Mechanical properties and microstructural evolution of TA15 Ti alloy processed by selective laser melting before and after annealing

Selective laser melting (SLM) is a promising additive manufacturing technique with growing acceptance in aerospace applications. In this work, a new aeronautical material of near-alpha Ti alloy (TA15) for SLM was firstly investigated and analyzed before and after annealing, mainly including mechanical properties, microstructural evolution. The distinctions between SLMed TA15 and wrought TA15 are also discussed in this study. Firstly, near full density TA15 samples (99.98%) were fabricated by SLM utilizing the optimized processing parameters. Then microstructures and textures are characterized and analyzed by optical microscope, X-ray diffractometer, scanning electron microscope and transmission electron microscope. Furthermore, mechanical properties of TA15 samples are measured via tensile and hardness test, considering the impacts of building direction. The results show that both the as-built and the annealed SLMed samples exhibit significantly weak textures and unconspicuous anisotropy of mechanical properties. It has been identified that alpha' martensite is dominant in the as-built microstructure thus contributing to similar to 1296 MPa in ultimate strength and similar to 398 HV in hardness which are 35% and 24% higher than those of wrought material. However, a low plasticity with similar to 7.6% of elongation at break was observed. After annealing, SLMed samples exhibited excellent comprehensive mechanical properties with 51% improvement at elongation through elimination of residual stress and precipitation of nanometer size beta phase in the fine basket-weave structure.