High-Performance Corrosion-Resistant Iron-Based Amorphous Metals - The Effects of Composition, Structure and Environment: Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4

Several Fe-based amorphous metal formulations have been identified that appear to have corrosion resistance comparable to (or better than) that of Ni-based Alloy C-22 (UNS No. N06022), based on measurements of breakdown potential and corrosion rate in seawater. Both chromium (Cr) and molybdenum (Mo) provide corrosion resistance, boron (B) enables glass formation, and rare earths such as yttrium (Y) lower critical cooling rate (CCR). SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) has no yttrium, and is characterized by relatively high critical cooling rates of approximately 600 Kelvin per second. Data for the SAM2X5 formulation is reported here. In contrast to yttrium-containing iron-based amorphous metals, SAM2X5 can be readily gas atomized to produce spherical powders which enable more facile thermal spray deposition. The reference material, nickel-based Alloy C-22, is an outstanding corrosion-resistant engineering material. Even so, crevice corrosion has been observed with C-22 in hot sodium chloride environments without buffer or inhibitor. SAM2X5 also experiences crevice corrosion under sufficiently harsh conditions. Both Alloy C-22 and Type 316L stainless lose their resistance to corrosion during thermal spraying, due to the formation of deleterious intermetallic phases which depletes the matrix of key alloy elements, whereas SAM2X5 can be applied as coatings with the same corrosion resistance as a fully-dense completely amorphous melt-spun ribbon, provided that its amorphous nature is preserved during thermal spraying. The hardness of Type 316L Stainless Steel is approximately 150 VHN, that of Alloy C-22 is approximately 250 VHN, and that of HVOF SAM2X5 ranges from 1100-1300 VHN [MRS12-13]. Such hardness makes these materials particularly attractive for applications where corrosion-erosion and wear are also issues. Since SAM2X5 has high boron content, it can absorb neutrons efficiently, and may therefore find useful applications as a criticality control material within the nuclear industry