Amorphous Alloy Powder: Comprehensive Analysis Of Composition, Production Technologies, And Advanced Applications In Magnetic And Structural Components

Fundamental Composition And Alloy Design Principles Of Amorphous Alloy Powder

Fe-Based Amorphous Alloy Powder: Compositional Frameworks And Glass-Forming Ability

Fe-based amorphous alloy powder constitutes the most widely investigated category due to its cost-effectiveness and excellent soft magnetic properties3613. The typical compositional formula is represented as Fe_a(Si_1-xB_x)_bC_c, where Fe content ranges from 76.0 to 81.0 at%, metalloid elements (Si, B, C) collectively occupy 16.0–22.0 at%, and minor additions of Cr (0.5–3.0 at%) and Mn (0.02–3.0 at%) enhance glass-forming ability and reduce magnetostriction614. Patent 3 discloses an optimized composition with 0<x<1, 76.0≤a≤81.0, 16.0≤b≤22.0, and 0<c≤5.0, achieving coercive force ≤4 Oe and oxygen content between 150–3000 ppm by mass, which balances magnetic softness with oxidation resistance6. The addition of Cr at 2.0–3.0 at% and Mn at 0.3–0.95 at% particularly promotes amorphization by suppressing heterogeneous nucleation and decreasing crystalline magnetic anisotropy6.

Alternative Fe-based formulations incorporate transition metals such as Mo, Cr, Co, and Ni to tailor magnetic saturation and thermal stability. Patent 4 describes a composition (B_aC_bSi_cMo_dCr_e)Fe_f with 4.50≤a+b+c≤8.25 wt%, 40.00≤d+e≤48 wt%, and f≥50 wt%, designed for high-temperature magnetic applications4. The synergistic effect of Mo and Cr elevates the crystallization temperature (T_x) above 450°C, enabling operation in thermally demanding environments813. Patent 16 further refines this approach by introducing Sn (0–3 at%) and adjusting P (6.8–10.8 at%), C (2.2–9.8 at%), and B (0–4.2 at%) to lower the glass transition temperature (T_g) while maintaining corrosion resistance and high saturation magnetization16.

Zr-Based And Ni-Based Amorphous Alloy Powder: Specialized Compositions For Structural And Functional Applications

Zr-based amorphous alloy powder, exemplified by ZrTiCuNiBe systems, exhibits exceptional glass-forming ability and mechanical strength, making it suitable for additive manufacturing and structural components1. Patent 1 reports surface-modified ZrTiCuNiBe powder with particle size distribution of 10–80 μm and surface roughness between 0.7–0.98, achieved through controlled ball milling under inert atmosphere followed by vacuum drying1. This surface modification enhances flowability—a critical parameter for laser powder bed fusion and directed energy deposition processes—by increasing inter-particle friction and reducing agglomeration1.

Ni-based amorphous alloys, such as Ni₆₀Fe₂₀P₁₆B₄ and compositions containing 40–60 at% (Nb, Ta) with balance Ni, are primarily employed in corrosion-resistant coatings and electromagnetic wave absorption applications91015. Patent 10 specifies flaky Ni-Cr-Mo-P-C-Fe powder with longitudinal/transversal dimensions of several tens to hundreds of micrometers and thickness ≤5 μm, optimized for anti-pitting corrosion, stress corrosion cracking, and hydrogen embrittlement resistance10. The high Cr content (5–25 at%) and Mo addition (0.3–5.0 at%) form a passive oxide layer that inhibits localized corrosion in aggressive chloride environments1015.

Metalloid Elements And Their Roles In Amorphization And Property Optimization

Metalloid elements—primarily P, B, C, and Si—serve as glass formers by disrupting long-range atomic ordering and stabilizing the supercooled liquid state. Phosphorus (P) at 8–13 at% significantly expands the supercooled liquid region (ΔT_x = T_x - T_g) to ≥20 K, facilitating powder consolidation via thermoplastic forming1316. Boron (B) at 8–13 at% reduces the melting point and enhances magnetic softness by minimizing magnetocrystalline anisotropy614. Carbon (C) at 1–3 at% improves wear resistance and hardness (Hv ≤1000) without compromising ductility613. Silicon (Si) at 10–14 at% increases electrical resistivity (ρ ≥1×10^-2 Ω·cm), thereby reducing eddy current losses in high-frequency magnetic cores61418.

The synergistic interaction between metalloids is critical: Patent 13 demonstrates that a Si-rich surface layer (formed during water atomization) acts as a diffusion barrier against oxygen ingress, maintaining oxygen content below 3000 ppm and preserving amorphous phase stability during subsequent heat treatment13. Patent 14 further reveals that heat-treating Fe-Si-B-C powder at 300–450°C for 0.5–2 hours under nitrogen atmosphere reduces coercivity to <398 A/m (5.0 Oe) while maintaining volume resistivity >1×10^-2 Ω·cm14.

Production Technologies And Microstructural Control Of Amorphous Alloy Powder

Gas Atomization: Process Parameters And Powder Morphology Optimization

Gas atomization remains the predominant method for producing spherical amorphous alloy powder with high amorphous content and controlled particle size distribution171920. The process involves melting the alloy in a crucible (typically induction-heated under inert atmosphere), ejecting the molten metal through a nozzle (orifice diameter 2–5 mm), and disintegrating the liquid stream using high-velocity inert gas jets (Ar or N₂ at 2–6 MPa)719. Patent 7 describes a gas-water hybrid atomization apparatus where molten metal naturally drops from the orifice into a chamber, is dispersed by atomizing gas, and subsequently cooled by water mist, achieving cooling rates of 10⁴–10⁶ K/s necessary for amorphization7.

Critical process parameters include:

• Gas-to-metal mass flow ratio (GMR): Increasing GMR from 2:1 to 6:1 reduces median particle diameter (D₅₀) from 80 μm to 15 μm and narrows size distribution1920. Patent 20 reports that GMR = 4.5:1 yields Fe-based powder with D₅₀ = 35 μm, amorphous content >95%, and oxygen content <0.15 wt%20.
• Melt superheat: Superheating 50–150°C above liquidus temperature decreases viscosity, promoting finer atomization and higher sphericity (>0.90)119. However, excessive superheat (>200°C) increases oxygen pickup and reduces amorphous fraction20.
• Atomization chamber atmosphere: Maintaining oxygen partial pressure <10 ppm prevents surface oxidation; Patent 1 specifies ball milling under Ar atmosphere (<5 ppm O₂) to preserve surface cleanliness for laser additive manufacturing1.

Powder morphology is quantified by aspect ratio (length/width) and sphericity. Patent 12 targets flaky powder with aspect ratio 5–10 for electromagnetic wave absorption, achieved by low-speed (12–14 hours) followed by high-speed (14–18 hours) ball milling, then drying at 260–340°C for 0.5–2 hours under N₂212. Conversely, spherical powder (aspect ratio <1.2) is preferred for dust cores and additive manufacturing, requiring optimized gas jet geometry and rapid solidification719.

Water Atomization And High-Speed Spinning Water Atomization: Advantages For Soft Magnetic Powder Production

Water atomization employs high-pressure water jets (5–15 MPa) to fragment molten metal, achieving cooling rates up to 10⁶ K/s—higher than gas atomization—thereby expanding the compositional range for amorphization613. Patent 6 states that water atomization of Fe-Cr-Mn-Si-B-C alloys produces powder with average particle diameter 3–100 μm, coercive force ≤4 Oe, and oxygen content 150–3000 ppm6. The rapid quenching suppresses crystallization even in alloys with marginal glass-forming ability, enabling cost-effective production of soft magnetic powder13.

High-speed spinning water atomization (HSSWA) combines centrifugal atomization with water quenching: molten metal is poured onto a rotating disk (5000–15000 rpm), ejected as ligaments, and immediately cooled by water jets13. This method yields flaky powder with thickness 1–10 μm and diameter 50–300 μm, ideal for dust cores with high packing density (>80%)1213. Patent 13 reports that HSSWA-produced Fe-Co-Ni-P-C-B-Si powder exhibits supercooled liquid temperature interval ΔT_x ≥20 K, hardness Hv ≤1000, and a Si-enriched surface layer that enhances oxidation resistance13.

Post-atomization treatments are essential to optimize magnetic properties:

• Passivation: Immersing powder in dilute phosphoric acid (0.1–0.5 wt%) or silane coupling agents forms a 5–20 nm oxide/silicate layer, reducing eddy current losses and improving insulation between particles19.
• Insulation coating: Applying epoxy resin, silicone, or phosphate coatings (0.5–2.0 wt% of powder mass) increases inter-particle resistivity to >10⁶ Ω·cm, critical for high-frequency applications1819.
• Stress-relief annealing: Heating at 300–450°C for 0.5–2 hours under vacuum or inert atmosphere relieves internal stresses from rapid solidification, reducing coercivity by 20–40%1419.

Solid-State Chemical Reduction And Electrolytic Deposition: Alternative Synthesis Routes

Patent 11 discloses a solid-state chemical reduction method where metal-bearing compounds (e.g., metal chlorides, oxides) are dispersed in a liquid medium (ethanol, water) and reduced using strong reducing agents (NaBH₄, LiAlH₄) at 20–80°C11. The resultant intimate mixture of reduced metals exhibits amorphous characteristics after heat treatment at 200–400°C for 1–4 hours11. This approach avoids the high-temperature melting required in atomization, enabling synthesis of thermally sensitive compositions and producing powder with particle size <10 μm suitable for nanocomposite applications11.

Electrolytic deposition, described in Patent 8, involves plating Fe-Co-P-W amorphous alloys from acidic baths containing phosphorous acid (H₃PO₃) and sodium tungstate (Na₂WO₄) at current densities of 10–50 mA/cm²8. The deposited alloy, with composition (Fe_1-aCo_a)_1-x-y-zP_xW_yM_z (0.9<a<1.0, 0.04<x<0.16, 0.005<y<0.05), exhibits crystallization temperature >450°C and saturation magnetization >1.5 T8. This method is advantageous for coating complex geometries and producing thin films, though powder yield is lower than atomization8.

Surface Modification Techniques For Enhanced Flowability And Additive Manufacturing Compatibility

Surface modification of amorphous alloy powder is crucial for laser additive manufacturing, where flowability (measured by Hall flow rate) and packing density directly impact layer uniformity and part density1. Patent 1 details a ball milling process under inert atmosphere (Ar, <5 ppm O₂) using zirconia media at ball-to-powder ratio 5:1, rotation speed 200–400 rpm, for 2–6 hours1. This treatment increases surface roughness from 0.3–0.5 to 0.7–0.98, improving inter-particle friction and reducing flowability time from >50 s to 25–35 s per 50 g (ASTM B213 standard)1. Subsequent vacuum drying at 80–120°C for 4–8 hours removes adsorbed moisture, preventing hydrogen porosity during laser melting1.

Alternative surface treatments include:

• Plasma spheroidization: Passing irregular powder through an Ar/He plasma torch (10–15 kW, 5000–8000 K) for 0.01–0.1 s melts surface asperities, yielding sphericity >0.95 and reducing satellite particles19.
• Chemical etching: Brief immersion (10–60 s) in HF/HNO₃ solution (1:3 vol ratio) removes surface oxides and contaminants, enhancing wettability for polymer-matrix composites10.

Magnetic Properties And Performance Optimization Of Amorphous Alloy Powder Cores

Coercivity, Permeability, And Core Loss: Fundamental Relationships And Measurement Standards

Coercivity (H_c) quantifies the resistance to demagnetization and is a primary indicator of soft magnetic performance. Fe-based amorphous alloy powder typically exhibits H_c = 1–5 Oe (80–398 A/m), significantly lower than crystalline Fe-Si alloys (H_c = 10–50 Oe)3612. Patent 6 specifies that H_c ≤4 Oe is achievable when Cr content is 2.0–3.0 at% and Mn content is 0.3–0.95 at%, attributed to reduced magnetocrystalline anisotropy and near-zero magnetostriction (λ_s <1×10^-6)6. Measurement follows ASTM A773/A773M using a DC hysteresis graph at maximum applied field H_max = 1000 A/m6.

Relative permeability (μ_r) at 10 kHz ranges from 20 to 120 for dust cores with 70–85% packing density, depending on insulation coating thickness and compaction pressure131619. Patent 16 reports μ_r =