Session BB4.3

2:00 PM BB4.3
ABRASION AND SLIDING FRICTION OF HVOF WC-Co COATINGS. Saifi Usmani, Sanjay Sampath, Steven De Palo, Center for Thermal Spray Research, State University of New York, Stony Brook, NY; David L. Houck, Osram Sylvania Inc., Towanda, PA.

Thermal spray cermet coatings, such as WC-Co, TiC-Ni, Cr₃C₂-NiCr, are widely applied for abrasion and friction control in a variety of industries. In this work, empirical relationships and mechanisms have been developed to explain the abrasion behavior of High Velocity Oxy-Fuel (HVOF) deposited WC-Co coatings. In addition, the friction behavior of the coatings has been examined as a function of carbide size distribution. It has been shown that indentation methods can be used to quantify the in-plane fracture behavior of WC-Co coatings. This method is a modification of the indentation fracture toughness measurement technique used for sintered WC-Co and was necessitated by short crack growth in the out-of-plane direction of coating cross-sections. It has been also shown that carbide size distribution and cobalt content in the starting powders affect the resultant coatingís W₂C content and their in-plane fracture behavior. Furthermore, it has been shown that there is a correlation between the normalized abrasion rate of the coatings and a combined microstructure/mechanical property parameter which includes their in-plane crack length, mean carbide size and distribution, the binder mean free path and applied stress. In addition, it has been shown that the coefficient of friction of the coatings is independent of the carbide size for the test duration used in the study. This work highlights the influence of the anisotropic microstructure, lamellar and interlamellar strength, and non-equilibrium phases on the abrasion and friction behavior of thermal spray coatings. It is envisioned that this work will provide the framework for developments in coating reliability analysis and design.