Synergistic effects of interstitial elements and TiB to overcome strength-ductility trade-off in titanium matrix composites

High-strength titanium matrix composites commonly show an inherent strength-ductility trade-off dilemma, which restricts their wide-range applications. Herein, we achieved synergistic strengthening of Ti-6Al-4V matrix composites by interstitial C, N, and TiB via powder metallurgy and obtained ultra-high tensile strength (1510±5 MPa) and good elongation (8.7%±0.3%). In situ-formed TiB promotes equiaxialization of matrix grains, hinders grain growth, and provides numerous nucleation sites for dynamically recrystallized grains. By evaluating the distribution of interstitial C and N in the Ti-6Al-4V matrix and their effect on the stability of the TiB/Ti interface, first-principles calculation results demonstrated that C and N tend to occupy the octahedral interstitial positions in α-Ti, thus inducing lattice distortion and significantly enhancing the (001)_TiB/(0001)_α-Ti interfacial strength. In addition, quasi-in-situ electron backscatter diffraction under tensile tests revealed the influences of interstitial C and N on the deformation mechanism of the composites. Interstitial C and N promote the activation of <c+a> dislocations in composites and increase the proportion of pyramidal <c+a> slip systems. The simultaneous activation of multiple slip systems is the primary factor in improving the composite’s ductility. Experimental and theoretical calculation results in this work provide a new strategy for designing and fabricating ultra-high-strength titanium matrix composites without sacrificing their ductility.