The use of impedance spectroscopy in damage detection in tetragonal zirconia polycrystals (TZP)

Tetragonal zirconia polycrystals (TZP) were chosen as a model material for evaluating the potential of impedance spectroscopy (IS) as a non-destructive method for the detection of microstructural damage. Cracks were introduced and propagated in these materials either by thermally induced phase transformation or by mechanical loading of pre-cracked specimens. In TZP, microcracking, its propagation and concomitant phase transformations were detected as changes in the capacitive and resistive parts of the electrical impedance at temperatures between 20 and 550°C. This can be correlated with in situ observation by optical microscopy of crack opening and phase transformation zones in four point bending test specimens. Qualitatively all aspects of microcracking described above have been shown to be measurable by IS. Quantitative sensitivity limits in terms of error bands and critical crack lengths are derived from the experimental results and numerical field simulations.