Wear mechanisms of coated carbide tools

Abstract

Cemented carbide inserts, both uncoated and coated with single or composite layers of TiC, TiN, or Al₂O₃, were used to cut En. 8 and En 24 steel at speeds between 183 and 305 min⁻¹ Quick-stop specimens and tool-temperature estimates demonstrated that conditions at the tool/work interface were essentially similar for uncoated tools and for all types of coated tool tested. The flank and rake-face wear rates of coated tools were estimated to be respectively ∼ 10 and 100 times less than that of an uncoated carbide, smaller differences between the rates of flank and rake-face wear of TiC, TiN, and Al₂O₃ coatings being observed. On the rake face, wear of TiC coatings was by atomic diffusion and discrete plastic deformation, while TiN coatings and uncoated cemented carbide were worn by atomic diffusion. Al₂O₃ coatings were worn principally by discrete plastic deformation. Flank wear of both coated and uncoated tools was principally by atomic diffusion. Al₂O₃ and TiN coatings showed a greater resistance to groove formation at the outside edge of the depth of cut than TiC coatings, which were worn at a similar rate to the uncoated carbide inserts. Grooves were formed by two distinct mechanisms involving oxidation and fatigue cracking, both of which were accelerated when cutting in a jet of oxygen and eliminated when cutting in jets of argon or nitrogen.