Deformation in Ceramics

Abstract

Deformation can be elastic or plastic. Understanding elastic deformation is very important in ceramics to eliminate instantaneous brittle fracture at some applied stress levels. The fracture stress is usually the same or very close to the elastic limit. Stresses have to be exercised with understanding of the limits of the specific ceramics and the level that it can endure before fracture. No dimensional changes in test pieces occur in elastic deformation. Plastic deformation of ductile ceramics at room temperature, and of low temperature brittle ceramics at elevated temperatures, produce slip marks due to the advance of dislocations. All the characteristic phenomena of plastic deformation are observed either at ambient temperature (of room temperature ductile materials) or at the elevated temperature (of brittle ceramics at low temperature) such as yielding, existence of resolved and critical shear stress and slip. Among the yield phenomena, serrated stress–strain curves and Luders bands can be noted as existing features. Twinning deformation, -mechanical or annealing twins-, are also observed to operate under proper conditions. Among the many factors influencing the mechanical properties, special consideration should be given to the effect of grain size. Preferred orientation in polycrystalline ceramics are seldom observed in its natural state but it may be induced during processing or fabrication. It might be of interest sometimes to get anisotropy for specific purposes of interest to enhance some directional property.