Regardless of the application, the efficiency of friction joints depends on the mechanical properties (hardness, brittleness, elasticity), surface roughness and operation conditions (load, speed, presence of lubrication etc.). Piezoelectric engines operate as high-frequency friction actuators [1,2]. Tribological properties of rotary piezoelectric motors of standing wave were investigated. The test results show that the speed and friction torque of piezo actuator with WC-CO8 coating were lower on the same test conditions comparing to TiC15-CO6 coating. In both cases, a gradual increase in speed up to the maximum value can be explained by surface running-in phenomenon, which in many cases depends on the hardness ratio of contacting surfaces and the initial roughness. a)  b) Fig.2. Typical rotating speed curves using the rotors with WC-Co8 (a) and TiC15-Co6 (b) coatings.  Instability of the speed could be interpreted upon the presence on the coating surface caused by electro-sparking technology. Size of craters is similar to the counter body contact area. Therefore, the rotor surface was not always contacting equally with the surface of the counter body.