Tribological behaviour of a hyperlox coating deposited over nitrided martensitic stainless steel

Abstract

Martensitic stainless steels are often used in machine components, where are exposed to different solicitations that require good surface properties. Different treatments such as plasma nitriding or coating deposition could be used to improve their wear and corrosion resistance, even combining both methods. In this work, the tribological behaviour of a TiAlN coating with a top layer of TiN, called ‘Hyperlox Gold’, deposited over both nitrided and non-nitrided martensitic stainless steels by PVD PEMS (Physical Vapour Deposition Plasma Enhanced Magnetron Sputtering) was studied. Quenched and tempered AISI 420 martensitic stainless steel was used as base material. A group of samples were plasma nitrided and were subsequently coated. Microstructure of the nitrided layer and the coating were analysed by SEM and XRD. Nanohardness was measured with a Berkovich tip. Wear behaviour was evaluated using pin-on-disk tests (ASTM G99 standard) under three different loads (5 N, 7 N and 10 N) with an alumina ball as a counterpart. Adhesion was evaluated using dynamic conditions such as variable load scratch test and under static condition with Rockwell indentation tests (using 60 kg, 100 kg, and 150 kg). Overall thickness of the coatings was 3.7 μm and their hardness about of 32 ± 2 GPa. The nitrided layer was about 10 μm thick, with a hardness of 17 ± 1 GPa. The coating had good mechanical resistance in sliding adhesive wear conditions under low loads and good adhesion was revealed in a static condition. The presence of a nitrided layer improved the wear behaviour under high loads and the adhesion in dynamic conditions. Critical load was higher for the duplex sample than the coated samples. This work is important for the development of the Argentinian industry where the use of coatings is not largely extended, especially with martensitic stainless steels as substrates.