Effect of dislocation density-associated strengthening factors on the thermal stability of composite ceramics

Abstract

Interest in composite ceramics based on oxide and nitride compounds is due to the combination of their structural, strength and thermophysical parameters. Moreover, in the case of composites based on xSi₃N₄ – (1-x)ZrO₂, the strength parameters, as well as resistance to thermal expansion, are determined by the characteristics of zirconium dioxide, while the thermophysical parameters are determined by silicon nitride, for which the thermal conductivity values are almost an order of magnitude higher than for zirconium dioxide. The main method for production of composite xSi₃N₄ – (1-x)ZrO₂ ceramics was the mechanochemical solid-phase synthesis method using high-speed grinding and thermal annealing, used to stabilize structural deformations caused by mechanical action. During the research, it was determined that a change in the ratio of ceramic components due to an increase in the contribution of Si₃N₄ in the composition leads to an increase in thermophysical parameters, the change of which is due to the higher thermal conductivity of silicon nitride. In turn, a change in thermophysical parameters, and as a consequence, an alteration in the rate of heat transfer due to phonon mechanisms, causes an elevation in resistance to external influences during thermal shocks. Experiments to determine resistance to thermal influences have shown that the presence of a high density of dislocations in the near-surface layer of ceramics contributes to a rise in resistance to temperature changes, alongside external mechanical influences, which is expressed in less pronounced trends in decreasing hardness indicators during heat resistance tests.