THE CORROSION BEHAVIOR OF AMORPHOUS FE-CR-MO-P-C AND FE-CR-W-P-C ALLOYS IN 6-M HCL SOLUTION

Polarization measurement shows that the additions of molybdenum and tungsten to amorphous Fe-8Cr-13P-7C and Fe-15Cr-13P-7C alloys significantly decrease the active dissolution current and passivation potential in 6 M HCl solution. XPS and electrochemical investigations reveal that molybdenum and tungsten prevent dissolution of chromium from the air-formed films during potentiostatic passivation, although small amounts of iron dissolve from the air-formed films and alloys. The tungsten addition is more effective than the molybdenum addition. This difference seems to result from the fact that molybdenum dissolves actively at low potentials in the active region of the alloys, while tungsten does not dissolve at potentials lower than 100 mV(SCE). When an excess amount of molybdenum or tungsten is added. the passivity becomes unstable and the passive film is less enriched in chromic ions, because of transpassive dissolution of molybdenum and tungsten.