Tribological properties of HVOF-sprayed WC-Co coatings deposited from Ni-plated powders at elevated temperature

• Published in: Surface & coatings technology Vol. 327; pp. 48 - 58
• Main Authors: Jafari, Majid, Han, Jong-Chan, Seol, Jae-Bok, Park, Chan-Gyung
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.10.2017; Elsevier BV
• Subjects: Aluminum oxide; Cemented carbides; Cobalt; Coefficient of friction; Deformation; Electroless plating; Electron microscopy; Field emission microscopy; High temperature; High velocity oxyfuel spraying; HVOF; Nickel plating; Protective coatings; Scars; Sintering (powder metallurgy); Sliding friction; Temperature; Tribology; Tungsten carbide; Tungsten oxides; WC-Co, WC-Co-Ni coatings; Wear resistance; High temperature; WC-Co, WC-Co-Ni coatings; HVOF; Tribology
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2017.08.026

WC-Co coatings with low degree of WC decomposition were deposited from electroless Ni-plated micro- and nano-structured feedstock powders using high velocity oxygen fuel (HVOF) spraying. Dry sliding friction and wear behavior of the resultant coatings, referred to as Ni/mc-WC and Ni/nc-WC, were investigated by using sintered alumina (Al2O3) as the mating material at 700°C. For the purpose of comparison, similar experiments were carried out on conventional micro- and nano-structured coatings, denoted as mc-WC and nc-WC. The worn scars were examined by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). The wear resistance of Ni/mc-WC and Ni/nc-WC coatings at 700°C was found to be 45% and 72% greater than that of mc-WC and nc-WC coatings, respectively. Moreover, Ni/mc-WC and Ni/nc-WC coatings exhibited a significantly lower friction coefficient with negligible fluctuations as compared to mc-WC and nc-WC. The microscopic analyses of mc-WC and nc-WC worn surface revealed the presence of plastically deformed and discontinuous tribofilms, made up of a mixture of MWO4/WO3 (M=Co) and Al2O3, severe cracking and delamination especially at the interface of tribofilm and the underlying surface. In contrast, examination of Ni/mc-WC and Ni/nc-WC substantiated that a large area of the coatings surface is covered by a dense and adhered MWO4-type oxide layer (M=Co, Ni), which provides a more protection against wear at elevated temperature. •Wear resistance of Ni/mc-WC at 700°C was enhanced by 45% compared to mc-WC coating.•Ni/nc-WC showed 72% improvement in wear resistance at 700°C relative to nc-WC.•Type of oxide layer formed on wear track at 700°C has a key role on wear resistance.•For mc-WC and nc-WC, tribofilm was comprised of a mixture of CoWO4/WO3 and Al2O3.•For Ni/mc- and Ni/nc-WC, dense and adhered MWO4 oxide formed on wear track at 700°C.