Ultralow friction between cemented carbide and graphite in water using three-step ring-on-ring friction test

• Effect of running-in on the friction behavior in water has been investigated.
• A three-step friction test method is presented to achieve ultralow friction.
• Surface microtopography and macrowaviness have been measured after running-in.
• The mechanism of ultralow friction is attributed to hydrodynamic effect.

Effect of running-in process on friction behavior of graphite sliding against cemented carbide in deionized water was investigated using a standard tribometer Plint TE92 in a ring-on-ring contact configuration. A stable and ultralow friction coefficient of about 0.003 between graphite and cemented carbide rings was obtained after a three-step friction test method: Step 1 was rapid pre-sliding at standard operating conditions and then the test apparatus was stopped; Step 2 was the accelerated running-in process under higher load and velocity, and the test apparatus was stopped again; The wear particles on the specimen surface were cleaned, and used water was replaced by new water from step 3. According to the measurements of suface microtopography and macrowaviness, surface geometric features in the interface after three-step friction test reached the optimal harmonious state. Variations of friction coefficient with speed and load were also investigated. The ultralow friction mechanism was attributed to the hydrodynamic effect.