Beneficial effects of yttrium on the mechanical failure and chemical stability of the passive film of 304 stainless steel

Recent studies demonstrated that yttrium improved the resistance of stainle ss steel to corrosive wear. However, the mechanism responsible for the bene ficial effect of yttrium was not well understood. In this work, the breakdo wn of passive films of Y-free and Y-containing 304 stainless steel specimen s during indentation and scratch testing was studied using a micro-mechanic al probe. The failure of the passive films during indentation and scratch w as detected by measuring changes in the electrical contact resistance durin g the processes. The passive films of 304 steel formed in air and in a 35% nitric acid solution were also tested. It was demonstrated that the critica l load that caused failure of the passive film on Y-containing 304 stainles s steel was higher than that of Y-free 304 steel. Morphologies of indents a nd scratch tracks were observed using SEM. The surface mechanical propertie s of the materials were studied using a nano-mechanical probe. A scanning K elvin probe was used to evaluate the electron stability of the passive film s by measuring their electron work functions. All the experiments demonstra ted that yttrium. enhanced the mechanical failure resistance and chemical s tability of the passive film on 304 stainless steel. (C) 2001 Elsevier Scie nce B.V. All rights reserved.