Crystallographic studies on some deformed hard materials.

X-ray line broadening techniques were used to investigate the deformation characteristics of various hard materials. A detailed comparison of the Warren-Averbach, variance and integral breadth methods of analysing a broadened X-ray diffraction peak showed that they give comparable results. The effect of temperature on the deformation characteristics of materials with different types of chemical bonding was investigated. Ionic and covalent bonds are extreme examples of the same type of bond, and in materials with these bond types it was found that the amount of covalency in the bond governed the microplastic behaviour. The behaviour of the transition metal carbides was less predictable on account of their complicated mixture of metallic, ionic and covalent bonding. Studies on tungsten carbide powders showed that considerable deformation was induced by ball milling. The deformation could be relieved by annealing. Deformation stacking faults, involving slip on the basal plane, were observed. Studies on the worn surfaces of sintered blocks and single crystals revealed plastic deformation that extended to a depth of several microns below the surface. Hafnium carbide showed a marked anisotropic behaviour when deformed. The deformation could be annealed out by recovery and recrystallisation processes as in metals. The hafnium carbide lattice was found to be remarkably stable at high temperatures compared with other transition metal carbides. Studies on the polymorphic refractory oxide, zirconia, showed that tetragonal zirconia was formed from monoclinic zirconia when the particle size was made sufficiently small by ball milling. The transformation normally occurs above 1000°C. Calculations showed that tetragonal zirconia formed by milling, or by thermal decomposition, is stable at room temperatures mainly because of its small particle size and resultant high free surface energy