Selective laser melting of pure tantalum: Densification, microstructure and mechanical behaviors

In this study, selective laser melting (SLM) of pure tantalum (Ta) was systematically investigated, with emphasis on densification, microstructure and mechanical properties of Ta specimen. The high laser scanning speed resulted in micropores and discontinuous scan tracks, owing to the elevated instability of the liquid induced by Marangoni convection and the balling effect. However, the interlayer thermal microcracks were produced at a low scanning speed, due to the thermal stress and balling effect. The microhardness and tensile strengths of the optimally SLM-processed Ta parts were improved to 445 HV and 739 MPa, respectively, which were considerably higher than specimens processed by cast (110 HV and 205 MPa) or powder metallurgy (120 HV and 310 MPa) method, due to the fine-grain strengthening. The fracture morphology of the tensile-failed SLM-processed specimens showed that the porosities and incompletely melted particles are responsible for the fracture of porous sample. While for dense sample, cleavage fracture and minor ductile fracture both account for the fracture. And the failure mechanisms were discussed. The reduced coefficient of friction of 0.3 and lowest wear rate of 7.1×10−3 mm3 N−1 m−1 in dry sliding wear tests were obtained for the optimally prepared Ta parts due to the formed adhesion of hardened tribolayers.