MODEL OF THE INFLUENCE OF THE STRESS STATE ON THE STRAIN RATE CURVE DURING HIGH-TEMPERATURE DEFORMATION OF SILICON NITRIDE-BASED CERAMICS

The deformation rate curves of ceramic materials of known compositions based on silicon nitride with high (Si3N4-5wt.%Y2O3-5wt.%Al2O3), medium (Si3N4-5wt.%Y2O3-2wt.%Al2O3) and low (Si3N4-2wt.%Y2O3-1wt.%Al2O3) content of sintering activators during high-temperature deformation according to the direct extrusion scheme were analyzed. The nature of the influence of the rotation of elongated grains on the processes of mass transfer and the rate of deformation is described. The stress state in the deformation zone is considered. The influence of moment stresses on the rotation of elongated grains is shown. The influence of the stress state and the rotation of elongated grains on the curve of the rate of deformation is considered. A mathematical model of non-uniform rotation of elongated β–Si3N4 grains in an inhomogeneous stress field in the transition cone of the matrix is considered. The presence of a constant velocity section on a typical strain rate curve during high-temperature deformation according to the direct extrusion scheme is explained.