Mechanism of synthesizing nanocrystalline TiC in different milling atmospheres

The nanocrystalline TiC powders were synthesized by mechanical alloying (MA) from the mixture of pure titanium and graphite in vacuum, argon and hydrogen milling atmospheres, respectively. The phase transformation and powder morphology characteristics were studied by using XRD and TEM. The results showed that synthesizing mechanism and reaction velocity changed when Ti and C mixture were milled in different atmospheres. It was found that nanocrystalline TiC powders were fabricated by mechanical alloying for 1 h at a ball-to-powder weight ratio of 40:1 and rotational speed of 450 rpm in planetary ball-mill in argon atmosphere and vacuum. The formation mechanism was mechanically induced self-propagating reactive synthesis (MSR). However, the formation of intermediate phase TiH2 changed the mole ratio of Ti and C, brittle phase proportion and energy aggregation in the powder, consequently resulted in reaction controlled by gradual diffusion when the milling atmosphere was hydrogen gas. So the synthesis time extended to 6 h under hydrogen atmosphere on the same milling process.