AN ATOM-PROBE STUDY OF PASSIVATED SURFACE OF A STAINLESS STEEL

The compositions of the passive film formed on stainless steel and the metallic phase below the film was analyzed by an atom-probe. FIM tips were prepared from a cold-worked type 316 stainless steel wire and field evaporated to obtain the clean surface. Then the tip was exposed to atomosphere and treated with nitric acid to form the passive film on the surface. The analysis shows that the passive film formed is at most 4 monolayers thick and consists mainly of Cr-compound. The alloying elements Cr and Ni are enriched in the film. As the passivation time becomes longer, the Cr enrichment tends to progress. It is shown that Mo is enriched at the film-metal interface.