MECHANICAL-BEHAVIOR, PERCOLATION AND DAMAGE OF MATERIALS WITH VISCOUSSOLID GRAIN-BOUNDARIES

The mechanical behaviour, percolation and damage mechanism of a alumin ium alloy with viscous solid grain boundaries (GBs) at 465-degrees-C h ave been characterized in experiments performed in tension or compress ion in the strain rate range of 10(-5)-10(-2) s-1. It was found that g rain-boundary sliding (GBS) occurs as strain rates below 10(-4) s-1. I t was shown that the viscous solid interphase migrates during the proc ess of deformation. In the case of tension, it was squeezed out of GBs parallel with the tension axis into GBs perpendicular to the axis and vice versa in the case of compression. This local percolation is disc ussed in terms of the viscosity of the interphase, gradient of local s tresses and percolation time. The viscosity of the solid interphase is estimated. It was also found that cavitation depends on the type of s tress (tension or compression) and the strain rate. Cavity nucleation occurs at multiple points when GBS happens or along GB facets in the a bsence of GBS. Cavity growth takes place along GBs at high normal stre sses and the cavity coalsescence leads to ''saw-tooth'' fracture.