Effects of chromium on the glass formation and corrosion behavior of bulk glassy Fe-Cr-Mo-C-B alloys

Bulk glassy Fe60-xCrxMo15C15B10 (x = 0, 7.5, 15, 22.5 and 30 at%) alloys with high thermal stability were synthesized and the effects of chromium on the glass formation and corrosion behavior were clarified. The maximum diameter for glass formation is 2-2.5 mm for the 7.5 and 15 at%Cr alloys and 1 mm for the other alloys. In the present glassy alloy system, the temperature interval of the supercooled liquid region (DeltaT(x)) changed with chromium and was enlarged from around 70 K at x = 0, 22.5 and 30 at% to over 80 K at x = 7.5 and 15 at%. Both corrosion rate and anodic current density by potentiodynamic polarization in HCl solutions decreased with an increase of chromium content in the alloys. For the Cr-free alloy, molybdenum was significantly concentrated in the surface film after immersion in 1N HCl solution. The bulk glassy alloys containing chromium was immune to corrosion by the formation of protective passive film enriched with chromium during immersion in the solution.