Tensile behavior of Ti-6Al-4V alloy fabricated by selective laser melting: effects of microstructures and as-built surface quality

selective laser melting (SLM) is a powerful additive manufacturing (AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6Al-4V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing (HIP) were investigated. The microstructures were analyzed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the as-deposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900 degrees C for 2-4 h and HIP at 920 degrees C/100MPa for 2 h, the brittle martensite could be transformed into ductile lamellar (alpha+beta) microstructure and the static tensile properties of SLM-processed Ti-6Al-4V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed Ti-6Al-4V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar (alpha+beta) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.