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 μm, 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 all 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 10³ 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.