Effect of graphite addition on wear behaviour of hybrid Cu/TiC-Gr infiltrated composites

Abstract

A composite of interest for high-temperature applications, where high thermal conductivity, dimensional stability, and wear resistance are required, is the Cu/TiC-Graphite hybrid system. The wear behaviour of three different composites with a graphite volume of 1%, 3% and 5% was investigated, for a total volume of 60% of reinforcement, in a pin-on-disc arrangement with a steel sphere counterpart of 66 HRC hardness. The composites were synthesized by capillary liquid copper infiltration into porous TiC-Gr preforms, obtaining materials with acceptable matrix-to-reinforcement bonding, homogeneous distribution of the reinforcing particles and absence of second phases. The tribological characterization indicated that the coefficient of friction decreases with the volumetric fraction of graphite in the composites as it enriches the wear surface. The pure copper matrix showed a wear rate up to four times that of the composites under maximum wear conditions. In all materials, the wear rate increased with applied load and sliding velocity. A higher graphite content led to a lower rate of wear so that the adhesion wear mechanism of pure copper changed to abrasion and delamination with tribochemical products on the surfaces of the Cu/TiC and Cu/TiC-Gr composites forming a mechanically mixed layer. The wear systems with graphite additions showed partial lubrication of the contact surfaces.