Passive film growth mechanism of nanocrystalline 304 stainless steel prepared by magnetron sputtering and deep rolling techniques

The passive film growth mechanisms of deep rolled bulk nanocrystalline (BN) 304ss and magnetron sputtered nanocrystalline (NC) 304ss thin film as well as that of the conventional rolled coarse crystalline (CC) 304ss has been studied by electrochemical measurements and in situ AFM observation in 0.05 M H2SO4 + 0.2 M NaCl solution. The growth of the passive film on all three materials was three-dimensional and the growth rates were, in decreasing order: NC thin film > BN 304ss > CC 304ss. Also, nanocrystallization caused the nucleation mechanism of the passive film to change from progressive to instantaneous. The passive films on the CC 304ss and BN 304ss displayed a monolayer structure while that on the NC thin film had a multi-layered structure.