Grain size effect on the mechanical properties of transparent spinel ceramics

Transparent ceramics receive increasing interest in technical window applications. The mechanical reliability of transparent MgAl2O4 with different grain sizes was characterized. The investigations were based on a combination of micro- and macro-mechanical methods to assess Youngʹs modulus, hardness, fracture toughness, crack kinetics and strength, the latter being analyzed using two- and three-parameter Weibull statistics. The effect of subcritical crack growth under ambient conditions was assessed using a strength–probability–time plot. It has been verified that increasing grain size decreases strength and increases slow crack growth sensitivity, but on the other hand appears also to increase the Weibull modulus and the impact and wear relevant hardness indentation size effect. Complementary fractography by optical, confocal and scanning electron microscopy permitted to gain insight into the failure origins.