Experimental visualization of the wear and scuffing evolution of a flake graphite cast iron cylinder liner

Abstract

Scuffing is a wear mechanism that can lead to catastrophic failure of various technical applications. Even though the mechanism has been researched in countless publications for decades, it is not fully understood yet. An experimental approach was used in this paper to investigate the origin and evolution of scuffing in a ring-on-liner contact. For this purpose, test runs in an application-oriented test rig were stopped at different points in time. A linear tribometer was used to transfer a reciprocating motion of a real piston ring segment to a specimen made from a real cylinder liner. Based on a comprehensive analysis, a four-stage scuffing hypothesis for a ring-on-liner contact was developed. In the first stage, smearing of the honing structure and the formation of surface cracks lead to the development of a scaly structure on the liner surface. Crack growth induced by adhesive shear forces leads to the formation of breakouts in the liner surface in the second stage. Both stages are stable and only the specific load increase of the used test strategy causes the transition to stage three. Here, large crack growth induced breakouts result in the local destruction of tribofilms and, subsequently in local metallic contact between the specimens. When this local destruction becomes rampant and expands to a macro scale, adhesive bonds lead to macroscopic scuffing. It can be deduced that the first occurring damage stage is a result of a surface fatigue process.