Abstract
To reduce the friction coefficient of cobalt-cemented tungsten carbide (WC-12Co) wear-resistant coatings, graphene was compounded into WC-12Co powder via wet ball milling and spray granulation. Self-lubricating and wear-resistant graphene coatings were prepared via detonation gun spraying. The presence, morphologies, and phase compositions of graphene in the powders and coatings that are obtained through different powder preparation processes were analyzed. The analysis was performed using the following technologies: energy-dispersive X-ray-spectroscopy (EDXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The mechanical properties of the coatings were studied using a microhardness tester and a universal drawing machine. The friction and wear properties of the coatings were studied using an SRV-4 friction and wear tester. The results showed that the graphene content in the WC-12Co coating modified with graphene was higher than that without modification; graphene was embedded in the structure in a transparent and thin-layer state. The adhesive strength of this coating at approximately 25 °C was approximately 60.33 MPa, and the hardness was approximately 984 HV0.3. After high-temperature treatment, the adhesive strength and hardness of the graphene oxide (GO)/WC-12Co coating decreased slightly (the lowest adhesive strength of 53.16 MPa was observed after treatment at 400 °C, and the lowest hardness of approximately 837 HV0.3 was observed after treatment at 300 °C). Compared to the friction coefficient (0.6) of the WC-12Co coating obtained at room temperature, the friction coefficient of the GO/WC-12Co coating was decreased by approximately 50% of that value. The graphene-modified coating was continuously exposed to the wear tracks on the surface of the contacting materials during friction, and a lubricating film was formed in the microareas in which the wear tracks were present. The coating exhibited improved self-lubricating and wear-resistant effects compared to the unmodified WC-12Co coating. The results of this study demonstrated that graphene could be effective in self-lubrication and wear-reduction in a temperature range of 100–200 °C, as a friction coefficient of 0.3 was maintained.
Highlights
In 2004, Novoselov et al [1] used adhesive tape to repeatedly adhere to and peel away from highly oriented pyrolytic graphite (HOPG) to prepare single layers of graphene
To develop self-lubricating and antiwear applications of graphene in cobalt-cemented tungsten carbide (WC–12Co) wear-resistant coatings, the spray granulation technique was used in this study to mix graphene with were tungsten carbide (WC)–12Co powder and to prepare a graphene oxide (GO)/WC–12Co coating via detonation gun (D-gun) spraying
During wear at 400 °C, the friction coefficient increases to 0.5, the amount of graphene film aggregating on the wear track surface is less than that at observed at other temperatures, and a small number of microcracks appear in the wear track, indicating abrasive wear caused by brittle peeling of the coating
Summary
In 2004, Novoselov et al [1] used adhesive tape to repeatedly adhere to and peel away from highly oriented pyrolytic graphite (HOPG) to prepare single layers of graphene. Many studies on the application of such lubricants as lubricating phases in coatings have been performed using currently available technologies. These additives all have certain limitations; for example, a sulfide-based lubricating phase that is added to a coating undergoes oxidation as the temperature increases during friction, which results in a serious decrease in the tribological properties, especially in humid environments. To develop self-lubricating and antiwear applications of graphene in cobalt-cemented tungsten carbide (WC–12Co) wear-resistant coatings, the spray granulation technique was used in this study to mix graphene with WC–12Co powder and to prepare a graphene oxide (GO)/WC–12Co coating (i.e., a graphene-modified self-lubricating wear-resistant coating) via detonation gun (D-gun) spraying. We studied the basic properties of the various obtained powders and coatings, focusing on their influence on the self-lubricating wear-resistance characteristics and mechanisms of graphene during a high-temperature wear process (over a temperature range from room temperature to 550 °C)
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