How do interlocked grains improve the toughness of ceramics?

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advanced structural ceramics Figure 1: Resistance to cracking in transformation-toughened zirconia. In a ceramic composed of tetragonal zirconia dispersed in a zirconia matrix, the stress field advancing ahead of a propagating crack transforms the small tetragonal particles to larger monoclinic particles. The larger particles exert a crack-closing force in the process zone behind the crack tip, effectively resisting propagation of the crack.

In advanced structural ceramics, the use of interlocked grains is a key strategy for improving fracture toughness by engineering microstructures that resist crack propagation and absorb energy.

These microstructures enhance toughness through two primary mechanisms:

Crack Deflection: As a crack advances, the interlocked grain structure forces it to deviate from a straight path. This deflection significantly increases the total length of the crack, which requires more energy to propagate.
Crack Bridging: Particles located behind the advancing crack tip act to bridge the gap, exerting a force that tends to hold the crack closed.

By combining these effects, the material achieves a greater fracture surface area and increased energy absorption, effectively mitigating the inherent brittleness typically associated with conventional ceramics.1