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

The crystallization behavior of Zr65.0Al7.5Ni10.0Cu17.5 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-Zr2Cu precipitates was observed in the Zr65.0Al7.5Cu27.5 specimen, while microstructures consisting of finer nanocrystalline bct-Zr2Cu, fcc-Zr2Ni and Zr6Al2Ni formed in the Zr65.0Al7.5Ni10.0Cu17.5 specimen. The oxidation resistance of the melt-spun Zr65.0Al7.5Ni10.0Cu17.5 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-Zr2Cu, fcc-Zr2Ni and Zr6Al2Ni from the matrix resulted in an improvement of the oxidation resistance, whereas a relative coarse nanocrystalline phase consisting of bct-Zr2Cu exhibited fast oxidation along grain boundaries. Although the oxide species for both specimens were composed of a large amount of CuO/Cu2O, some tetragonal and monoclinic-ZrO2 as well as a minor amount of the oxide state of Cu3+, the amount of oxides especially for ZrO2 in the Zr65.0Al7.5Ni10.0Cu17.5 specimen was lower, which was probably due to suppressed oxygen diffusion in ZrO2.