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

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>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 (Al<SUB>2</SUB>O<SUB>3</SUB>) 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 MWO<SUB>4</SUB>/WO<SUB>3</SUB> (M=Co) and Al<SUB>2</SUB>O<SUB>3</SUB>, 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 MWO<SUB>4</SUB>-type oxide layer (M=Co, Ni), which provides a more protection against wear at elevated temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Wear resistance of Ni/mc-WC at 700°C was enhanced by 45% compared to mc-WC coating. </LI> <LI> Ni/nc-WC showed 72% improvement in wear resistance at 700°C relative to nc-WC. </LI> <LI> Type of oxide layer formed on wear track at 700°C has a key role on wear resistance. </LI> <LI> For mc-WC and nc-WC, tribofilm was comprised of a mixture of CoWO<SUB>4</SUB>/WO<SUB>3</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB>. </LI> <LI> For Ni/mc- and Ni/nc-WC, dense and adhered MWO<SUB>4</SUB> oxide formed on wear track at 700°C. </LI> </UL> </P>