Friction and wear behavior of magnetron co-sputtered V-Si-N coatings

Cutting tool life can be extended by using coatings, and that presents many opportunities to reduce manufacturing cost. In this study, V-Si-N coatings with 3.1 and 4.4 at% Si were prepared on high speed steel substrates (HSS) by reactive magnetron co-sputtering deposition. In addition to characterizing the microstructure, mechanical properties, and coating adhesion, the sliding friction and wear behavior were investigated. The V-Si-N coatings exhibited a dense growth structure, high nano-indentation hardness (>30 GPa) and good scratch adhesion (critical load >80 N). Unlubricated ball-on-plate tribological tests were performed against Al2O3 or WC-Co counterparts at room temperature. Wear tracks were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray spectrometry (EDX). Under a normal load of 5 N, the friction coefficients against Al2O3 or WC-Co were less than 0.5, and the specific wear rates were in the range of 10−8 mm3/N m. There was no obvious effect of relative humidity (RH) on the friction and wear behavior in the range of 30-80% RH. Mild wear continued up to ~105 sliding cycles, corresponding to a layer-by-layer removal mechanism. When the load was doubled to 10 N, a transition from mild to severe wear occurred after about 104 sliding cycles. Cracking and spallation increased at this point. It is suggested that a combination of rich V content and nanocomposite microstructure favors the excellent wear resistance of Vi-Si-N hard coatings.