Characterization of thin metallurgical coating systems by repetitive inclined impact test in dry condition

This study evaluates the effectiveness of a non-lubricated repetitive inclined impact test to differentiate the fatigue behavior of thin tribological coatings. Three coatings were studied. One is W-diamond-like carbon (DLC) and the other two are Cr-DLC made from different deposition recipes. These coatings display unique impact failure curves. The impact failure curve, analogous to the ‘S–N’ curve (a semi-log plot of load vs. number of cycles to failure), exhibits a high-load and a low-load linear segment with steep and gentle slope, respectively. The typical wear events that lead to failure of the coating, characterized by exposure of the substrate, are (1) formation of partial ring cracks at the trailing edge of the impact crater, (2) thinning of the top coating due to sliding wear, (3) formation of through-thickness shear cracks in the top layer, (4) delamination of the top layer from the interlayer, (5) formation of through-thickness cracks in the interlayer, (6) delamination of the interlayer from the substrate. The wear evolutions of the coatings, which correlate with the failure curves, differ in terms of the duration, and absence or presence of these wear events.