Processing Optimization and Dry-Sliding Tribological Performance of Cu-Ni-Graphite Self-Lubricating Composites

Cu-Ni-graphite self-lubricating composites were developed for railway switch slide baseplate applications, which require a low dry friction coefficient and adequate load-bearing capacity under low-speed sliding. The powder-metallurgy route—comprising planetary ball milling, cold compaction, and vacuum sintering—was systematically evaluated. The selected processing window consisted of a ball-to-powder ratio of 1:10, milling at 200 rpm for 15 h, compaction at 700 MPa, sintering at 850 °C, and a holding time of 2 h. Under these conditions, the Cu-8Ni-8graphite composite achieved a Vickers hardness of approximately 83 HV and a flexural strength of about 348 MPa. Under dry sliding against U75V rail steel at 20 N and 0.065 m/s, the composite exhibited a steady-state friction coefficient of 0.212 ± 0.012 and a specific mass wear rate of (4.20 ± 0.30) × 10−5 g/(N·m)—reductions of 76% and 49%, respectively (p < 0.05, t-test, n = 5), relative to the graphite-free Cu-8Ni alloy. The improved tribological response was attributed to the formation of a compact mechanically mixed tribofilm comprising the Cu-Ni solid-solution phase, fragmented graphite, and minor oxides. This film reduced direct metal-to-metal contact, adhesive transfer, and micro-cutting. These results establish a process–microstructure–property relationship for Cu-Ni-graphite composites and provide a basis for further component-level and long-duration validation.