A. Ghabchi, T. Varis, T. Suhonen, E. Turunen, VTT Technical Research Centre of Finland, Espoo, Finland; X. Liu, S. P. Hannula, Helsinki University of Technology, Espoo, Finland
One potential approach to improve the wear performance of HVOF sprayed WC-CoCr -coating in nano- or micro particle wear applications is to reduce carbide size. Better wear performance and smoother worn surface of fine, evenly distributed carbide grains might be due to smaller free path of matrix between carbides. In this study, a modified ASTM G 65 rubber wheel test was used with fine slurry abrasion particles (220 nm) to address effect of coating carbide size, conventional (1 µm), sub-micron (400 nm), and nano on its wear performance. To understand the wear mechanism the wear tracks were analysed in detailed by using SEM and 3-D profilometer. It was shown that the mechanism of the wear depends on the relative size of the carbide and abrasive particle. By tailoring the carbide size the wear performance can be improved.
Summary: The wear performance of the WC-CoCr –coatings having different carbide size distribution was studied in fine particle slurry abrasion environment. The carbide size was conventional, sub-micron and nano. The spray parameters were optimized for each powder individually. By detailed SEM studies from same locations before and after the wear test it was shown that wear mechanism depends on the relative size of the carbide particles and abrasive particle. Following mechanisms based on relative size of carbide to abrasive particle were observed: disappearing of carbides with cutting the binder by abrasive, and crushing of carbide particles and remove of crushed carbides. By using appropriate carbide size the wear resistant can be improved. Nevertheless, if the carbide particle size compared to abrasive particle is approximately two times smaller (nano), the advantage from the use of finer carbides was minor.
