Effects of the Extrusion Ratio on the Microstructure and Mechanical Properties of Columnar Network Structured TiBw/TA15 Composites

Novel columnar network structure TiB whisker-reinforced TA15 titanium alloy matrix composites (TiBw/TA15 composites) were successfully prepared by low-energy ball milling and subsequent powder compact extrusion process. Detailed investigation of microstructure evolution in TiBw/TA15 composites indicated that TiBw formed the two-dimensional network structure in the transversal section and the ‘parallel whisker wall’ structure in the longitudinal section, i.e., three-dimensional columnar network structure. The columnar network structure could refine the microstructure and strengthen the grain boundary of prior β grain; thus, the composites possessed excellent comprehensive mechanical properties. Compared with the TA15, the UTS of the TiBw/TA15 composites was increased by 8.6% (λ = 6). The dimension of the columnar network decreased with the increase of extrusion ratio. The mechanical property test results showed that with the increase of extrusion ratio, the tensile strength (from 1240 MPa to 1355 MPa) and hardness (407.5–446.7 HV) of the TiBw/TA15 composites increased, while the ductility (from 9.72% to 4.10%) decreased. However, when extrusion ratio was too large (λ = 17), the debonding of TiB/matrix interface was observed during the tensile test, and this phenomenon was not conducive to the plasticity of TiBw/TA15 composites.