Grain Growth Kinetics and Densification Mechanism of Ti/Cab6 Composites by Powder Metallurgy Pressureless Sintering

Sintering titanium (Ti) materials to high densities while maintaining fine grain sizes is a great challenge, which severely restrains their engineering application. Herein, we fabricated a high-density and fine-grain Ti material by a small addition of CaB6 via powder metallurgy (PM) pressureless sintering route. The effect of CaB6 addition on the grain growth kinetics and sintering densification mechanism were systematically investigated. The CaB6 oxygen-scavenger breaks the surface oxide layer and promotes the mutual diffusion of Ti atoms during sintering, resulting in the in-situ formation of nano-sized CaTiO3 particles and increase the sintered density. Moreover, the micro-sized TiB whiskers with the length from 10 gm to 30 gm and width from 1 gm to 4 gm are also formed in the Ti matrix. The grain microstructure of Ti/CaB6 composite displays a random orientation feature with the fine and uniform equiaxed crystallites. The presence of in situ TiB and CaTiO3 second-phase particles makes a greater grain growth activation energy Q for Ti/CaB6 composites, from the 373 kJ/mol of pure Ti to the 522 kJ/mol of Ti-1.0CaB6 composite, creating a smaller grain size. The grain refining effect by CaB6 addition is more effective at high temperature. As a result, the grain size of Ti-1.0CaB6 composite sintered at 1300 celcius/2 h is only 74 gm, much smaller than the 163 gm of pure Ti. This study offers a feasible way to produce the high-density and fine-grain Ti materials. (c) 2023 Elsevier B.V. All rights reserved.