Nondestructive Evaluation of Adhesive Strength of CVD Polycrystalline Diamond Coatings Deposited on Sialon Substrates

In this report we demonstrate the use of optical and acoustic microscopy to nondestructively examine chemically vapour deposited (CVD) diamond coatings with simulated machining damage. During machining, a coated tool insert is subjected to both normal and shearing stresses in the process zone. Machining tests conducted early in this investigation revealed that these stresses resulted in spalling of the CVD diamond coating on the tool flank and rake face resulting in substantially increased wear. Further, it was discovered that the adhesive strength of the coating was extremely sensitive to many of the coating parameters such as roughness of the substrate, coating thickness, percent methane, coating temperature and pressure, etc. A decision was therefore made to utilize a simpler test to evaluate the adhesive strength of a particular coating and thus demonstrate a nondestructive evaluation method in order to optimize the parameters of the coating test matrix prior to conducting machining tests.