Effects of the dispersion time on the microstructure and wear resistance of WC/Co-CNTs HVOF sprayed coatings

• Published in: Surface & coatings technology 2014-11, Vol.258, p.38-48
• Main Authors: Rodríguez, M.A., Gil, L., Camero, S., Fréty, N., Santana, Y., Caro, J.
• Format: Article
• Language: English
• Subjects: Abrasion resistance; Abrasion resistant coatings; Abrasion wear; Applied sciences; Chemical Sciences; CNTs; Coatings; Cobalt; Cross-disciplinary physics: materials science; rheology; Dispersion; Exact sciences and technology; HVOF; Material chemistry; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microhardness; Nonmetallic coatings; Physics; Production techniques; Raman; Sand; Surface treatment; Surface treatments; Tungsten carbide; WC–Co; Wear resistance
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2014.10.014

WC–Co is widely used as a tribological coating material providing a combination of high toughness, high hardness, and good strength. Herein, an attempt has been made to further enhance the mechanical and wear properties of tungsten carbide cobalt coatings by reinforcing them with multiwall carbon nanotubes (CNTs) using thermal spraying. In this work, 0.35wt.% of CNTs were mixed by jar-milling in ethanol solution with WC–12%Co microcrystalline powders for different blending times. The mixture was thermally sprayed using the HVOF process onto a plain steel substrate. Also, coatings deposited with both WC-12%Co microcrystalline and nanostructured powders, using the same thermal spray process, were evaluated and compared with samples reinforced with CNTs. The microstructures of the coatings were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and X-ray diffraction (XRD). The microhardness was measured by Vickers indentation and the abrasive wear resistance was evaluated using a dry sand rubber wheel technique according to ASTM G-65-00 standard. Effects of blending times of CNTs on the microstructure, abrasion wear and microhardness of the coatings were investigated. Experimental results have shown that 36h of milling time was suitable to disperse CNTs with WC–Co feed powders since it produces an adequate relationship between CNTs' dispersion time and particle size which enhances the microhardness and porosity of the coatings. The C-36 coating showed an increase in wear resistance of almost 80% and 70% compared with conventional and nanostructured coatings, respectively. This was attributed to the CNTs acting as bridges, promoting the cohesion between lamellas and reducing the decarburization. All reinforced coatings showed a higher abrasive wear resistance than non-reinforced indicating that CNTs are a good alternative to improve abrasion wear resistance of WC–Co coatings. •The influence of blending time on WC–Co coatings reinforced with CNTs was investigated.•Microhardness and wear tests were performed on coatings unreinforced and reinforced with CNTs at different milling times.•36h milling time caused a significant decrease in abrasion loss.•Good wear performance is due to the CNTs acting as bridges between particles avoiding the matrix removal.•Doping with CNTs is a good alternative to improve mechanical properties on WC–Co coatings.