THE EFFECT OF ELECTROLESS NICKEL FILM ON THE TRIBOLOGICAL CHARACTERISTICS OF ALUMINA COATINGS

Extensive research has been done to examine the differences in tribolo gical behavior of alumina coatings with and without electroless nickel film as underlayer. Dry sliding wear tests were carried out using the thrust-on-washer adapter on a wear test machine. An ECR (electrical c ontact resistance) device was mounted on this machine to allow researc hers to evaluate the wear life of the alumina coating on the lower spe cimen from observation of the abrupt drop in electrical voltage that m ay occur when the maximum depth of the wear track is greater than the thickness of the alumina coating. Both the WC +Co coating of the upper specimen and the alumina coating of the lower specimen were prepared by plasma spraying. The investigation aims to gain a better understand ing of the effect of electroless nickel film deposited as the underlay er of the lower specimen on its adhesion strength with the steel subst rate and the wear life of the alumina coating. The experimental result s reveal that the deposition of the electroless nickel film has a nota ble effect on the wear life and adhesion strength. The wear life of sp ecimens with an electroless nickel film is much longer than that of sp ecimens without it, unless the alumina layer is thinner than 0.3 mm. T he adhesion strength between the underlayer and the steel substrate is attenuated by plating an excessively thick or a very thin electroless nickel film. The deposition of the electroless nickel him impeded the oxidation of the steel substrate and the third body wear in dry slidi ng. The specimen temperatures measured at the steel substrate of the l ower specimen, irrespective of the application of the electroless nick el film, can be fitted well by the power form of the friction power pa rameter. (C) 1997 Elsevier Science S.A.