Wear and erosion of arc-PVD multilayer Ti-Al-Mo-N coatings under various conditions of friction and loading

Abstract

Wear resistance and failure of arc-PVD Ti-Al-Mo-N coatings under different conditions were investigated. Under dry friction, coatings have high tribological properties: friction coefficient was about 0.4–0.5 vs. 0.6–0.7 for TiAlN at 20 and 500 °C, respectively. The depth of the wear track of the studied Ti-Al-Mo-N coatings was comparable to the original surface roughness, while the TiAlN coating wear under the same conditions was about 6 ‧ 10−5 mm3 N−1 m. This is due to the adaptation phenomenon, associated with the formation of MoO3 acting as a solid lubricant during friction. Simulation of abrasive particle moving along the coating surface by scratching with a diamond indenter at increasing load showed that coating failure occurs cohesively by the mechanism of plastic deformation without significant cracking and chipping of large fragments. This is due to the high fracture toughness of the coating (relative work of plastic deformation ~ 60%), along with its high hardness (up to 40 GPa). Under such conditions, the partial abrasion of the coating to the substrate occurred at the load of about 75 N. Under hydroabrasive wear using Al2O3 abrasive particles, 4-μm-thick Ti-Al-Mo-N coating on the cemented carbide substrate had several times increase in durability compared with the uncoated sample. Impact test indicated that the Ti-Al-Mo-N coating is highly resistant to impact loads compared with TiAlN coating, through a combination of high hardness and plasticity and high adhesion to the substrate.