Abstract
The present study describes the applicability of a surface modification process developed on the basis of mechanical methods, to the sliding interfaces of engine components such as piston skirts. The developed process consisted of a micro shot peening and a roller burnishing. A solid lubricant, such as molybdenum disulfide (MoS2), was supplied into the micro dimples formed by the shot peening, and was then made to penetrate by means of the roller burnishing. The resulting surface was flat and consisted of a densely penetrated MoS2 phase and a truncated substrate. The surface modification process was applied to an aluminum cast alloy (AC8A). The tribological properties were evaluated using a ring-on-disc-type testing apparatus under lubricated conditions using a cast iron (FC230) ring as a mating specimen. The friction coefficient of the modified surface was low and stable. In addition, a tin (Sn) coating applied to the AC8A surface in advance of the roller burnishing was an effective way to increase the adhesion strength of the MoS2. A similar surface modification was applied to a piston skirt and was evaluated under firing conditions. It was confirmed that the application of the surface modification was an effective way to decrease the friction loss of the piston skirt. Furthermore, the multiplied effects of the surface modification and a surface texture fabricated using an interrupted micro cutting process were also evaluated.
