Wear of TiAlCN Coating on HCR Gear

Wear of TiAlCN coatings deposited on HCR (High Contact Ratio) gears was studied by the Niemann test during which the tested gears were loaded up to the 12th load stage. The resistance against scuffing was evaluated based on the criteria of allowable roughness (max. Rz 7 mu m) and weight loss (max. 10 mg). The extent and character of wear were influenced by coating thickness, contact pressure and meshing frequency. The wear of thicker TiAlCN coatings on the tooth face started with the smoothing of surface protrusions. The next stage of wear was characterized by depletion of TiAlCN coating. After depletion to a thickness of about 2 mu m, the layer was pressed into the soft substrate, and it subsequently cracked. At higher load stages, the layer was partially detached, but the critical roughness indicating scuffing was not exceeded. Thinner TiAlCN coating on the tooth flank cracked and fully detached at lower load stages compared to thicker layers and wear of uncoated soft substrate caused the increase in roughness above the critical value representing scuffing.