Adhesion of thin coatings—the VAMAS (TWA 22-2) interlaboratory exercise

An interlaboratory exercise on 5-μm-thick chromium nitride (CrN) coated AISI 304 austenitic stainless steel coupons was undertaken to evaluate and compare test methods for adhesion of thin coatings. Test coupons were deposited with and without thin (25 and 50 nm) gold–palladium interlayers. These interlayers were designed to vary the effective adhesion of the CrN in a controlled way without significantly altering the CrN coating fracture properties. The interlaboratory exercise was conducted by an international group of laboratories examining Rockwell indentation, scratch testing, uniaxial tensile and four-point bend. None of the tests were able to discriminate between coupons with or without the interlayer. The new EU Community Bureau of Reference scratch test reference material (BCR-692), distributed to participants to assist in the calibration of scratch test instruments used in this study, was shown to be able to diagnose instrument problems.