On structural and thermal relaxation in non-crystalline Zr-Ni-Al alloys

The differences in the non-crystalline structures and thermal relaxation ph enomena of a planar flow-cast (rapidly quenched) and a water-cooled (slowly cooled) metallic glass and a planetary ball-milled (mechanically alloyed) amorphised alloy of the same nominal Zr-Ni-Al composition were studied the actual compositions being slightly different. The differential scanning cal orimetry and X-ray diffraction methods were used. It was found that short-r ange order is qualitatively similar in the bulk and ribbon samples, the for mer being better ordered within the first coordination shell. In the powder sample, the interatomic correlations decay more rapidly with increasing di stance than in the other two samples, pointing to a less ordered packing of basic structural units composed of nearest neighbours. Therefore, the powd er sample exhibits a different type of short-range order than the glassy sa mples. The observed structural relaxation phenomena in both glassy samples were entirely interpreted using the distribution of non-linear relaxation t imes model (DNLR). The thermal relaxation of amorphised powder consists of several independent processes, the traditional glass-like structural relaxa tion being the final stage only at the highest temperatures. (C) 2000 Elsev ier Science S.A. All rights reserved.