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

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.