<title>Iron oxide films in tribological surfaces of alloy steel</title>

Abstract

The formation of iron oxide films and their roles in determining the dry wear properties of low alloy steel couples are described. Essentially, alpha-Fe<SUB>2</SUB>O<SUB>3</SUB>, haematites (Fe<SUB>3</SUB>O<SUB>4</SUB>), wustite (FeO) and oxide mixtures were the predominant compositions found in four regions of mild oxidational wear. The oxides were initially formed during subsequent rubbing and removal of material from the surfaces where oxidation, nucleation and agglomeration processes took place, followed by plastic deformation and work-hardening of underlying layers which supported the films. These films were found to be protective against wear; stable film of Fe<SUB>3</SUB>O<SUB>4</SUB> reduced wear rate down to as low as 10<SUP>-13</SUP> m<SUP>3</SUP>m<SUP>-1</SUP>, while loose particles of FeO maintained wear rate greater than 10<SUP>-12</SUP> m<SUP>3</SUP>m<SUP>-1</SUP>. The wear protective nature of (alpha) -Fe<SUB>2</SUB>O<SUB>3</SUB> and mixed films were found to lie between these extreme limits. Hence, the role of oxide films, in particular Fe<SUB>3</SUB>O<SUB>4</SUB>, is very significant in minimizing the wear and friction of alloy steel.