Characterization of the Anisotropy in the Microstructure and Mechanical Properties of Laser Powder Bed Fusion Ti6Al4V Alloys

Herein, near-full-density Ti6Al4V components are prepared by laser powder bed fusion (LPBF). The microstructural evolution and mechanical properties in different deposition planes are investigated to explore their anisotropic behavior. The internal defects of the LPBF-fabricated Ti6Al4V components mainly included round-like pores, primarily caused by metal vapor and entrapped gas during solidification. The microstructure of the horizontal plane consists of a large amount of alpha '/alpha martensite within a near-equiaxed beta matrix. In addition to similar acicular martensites, the columnar beta grains within the vertical plane are induced by the steep thermal gradient along the deposition direction. Compared to that in the vertical plane, the microhardness in the horizontal plane is improved mainly due to the grain boundary strengthening mechanism. The transverse tensile strength and elongation are superior to the longitudinal ones, and the failure mode is transformed from ductile to brittle. Such anisotropic behavior in the tensile properties is primarily attributed to the varied microstructural evolution in the different deposition planes. This work demonstrates that LPBF-fabricated Ti6Al4V alloys contain acicular alpha '/alpha martensites, which consequently enhance the strength/hardness properties, despite the anisotropic performances caused by the columnar beta grains.