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

摘要

The crystallization behavior of Zr_(65.0)Al_(7.5)Ni _(10.0)Cu_(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_(65.0)Al_(7.5)Cu_(27.5) specimen, while microstructures consisting of finer nanocrystalline bct-Zr_2Cu, fcc-Zr_2Ni and Zr_6Al_2Ni formed in the Zr _(65.0)Al_(7.5)Ni_(10.0)Cu_(17.5) specimen. The oxidation resistance of the melt-spun Zr_(65.0)Al_(7.5)Ni _(10.0)Cu_(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_(65.0)Al_(7.5)Ni_(10.0)Cu_(17.5) specimen was lower, which was probably due to suppressed oxygen diffusion in ZrO_2.