CORROSION STUDY OF AMORPHOUS METAL RIBBONS

Corrosion costs the Department of Defense billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial. The potential advantages of amorphous metals have been recognized for some time [Latanison 1985]. Iron-based corrosion-resistant, amorphous-metal coatings under development may prove important for maritime applications [Farmer et al. 2005]. Such materials could also be used to coat the entire outer surface of containers for the transportation and long-term storage of spent nuclear fuel, or to protect welds and heat affected zones, thereby preventing exposure to environments that might cause stress corrosion cracking [Farmer et al. 1991, 2000a, 2000b]. In the future, it may be possible to substitute such high-performance iron-based materials for more-expensive nickel-based alloys, thereby enabling cost savings in a wide variety of industrial applications. It should be noted that thermal-spray ceramic coatings have also been investigated for such applications [Haslam et al. 2005]. This report focuses on the corrosion resistance of iron-based melt-spun amorphous metal ribbons. Melt-Spun ribbon is made by rapid solidification--a stream of molten metal is dropped onto a spinning copper wheel, a process that enables the manufacture of amorphous metals which are unable to be manufactured by conventional cold or hot rolling techniques. The study of melt-spun ribbon allows quick evaluation of amorphous metals corrosion resistance. The melt-spun ribbons included in this study are DAR40, SAM7, and SAM8, SAM1X series, and SAM2X series. The SAM1X series ribbons have Ni additions in increments of 1, 3, 5, and 7 atom percent, to DAR40. For example, 1X7 means a composition of 7-atom% Ni added to 93-atom% of DAR40. Similarly, The SAM1X series ribbons have Mo additions in increments of 1, 3, 5, and 7 atom percent, to DAR40. For example, 2X3 means a composition of 3-atom% Mo added to 97-atom% of DAR40. SAM7 ribbon is a Fe-Cr-Mo-Y-C-B metal glass, commonly called Alloy1651. SAM8 is SAM7 with an additional 3-atom% W. The nominal compositions of DAR40 and SAM7 are listed in Table 1. SAM7 ribbon is extremely brittle and hard to manufactured by melt-spinning, only limited number of SAM7 ribbons were tested