High-temperature deformation mechanism in substoichiometric titanium carbide - correlation with carbon vacancy ordering

In order to clarify the reason for the marked nonstoichiometry-effect on the mechanical properties of TiCx, the order structure has been investigated in a wide range of C/Ti atom ratios, x, from 0.59 to 0.95 by the transmission electron microscopy. It is found that the as-grown crystals are weakly or strongly short-range ordered (SRO) depending on x and have a long-range ordered structure (LRO) at x=0.59 at room temperature. As temperature rises, the degree of order tends to decrease, and around 1300 K, where a marked x-effect on mechanical properties was observed, the diffuse electron scattering due to SRO becomes very weak for x> or approx.0.85, but still strong for x=0.75, and there exist micro domains of LRO for x=0.59. From the order structure and the additional experiment of aging effect on the initial deformation behaviour, it is concluded that the x-dependence of deformation behaviour can be understood as an ordering effect of carbon vacancies. (orig.)