SLIDING WEAR BEHAVIOR OF TIN COATINGS DEPOSITED BY FILTERED ARC

Filtered are deposition system (FADS) is rapidly emerging as a powerful physical vapour deposition technology for the application of hard coatings. In this work, the tribological behaviour (friction and wear) of TiN coatings applied by FADS at 450 degrees C was studied using a ball-on-disc configuration. The substrate bias voltages were systematically varied to investigate the effect of ion bombardment on the hardness, roughness, adhesion and wear resistance of the coatings. The hardness of coatings was determined using Knoop microhardness and an automatic scratch tester was used to assess the adhesion of the coatings. The wear behaviour and dominant wear mechanism(s) of coated and uncoated tool steels were investigated as a function of applied load and sliding distance. It has been found that, at low load (5 N), the wear behaviour of the uncoated tool steel was dominated by a mild oxidative wear regime. At higher load (20 N), a combination of adhesive and abrasive wear modes was operative and the wear tracks exhibited severe gouging. In the case of TiN coatings, the wear resistance, adhesion, roughness, and hardness of the coatings were strongly influenced by the substrate bias voltage. The optimum wear resistance, at both 5 and 20 N loads, occurred at 50-100 V substrate bias voltages. At zero bias voltage, the coating exhibited higher hardness but was exfoliated during wear tests owing to its brittleness. At the highest bias voltage (400 V), a reduction in adhesion and hardness was noticed, and the coating was delaminated from the substrate resulting in a high friction-high wear regime.