Dry Sliding Wear of TiN x PVD Coating on 7075-T6 Aluminium Alloy

Abstract

The present paper studies the dry sliding wear behaviour of a 7075-T6 aluminium alloy coated with a substoichiometric TiN_x film. The coating was deposited industrially (Teer Coatings Ltd) using the closed field unbalanced magnetron sputtering ion plating (CFUBMSIP) deposition technique. Coating characteristics such as morphology, thickness, compositional variation with thickness, residual stress, composite hardness and absolute hardness are also presented. The wear tests were conducted in a ball on disc tribometer, where a constant sliding velocity of 0.1 m s^–1 and normal loads of 1, 2 and 5 N were used. The static counterparts employed during the test were 6 mm diameter balls made of AISI type 52100 steel. For comparison, the wear behaviour of the uncoated alloy is also reported. Both the maximum Herztian pressure and the von Mises stress values in the TiN coated aluminium alloy for each normal load used during the wear test were calculated, employing a commercially available software package Elastica 2.0.5, and the results were related to the wear performance. It was shown that the coated alloy presented an improved wear resistance only when the wear tests were performed at normal loads as low as 1 and 2 N, when the material from the static counterpart was transferred to the surface of the coated discs, and the TiN coating was able to protect the aluminium alloy from plastic deformation. However, when the wear test was carried out at a load of 5 N, the coating presented low wear resistance with a wear coefficient as low as 10^–4 mm³ (N m)^–1. This behaviour could be attributed to the fact that, in these conditions, the coating could not protect the substrate from plastic flow and fracture, producing a large amount of debris, which contributed to the abrasive wear of the system. SE/S277