Mechanically induced crystallization of an amorphous CoFeZrB alloy

Abstract

The short-time ͑12 h͒ ball milling of the amorphous Co 56 Fe 16 Zr 8 B 20 ͑at. %͒ alloy resulted in the formation of bcc-Fe nanocrystals embedded in an amorphous matrix. X-ray diffraction ͑XRD͒ using synchrotron radiation, differential scanning calorimetry ͑DSC͒, vibrating sample magnetometery ͑VSM͒, and the Faraday magnetic balance experiments were used to characterize the materials. XRD and DSC show that the fraction of crystallized bcc-Fe gradually increases with the milling time. The VSM measurements confirm the structure observations showing that the saturation magnetization increases with the milling time as the fraction of crystallized bcc-Fe increases. After 12 h of milling, the powder sample exhibited a Curie temperature of the amorphous phase T C am , which is approximately 55 K higher compared to the as-quenched ribbon ͑T C am = 601 K͒. Thermomagnetic measurements of heat-treated ribbons suggest that such an increase in T C am is not only due to temperature rises during the milling but may also be attributed to the combination of mechanical and thermal effects connected with the nature of milling.

Influence of cryomilling on structure of CoFeZrB alloy

“…In comparison with previous studies [4] it is seen that lowering of the milling temperature (case of cryomilling) retards the mechanically-induced crystallization. After 12 h of milling, the sample consists mostly of an amorphous component and a tiny fraction of bcc-Fe like phase.…”

“…The change of the crystallization behavior from single to two-stage and gradual vanishing of super-cooled liquid region also confirm strong impact of cryomilling on microstructure of CoFeZrB alloy. It should be noted here that similar milling done without additional cooling does not change the crystallization behavior and powders crystallize in one step [4]. Relatively steep decrease of the crystallization enthalpy together with disappearance of the super-cooled liquid region DT x during cryomilling may be related to the changes of amorphous phases, perhaps due to early stages of nanocrystallization.…”

“…X-ray diffraction experiments were performed in Debye-Scherrer geometry using monochromatic beam with energy of 100 keV (k = 0.12398 Å). All details regarding X-ray data treating can be found elsewhere [4]. The thermal stability of the samples was examined at a heating rate of 10 K/min by differential scanning calorimetry (DSC) using a NETZSCH DSC 404C.…”

“…high permeability in the frequency range up to 1 MHz [3]. In a previous work [4] we have shown that short-time BM of this alloy results in mechanically-induced crystallization. The present paper focuses on the role of the milling temperature and investigates the influence of cryomilling on the structure of the CoFeZrB metallic glass.…”

Influence of Plastic Deformation on Devitrification of Fe_{73.5}Nb_{3}Cu_{1}Si_{13.5}B_{9} Amorphous Alloy

“…This was conrmed by the examination of fracture surfaces [1,2] or by direct measurement of the temperature near the shear bands [3]. Intensive plastic deformation stored into the amorphous structure by long time milling tends to the partial or total crystallization of metallic glasses [4,5]. During milling the mechanical alloying processes can cause the change of chemical composition of the milled powder.…”