Devitrification of Fe-Based Amorphous Metal SAM 1651 and the Effect of Heat-Treatment on Corrosion Behavior

Abstract

Devitrification of amorphous alloys is a process in which thermodynamically preferable crystalline phases form from the metastable amorphous phase. The corrosion behavior of the crystalline phases and the remaining amorphous material is likely to be different from that of the fully amorphous material and could have detrimental effects on the corrosion resistance of the devitrified material. The effect of heat-treatment on the corrosion behavior of an Fe-based bulk metallic glass Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 ͓struc-tural amorphous metal ͑SAM͒ 1651͔ was examined, which revealed a degradation in the corrosion resistance of SAM 1651 upon annealing at 700°C. However, the partially devitrified material still exhibited good corrosion resistance even in the highly aggressive environments of 6 M HCl. The preferential corrosion sites of nanoscale in both fully amorphous and partially devitrified materials were identified with transmission electron microscope analysis. The corrosion resistance of both fully amorphous and partially devitrified materials was explained in terms of chemical and structural characteristics of the alloys.Bulk metallic glasses ͑BMGs͒ are an emerging class of alloys, which are of high interest due to their ability to be designed for special properties not attainable with crystalline alloys. While all metallic glasses do not necessarily have a high corrosion resistance, recent reviews document substantial progress for the development of corrosion-resistant BMG alloys. 1-3 Metallic glasses with interesting physical, mechanical, and corrosion properties have been studied for several decades. However, one of the challenges for fabricating amorphous alloys is that they typically require extremely high cooling rates to avoid crystallization on cooling. Significant advances to overcome this challenge have been made by alloy composition design. [4][5][6][7] Several Fe-based structural amorphous metal ͑SAM͒ compositions have been developed. [8][9][10][11][12][13][14][15][16][17][18] Farmer et al. reported an Fe-based BMG with a nominal composition of Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 ͑SAM 1651͒ having a high corrosion resistance in hot, concentrated calcium brine. 8 Shan et al. investigated the corrosion behavior of SAM 1651 and crystalline Ni-based alloy 22 in hot concentrated brine and showed that SAM 1651 was more corrosion resistant than alloy 22 at high oxidizing potentials. In concentrated brine, crevice corrosion was more difficult to initiate on SAM 1651, and once it initiated the corrosion current was sustained at a lower value than that of alloy 22. 11 Pang et al. developed an Y-free modified version of SAM 1651 with the composition of Fe 50−x Cr 16 Mo 16 C 18 B x ͑x = 4, 6, and 8 atom %͒ and measured the corrosion rate of these alloys in the range of 10 −3 -10 −2 mm year −1 in 1, 6, and 12 N HCl solutions at room temperature. The alloys did not suffer pitting corrosion even when polarized anodically in a 12 N HCl solution up to 1.0 V ͑Ag/AgCl͒. 12 The addition of P in the Fe-Cr-Mo-C-B system had a ...

Corrosion Resistance and Electrocatalytic Properties of Metallic Glasses

“…A comparison of passive current density I pass , corrosion/transpassivation potential E corr and corrosion rate CPR for some Fe-based metallic glasses and their crystalline alloy is summarized in Table 4 [69][70][71]. It can be observed from Table 4 that the corrosion/passive current density and corrosion rate increase for the crystalline alloys compared with metallic glass, while corrosion/transpassivation potential depends on their compositions.…”

“…BF-TEM micrographs of (a) fully amorphous, (b) devitrified SAM 1651 after immersion in 6 M HCl for different periods of time [69].…”

“…Long et al thought the galvanic effects between adjacent phases with different composition were resulted in the deterioration of corrosion resistance for Fe-Co-B-Si-Nb metallic glass [72]. A comparison of BF-TEM morphologies for amorphous and devitrified SAM 1651 [69] is shown in Figure 9. It indicates that the lacier morphologies for devitrified SAM 1651 mean the degradation in the corrosion resistance.…”

Devitrification of Fe-Based Amorphous Metal SAM 1651: A Structural and Compositional Study

“…A more detailed examination of the effect of the thermal treatment on the corrosion behavior of SAM 1651 is presented in a companion article. [23] The effect of the heat-treatment temperature on the corrosion resistance of SAM 1651 was also investigated, and the results showed that the extent of degradation increased with the heat-treatment temperature. The degradation of the corrosion resistance was attributed to nanosensitization.…”

“…A more complete study on the effects of devitrification on the corrosion behavior of SAM 1651 is presented in a companion article. [23] II. EXPERIMENTAL METHODS…”