Abstract
We have examined heating-induced phase decomposition and its kinetics for Zr65Ni30Pd5 amorphous alloy in an argon atmosphere. The amorphous phase decomposes through three stages in the order of amorphous → icosahedral quasicrystal (I-Q) + amorphous → approximant cubic Zr2(Ni,Pd) → tetragonal Zr2Ni + tetragonal Zr2Pd phases. The approximant crystalline (APC) Zr2(Ni,Pd) phase includes icosahedral-like local atomic arrangements and the structural similarity between the I-Q and APC phases seems to enable the multistage phase decomposition through the precipitation of the APC phase. The primary precipitation of the I-Q phase from the amorphous phase occurs through nucleation and growth mechanisms through two-dimensional (2D) growth mode at lower heating rate and 3D growth mode at a high heating rate.
Highlights
The three transition metals Zr, Ni and Pd have high negative heats of mixing with hydrogen and the ternary Zr-Ni-Pd amorphous alloys are expected to exhibit a high hydrogen absorption ability.[1,2,3,4,5,6,7,8,9] On the other hand, the reactivity with oxygen for the ternary alloys is much larger for Zr, while that for Pd is negligible
Based on the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data, it is concluded that the crystallization of the Zr65Ni30Pd5 amorphous alloy occurs through the multistage process of amorphous → icosahedral quasicrystalline (I-Q) + amorphous → approximant crystalline (APC) Zr2Ni(Pd) → Zr2Ni + Zr2Pd
It is noticed that the metastable I-Q and APC cubic Zr2(Ni,Pd) phases precipitate only for the ternary amorphous alloy and this three-stage phase decomposition process is significantly different from the two-stage crystallization mode for binary Zr-Ni and Zr-Pd or even for the ternary Zr70Ni10Pd20 amorphous alloys
Summary
The three transition metals Zr, Ni and Pd have high negative heats of mixing with hydrogen and the ternary Zr-Ni-Pd amorphous alloys are expected to exhibit a high hydrogen absorption ability.[1,2,3,4,5,6,7,8,9] On the other hand, the reactivity with oxygen for the ternary alloys is much larger for Zr, while that for Pd is negligible. The addition of late transition metals (LTM) such as Fe, Co, Ni and Cu to Zr-Pd binary alloys is expected to enhance the amorphous forming ability through the multicomponent effect leading to the atomic size mismatches of Zr > Pd > LTM. The significant atomic size mismatches are thought to be effective for the increase in the thermal stability of metastable phases of amorphous and I-Q phases
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