Acoustic emission responses of plasma sprayed ceramics during four point bend tests

Free standing ceramics including alumina-13 wt.% titania (AT13), alumina-3 wt.% titania (AT3), alumina-40 wt.% zirconia (AZ40), and calcia-stabilized zirconia (CSZ), were produced by water-stabilized plasma spraying. Four point bend tests were performed in the in-plane direction (i.e., spray direction) to obtain the modulus of rupture of the materials. In situ acoustic emission (AE) monitoring was used to detect cracking during the tests. The AE characteristics such as ring down counts, event duration, peak amplitude, and energy were recorded and analyzed to evaluate different cracking mechanisms. The AE responses versus time for individual tests were evaluated and two basic types of cracking mechanisms; i.e., catastrophic failure and microcracking before failure, can be observed. AT3 and AZ40 tend to exhibit microcracking before failure and CSZ shows catastrophic failure. However, both mechanisms can be observed for AT13. For the total AE responses, the amplitude distributions are skewed to the right and the energy distributions show multi-modal distributions. Micro-, transitional, and macro-cracks can be better distinguished by the energy distribution. The relative proportion of these cracks was also determined.