Application of the acoustic emission technique to studying the damage accumulation in a functional ceramic coating

The article is devoted to an experimental study of the mechanisms of damage accumulation in functional ceramic coatings by using the acoustic emission technique. The study and description of the damage evolution in a functional coating makes it possible to determine the destruction moment of this material under operating conditions. Mechanical tensile tests were conducted on steel samples and steel samples coated with a ceramic coating on the universal electromechanical system Instron 5989 at room temperature. A continuous recording of acoustic emission signals was conducted using the AMSY-6 system and AE144A broadband sensors with a frequency range of 100-500 kHz. As an additional method of fixing the moment of destruction of a ceramic coating a system was used to register non-uniform fields of displacements and deformations based on the method of correlation of digital images. During the tests the acoustic emission system, the optical system, and the testing machine were synchronized. The recorded acoustic emission signals were filtered by a threshold value and were filtered using a band-pass digital filter. The frequencies of the spectral maximum are extracted using the fast Fourier transform. Diagrams of dependences of acoustic emission parameters (peak amplitudes, frequencies of the spectral maximum, energy parameter) versus time for all the samples were plotted. A comparison of the obtained graphs for the samples with and without coating is made. The ranges of amplitudes and frequencies that characterize the damage accumulation and destruction of the ceramic coating were determined. Thus, during these works, a technique was implemented to evaluate the behavior of the functional coating applied to the material. The effectiveness of applying the method of recording and analyzing acoustic emission signals to solve this problem was shown.