Evaluation on Thermal Shock Damage of TiN Ceramics Film by Repeated Laser Irradiation. 1st Report. Application of Wavelet Transform and AE Features.

Abstract

Structural ceramics are attracting attention in the development of space ships, aircraft and nuclear fusion reactors because they have excellent heat-resistant characteristics. Therefore, various structural ceramics have been developed as heat-resistant materials. Especially, ceramics coating materials are widely used because the materials have the characteristics of both the base materials and the coating materials. However, the ceramics are damaged easily by the thermal stress result from the thermal shock. Therefore, it is necessary to understand their thermal shock properties and to investigate their thermal shock characteristics. In this report, it is discussed to evaluate the cyclic fatigue damage (i.c. crack initiation, crack growth and fracture) for TiN ceramic film during the repeated thermal shock tests. Concurrently with the repeated shocks that irradiated the coating surface with YAG laser, acoustic emission (AE) monitoring was carried out to detect the onset of the thermal shock damage, and the surface appearance was assessed by optical microscope observations. Wavelet Transform (WT) was applied for distinguishing the signals on damage of TiN from a signal on thermal shock in the first 5 msec of the detected signals. After this processing, the features of the AE signals on the damage of TiN film were analyzed. As the results, it was found that the fatigue damage during the thermal shock tests were evaluated by monitoring the 3-D data which represented the relationship between the slope of amplitude distribution of AE signal, AE events and the number of the repeated thermal shock.