Oxidation Behavior of Ca-Based Bulk Amorphous Materials

Abstract

In this study, the room-temperature oxidation behaviors of three Ca-based bulk amorphous alloys, Ca 65 Mg 15 Zn 20 , Ca 50 Mg 20 Cu 30 , and Ca 55 Mg 18 Zn 11 Cu 16 , were examined under normal flowing laboratory air and compared with the oxidation behaviors of these alloys in the crystalline form under identical conditions. The degree of oxidation for alloys in the amorphous and crystalline conditions was investigated by periodically measuring the mass change over the oxidation time. From the results of the oxidation mass change, and oxide thickness measurements obtained from scanning-electron-microscopy (SEM) studies, it was determined that the Ca 55 Mg 18 Zn 11 Cu 16 BMG possessed the most favorable oxidation resistance, followed closely by the Ca 50 Mg 20 Cu 30 BMG, with the Ca 65 Mg 15 Zn 20 BMG having the least favorable oxidation resistance. The trend in glass-forming abilities of the three compositions follows the same trend as the oxidation resistance in the three alloys. In all cases, the oxidation resistance of the amorphous alloys was superior to the oxidation resistance of the same alloys in the crystalline state.

Effect of Al Addition on Glass Forming Ability and Glass Stability of Ca-Mg-Zn-Cu Based Bulk Metallic Glasses

“…The ternary Ca-Mg-Zn and Ca-Mg-Cu glassy alloys also have marginal oxidation and corrosion resistance. [13][14][15] Quaternary Ca-Mg-Zn-Cu BMGs have better oxidation and corrosion resistance, which improves even further with addition of Al. [15] Partial substitution of Cu or Zn with Al also reduces the density of these alloys.…”

Development and Characterization of Low-Density Ca-Based Bulk Metallic Glasses: An Overview

“…Cu 16 , was examined under normal flowing laboratory air and compared with the oxidation behaviors of these alloys in crystalline form under identical conditions. [26] The dependences of net mass change due to oxide formation per unit surface area, W, on the oxidation time, t, are presented in Figures 9(a) through (c) for amorphous and crystalline specimens. For each alloy, oxidation occurs at a faster rate in the crystalline condition than in the amorphous condition.…”

“…[62] The results are shown in Figure 10. Ternary Ca-Mg-Zn and Ca-Mg-Cu BMGs experienced destructive corrosion reactions, resulting [26] in a net loss of mass from the samples due to spallation of the corrosion products. The weight loss of Ca 65 Mg 15 Zn 20 BMG occurred immediately after immersion in water, but the rate of the weight loss continuously decreased with time, reached a minimum after about 400 hours of holding, and then suddenly increased again, leading to a second cycle of corrosion that was similar to the first cycle; after~700 hours of holding in water, the sample lost about 65 pct of its mass (Figure 10(a)).…”

“…[11] While most Ca-based crystalline alloys oxidize in air in a matter of days, many Ca-based metallic glasses have improved oxidation resistance and retain shiny surfaces long after casting. [26] In the following sections, the composition and properties of Ca-based BMGs are described in more detail.…”

Development of Low Density Ca-Mg-Al-Based Bulk Metallic Glasses

“…The amorphous state considerably improves the oxidation and corrosion resistance of these alloys, although these properties also depend on the alloy constitution. [21][22][23] For example, recent studies of four Ca-Mg-Zn, Ca-Mg-Cu, Ca-Mg-Zn-Cu and Ca-Mg-Al-Zn-Cu metallic glasses have shown that the ternary Ca-Mg-Zn glass has the least oxidation and corrosion resistance. Substitution of Zn with Cu and/or Al improves these properties, and the alloy containing Al has the best corrosion resistance.…”