The influence of grain size and surface treatment on the tribofilm formation on alumina components

Ball-on-disc experiments have been performed in order to simulate the friction behaviour of, and tribofilm formation on the alumina friction drive system of an ultrasonic motor. The coefficient of friction between the counter surfaces of the friction drive system is important since the driving force of the motor is limited to the available maximum friction force. The experiments have been performed with alumina balls against alumina discs with different surface treatments and grain sizes. The tribofilm formation depends on the amount and size of particles generated during wear. Surface treatment by grit blasting contributes to the formation of more extensive and thicker tribofilm. The coefficient of friction showed to be substantially higher and more fluctuating with grit blasted surfaces than with the other types. There was no tribofilm formation on top of the ground surfaces, however the level of the coefficient of friction was about the same as on the as-sintered surfaces with tribofilm, irrespectively of grain size.