Nondestructive characterization of morphological development in sintered powder compacts

Abstract

Values of parameter x are evaluated by means of the morphological kinetic equation, using sintering data from a variety of differently prepared alumina compacts obtained by precision digital dilatometry. For specimens with high green densities, which lead to uniform microstructures with few small pores remaining, the values of parameter x are initially larger than 1, but decrease to less than 1 near D = 0·84; i.e. the pores grow at the beginning but become sinterable later. For specimens with low green densities, which lead to uniform microstructures with few large pores remaining, x values never fall below 1;i.e. pore growth accompanies the sintering process throughout. These predictions agree qualitatively with observed final microstructures. It is shown that the morphological parameters of microstructures (relative average pore radius, relative total length (or number) of pores per unit volume, relative average grain size and relative width of pore size distribution) can be evaluated in situ with data from a single dilatometric run. Moreover, the onset points of the late stages of sintering calculated from the dilatometric data are in reasonable agreement with theoretical predictions and with other experimental observations. The ‘breakup’ mechanism of cylindrical pores is shown to be an important and rate-sensitive step in the evolution of sintered microstructures.