Abrasive wear of ion-plated titanium nitride coatings on plasma-nitrided steel surfaces

The abrasive wear of ion-plated titanium nitride coatings on hardened tool steel and on hardened and plasma-nitrided tool was studied. Wear tests were made with a dry sand-rubber wheel set-up, and the initial surface roughness of the specimen was one of the test parameters.A wear mechanism for hard coatings on softer substrates under abrasive wear conditions was suggested. The wear initiates on the tops of the asperities where the base material is exposed first. Wear proceeds with the formation of craters at these sites and the growth of these crystals by fractures on the ridges formed by the coating material.The wear rate of coated steel increases with increasing initial surface roughness. A considerable increase takes place when the scale of the surface roughness is of the same order of magnitude as the coating thickness. This increase can be shifted to a higher surface roughness if a subsurface hardening process, in this case plasma nitriding, is used.