Protective effect of yttrium additive in lubricants on corrosive wear

The effect of oxygen-active element, yttrium, as additive in commercial lubricants on corrosive wear resistance of Al alloy 6061 and stainless steel 304 was studied. By sliding wear tests in a corrosive environment, weight losses of the materials lubricated by oil and thin grease, respectively, with and without yttrium additive were measured. The lubricants were mixed with a small amount of 10% H2SO4 for the corrosive wear testing, and the wear testing was performed on a pin-on-disc tribometer with the capability of measuring wear in lubricant. The experimental results manifest that yttrium is beneficial to protection of the materials from corrosive wear. SEM analysis of worn surfaces shows that yttrium significantly diminished the corrosive wear. The increase of the resistance to corrosive wear by yttrium additive could be attributable to the fact that yttrium can enhance the surface passivation and promote the adherence of the protective oxide film developed during the corrosive wear process. A possible mechanism responsible for the protective effect of yttrium additive on corrosive wear is discussed. (C) 1999 Published by Elsevier Science S.A. All rights reserved.