Insight into the Formation of Ultrafine Nanostructures in Bulk Amorphous Zr_(54.5)Ti_(7.5)Al_(10)Cu_(20)Ni_8

摘要

Bulk amorphous Zr_(54.5)Ti_(7.5)Al_(10)Cu_(20)Ni_8 is investigated by means of small-angle neutron scattering (SANS), differential-scanning calorimetry (DSC), high-resolution electron microscopy (HREM) and other methods. The formation of ultrafine nanostructures in the glassy phase is observed and explained by a new model. Structural fluctuations of randomly distributed partially ordered domains grow during annealing just below the glass transition temperature by local re-ordering. During annealing the DSC gives evidence for a increasing volume fraction of the locally ordered domains. At high volume fractions of impinging domains a percolation threshold on the interconnected domain boundaries occurs and enhanced diffusion becomes possible. At that stage SANS measurements lead to statistically significant scattering data. The SANS signals are analyzed in terms of a model taking into account spherical particles surrounded by diffusion zones and interparticle interference effects. The mean radius of the nanocrystalline particles is determined to 1nm and the mean thickness of the depletion zone is 2nm. The upper limit for the volume fraction after annealing at 653K for 4 hours is about 20%. Electron microscopy confirms the size and shows that the particle are crystalline.