Creep and anelastic recovery of whisker- and platelet-reinforced ceramics

The addition of whiskers to ceramic matrices is known to increase the creep resistance by two or three orders of magnitude and platelet additions have a similar (though smaller) effect. Moreover, creep in such materials is known to be followed by large anelastic relaxations. In this paper a series of models are developed to help explain these results. They are based on three postulated mechanisms. These are the unfettered rotation of particles (i.e. whiskers or platelets) at low volume fraction, the extrusion of matrix material from regions of near particle contact, and the elastic bending of particles within a well-percolated network. A mechanism map is developed which predicts the conditions under which each mechanism dominates as a function of volume fraction, aspect ratio and packing efficiency of the particles. The creep resistance is found to be sensitive to details of the packing arrangement, suggesting that processing will have a considerable effect on properties.