Exploitable results
Test methods for hard coatings have been investigated by carrying out research and round-robin intercomparisons in the following sections: non-destructive thickness measurement by acoustic microscopy; adhesion testing by scratch test; elastic properties determination with three methods (depth sensing indentation, impulse excitation, acoustic microscopy); tribological testing and the fabrication of reference samples (titanium nitride and carbon doped chromium coatings on steel substrates). Hard coatings of high quality could be produced successfully on a research scale. The conditions necessary for fabricating reference samples in an industrial scale can be given. The best success in coating production occurred in systems with a high degree of control over the process environment and individual deposition parameters. Different acoustic microscopes have been calibrated, a standard method for measuring acoustic velocities has been outlined and coating thickness was extracted, benchmarked with other techniques, namely cap grinding and step height profilometry. With respect to scratch testing, acoustic emission and friction force monitoring cannot be used as stand-alone methods for determining critical load. A microscopic inspection of the scratch track remains the most reliable means of associating a failure event with a measured critical normal load. Uncertainties in the Rockwell C stylus tip shape are the major source of error. Its inspection and cleaning before each scratch is essential. Scratch tester manufacturers will exploit the outcome concerning instrumental optimization. The results of this study will be used to produce an improved European prestandard on the scratch test. Substantial progress has been made in tribologial testing which has revealed the complexity and difficulty in measuring the tribological properties of hard coatings. Two test procedures developed will be submitted to the relevant standards committee. A good correspondence was achieved between the Young's modulus determined with the three methods. The precision is excellent for uncoated specimens. Coatings lead to an increase in data scattering, mainly for depth sensing indentation. A standard approach to thin film thickness and Young's modulus determination using acoustic microscopy now exists.
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