Deformation and Fracture Processes in Calcium Fluoride Single Crystals

The plastic properties of calcium fluoride single crystals tested in compression were investigated in the temperature range 25° to 1000°C. Above 400° C., the crystals showed appreciable ductility. The critical resolved shear stress, t, decreased with absolute temperature, T, according to the equation t = t0e+K/T. The rate of work‐hardening decreased rapidly as the temperature increased but retained a relatively high value even as the melting point was approached. Air‐annealed crystals were harder than as‐cleaved crystals. Crystals with a (111) plane normal to the applied stress hardened less rapidly than crystals with a (110) plane normal to the applied stress. The dislocation density increased linearly with strain. (100), (110), and (111) fractures were observed.