Evaluation of PVD nitride coatings, using impact, scratch and Rockwell-C adhesion tests

In this work the scratch test, the impact test and the Rockwell-C adhesion test were compared by investigating the adhesion properties of three types of sputtered physical vapour deposition coatings: TiN, CrN and Cr2N. Each coating type was deposited on polished SAE 52100 steel, with different thicknesses in the nominal range of 2-20 mu m, to evaluate the thickness influence on the test results. All the tests showed a ductile behaviour for the TiN coating with small delaminations and a brittle behaviour for the CrN and Cr2N coatings with relatively large delaminations. An increase of the dimensions of the delaminations with increased coating thickness was detected for all layer types. With the scratch test a significant increase in upper critical load with layer thickness was observed for ail of the coatings. However, there was considerable variability especially for the Cr2N coatings. The impact tests showed no coating failure for the TiN layer, and a decreasing impact crater volume with increasing layer thickness, whereas the CrN and Cr2N layers failed after 10(3) impacts and showed an increasing impact crater volume with increasing layer thickness. The studies demonstrate the usefulness of using these test methods for differentiating between the behaviour of different coatings under various contact conditions.