ИСТИНА

Grain boundary (GB) infiltration of a liquid L into a polycrystalline material composed of phases A, B... is governed by interrelations between free interface energies at solid-solid AA, BB, AB... and solid-liquid AL, BL… boundaries. As in the case of monophase polycrystals, knowing the degree of connectivity of the liquid inside the material is crucial for understanding its permeability as well as mechanical, rheological and other properties. The percolation theory proved to be an efficient tool for analyzing the behaviour of one component systems, provided that the coordination number of boundaries and the average wetting probability for each kind of boundary are known. However, GB wetting in multicomponent solids cannot be adequately described on the basis of averaged wettabilities and coordination numbers, but requires taking into account topologies of respective subsystems, due to correlation effects. An attempt to solve such a "polychromatic percolation" problem has been made in this work, on the basis of numerical and physical experiments. A marked nonlinearity in deviations of percolation thresholds from noncorrelated values has been found. Mechanical response of internally wetted materials typically involves a tendency to liquid-induced embrittlement (Rehbinder effect) and dissolution-reprecipitation (pressure solution) creep mechanism, but here again the properties of polycomponent systems may vary in a nonlinear way with their composition. Numerical models have been found to fit quite well experimental results obtained on some metallic composites and on NaCl – silica – water. The latter system was chosen as an example of contrasting properties of grains and interfaces involved in failure and creep. Increase in liquid induced fracture probability and decrease in pressure solution creep rate with increasing silica content are in agreement with theoretical predictions.