Slip system determination in cubic carbides by hardness anisotropy

Hardness has been examined as a function of indenter orientation on the (001) surfaces of the cubic transition-metal carbides titanium carbide, vanadium carbide, zirconium carbide and niobium carbide. To emphasize the observed anisotropy a Knoop indenter was used. Experiments have been performed in the temperature range -196 to 610$^{\circ}$C. The anisotropy curves obtained at each temperature have been analysed in terms of operative slip systems. Three different temperature regimes for the anistropy have been identified. These correspond to the {110} $\langle 1\overline{1}0\rangle $ slip systems for the low-temperature regime, the {111} $\langle 1\overline{1}0\rangle $ slip system for the high-temperature regime and a combination of these two systems for the intermediate-temperature regime. To explain this change in slip system it is proposed that an important temperature dependent change in bonding occurs. A qualitative model is suggested for this change in which an increased density of high mobility electrons increasingly screens the directional covalent bonds as the temperature is raised.