Corrosion Resistance of Iron-Based Amorphous Metal Coatings

Abstract

New amorphous-metal thermal-spray coatings have been developed recently that may provide a viable coating option for spent nuclear fuel & high-level waste repositories [Pang et al. 2002; Shinimiya et al. 2005; Ponnambalam et al. 2004; Branagan et al. 2000–2004]. Some Fe-based amorphous-metal formulations have been found to have corrosion resistance comparable to that of high-performance alloys such as Ni-based Alloy C-22 [Farmer et al. 2004–2006]. These materials rely on Cr, Mo and W for enhanced corrosion resistance, while B is added to promote glass formation and Y is added to lower the critical cooling rate (CCR). Materials discussed in this paper include yttrium-containing SAM1651 with CCR ∼ 80 K/s and yttrium-free Formula 2C with CCR ∼ 600 K/s. While nickel-based Alloy C-22 and Type 316L stainless steel lose their resistance to corrosion during thermal spraying, Fe-based SAM1651 and Formula 2C amorphous-metal coatings can be applied with thermal spray processes without any significant loss of corrosion resistance. In the future, such corrosion-resistant thermal-spray coatings may enable the development of less expensive containers for spent nuclear fuel (SNF) and high-level waste (HLW), including enhanced multipurpose containers (MPCs), protected closure welds, and shields to protect containers from drips and falling rocks. These materials are extremely hard and provide enhanced resistance to abrasion and gouges from backfill operations. For example, Type 316L stainless steel has a hardness of approximately 150 VHN, Alloy C-22 has a hardness of approximately 250 VHN, while the Fe-based amorphous metals typically have hardness values of 1100–1300 VHN. Both Formula 2C and SAM1651 have high boron content which allow them to absorb neutrons, and therefore be used for enhanced criticality control. Cost savings can also be realized through the substitution of Fe-based alloy for Ni-based materials. Applications are also envisioned in oil & gas industry.

Criticality-Control Applications in the Nuclear Industry for Thermal Spray Amorphous Metal and Ceramic Coatings

“…One of the most promising formulations within this family was found to be Fe 49.7 Cr 17.7 Mn 1.9 Mo 7.4 W 1.6 B 15.2 C 3.8 Si 2.4 (SAM2X5), which included chromium (Cr), molybdenum (Mo), and tungsten (W) for enhanced corrosion resistance, and boron (B) to enable glass formation and neutron absorption [11][12][13][14][15] Figure 1. These new iron-based amorphous metals have exceptional neutron absorption characteristics, and are stable at high dose.…”

Corrosion Resistances of Iron-Based Amorphous Metals with Yttrium and Tungsten Additions in Hot Calcium Chloride Brine & Natural Seawater: Fe48Mo14Cr15Y2C15B6 and W-Containing Variants

“…Several Fe-based amorphous metal formulations have been found that appear to have very good corrosion resistance, based on measurements of the passive film breakdown potential, the corrosion rate and performance during salt fog testing [8][9][10]. These formulations use chromium (Cr), molybdenum (Mo), and tungsten (W) to provide corrosion resistance, boron (B) to enable glass formation, and yttrium to lower the critical cooling rate (CRR).…”

Applications in the Nuclear Industry for Corrosion-Resistant Amorphous-Metal Thermal-Spray Coatings

“…One of the most promising formulations within this family was found to be Fe 49. 7 Cr 17.7 Mn 1.9 Mo 7.4 W 1.6 B 15.2 C 3.8 Si 2.4 (SAM2X5), which included chromium (Cr), molybdenum (Mo), and tungsten (W) for enhanced corrosion resistance, and boron (B) to enable glass formation and neutron absorption [11][12][13][14][15]. The parent alloy for this series of amorphous alloys, which is known as SAM40 and represented by the formula Fe 52.3 Cr 19 Mn 2 Mo 2.5 W 1.7 B 16 C 4 Si 2.5 , has less molybdenum than SAM2X5 and was originally developed by Branagan [16][17].…”