Flow stress in a material with liquid grain boundaries under different test conditions

A geometrical model for materials with liquid grain boundaries (GB) is proposed, which allows one to determine the solid contact length between grains. During uniaxial compression, the evolution of this length caused by different conditions, such as annealing, hydrostatic pressure, power-law creep, diffusion and grain boundary sliding (GBS), was estimated. It is shown that the contact length increases mainly as a result of the disappearance of the liquid phase during deformation, i.e. the annealing effect is predominant. Furthermore, the relation between flow stress and contact length was established and a good agreement between the magnitudes of the experimental and estimated how stress obtained. In the case of triaxial compression, the result of effective pressure was prevalent, leading to the densification of the material and consequently, to the increase in contact length. It was found, that for a given applied hydrostatic pressure, this length rapidly reaches a corresponding equilibrium value. Copyright (C) 1996 Acta Metallurgica Inc.