Material properties of selective laser melting additive-manufactured Ti6Al4V alloys with different porosities

Abstract

In this study, Ti6Al4V specimens with a variety of porosities were prepared using selective laser melting (SLM) by changing its laser hatch spacing. The pores on the surfaces perpendicular (SPER) to the stacking direction (SD) and surfaces parallel (SPAR) to SD of the cube samples were totally different from each other. The topography of SPER was dominated by the laser hatch spacing, whereas SPAR was almost entirely covered with non-molten powder particles having different looseness values. Thus, an optimal modeling direction exists for the real-time application of the alloys. The SLM-manufactured samples were scanned by computed tomography (CT) and then analyzed using the binarization method to investigate their internal porosity, which ranged from 20% to 45%. Tensile tests were conducted to describe their tensile behavior and evaluate their elastic moduli. These analyses revealed an inverse relationship between the porosity and elastic modulus as laser hatch spacing increased. An elastic modulus less than 2000 MPa was obtained using the SLM process, which is sufficient for applications requiring a low elastic modulus. Furthermore, their grain details were observed using electron backscattered diffraction (EBSD). The samples had typical fine acicular grains but with smaller average diameters as the laser hatch spacing increased. Furthermore, the average fraction of misorientation decreased because of the increasing small-angle grains and decreasing large-angle grains, indicating a significant influence of the laser hatch spacing on the grain orientation. Additionally, surface qualities were quantitatively assessed to reveal how laser hatch spacing affected the morphology. By comprehensively analyzing the surface morphology and quality, porosity and tensile properties, and grains details, a vivid material forming theory of the SLM process was concluded.