A new 1/1 crystal approximant to the stable Ti-Zr-Ni icosahedral quasicrystal

We report here the discovery of a new bcc 1/1 crystal approximant (W-phase) to the stable icosahedral quasicrystal (i-phase) discovered recently in Ti-Zr-Ni alloys. As-cast Ti-Zr-Ni ingots, which originally contain only the Cl4 Laves and the hcp solid-solution phases, transform almost completely to the i-phase after annealing at 570 degrees C for 64h. Anneals at higher temperature (610 degrees C) lead to the formation of the bcc W-phase, with a(0) = 1.432nm. Preliminary X-ray diffraction studies indicate that the structure of the W-phase is similar to that of the Al-Mg-Zn Bergman phase, or the isostructural Al-Li-Cu R-phase, supporting a previous proposal that i-(Ti-Zr-Ni) is structurally different from i-(Ti-Cr-Si-O) or i-(Ti-Mn-Si-O), but similar to i-(Al-Li-Cu) or i-(Al-Mg-Zn).