Microstructural evolution and mechanical properties of titanium matrix composites with second-phase dendritic TiC improved through B4C additions

Abstract

Titanium matrix composites with high TiC content have multiple excellent properties. However, their dendritic TiC morphology poses challenges to their room-temperature plasticity. In this study, (TiC + TiB)-reinforced titanium matrix composites were developed by incorporating B4C into dendritic TiC composites. The impact of B4C additions on the microstructure evolution and mechanical properties of dendritic TiC in the composites was systematically investigated. The results revealed that the in-situ synthesis of TiC and TiB significantly refines the matrix grains of the composites with the addition of B4C. Notably, TiB serves as a nucleation substrate for dendritic TiC, forming an intergrowth microstructure of TiC and TiB during solidification–precipitation. This effectively reduces the number of dendritic TiC. The interfacial orientation relationships between TiC and TiB were studied through high-resolution transmission electron microscopy, revealing [110]TiC//[311]TiB and (111)TiC//(210)TiB, with a two-dimensional lattice mismatch of 6.43% between (111)TiC and (210)TiB. At room temperature, the ultimate tensile strength and fracture strain of the composite with 1 wt% B4C were 1059.52 MPa and 5.58%, respectively. Compared with the original composite, the tensile strength increased by 39.4%, and the corresponding elongation was remarkably increased. This enhancement is attributed to the synergistic strengthening effect and fine grain strengthening effect of the intergrowth structure of TiC and TiB in the composite. The microstructure refinement mechanism and strengthening mechanism are discussed in detail, providing new ideas and methods for the design and preparation of composites.