THE EROSION AND ABRASION CHARACTERISTICS OF ALUMINA COATINGS PLASMA-SPRAYED UNDER DIFFERENT SPRAYING CONDITIONS

A series of plasma sprayed alumina coatings was evaluated regarding th eir erosion and abrasion characteristics. The coatings were deposited under different spraying conditions, using a commercial axial injectio n plasma spray system, and with powders of different grit sizes and cr ystallinity. A sintered bulk alumina and a conventionally sprayed coat ing, produced by a radial injection air plasma spray technique, were t ested as reference materials. To evaluate the importance of energy inp ut the coatings were produced using two different torch nozzle sizes a nd gas mixtures with a varied amount of hydrogen. The erosion and abra sion results indicate that hydrogen concentration, nozzle size and pre cursor powder type and size influence the tribological characteristics of the coatings. The wear resistance of the coatings seems to benefit from an increase in hydrogen concentration or torch nozzle size. The effect of precursor powder size on the wear resistance was more comple x but indicates that sapphire powders of medium precursor sizes are ad vantageous to ordinary plasma spraying powders of alumina. (C) 1998 Pu blished by Elsevier Science Ltd. All rights reserved.