WEAR OF NITROGEN CERAMICS AND COMPOSITES IN CONTACT WITH BEARING STEEL UNDER OSCILLATING SLIDING CONDITION

The wear of nitrogen based ceramics in contact with bearing steel ball s (SAE 52100) was investigated under reciprocating sliding conditions at a velocity of 0.1 m/s, and 20 N, 40 N and 100 N load. Three types o f ceramics were studied: viz. hot pressed silicon nitride (:HPSN) sint ered with selected liquid in the system yttria-aluminium nitride-silic a and composites of HPSN with BN and TIG; SiAlON formulated with diffe rent amounts of alumina and silica; and alumina-titanium nitride compo site having 60mol% TIN. Among the HPSM composites, HPSN 15 vol% TiC ha d the lowest average wear factor (K) of 2.0 x 10(-5) mm(3)/m/N. The Si AlONs, in general, had the highest K and this increased with increasin g O concentration. The lowest K value for SiAlON ceramic was 6.9 x 10( -5) mm(3)/m/N. The high K value of SiAlON is attributed to O substitut ion, which promotes adhesive wear resulting in mutual material transfe r. The lowest wear of all the ceramics tested was found for the alumin a-titanium nitride composite, the wear factor being of the order of 4. 4 x 10(-7) mm(3)/m/N, which is one order of magnitude lower than the o ther nitrogen ceramics. In the case of HPSN and alumina-titanium nitri de composites, abrasive wear and wear due to microfracture were the ma in wear mechanisms. Wear of the steel ball was lowest when in contact with HPSN-TiC composites, being almost equal to that of the ceramic, w hereas the alumina-titanium nitride composite wore away the steel almo st 20 times faster than the ceramic and will thus be unsuitable as a c ounterface material for 52100 steel. (C) 1997 Elsevier Science Limited and Techna S.r.l.