Influence of grain size on the toughness and thermal shock resistance of polycrystalline YBa 2Cu 3O 7−δ

Abstract

The toughness and thermal shock resistance (quenching from RT in air into liquid nitrogen) have been investigated on four grades of polycrystalline ‘YBaCuO’ of almost equal porosity using the Vickers indentation technique. The mean grain sizes varied from 1.5 to 10 μm. The change in toughness with increasing grain size is described by a bell-shaped curve as already published by Rice et al. for the case of other non-cubic ceramics. For the determination of the thermal shock resistance, an original method, based on the relative increase of the length of Vickers indentation radial cracks, as the sample is quenched, has been used. The ranking of the four grades can only be explained if the increase of the thermal residual mismatch stresses, as the samples are put into liquid nitrogen, is taken into account such as to predict a shift of the bell-shaped change of toughness with increasing grain size as the temperature reaches that of liquid nitrogen. The proposed methodology delivers a powerful tool for investigating non-cubic polycrystalline structural or functional ceramics in the R&D stage.