Effect of starting composition on the synthesis of nanocrystalline TiC during milling of titanium and carbon

Titanium and carbon powder mixtures with compositions of Ti100−xCx (x = 50, 40, 30) were milled under a helium atmosphere using a magneto ball mill. For Ti50C50 and Ti60C40 powder mixtures, nanocrystalline TiC was formed via a mechanically induced self-propagating reaction (MSR), indicated by an abrupt increase in the temperature of the milling vial that corresponded to the formation of TiC. The sudden temperature increase occurred after milling for approximately 70 h for Ti50C50 and after approximately 40 h for Ti60C40. No such abrupt temperature increase was detected when milling Ti70C30 and XRD analysis indicated that, for Ti70C30, the reaction to form TiC proceeded gradually as milling progressed. These results demonstrate that, for milling conditions that lead to the formation of TiC via MSR, a minimum carbon content is required to sustain the self-propagating reaction to form TiC, below which TiC is formed via a gradual reaction.