Abstract
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.
Highlights
Plasma spraying is a popular technique to fabricate various protective coatings in surface engineering, owing to its cost-effective qualities, large-scale fabrication, high deposition efficiency, flexibility, etc. [1,2]
The results showed that the electrical conductivity of the composite was remarkably improved through the addition of ~2 wt.% Graphene nanoplatelets (GNPs) due to the formation of a GNPs electrical pathway in the matrix
As can be seen from the higher magnification images of AG, AG850, and AG1280 powders (Figure 2d,f,h), transparent graphene nanoplatelets, similar to that observed in the pristine GNPs (Figure 1), were found to be enclosed and wrapped into nanostructured alumina particles
Summary
Plasma spraying is a popular technique to fabricate various protective coatings in surface engineering, owing to its cost-effective qualities, large-scale fabrication, high deposition efficiency, flexibility, etc. [1,2]. Plasma spraying is a popular technique to fabricate various protective coatings in surface engineering, owing to its cost-effective qualities, large-scale fabrication, high deposition efficiency, flexibility, etc. Among the various materials which could be sprayed, plasma-sprayed alumina (Al2 O3 ) coating is widely used in corrosion and wear resistance applications due to its chemical stability, high hardness and elastic modulus, excellent wear resistance, etc. Graphene has been proven to be an ideal nano-filler, owing to its various attractive and outstanding properties, such as its high surface area, excellent mechanical properties, and high electrical and thermal conductivity [12,13,14]. The single-layered graphene offers some intrinsic challenges and drawbacks as well, mainly its relatively high cost, poor wetting ability, and difficulty in dispersion, limiting its wider application. GNPs have been proved to preserve most of the remarkable properties of graphene together with relatively low production cost as compared to graphene [11,15,16]
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