MODEL OF THE EFFECT OF STRESS STATE ON THE GROWTH OF ELONGATED GRAINS β–Si3N4 DURING HIGH-TEMPERATURE DEFORMATION OF SILICON NITRIDE-BASED CERAMICS

Abstract

The structures 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 after high-temperature deformation according to the direct extrusion scheme were analyzed. An increase in grain size and an increase in the number of anisometric grains in the structure of the deformed material were recorded, with the vast majority of anisometric grains being located coaxially with the longitudinal axis of symmetry of the matrix. The stress state in the deformation zone is considered. The influence of the stress gradient in the deformation zone on mass transfer processes is shown. The mathematical model of the influence of the stress state on the growth of elongated β–Si₃N₄ grains in an inhomogeneous stress field in the transition cone of the matrix is considered.