The Mechanical Properties of WC-CoFe Coating Sprayed by HVOF

HVOF thermal spray coating of 80%WC-CoFe powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and hard ceramics coating because of the environmental prob- lem of the very toxic Cr known as carcinogen by chrome plating and the brittleness of ceramics coatings. 80%WC-CoFe powder was coated by HVOF thermal spraying for the study of durability improvement of the high speed spindle such as air bearing spindle. The coating procedure was designed by the Taguchi program, includ- ing 4 parameters of hydrogen and oxygen flow rates, powder feed rate and spray distance. The surface proper- ties of the 80%WC-CoFe powder coating were investigated roughness, hardness and porosity. The optimal condition for thermal spray has been ensured by the relationship between the spary parameters and the hard- ness of the coatings. The optimal coating process obtained by Taguchi program is the process of oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min and spray distance 8 inch. The coating cross-sectional structure was observed scanning electron microscope before chemical etching. Estimation of coating porosity was performed using metallugical image analysis. The Friction and wear behaviors of HVOF WC-CoFe coating prepared by OCP are investigated by reciprocating sliding wear test at 25 C and 450 C. Fric- tion coefficients (FC) of coating decreases as sliding surface temperature increases from 25 C to 450 C. (Received October 31, 2011; Revised November 15, 2011; Accepted December 16, 2011)