Effect of Ni-addition on the crystallization behavior and the oxidation resistance of Zr-based metallic glasses below the crystallization temperature

Abstract

The crystallization behavior of Zr 65.0Al 7.5Ni 10.0Cu 17.5 metallic glasses by addition of Ni with 753 K annealing treatment and its effect on the oxidation resistance around the supercooled liquid region at 663 K were studied. By annealing at 753 K, the nanocrystalline phase of bct-Zr 2Cu precipitates was observed in the Zr 65.0Al 7.5Cu 27.5 specimen, while microstructures consisting of finer nanocrystalline bct-Zr 2Cu, fcc-Zr 2Ni and Zr 6Al 2Ni formed in the Zr 65.0Al 7.5Ni 10.0Cu 17.5 specimen. The oxidation resistance of the melt-spun Zr 65.0Al 7.5Ni 10.0Cu 17.5 specimen was improved by addition of Ni, which is evidenced by less mass gain and thin oxide scale. The microstructural refinement by the formation of numerous nanocrystalline phases of bct-Zr 2Cu, fcc-Zr 2Ni and Zr 6Al 2Ni from the matrix resulted in an improvement of the oxidation resistance, whereas a relative coarse nanocrystalline phase consisting of bct-Zr 2Cu exhibited fast oxidation along grain boundaries. Although the oxide species for both specimens were composed of a large amount of CuO/Cu 2O, some tetragonal and monoclinic-ZrO 2 as well as a minor amount of the oxide state of Cu 3+, the amount of oxides especially for ZrO 2 in the Zr 65.0Al 7.5Ni 10.0Cu 17.5 specimen was lower, which was probably due to suppressed oxygen diffusion in ZrO 2.