Influence of carbide substrates on tribological properties of chromium and chromium nitride coatings: application to wood machining

This work aims to improve the wear resistance of carbide materials by application of PVD hard coatings; chromium and chromium nitride coatings were applied to six types of carbide and their tribological properties were studied. Scratch adhesion strength, micro-abrasion wear resistance and ultra-micro hardness tests of the coatings were held to find a relationship between the tribological properties and the carbide substrate specifications. Furthermore, using an industrial type of milling machine, wear tests have been conduced in machining of Oriented Strand Board (OSB), a wood product material particularly abrasive and heterogeneous. A cohesive failure has been observed during the scratch adhesion tests held on the chromium nitride coatings. Similar failure mode has been observed on the cutter clearance face after machining. Then abrasion wear was studied on a micro-abrasion tester. It appears that both abrasion resistance and coating hardness depend on the carbide grain size. Furthermore, by decreasing the nitrogen content in the coating condition, the wear resistance in wood machining tests is improved as well as the scratch adhesion strength. Similar trends have been found when the carbide grain size decreases.