A study of mechanical and tribological properties as well as wear performance of a multifunctional bilayer AlTiN PVD coating during the ultra-high-speed turning of 304 austenitic stainless steel

In this study, a novel bi-layer AlTiN PVD coating was deposited on a tungsten carbide substrate. The bi-layer coating, with a total thickness of 3.5 μm consists of a 1.0 μm Al60Ti40N top layer and a 2.5 μm Al50Ti50N sublayer. Monolayer Al60Ti40N and Al50Ti50N coatings (each around 3.5 μm) were used as benchmarks. All the studied coatings were deposited by an industrial cathodic arc PVD coater. The ultra-high-speed finish turning of austenitic stainless steel 304 (SS304) was performed under a cutting speed of 420 m/min. The coatings' mechanical properties (hardness, elastic modulus, toughness, and adhesion) were evaluated using nano-indentation and scratch methods. The obtained data illustrated the influence of the mechanical properties of the coatings on tool wear performance. Cutting tests showed that the longest tool life was achieved by the bi-layer coated tool. Wear morphology studies had revealed that a combination of oxidation/diffusion wear mechanisms resulted in cratering whereas abrasion/attrition led to flank wear. An investigation of tribological characteristics had shown that the bi-layer coated tool produced improved chips. This indicates an optimal frictional condition at the cutting zone. Finally, a chip cross-section analysis was performed to verify the microstructure variations and work-hardening effect in the chips.