Effect of crystallization behavior on the oxidation resistance of a Zr–Al–Cu metallic glass below the crystallization temperature

The crystallization behavior of Zr_65.0Al_7.5Cu_27.5 (at.%) metallic glass with 753 and 1053 K annealing treatment and its effect on oxidation resistance around the supercooled liquid region at 623 and 663 K was studied. The crystalline phase of bct-Zr₂Cu precipitates for the specimen annealed at 753 K was observed, while duplex structures of bct-Zr₂Cu and Zr₂Al formed in the specimen annealed at 1053 K. The oxidation resistance of the specimen depended on the amount of crystalline precipitates. Regardless of the exposure temperature, the annealed specimens showed higher oxidation resistance than the melt-spun one, especially for the specimen annealed at 1053 K. The formation of numerous crystalline phases of bct-Zr₂Cu and Zr₂Al from the matrix was responsible for improving the oxidation resistance due to their higher oxidation resistance and promotion of the development of Al₂O₃ and oxides of copper. The oxide constituents of the amorphous alloy after long exposure depended on the temperature. The oxide was composed of a large amount of CuO, some tetragonal and monoclinic-ZrO₂ and a minor amount of Cu₂O as well as a slight amount of Al₂O₃ for the melt-spun specimen during exposure at 623 K. Under the 663 K exposure, however, the oxide state of Cu³⁺ in the scale was also detected.