Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy
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INTRODUCTION
IN recent years, amorphous alloys that have large supercooled liquid regions before crystallization and high resistance against crystallization have been developed, and this has enabled the production of bulk amorphous alloys in the thickness range of 1 to 100 mm by using various casting processes.[1–4] These bulk amorphous alloys exhibit a number of useful properties, such as high mechanical strength, high hardness, and, for some compositions, high corrosion resistance.[2,5] In addition, Fe- and Co-based bulk amorphous alloys also show good soft magnetic properties which cannot be obtained from crystalline-type magnetic alloys.[2,5] The high boron content of the Fe-Cr-Mo-C-B–based amorphous alloys also makes them an effective neutron absorber and suitable for nuclear criticality control applications. These bulk amorphous alloys extend their possible applications and have attracted much attention as new materials in scientific and engineering fields. Recent reviews cover several classes of corrosion-resistant amorphous alloys.[6,7] Several Fe-based bulk amorphous alloys with X. SHAN, Senior Research Associate, H. HA, Graduate Student, and J.H. PAYER, Professor, are with the Materials Science and Engineering Department, Case Western Reserve University, Cleveland, OH 44106. Contact e-mail: [email protected] This article is based on a presentation given in the symposium entitled ‘‘Iron-Based Amorphous Metals: An Important Family of High-Performance Corrosion-Resistant Materials,’’ which occurred during the MSandT meeting, September 16–20, 2007, in Detroit, Michigan, under the auspices of The American Ceramics Society (ACerS), The Association for Iron and Steel Technology (AIST), ASM International, and TMS. Article published online November 18, 2008 1324—VOLUME 40A, JUNE 2009
high corrosion resistance have been reported.[7–11] Pang et al.[9,10] reported that Fe-Cr-Mo-C-B–based amorphous alloys had a corrosion rate of 10-3 to 10-2 mm/year in 1, 6, and 12 M HCl solutions at room temperature and did not suffer pitting corrosion even when the alloys were polarized anodically up to 1.0 V (Ag/AgCl) in 12 M HCl solution. Farmer et al. reported that one of the Fe-Cr-Mo-C-B–based amorphous alloy SAM1651 (Fe48Cr15Mo14B6C15Y2), also known as SAM7, showed much more resistance to corrosion in aggressive environments, such as 5 M CaCl2 at 105 C, than crystalline type 316L stainless steel and Ni-Cr-Mo-based alloy C-22.[12,13] Farmer et al. also reported that the corrosion resistance of Fe-based amorphous alloy SAM295 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8 Si2.4) was comparable to that of Ni-Cr-Mo–based crystalline alloy C-22 in natural seawater at 30 C and 90 C.[14] The bulk metallic glass exhibited thermal stability, and the corrosion resistance was maintained after prior exposure to temperatures up to the glass transition temperature (approximately 570 C).[14] The Fe-based amorphous alloys can be applied as thermal-spray coating. The results of standard salt-fog tests of ASTM B 117 showed that the amorphous alloy co
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