Effect of microstructure on abrasive wear behavior of thermally sprayed WC–10Co–4Cr coatings

Abstract

Thermally sprayed WC–Co coatings have been widely used in the coatings industry for its superior sliding, abrasive and erosive wear properties. In applications where corrosion resistance is also required in addition to wear resistance, WC–10Co–4Cr is the preferred coating composition. The coatings produced by different thermal spray processes exhibit a broad range of coating hardness, porosity and microstructural features like grain size and volume fraction of individual phases. In this study, we have evaluated the coating microstructures of various WC–10Co–4Cr coatings produced from different spraying processes, such as high velocity oxy-fuel (HVOF) and pulsed combustion. The objective of our study is to explore the abrasive wear mechanism of WC–10Co–4Cr coatings in great detail, and determine how these mechanisms are influenced by the coating microstructure. Dry sand rubber wheel abrasion test rig (based on ASTM G65) is used for evaluating the three-body abrasive wear properties of the coatings, using alumina as the abrasive material. The coating microstructural parameters including WC grain size, volume fraction, binder mean free path have been quantitatively measured, and correlation between abrasive wear behavior of coatings and its microstructural parameters is sought. This study shows that binder mean free path of carbides (which is a function of WC grain size and volume fraction) is a very important parameter affecting the abrasion resistance of good quality coatings (containing low porosity). The lower the binder mean free path, the higher is the abrasive wear resistance offered by the coating. This is because the abrasive wear mechanism of these coatings is dominated by preferential removal of the binder phase, followed by pullout of WC grains.