Gas Atomization of Nanocrystalline Fe₆₃Nb₁₀Al₄Si₃B₂₀ Alloy

Abstract

Powder of Fe 63 Nb 10 Al 4 Si 3 B 20 (%at) alloy was processed by gas atomization to investigate the formation of novel microstructures due to the high cooling rates involved in this process. The ratio between the gas volumetric flow rate and the metal mass flow rate used was 0.23, and nitrogen was used as the atomization gas. The powder, with a median particle diameter about 120µm, was sieved in the granulometric size ranges of 5-20, 20-30, 30-45, 45-75, 75-106, 106-150, 150-180, >180µm, and then were characterized by X-ray diffratometry (XRD), differential scanning calorimetry (DSC), scanning and transmission electron microscopy (SEM and TEM, respectively) both equipped with energy dispersive spectroscopy (EDS). Powder in the range of 5-45µm contain α-Fe nanocrystals embedded in an amorphous matrix. In the size range of 45-150µm, the powder contains, besides α-Fe nanocrystals embedded in an amorphous matrix, particles of FeB and Fe 23 B 6 intermetallic phases. For the size range > 150µm, the powder showed particles with Fe-α nanocrystals embedded in an amorphous matrix and partially crystalline particles with Fe-α, FeNbB and FeB phases. The volume fraction of the amorphous phase decreased with the increase of the granulometric size range. The nanocrystallization of the powder in the smaller size ranges opens the possibility for the production of a bulk nanocrystalline deposit produced by spray forming and its application as a soft ferromagnet.

In-situ crystallization of amorphous Fe73−xNbxAl4Si3B20 alloys through synchrotron radiation

“…Crystallization sequence is: (first peak) a-Fe nanocrystals (12 nm) embedded in an amorphous matrix; (second peak) a-Fe nanocrystals + Fe 23 B 6 phase; (third peak) a-Fe nanocrystals + FeNbB phase; (fourth peak) a-Fe + FeNbB + FeB phases. Same phases have been already identified for the same alloy composition processed by gas atomization [17]. Addition of 10% Nb instead of 5% Nb modifies significantly the crystallization sequence of Fe 73Àx Nb x Al 4 Si 3 B 20 (x = 5, 10) alloys.…”

“…Fe 63 Nb 10 Al 4 Si 3 B 20 alloy showed soft magnetic properties of B s , H c and l max such as 0.58 and 0.77 T, 11.0 and 7.0 A/m and 6000 and 11 000, respectively. As Fe 63 Nb 10 Al 4 Si 3 B 20 alloy presents nanocrystallization phenomenon, the annealing of the sample in first crystallization peak temperature improved soft magnetic properties of the alloy, due to the formation of a microstructure composed by a fine dispersion of nanocrystals of primary a-Fe phase embedded in an amorphous matrix [17][18][19]. The mechanism, which provides that improvement, relies on formation of magnetic exchange coupled pairs between grains of a-Fe and the remaining amorphous phase in the matrix.…”

Two Fe-Zr-B-Cu Nanocrystalline Magnetic Alloys Produced by Mechanical Alloying Technique

“…Thus, MA powders have more specific surfaces and irregular shaped particles than atomised particles of a similar radius. Gas atomisation favours the formation of the amorphous phase, however, if a high dispersion of particle sizes is produced, depending on the particle size, the structure can be amorphous or a mixture of amorphous and nanocrystalline [18]. With this technique, contamination from the MA milling tools is avoided.…”