Ultrasonic-Assisted Hot-Press Sintering: A Novel Method to Reduce the Densification Temperature and Enhance the Mechanical and Tribological Properties of Cu–Graphite Composites

Cu–graphite composites are widely used in pantograph sliders and crane brushes. Conventional sintering protocols, however, mandate processing temperatures above 860 °C with prolonged holding periods, which inevitably introduce defects within copper matrices. Drawing inspiration from ultrasonic machining, this study presents an innovative ultrasonic-assisted hot-press sintering (UAHP) technique. Using this novel method, Cu–graphite composites with graphite contents ranging from 0 to 30 vol.% were fabricated at a reduced temperature of 700 °C and a short holding time of 10 min, achieving a ca. 160 °C reduction in densification temperature. Aside from the high densification efficiency, enhanced mechanical properties were also obtained for UAHP-sintered Cu–graphite composites. The Cu–15 vol.% graphite composite exhibited a yield strength of 232 MPa, showing only a 7.2% decrease compared to pure Cu. The friction coefficient decreased with increasing graphite content, reaching a plateau value of 0.140 at 15 vol.% graphite, representing a 77.16% reduction compared to pure Cu. The wear rate initially decreased but gradually increased with the increase in graphite content. The superior tribological performance is attributed to the insitu-formed graphite lubricating film, while the primary wear mechanisms are deemed to be oxidative and abrasive wear. The ultrasonic vibration provides additional sintering driving force and enhances elemental diffusion, establishing UAHP as an innovative technical route for fabricating composites with an optimized microstructure and superior comprehensive properties.