Slow Growth of Microcracks: Evidence for One Type of ZrO2 Toughening

Abstract

Alumina containing 15 vol% monoclinic ZrO2 dispersed at the grain boundaries exhibited very high room‐temperature fracture toughness (∼11 MPa·m1/2) on cooling from 1275°C when microcrack precursors nucleated at T<Ms. With increasing time (up to ∼12 h) at room temperature, KIc and Young's modulus decreased when dilational and thermal‐expansion strains subcritically propagated inter granular microcracks. Thus, transformation toughening of ceramics with inter crystalline ZrO2 dispersions is to a great extent caused by microcrack nucleation and extension.