A Study of the Microstructure and Tribological Properties of Copper-Based Cr@graphite Alloy Modified by Nano Cr3C2 and CrC

Abstract

Railway switch plates are important components in railroads, and copper-based graphite alloys have potential as substitutes for traditional materials. Graphite as an anti-friction phase could decrease both the friction coefficient and mechanical properties, with an increasing mass fraction for their poor interface bonding strength. Chromium, a multifunctional metal plated on the graphite (Cr@graphite), has solved this problem. Results have shown that a copper-based Cr@graphite alloy is composed of copper as a base, and graphite and Cr compound transition phase as reinforcements. The transition phase is made up of nano Cr3C2 and dispersed CrC, which offers a stable combination with both graphite and copper. The tribological property of copper-based graphite alloy exhibits a steadily decreasing slope with reinforcement content increasing, and the Cr@graphite samples show lower values than the alloy without any coating treatment. Both graphite and chromic oxide play role in antifriction, and are more efficient than graphite alone. Microcutting is the dominant wear method when copper-based Cr@graphite alloy has a 1~4 wt.% reinforcements content; additionally, adhesion wear and oxidation are also generated. When the anti-friction phase increases, the wear mechanism is affected, and fatigue deformation is the dominant wear method at 4~6 wt.% content. The formation of the chromic oxide phase, as well as the graphite phase, control the formation of an anti-friction layer. In that case, the tribological properties are dramatically improved with reinforcement content enhance.