Grain growth kinetics and densification mechanism of Ti/CaB6 composites by powder metallurgy pressureless sintering
Yu Pan, Jinshan Zhang, Xinxin Wu, Yucheng Yang, Fan Kuang, Ce Zhang, Dong Lu, Xin Lu
Abstract
： 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 CaB 6 via powder metallurgy (PM) pressureless sintering route. The effect of CaB 6 addition on the grain growth kinetics and sintering densification mechanism were systematically investigated. The CaB 6 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 CaTiO 3 particles and increase the sintered density. Moreover, the micro-sized TiB whiskers with the length from 10 µm to 30 µm and width from 1 µm to 4 µm are also formed in the Ti matrix. The grain microstructure of Ti/CaB 6 composite displays a random orientation feature with the fine and uniform equiaxed crystallites . The presence of in situ TiB and CaTiO 3 second-phase particles makes a greater grain growth activation energy Q for Ti/CaB 6 composites, from the 373 kJ/mol of pure Ti to the 522 kJ/mol of Ti-1.0CaB 6 composite, creating a smaller grain size. The grain refining effect by CaB 6 addition is more effective at high temperature. As a result, the grain size of Ti-1.0CaB 6 composite sintered at 1300 ℃/2 h is only 74 µm, much smaller than the 163 µm of pure Ti. This study offers a feasible way to produce the high-density and fine-grain Ti materials.