Residual stresses in ceramics, as for example arising from thermal expansion anisotropy, exert an important influence on the mechanical behaviour of polycrystalline materials. They can lead to crack initiation in the sense of microcracking but can also influence crack propagation by determining the evolution of the crack path and contribute to the effectiveness of crack bridging or by microcrack shielding. Various methods have been utilised to measure residual stresses. In this paper, a method based on the piezospectroscopic (PS) effect is discussed by application to Ce-ZrO2/Al2O3 nanocomposites having 0-90 vol. % of alumina. The compressive stress in Al2O3 was determined from the frequency shift of the R2 luminescence band using the well-known piezospectroscopic coefficient. The tensile stress in t-ZrO2 has been found in two ways. In the first one, it has been derived from the equilibrium of forces in a free-standing piece of two-phase material. The frequency shifts of each Raman band of t-ZrO2 have been plotted against the calculated stress and the slopes provided the PS coefficients. In the second method, external compressive stress introduced into composite samples by Vickers indentation was used for a new PS calibration due to a linear dependence observed between the t-ZrO2 Raman line shift for all Raman lines of zirconia and those of the Al2O3 R2-line luminescence. This way, having new PS coefficients a new value of stress in t-ZrO2 was calculated. Good correspondence of PS and stress in t-ZrO2 obtained from these two methods was found. As a result new indirect methods for determining PS coefficients of t-ZrO2 are suggested.

Keywords: ceramic nanocomposites, residual stresses, Raman spectroscopy, piezospectroscopic coefficients