FORMATION OF QUASI-CRYSTALS IN BULK GLASS-FORMING ZR-CU-NI-AL ALLOYS

Zr65Cu17.5Ni10Al7.5 as well as Zr69.5Cu12Ni11Al7.5 belong to the best glass forming alloys known. Glass transition temperatures of melt-spun ribbons are 372 and 360 degrees C, respectively. TEM and x-ray analys is of samples annealed above the glass transition temperature exhibit the formation of quasicrystalline microstructures with small amounts o f crystalline phases. The metastable icosahedral phase is primitive wi th a quasilattice constant a=0.253 nm; its composition as determined b y EDX is close to Zr69.5Cu12Ni11Al7.5. In both glasses, growth of the quasicrystals has been observed to be time-dependent (r(proportional t o)t(1/2)), thus indicating a diffusion controlled transformation.