Nano-impact testing—an effective tool for assessing the resistance of advanced wear-resistant coatings to fatigue failure and delamination

Thin films and coatings can fail by fatigue at lower loads than predicted by static tests. The nano-impact technique is a low load impact test capable of revealing marked differences in performance that can be used to optimize the design of coating systems for improved durability. Instead of simply “characterizing” coatings and thin films, their actual tribological performance under “in-service” conditions can now be assessed. The technique can be used to find the optimum coating process parameters for enhanced toughness and damage tolerance and can also differentiate between cohesive (chipping) and adhesive failure (delamination). This paper introduces the concepts behind the nano-impact technique and presents results on compositionally graded a-C:H, a-C and CrAlTiN coatings on tool steel. The performance of the CrAlTiN system was dependent on the impact load. The a-C showed greatly improved impact resistance compared to the a-C:H coating due to its graphite-like structure.