| Abstract: |
Nanocomposite coatings are known to exhibit superior wear behaviour compared to bulk ceramic coatings, owing to the low friction properties attributed to the reinforcing materials. Graphene has been identified as a suitable reinforcement material for nanocomposite coatings and the nanocomposite coatings are finding applications in extreme wear scenarios. Suspension high velocity oxy fuel (SHVOF) is a promising method to deposit coatings from sub-micron particles and the use of suspension allows to easily incorporate graphene in the feedstock. As of yet, the use of graphene, or GNPs, in materials deposited by thermal spraying methods, has not been investigated, and the survivability of GNPs in the thermal spraying process is not known. In this study, a powder feedstock of sub-micron sized alpha alumina particles, with 1% by weight GNPs, was prepared in a water based suspension and sprayed by SHVOF onto stainless steel substrates. The suspension was prepared using ultrasonic dispersion of the GNPs to achieve a uniform distribution, after which it was mixed with the alumina suspension and further dispersed for 1 hour by mechanical stirring. Using Raman spectroscopy, SEM and TEM imaging, it was shown that the GNPs survived the SHVOF process. Dry sliding wear testing against an alumina counter body showed superior wear performance of the alumina/ GNP coating, compared with the alumina coatings, by a factor of an order of magnitude of wear volume loss. Effective lubrication of alumina particles in the coating by the GNPs is perceived to facilitate the reduced friction co-efficient and hence improved wear behaviour.
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