Friction and Wear Properties of Spark Plasma Sintered Cu-15Ni-8Sn/Graphite Self-Lubricating Composites

The Cu-15Ni-8Sn/graphite self-lubricating composites with different graphite contents were prepared by spark plasma sintering. The Cu-15Ni-8Sn alloy was used as matrix while graphite was used as lubricant. The microstructure, phase composition and room-temperature mechanical property of the composites were investigated using scanning electron microscopy, X-ray diffractometer and universal testing machine. The frictional and wear properties of the composites were tested by ball-disk friction testing machine at 3, 5 and 10 N, respectively. The wear volume of the composites was measured by a 3D profilometer. The wear scar morphology was characterized by a scanning electron microscope. The results showed that the relative density of the Cu-15Ni-8Sn alloy was 93%, the compressive strength was 1 143 MPa. The average friction coefficient and wear rate of the alloy gradually decreased as the load increases and achieves to its minimum 0.5, when the load was 10 N. The minimum wear rate was 3.0×10⁻⁴ mm³/(N·m) and its wear mechanism was mainly on adhesive wear. The relative density of Cu-15Ni-8Sn/graphite self-lubricating composites increased with the increase of graphite content while the maximum fracture strain and compressive strength of the composites showed an opposite trend. When the graphite content was 5%, the compressive strength of the composite was 614.6 MPa. This was due to the increase graphite content breaking the continuity of the internal matrix material. The hardness firstly increasing and then decreasing with the increase of graphite content maybe because a three dimensional microstructure was formed in the composite of 3% graphite content. In particular, the graphite content had little influence on the yield strength of the composites. The friction coefficient of the materials reduced significantly after adding graphite. The influence of load on the friction coefficient of the composites was little, and the friction coefficient of the composites with different graphite contents was about 0.1~0.2. The addition of graphite also decreased the wear rate of the Cu-15Ni-8Sn alloy by about two orders of magnitude, however, the composites had better wear resistance. Compared with other composites with graphite content, the Cu-15Ni-8Sn/graphite self-lubricating composite with a mass fraction of 3% graphite had the highest hardness and the best wear resistance, and that the wear rate of the composite was the most stable under different loads, with a minimum wear rate of 3.0×10⁻⁶ mm³/(N·m). The wear mechanism of the composite was mainly based on abrasive wear and stripping of graphite lubrication film. The excellent friction and wear properties of Cu-15Ni-8Sn/graphite self-lubricating composites are attributed to the formation of a more complete graphite-rich lubricating film during the friction process, and the complete graphite lubricating film plays an great effect of friction and wear reduction on the surface.