Effects of in-situ formed TiB whiskers on microstructure and mechanical properties of spark plasma sintered Ti-B4C and Ti-TiB2 composites

Abstract

Monolithic titanium, Ti-1 wt% B4C, and Ti-2.5 wt% TiB2 were spark plasma sintered at 1050°C for 5 min under 50 MPa. The effects of B4C and TiB2 additions on densification process, microstructural development, and mechanical properties of titanium were investigated. The results revealed that relative density of undoped as well as B4Cand TiB2-doped Ti samples reached ∼98-99%. X-ray diffraction patterns, thermodynamic assessments, and microstructural investigations verified the in-situ formation of TiB whiskers in both composite samples as well as the appearance of TiC spheres in Ti-B4C composite. However, trace unreacted TiB2 and B4C additives remained in the composites as a result of incomplete chemical reactions due to short-time SPS process. Compared to undoped Ti sample, grain growth was hindered when the sample was doped by B4C or TiB2. Elongation, ultimate tensile strength, and Vickers hardness of B4C-or TiB2-doped samples were higher than those of monolithic titanium, but bending strength of ceramicdoped samples was significantly lower, compared to undoped titanium. These outcomes were discussed in detail and related to the presence/formation of several ceramic phases with different morphologies in Ti matrix.