Characterisation and applications of Cr–Al–N coatings

There is an increasing number of applications for hard coatings in engineering where both high oxidation resistance and hot hardness are required. One way to address this problem is to use hard ceramic coatings which are a combination of more than one metal so that the coating performance will benefit from the combined mechanical properties of the metals present. In this study, chromium aluminium nitride (Cr–Al–N), titanium nitride (Ti–N), titanium aluminium nitride (Ti–Al–N) and chromium nitride (Cr–N) coatings were deposited on 6.35 mm HSS drills and on hardened and polished AISI M2 steel test discs by means of electron beam plasma-assisted physical vapour deposition. For all depositions, the coating temperature was below 500 °C. Laboratory tests were performed to characterise the mechanical and tribological properties of the coatings. Along with the laboratory tests, accelerated drilling tests and actual industrial applications (punching and gear-shaping) were also used to evaluate the performance of the coatings. The results from the laboratory characterisation, drill tests and industrial applications all showed that Cr–Al–N performs exceptionally well compared to the industry “standards” of Ti–N, Ti–Al–N and titanium carbo-nitride (Ti–C–N). The exceptional performance of Cr–Al–N compared to the other coatings is considered with reference to the coatings’ characteristics.