Sliding wear behavior of high velocity oxy-fuel and high power plasma spray-processed tungsten carbide-based cermet coatings
Tungsten carbide (WC)-based composites are widely used for fabricating bulk components employed in various wear applications requiring a combination of high toughness, high hardness, and good strength. For some applications, it has been shown that there are several advantages to replacing a bulk WC-based component by a WC-coated steel substrate. In the present study, coatings of two WC-based cermet compositions (12Co–WC and 10Ni–WC) were produced on steel substrates using two thermal spraying techniques: high velocity oxy-fuel (HVOF) and high power plasma spraying (HPPS). The performance of the resulting coatings was compared using carbon disks as counterparts in sliding wear tests. During these trials, the coefficient of friction between the two sliding parts was monitored at regular intervals. For each couple, the wear of both the coating and the carbon disk during the trial was determined by measuring the weight loss following the test. Analysis of the wear debris and of the wear track on both the coating and carbon disk was performed using a scanning electron microscope. The study showed that although the coefficient of friction was approximately the same for all the couples under investigation regardless of the thermal spraying technique used to deposit the coatings, there were differences in the wear performance. In particular, the results indicated that the rotors having HPPS-deposited coatings, which had a higher level of porosity, exhibited better wear resistance than the HVOF-processed coatings. A similar trend was observed for the wear of the corresponding carbon-graphite stator for the various couples. The results have been interpreted in terms of the effect of porosity on the role of debris in the friction and wear process.