engleski

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

We have synthesized Ti-Zr-Ni- and Ti-Hf-Ni-based quasicrystals by mechanical alloying of elementary powders with an average grain size of 35  m in a high-energy planetary ball mill. The XRD spectra indicate that the mixture was amorphous after alloying for more than 40 hours. Amorphous precursors after various times of mechanical alloying were subsequently analysed by means of DSC in order to obtain the kinetic parameters of crystallization, such as the temperature and activation energy of the crystallization. DSC was used in combination with XRD to identify the structural changes related to that peaks in DSC scans. The morphology and composition were analysed by SEM with an EDS probe. We observed agglomerates ranging in size from 5 to 50  m ; these agglomerates consisted of smaller particles with sub-micrometer diameters. The composition of the agglomerates was not homogenous, since small areas (~1 μ m) of Zr-rich secondary phase was 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 the heat treatment. The saturation magnetization (Ms) decreases fairly linearly, from the initial mixture of crystalline elements, which is ferromagnetic due to nickel, through to an amorphous phase, and then to the quasicrystalline phase, where the Ms value is the lowest. As a result, measuring the magnetic properties allows us to probe the structural transformations in the material.

amorphous materials ; quasicrystals ; amorphisation ; magnetic measurements ; X-ray spectroscopy

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