Preparation and characterization of bulk amorphous and nanostructured iron-40 nickel-40 phosphorus-14 boron-6 alloys.

摘要

The reduced glass transition temperature of ferromagnetic Fe₄₀Ni ₄₀P₁₄B₆ alloy is 0.57 and it implies moderate glass formability. In the past thirty years this alloy system has been investigated extensively. By means of some novel methods, bulk amorphous and nanostructured Fe₄₀Ni₄₀P₁₄B₆ alloys had been prepared in our experiment and their properties had been studied in details.; By means of a rapid quenching technique, ferromagnetic bulk amorphous Fe₄₀Ni₄₀P₁₄B₆ alloy rods with a diameter of ∼1.2 mm were prepared. When a fluxing technique was also employed, amorphous rods with a diameter as large as ∼2.5 mm were synthesized. The corresponding critical cooling rate R_c for the glass formation Fe₄₀Ni₄₀P₁₄B₆, according to earlier reports, is estimated to be on the order of 102 K s −1. The measurements on the as-prepared specimens indicate that the thermal stability and magnetic properties of bulk Fe₄₀Ni ₄₀P₁₄B₆ amorphous rods prepared in our work are comparable to those obtained from thin Fe₄₀Ni₄₀P ₁₄B₆ glassy ribbons prepared at a cooling rate of 10 5 K s−1. Small differences between them can be explained by the reason that the atom arrangement of bulk Fe₄₀Ni ₄₀P₁₄B₆ amorphous specimens prepared at a cooling rate of ∼102 K s−1 in our work is closer to the ideal glass state than that of the specimens prepared by means of the melt-spinning technique.; It was pointed out that when a molten eutectic alloy is undercooled to a temperature T that is substantially below its liquidus T₁, it will undergo metastable liquid state spinodal decomposition (LSD) to become a system of intertwining liquid networks of wavelength λ. The larger undercooling will result in the smaller λ. When the undercooling is large enough, subsequent crystallization transforms the system into a nanostructure, characterised as bulk, pore-free, and of narrow grain-size distribution. Based on the above principles, bulk nanostructured Fe₄₀Ni₄₀P ₁₄B₆ alloy ingots of diameter 3 ∼ 5 mm had been synthesized in our experiment. The molten Fe₄₀Ni₄₀P₁₄B ₆ alloy was purified by means of the fluxing technique and thus a large undercooling could be achieved. For ΔT > 260 K, the microstructure of the undercooled specimen had exhibited LSD in the undercooled liquid state. The microstructure could be described as two intertwining networks with small grains dispersed in them. For ΔT > 290 K, the overall microstructure of the specimen changed into a granular morphology. The average grain sizes of the small and large grains are ∼30 nm and ∼80 nm, respectively.