High temperature microhardness of ZrB₂single crystals

Abstract

Vickers microhardness of (0001), (100) and (110) planes of ZrB2 single crystal prepared by the floating zone method has been investigated at various temperatures and loading times. As the temperature increases from 25°C to 1000°C, hardness drops from ∼20.9 GN m−2 of all planes to ∼7.85 GN m−2 for (0001) plane and ∼4.91 GN m−2 for (100) and (110) planes. The hardness of (100) and (110) planes exhibits almost same tendency and is always lower than that of (0001) plane by about 35%. The thermal softening coefficients of all three planes strongly depends on the temperature range with clear inflections at 400°C and 700°C. The loading time dependence of hardness is used to calculate the activation energy for creep. In addition, a relationship was found that shows the variation of hardness with temperature to be proportional to the variation with the loading time in a specific temperature range.