Effects of dichromate treatment on mechanical properties of passivated single crystal iron () and () surfaces

An in situ nanoindentation technique combined with an AFM was applied to evaluate the effects of dichromate treatment on the mechanical properties of the single crystal iron (1 0 0) and (1 1 0) surfaces passivated in pH 8.4 borate solution. The dichromate treatment was performed with natural immersion of the iron specimens in 5×10 ⁻² M K ₂Cr ₂O ₇ solution for 24 h prior to passivation at 0.25 V (SHE) for 1 h. The hardness, H and the works (elastic work, W _e, plastic work, W _p, and total work, W _t= W _e+ W _p) made during nanoindentation were obtained from the measured load–depth curves. The values of H and W _e/ W _t at the indentation depth larger than 30 nm for the passivated single crystal iron surfaces were increased by the dichromate treatment. The increases in H and W _e/ W _t due to the dichromate treatment were attributed to the promotion of repassivation at the sites of passive film ruptured during nanoindentation process.