Experimental Investigations of Steel Scuffing and Coatings for Scuffing Prevention

Abstract

To improve the lifetime, enhance engine performance, decrease emissions, and inhibit tribological failures of fuel injection system components, the component materials need to resist scuffing under conditions of high temperatures, high pressures, and low viscosity fuel lubrication. The objectives of this dissertation are to improve the materials implemented in future fuel injection system designs by developing a laboratory-scale experimental method to induce scuffing on baseline steel materials and use this experimental method to evaluate various materials for their resistance to scuffing failures. An experimental method to reliably produce scuffing events on AISI 52100 steel was developed by altering the contact condition parameters of previous experimental methods, such as the counterbody material, sliding velocities, and normal loads, amongst other parameters. The proposed method allows for the rapid evaluation of surfaces and coatings for their suitability in fuel injection system applications. Multiple materials were evaluated for their friction and wear reduction properties, including three different compositions of additively manufactured steels, tungsten carbide and cobalt-based thermal spray coatings, chromium nitride coatings, diamond-like carbon coatings, and tribocatalytic MoVN-Cu coatings. The results indicate that several of the coating materials and one of the additively manufactured steel alloys are promising candidates for implementation in emerging fuel injection systems to lower friction and prevent scuffing and wear. The properties of these materials responsible for their superior tribological behavior, such as the mechanical and thermal properties, were characterized and discussed.