Towards strength-ductility enhancement of titanium matrix composites through heterogeneous grain structured Ti matrix design

To achieve a good combination of strength and ductility of titanium matrix composites, a kind of TiB/Ti-TiB/TA15 laminated composite was designed, and a heterogeneous grain structure was introduced in the matrix. The TiB/Ti-TiB/TA15 composite was fabricated by reaction hot pressing and hot rolling. Through subsequent short-term (10 min) annealing at 800 °C, a heterogeneous grain structure consisting of equiaxed α in the Ti matrix, elongated α and nano-recrystallized α in the TA15 matrix was formed. The composite herein showed significant improvement in ductility. The tensile elongation reached nearly 20%, which was almost three times that of the as-sintered one. The tensile strength was also enhanced by over 160 MPa compared with the as-sintered composite. The strength-ductility synergy was improved. The result of slip trace analysis exhibited that nearly 30% α grains stimulated the pyramidal slip system, which can coordinate deformation at the layer interface and relieve stress concentration caused by TiB whiskers. The heterogeneous grain structure contributed to the extra back stress strengthening effect, which enhanced the strain hardening ability of the composite. It was estimated that the heterogeneous structured titanium matrix provided extra back stress of approximately 250 MPa.