Solid-state amorphization of CoV crystalline intermetallic compound by mechanical milling

Abstract

The mechanical milling process of the intermetallic compound CoV was studied by X-ray diffraction, high-field magnetization measurements and subsequently by differential scanning calorimetry (DSC). It turns out that starting from ordered tetragonal CoV, mechanical milling generates atomic disorder during the early stage of milling and transforms the material to an amorphous state after continued milling. The magnetization at 4·2 K of CoV increases continuously with increasing milling time in the early stage of milling and it tends to become constant after continued milling. The results obtained by DSC analyses give detailed and precise information about the process of structural changes. In the DSC scans of CoV milled for various periods up to 20 h, exothermic heat effects corresponding to the atomic reordering process of the disordered compound and to the growth of small crystallites are observed. Starting from the sample milled for 40 h, an exothermic heat effect due to crystallization of the amorphous phase is detected. This effect develops rapidly upon further milling. After prolonged periods of milling, all physical parameters measured in the present investigation tend to become constant and amorphization is completed. Since, during heating of the ball-milled samples, the heat released in the atomic reordering and in the grain growth are comparable, it is concluded that both atomic disorder and grain boundaries are the important sources of energy storage during the ball-milling and eventually induce amorphization of crystalline CoV.