Failure behavior of the plasma-sprayed yttria stabilized zirconia thermal barrier coatings under the three point bending test via acoustic emission technique

摘要

In this paper, the failure behavior of plasma-sprayed yttria stabilized zirconia thermal barrier coatings fabricated by atmospheric plasma spraying(APS-TBCs) under three-point bending (3PB) has been characterized via acoustic emission (AE) technique. Linear Position Sensing (LPS) method has been adopted to monitor dynamic failure process of the APS-TBCs under 3PB. The investigation results indicate that the variation of AE parameters (ring down counts, amplitudes and cumulative energy) correspond well with the change of stress-strain curve of the loading processes. The failure mechanism can be analyzed systematically based on the characteristics of AE parameters. The distribution of frequency of crack propagation has been revealed. The AE signals came from plastic deformation of substrates and cracking of coatings. The different types of cracks and modes of cracks propagation have been distinguished. LPS method has indicated that many segmentation cracks initiate at the inner of the top-coat. And some main cracks tend to propagate toward the interface. The actual failure mechanism of the APS-TBCs under 3PB results from debonding of ceramic coating from the substrates and then horizontal crack propagate along the bond-coat/top-coat interface under action of flexural moment. The additional digital image technique (DIC) has been used and further testified variation of deformation process of the APS-TBCs.