Dept. of Electrical Engineering, InHa University, Incheon 402-751, Korea (Received December 27, 2014; Revised February 21, 2015; Accepted February 23, 2015)Abstract − A magnetorheological (MR) fluid is a smart material whose rheological behavior can be controlledby varying the parameters of the applied magnetic field. Because the damping force and shear force of an MRfluid can be controlled using a magnetic field, it is widely employed in many industrial applications, such as invehicle vibration control, powertrains, high-precision grinding processes, valves, and seals. However, the char-acteristics of friction caused by iron particles inside the MR fluid need to be understood and improved so thatit can be used in practical applications. Surface process technologies such as polytetrafluoroethylene (PTFE)coatings and diamond-like carbon (DLC) coatings are widely used to improve the surface friction properties. Thisstudy examines the friction characteristics of an MR fluid with different surface process technologies such asPTFE coatings and DLC coatings, by using a reciprocating friction tester. The coefficients of friction are in thefollowing descending order: MR fluid without any coating, MR fluid with a DLC coating, and MR fluid witha PTFE coating. Scanning electron microscopy is used to observe the worn surfaces before and after the exper-iment. In addition, energy dispersive X-ray spectroscopy is used to analyze the chemical composition of the wornsurface. Through a comparison of the results, the friction characteristics of the MR fluid based on the differentcoating technologies are analyzed.Keywords − MR fluid(자기유변유체 ), friction characteristics(마찰특성), surface coating(표면코팅), DLC, PTFE,magnetic field(자기장)