On the effect of cooling rate during melt spinning of FINEMET ribbons

Abstract

The effect of quenching wheel speed on the structure and Curie temperature of Fe73.5Si13.5B9Nb3Cu1 alloy has been investigated using X-ray diffraction, differential scanning calorimetry, transition electron microscopy and a SQUID magnetometer. Ribbons were melt-spun at different wheel speeds and then were annealed to nucleate nano crystals embedded in the amorphous matrix. The results indicated that the thickness of the ribbons was inversely proportional to the wheel speed following the power law of the type t∝V(s)(-1.231). DSC and XRD results showed that at higher wheel speeds the greater potential energy triggers the formation of Fe (Si) crystallites and thus, increases the crystallinity. TEM observations confirmed the presence of an α-Fe (Si) phase with ∼11 nm crystallite size in the amorphous matrix of annealed ribbons. Special emphasis was placed on the effect of the quenching wheel speed on the Curie temperature during the measurements. To this end, the magnetization variations versus temperature were studied before and after annealing. It was found that increasing the wheel speed results in the reduction of the Curie temperature in as-spun ribbons. Moreover, the Curie temperature of the intergranular amorphous region in the annealed ribbons was at least 80 °C higher than that of corresponding amorphous phase in as-spun ribbons due to exchange interaction penetration of the adjacent Fe (Si) crystallites and relaxation processes.

Microstructure Analysis and Thermoelectric Properties of Melt-Spun Bi-Sb-Te Compounds

“…As shown in Figure 1, increasing wheel rotation speed from 1000 rpm to 4000 rpm results in a decrease of the ribbon thickness from 17.8 μm to 3.38 μm. The thickness is inversely proportional with the wheel rotation speed, which is in good agreement with the previous reports [24,25], and the meltspun ribbon is composed of non-crystalline contact surface and crystalline free surface [20]. The nanostructure of the free surface also changes with the wheel rotation speed, as shown in Figure 2.…”

Amorphous alloys and differential scanning calorimetry (DSC)

“…As the heating rate increases, of course, the peak temperatures shift towards higher temperatures. The onset temperature of melting greatly increases above a heating rate of 1000 °C s -1 [98]. S. Pogatscher et al [98] determined the critical cooling rate required to reach the amorphous state from melt in the case of Au 49 Ag 5.5 Pd 2.3 Cu 26.9 Si 16.3 alloy using the fast scan DSC.…”

“…The onset temperature of melting greatly increases above a heating rate of 1000 °C s -1 [98]. S. Pogatscher et al [98] determined the critical cooling rate required to reach the amorphous state from melt in the case of Au 49 Ag 5.5 Pd 2.3 Cu 26.9 Si 16.3 alloy using the fast scan DSC. Due to the use of fast and ultra-fast DSC, it is possible to study several things that have not been done so far with the use of traditional DSC: J.Schawe et al [99] found that monotropic polymorphism exists in Au-based amorphous alloys, M.Gao et al [100] determined the delay time for primary crystallization of Al-based metallic glasses with poor glass formation ability.…”

Mechanism of Mechanically Induced Nanocrystallization of Amorphous FINEMET Ribbons During Milling

“…In the structure of sample milled for 45 minutes, the mean crystallite size is measured~9 nm. It is evident that the size of crystallites produced by mechanical milling is smaller than that of thermal annealing, [1] which might be the result of a fragmentation mechanism at high deformation levels. According to the SAED pattern, the main ring pattern is ascribed to Fe(Si) phase; however, some ring patterns representing the presence of small volume fraction of Fe 23 B 6 and Fe 3 B phases might be detected as well.…”

“…These properties originate from the heterogeneous structure consisting of nanocrystalline a-Fe(Si) grains embedded in an amorphous precursor produced by melt spinning. [1][2][3][4] Unfortunately, melt spinning ribbons are not suitable for applications where a large volume of soft magnetic materials with complex shapes is required. In contrast, Mechanical alloying can produce powders suitable for compaction and consolidation.…”