Anisotropic microstructure and mechanical properties of as-forged (Ti, Nb)B/Ti₂AlNb composites

In situ boride reinforced Ti2AlNb-based composites are a new type of lightweight material that has excellent high-temperature performance exceeding that of Ti-based composites. Forging is one of the effective methods to improve the microstructure and mechanical properties of Ti2AlNb-based composites. After forging, the mechanical properties of the composites exhibit evident anisotropy, but the anisotropic mechanism remains unclear. In this study, the anisotropic mechanical properties of the as-forged (Ti, Nb)B/Ti2AlNb composite and its formation mechanism were investigated. It was found that the as-forged composite possessed higher yield strength along the radial direction (RD) and better plasticity along the compression direction (CD). The microstructural analysis results demonstrated that the O phase formed [100]_O//CD fiber texture, and the (Ti, Nb)B reinforcement exhibited [010]_{(Ti, Nb)B}//RD fiber texture in the as-forged composite. The analysis based on In-Grain Misorientation Axes (IGMA) suggested that the {1 1‾ 0}<110> was the main activated slip system of the O phase during the deformation. The difference in both the Schmid factor of {11‾ 0}<110> slip system caused by the [100]_O//CD texture and the strengthening efficiency induced by [010]_{(Ti, Nb)B}//RD texture led to the anisotropy of yield strength. The anisotropy of prior particle boundaries (PPBs) contributed to the different crack propagation modes of the as-forged composite under different loading directions, resulting in plastic anisotropy.