Experimental and first-principles study on TiB/TiC interface in hybrid (TiB+TiC)/Ti6Al4V composite

To understand the synergistic strengthening mechanism of hybrid TiB + TiC reinforcements in Ti matrix composites, the corresponding TiB/TiC interfacial characters and load-bearing capacity were revealed in this work through a coupled method of high-resolution transmission electron microscopy (HRTEM), ab-initio calculations, and Vickers indentation test. Results show the interfacial orientation relationship (OR) between TiB and TiC phases is [010]TiB//[11 2‾]TiC, (2 2‾ 0)TiC//(102)TiB, which exhibits an interface formation energy of 3.32 J/m2 estimated via first-principles calculations. The TiB/TiC interface shows a high adhesion strength of 5.78 J/m2 owing to the formation of strong B–C covalent bond, which is also slightly higher than the strength (5.52 J/m2) obtained within TiB. Moreover, the strong TiB/TiC interface contributes to the superior load-bearing capacity of the intergrowth ceramic structure with relatively higher hardness (∼2100 HV0.2) than that of individual TiB and TiC phases (around 2020–2030 HV0.2). Consequently, the hybrid TiB + TiC reinforcements exhibit a synergistic strengthening effect in Ti matrix composites due to the intergrowth microstructure characteristic with superior load-bearing capacity.