Measurement and Control of Interface Strength and Mechanical Properties of Coatings by Laser Spallation Experiment

Abstract

The strength of planar interfaces between a substrate and a coating (1-2 µm ) can be measured quite effectively by a laser spallation technique. In this technique a laser pulse of high energy and a predetermined length is converted into a pressure pulse of a critical amplitude and width, which is then sent through the substrate toward the free surface of the coating. The compressive pressure pulse is reflected into a tension pulse from the free surface of the coating and loads the coating/ substrate interface in tension. The laser flux is tuned to a threshold level at which the interface comes apart. In the previous version of the technique, the critical stress amplitude that accomplishes the removal of the coating was determined by computer simulation. The simulation itself was verified by means of a piezoelectric crystal probe capable of mapping out the profile of the stress pulse generated by the laser pulse. In the current version, this is achieved directly by a laser Doppler displacement interferometer. A brief description of the current laser spallation experiment is given.