Determination of the Effect of Size Factor and Phase Composition in Lithium-Containing Ceramics on Resistance to External Mechanical and Thermal Influences

The paper presents data on the effect of size factors that cause a change in dislocation density, as well as the phase composition of two-phase lithium-containing ceramics based on lithium metacirconate on the strength characteristics of ceramics, as well as resistance to high-temperature tests. The size effect, dislocation density and the presence of interphase boundaries, the change of which is due to the effect of variation in the phase composition of ceramics, were considered as hardening factors during assessment of the strength properties, alongside resistance to temperature influences. During the studies, it was found that alteration of the grinding speed above 400 rpm results in more than twofold decrease in grain size, which in turn elevates the dislocation density, the change in which is a hardening factor for growth of hardness and crack resistance. During determination of the strength characteristics, it was found that a change in the phase composition due to the dominance of the Li 6 Zr 2 O 7 phase in the composition of ceramics leads to an elevation in hardness and resistance to cracking due to an increase in interphase boundaries, which serve as additional barriers to the propagation of microcracks under external influences. During experiments conducted to determine resistance to long-term thermal annealing and heat resistance tests, it was found that grain size reduction to less than 250 nm for all three types of ceramics under study leads to a rise in degradation resistance of strength properties due to dislocation hardening, and the presence of interphase boundaries, which is most pronounced for samples with a predominance of the Li 6 Zr 2 O 7 phase in the ceramic composition.