Formation and Thermal Stability of the Quasicrystalline Phase in Ti-Zr-Ni Alloys

초록

Most Ti-based quasicrystals are obtained by rapid quenching, suggesting that they are metastable. Ti-Zr-Ni alloys, however, are known to thermodynamically stable. To investigate the structural stability of quasicrystals formed by 3d-transition-metal alloys, we prepared samples of Ti33+xZr50-xNi17 made with 1) different atomic concentrations of Ti and Zr (x = 0, 5, 12, 17 and 22) and 2) various quenching rates from liquids. The existence of quasicrystal phases was examined by using X-ray diffraction (XRD) and was confirmed by obtaining a five-diffraction pattern, which is a forbidden symmetry in solid state physics. Our observations are as follows: 1) with increasing Ti concentration from 33 to 55 at.%, the quasilattice constants decreased from 5.29 angstrom to 5.15 angstrom, 2) the coherence length of the quasicrystals was estimated to 195 angstrom and 3) the quasicrystal phase readily formed over a wide range of concentrations (0 <= x <= 22 at.%). All our results suggest that the Ti-Zr-Ni quasicrystal phase is found in a wide range of compositions and can be obtained in a thermally stable state.

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