical characterization of vertical Ti6Al4V tensile specimens produced by laser powder bed fusion (LPBF) processing and then heat-treated according to AMS2801 standard. The surfaces were kept in the as-built condition for the evaluations. Three rectangular specimen geometries were considered, with a reduced section of 6 x 6 x 25, 3 x 3 x 12.5, and 1 x 1.5 x 7 mm3 respectively. The surface roughness, lengthscale of the microstructure, and average microhardness were compared and found to be unaffected by part section, in the range of sizes explored. The non-destructive measurement of the cross-sectional area of the tested specimens affected the accuracy on the measurement of the tensile strength. The use of conventional tools, such as calipers and micrometers, led to an overestimation of the cross-sectional area by 7 to 15 %, which caused an underestimation of the tensile stresses. When calculating the stress with the cross-sectional area measured from computed tomography images, the Young's modulus, yield strength and ultimate tensile strength were comparable for all geometries. However, the elongation at break was 9 % for the smallest specimens compared to 12 % for ASTM E8 coupons. The reduction of ductility was explained by a higher slimness ratio for smaller specimens, in addition to an increased effect of pores and the surface roughness. These results highlight the importance of using specimens representative of a part wall thickness when characterizing the mechanical properties of LPBF Ti6Al4V. The methodological recommendations established in this study can be applied to other LPBF materials and other small scale manufacturing processes.