Abstract
Copper–graphite sandwich composites are new functional composites with excellent tribological and mechanical properties. More and more researchers prepare the sandwich composites by accumulative roll-bonding processes due to severe plasticity deformation. The microstructure and properties of copper–graphite sandwich composites prepared by continual annealing and accumulative roll-bonding processes for eight rolling cycles were investigated. The results showed that with the increase of rolling cycles, the dispersion of graphite particles between two copper layers along a rolling direction became more uniform, the pores at the interface between graphite particles and the Cu matrix gradually disappeared, and the hardness of copper–graphite composites gradually increased. After eight rolling cycles, the Vickers hardness of the composites increased by 140.8% as compared with that of annealed pure copper. During friction, the steel balls can meet some graphite particles in the composites rolled by four cycles. The friction coefficient and wear loss of copper–graphite composites gradually decreased with the increase of rolling cycles. Compared with the composites rolled by one cycle, the friction coefficient and wear loss of the composites rolled by eight cycles were reduced by 32.5 and 49.0%, respectively. The main wear mechanism gradually evolved from fatigue wear and abrasive wear to adhesive wear, and then to fatigue wear.
Highlights
Copper–graphite composites (CGCs) have attracted much attention in recent years
For the CGC prepared by accumulative roll bonding (ARB) process, there are few reports about the bonding interface between graphite particles and the Cu matrix at different rolling cycles
ARB includes the following steps: 1) cleaning the annealed copper strips. The grease on their surfaces was eliminated by ultrasonic wave in acetone for 10 min; 2) removing the oxide scale on their surfaces by using hydrochloric acid; 3) polishing these surfaces to a fresh Cu matrix with a steel wire brush; 4) smearing a certain amount of graphite particles to the surfaces; 5) rolling more than 50% reduction by a two-roller mill at a rolling speed of 0.5 m/min; 6) annealing these rolled samples at 550°C for 1 h in argon atmosphere, and cutting off at the middle of them, and repeating these above steps
Summary
Copper–graphite composites (CGCs) have attracted much attention in recent years. Due to their excellent thermal and electrical conductivity and significant friction and wear properties, CGCs have been widely used as electrical brush and bearing materials in many fields (Wang et al, 2017a; Zhang et al, 2019a; Xu et al, 2019). Some other researchers formed CGCs by using HPS or SPS at about 40 Mpa (Zhu et al, 2016; Nie et al, 2020) These processes can improve the bonding interface to some extent, the pressure exerted on these sintered samples is very limited to prevent the deformation of mold at high temperature. In these processes, the deformation degree of copper particles is not enough to make them completely welded together. For the CGC prepared by ARB process, there are few reports about the bonding interface between graphite particles and the Cu matrix at different rolling cycles
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