A NEW 1 1-CRYSTAL APPROXIMANT TO THE STABLE TI-ZR-NI ICOSAHEDRAL QUASI-CRYSTAL/

We report here the discovery of a new bcc 1/1 crystal approximant (W-p hase) to the stable icosahedral quasicrystal (i-phase) discovered rece ntly in Ti-Zr-Ni alloys. As-cast Ti-Zr-Ni ingots, which originally con tain only the Cl4 Laves and the hcp solid-solution phases, transform a lmost completely to the i-phase after annealing at 570 degrees C for 6 4h. Anneals at higher temperature (610 degrees C) lead to the formatio n of the bcc W-phase, with a(0) = 1.432nm. Preliminary X-ray diffracti on studies indicate that the structure of the W-phase is similar to th at of the Al-Mg-Zn Bergman phase, or the isostructural Al-Li-Cu R-phas e, supporting a previous proposal that i-(Ti-Zr-Ni) is structurally di fferent from i-(Ti-Cr-Si-O) or i-(Ti-Mn-Si-O), but similar to i-(Al-Li -Cu) or i-(Al-Mg-Zn).