THE EFFECT OF TUNGSTEN ON THE CORROSION BEHAVIOR OF AMORPHOUS FE-CR-W-P-C ALLOYS IN 1M HCL

The active current density of Fe-8Cr-7W-13P-7C alloy is almost three orders of magnitude lower than that of the Fe-8Cr-13P-7C alloy. The passive current density in the low potential region also decreases with increasing alloy tungsten content. The surface analysis by XPS reveals that chromium and tungsten ions are concentrated in the surface film on a tungsten containing alloy in the active region. The thickness of the surface film formed on the low tungsten alloy in the active region is x-ray photoelectron spectroscopically infinite, whereas the film thickness on the Fe-8Cr-7W-13P-7C alloy in the active region is of the same order of magnitude as the thickness of the passive film. The chromium enrichment in the passive film becomes more significant with increasing tungsten content. Passivation of low tungsten alloys seems to occur by the formation of the passive film with the least enrichment of chromium ions necessary for passivation due to different dissolution rates of iron and chromium during a large amount of alloy dissolution. Passivation of tungsten containing alloys takes place through transformation of the air-formed film to the passive film as a result of preferential dissolution of a small amount of iron without dissolution of chromium ions.