WEAR AND FRICTION PROPERTIES OF HARD PVD COATINGS

Tribological properties of physically vapour deposited coatings of TiN , TiAIN, TiCN, and CrN deposited on discs made of two different tool s teels have been studied using different pin-on-disc test procedures. S eizing and adhesive wear were studied by a step-load test using a stee l ball, friction properties by using a flat steel pin under low load, and the wear resistance was studied by using an Al2O3 ball, simulating a more abrasive wear situation. In all tests, coating improved the pe rformance of the samples, reducing seizing and wear considerably. TiAI N exhibited the most stable friction and wear mode, which is attribute d to a stable aluminium oxide surface layer. The wear tests against Al 2O3 showed that the Ti-based coatings reduced the severe wear of the u ncoated hardened steel by approximately 4 times, while the softer, but more ductile, CrN reduced the wear by a factor of 2. The results have been related to nanoindentation hardness measurements and compared wi th results from held tests of coated tools. In particular, the test re sults for TiAIN seem to be in very good accordance with practical resu lts from field tests. Thus, pin-on-disc tests can make up a relevant a nd convenient test method for evaluation of fundamental tribological p roperties of physically vapour deposited coatings. However, proper tes t conditions must be carefully chosen in order to evaluate the relevan t applications.