Plastic deformation of single crystals of CrB2, TiB2 and ZrB2 with the hexagonal AlB2 structure

Abstract

The plastic deformation behavior of single crystals of three transition-metal diborides with the AlB2 structure, CrB2, TiB2 and ZrB2 has been investigated as a function of crystal orientation in the temperature range from room temperature to 1500 °C. Plastic flow is observed above 800 °C by the operation of slip on {11¯00}<112¯3> in CrB2, while in ZrB2, the onset temperature for slip on {11¯00}<112¯3> is 700 °C and that for slip on (0001)<112¯0> is 800 °C. In contrast, any appreciable plastic flow is not observed in TiB2 at 1500 °C and below. The critical resolved shear stress (CRSS) for slip on {11¯00}<112¯3> in CrB2 monotonously decreases with increasing temperature up to 1500 °C. On the other hand, the CRSS for slip on {11¯00}<112¯3> in ZrB2 decreases with increasing temperature up to 1000 °C and then increases anomalously with increasing temperature. Similarly, the CRSS for slip on (0001)<112¯0> in ZrB2 decreases with increasing temperature up to 1200 °C and then increases anomalously with increasing temperature, followed again by the decrease above 1400 °C. Generalized stacking fault (GSF) energy calculations well explain slip direction on the relevant slip plane, dislocation dissociation scheme and relative ease of slip among the three transition-metal diborides. The existence of planar growth faults on prism planes in CrB2 and TiB2 significantly affects the plastic deformation behavior so that the high onset temperature for plastic flow for these two diborides cannot be predicted solely by GSF energy calculations.