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T i-6Al-4V is a typical α+β duplex-phase titanium alloy with outstanding specific strength, corrosion resistance and bio-compatibility, which has been widely applied in biomedical, aerospace, automotive, energy, chemical, and other industries [1] . However, the poor machinability and high cost of Ti-6Al-4V using a traditional processing route limit its more extensive application. Furthermore, the production of titanium alloy by conventional processing technology leads to Abstract: 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 fi ne brittle martensite and the asdeposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900°C for 2-4 h and HIP at 920°C/100MPa for 2 h, the brittle martensite could be transformed into ductile lamellar (α+β) 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 (α+β) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.

Selective laser melting (SLM) opens the possibility to produce porous structures with designed mechanical characteristics. This study focuses on the coupling effect between unit cell topology (Dode and body‐centered cubic (BCC)) and forming orientation (horizontal and vertical) with regard to the actual geometric characterization and mechanical properties of SLM produced Ti6Al4V porous structures. The results show that for the mechanical response, there is a coupling effect between forming orientation and unit cell topology. This is most pronounced for the Dode topology, where the compressive and yield strength for specimens produced in vertical orientation are increased with 14.6% and 7.5% compared with those build horizontally. However, for the BCC topology, this effect cannot be seen. The fatigue properties for specimens processed vertically are better compared with those processed horizontally, especially for the BCC topology, it shows an increase of 51.6%. This study presents initial findings on how to handle the selection of unit cell topology and forming orientation for porous structures prepared using SLM, which may be beneficial for different applications.