Enhancing Graphene Retention and Electrical Conductivity of Plasma-Sprayed Alumina/Graphene Nanoplatelets Coating by Powder Heat Treatment

Burning loss of graphene in the high-temperature plasma-spraying process is a critical issue, significantly limiting the remarkable performance improvement in graphene reinforced ceramic coatings. Here, we reported an effective approach to enhance the graphene retention, and thus improve the performance of plasma-sprayed alumina/graphene nanoplatelets (Al2O3/GNPs) coatings by heat treatment of agglomerated Al2O3/GNPs powders. The effect of powder heat treatment on the microstructure, GNPs retention, and electrical conductivity of Al2O3/GNPs coatings were systematically investigated. The results indicated that, with the increase in the powder heat treatment temperature, the plasma-sprayed Al2O3/GNPs coatings exhibited decreased porosity and improved adhesive strength. Thermogravimetric analysis and Raman spectra results indicated that increased GNPs retention from 12.9% to 28.4%, and further to 37.4%, as well as decreased structural defects, were obtained for the AG, AG850, and AG1280 coatings, respectively, which were fabricated by using AG powders without heat treatment, powders heat-treated at 850 °C, and powders heat-treated at 1280 °C. Moreover, the electrical conductivities of AG, AG850, and AG1280 coatings exhibited 3 orders, 4 orders, and 7 orders of magnitude higher than that of Al2O3 coating, respectively. Powder heat treatment is considered to increase the melting degree of agglomerated alumina particles, eventually leaving less thermal energy for GNPs to burn; thus, a high retention amount and structural integrity of GNPs and significantly enhanced electrical conductivity were achieved for the plasma-sprayed Al2O3/GNPs coatings.