Amorphous-to-quasicrystalline transformations in the Ti–Zr–Ni and Ti–Hf–Ni systems

Abstract

We have synthesized Ti–Zr–Ni- and Ti–Hf–Ni-based quasicrystals by the mechanical alloying of elementary powders with an average particle size of 35 μm in a high-energy planetary ball mill followed by a vacuum heat treatment. The X-ray diffraction (XRD) spectra indicate that the mixture was to a large extent amorphous after mechanically alloying for more than 40 h. These largely amorphous precursors, after various times of mechanical alloying, were subsequently analysed by means of differential scanning calorimetry (DSC) in order to obtain the kinetic parameters of crystallization, such as the temperature and the activation energy. DSC was used in combination with XRD to identify the structural changes related to the peaks in the DSC scans. The morphologies and compositions were analysed using scanning electron microscopy with an energy-dispersive spectrometer. We observed agglomerates ranging in size from 5 to 50 μm; these agglomerates consisted of smaller particles with sub-micrometer diameters. The composition of the agglomerates was not homogenous, since small areas (∼1 μm) of Zr-rich secondary phase were observed inside them. Using a vibrating-sample magnetometer (VSM) we found that the saturation magnetization decreases with mechanical treatment, and is additionally decreased with the time and temperature of a subsequent vacuum heat treatment. The saturation magnetization ( M s) decreases fairly linearly, from the initial mixture of crystalline elements, which is ferromagnetic due to nickel, through to a largely amorphous phase, and then to the quasicrystalline phase, where the M s value is the lowest. As a result, measuring the magnetic properties allows us to probe the structural transformations in the material.