Low Friction Coefficient Nanocomposite CrAlSiN/Gradient-CrAlSiCN Coatings for High Speed/Dry Machining Applications

Abstract

Providing advanced coating solutions for high-speed dry machining applications is gaining importance by the day especially with the increasing employment of difficult-to-machine materials in niche areas. Taking into account the recent demands in developing such coatings, in the present study, a novel low-friction coefficient nanocomposite coating: CrAlSiN/gradient (G)-CrAlSiCN was developed which can be used in high-speed or dry machining applications. Initially, CrAlSiN nanocomposite coating and carbon incorporated CrAlSiN coating were deposited separately using the cylindrical cathodic arc physical vapor deposition (PVD) technique. The as-deposited films were comprehensively analyzed to determine their adhesion strength, phase composition, sliding wear properties (friction coefficient), hardness, and tool life. Preliminary observations revealed that the films did not show evidence of diamond-like carbon (DLC) formation (from Raman analysis). Further, an increase in the carbon content led to a steep decrease in the adhesion strength. This result persuaded a study on developing a novel coating with gradient carbon architecture that would retain the properties of a nanocomposite whilst supporting the nanocomposite underlayer by reducing the coefficient of friction. In comparison with the CrAlSiN nanocomposite coating and a standard DLC coating, the novel gradient carbon coating showed superior tribological properties along with better tool life. This study marks the first such attempt at studying the influence of carbon incorporation to the CrAlSiN nanocomposite coating on improving the overall mechanical and tribological properties of the coating architecture (CrAlSiN/G-CrAlSiCN) for dry machining applications.