Combinative influence of impact and pressing forces on coating failure behaviour

In this work, a ball-on-plate impact fatigue test was proposed as an experimental technique to investigate the failure behaviour of coating–substrate systems under simulated stamping force conditions. Each impact cycle consisted of an impact force and a pressing force which could be adjusted by changing the distance between the impact ball and the plate surface and by regulating air pressure in the air cylinder of the impact tester, respectively. Two PVD (CrN and TiAlN) and one CVD (TiC) coatings on D2 substrates were tested at combinations of different impact/pressing loads (i.e., 200 N/400 N, 400 N/400 N and 600 N/400 N) for 10,000 cycles. It was found that the sizes of the impacted craters were linearly increased with the impact forces and were more dependent on the substrate than the coatings. The possible failures of the tested coatings included not only cohesive and adhesive failure modes but also fatigue cracking. The CrN coating was the best against the failures at all load combinations. While the TiC coating only showed a small degree of chipping after the test at the highest impact/pressing load, all cohesive and adhesive failures and fatigue cracks could be observed on the TiAlN coating even at the lowest impact/pressing load condition.