Ae Monitoring from Cvd-diamond Film Subjected to Micro-indentation and Pulse Laser Spallation

We monitored AEs during micro-indentation and pulse laser spallation test of CVD diamond film deposited on sintered SiC, and classified the fracture type by Lamb wave AE analysis. In the indentation test with a Rockwell sphere indenter, we observed Hertz ring cracks and simultaneously detected AEs from Mode-I fracture. Crack types were classified from polarity distribution of the first arrival So-mode Lamb waves. Fracture strength of the diamond film was estimated as 7.1 GPa by FEM analysis, using the critical indentation force, indentation depth and Hertz crack diameter, In the laser spallation test, strong pulse expansion-wave was produced by the pulse laser ablation of the confined silicone grease on the opposite surface of the diamond film and utilized to cause Mode-I delamination of diamond film. Critical tensile stress to cause the spallation was calculated as 222 MPa. We attempted to detect the spallation initiation by monitoring the in-plane motion of So-mode Lamb wave AE using broad-band pinducer mounted on the edge planes. Waveform change due to the Mode-I spallation was detected.