Fracture resistance behavior of alumina–zirconia composites

R-curve behavior has been examined in alumina–zirconia composites Al2O3–10 wt.% ZrO2 containing two types of ZrO2 particles: 3 mol% yttria doped ZrO2 and pure ZrO2. For comparison alumina ceramics was tested too. The R-curve behavior has been evaluated using two techniques for the different crack-length regimes: a small-crack R-curve by means of indentation-induced controlled Vickers crack growth in bending (ICVC) and pronounced long-crack using load-relaxation technique. The latter technique bases on the three-point bending (3PB) of the single edge notched beam (SENB). A combination of in situ microscopic crack growth observation and mechanical testing enabled measurement of crack growth resistance curves. These observations reveal the existence of increasing R-curve at the long-through thickness cracks method for tested composites. In view of contributions of residual indentation stress intensity and applied bending stress intensity, the residual stress factor χ and the fracture toughness behavior KR have been determined. SEM micrographs of typical crack profiles in tested ceramic composites were observed. Indentation strength in bending method (ISB) was used for determination fracture toughness as well.