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Description
Co-based amorphous alloys combine high strength, favorable magnetic properties and chemical stability. Co–Fe–Ta–B alloys show excellent glass-forming ability and a supercooled liquid region near 70 K [1], with compressive yield strength exceeding 5000 MPa [2]. Their potential is also enhanced by high magnetic permeability, nearly zero magnetostriction and coercivity as low as 0.25 A/m [3]. Giant magnetoimpedance and high corrosion resistance [4] make them promising for magnetic and structural applications.
This work compares the structural transformations of Co$_{43}$Fe$_{20}$Ta$_{5.5}$B$_{31.5}$ (at.%) and Co$_{43}$Fe$_{20}$W$_{5.5}$B$_{31.5}$ (at.%) powders induced by wet mechanical alloying in hexane for up to 100 h. Their evolution was examined by synchrotron high-energy X-ray diffraction, pair distribution function analysis, X-ray absorption spectroscopy and high-resolution transmission electron microscopy, complemented by room-temperature magnetic and thermomagnetic measurements.
Prolonged milling caused crystallite refinement, increasing structural disorder and progressive loss of long-range atomic correlations in both alloys, but their amorphization pathways differed markedly. The Ta-containing alloy transformed through intermediate nanocrystalline phases and became fully amorphous after 100 h. Replacing Ta with W prevented complete amorphization under identical processing conditions. The final W-containing powder instead consisted of an amorphous Co–Fe–B matrix with residual nanocrystalline bcc-W. Element-specific analysis revealed extensive atomic-scale mixing in the Ta-based material, whereas W retained a local coordination resembling crystalline bcc-W. This remaining crystalline fraction was associated with higher saturation magnetization and coercivity of the W-containing powder.
Wet mechanical alloying is therefore an effective route to amorphous Co–Fe–Ta–B powders, while W stabilizes a nanocomposite structure and suppresses glass formation. The results highlight the decisive role of elemental interactions in controlling amorphization kinetics and support the design of powder precursors for consolidation or additive manufacturing.
References
[1] Taghvaei, A.H.; Stoica, M.; Khoshkhoo, M.S.; Kaban, I.; Bednarčík, J.; Jóvári, P.; Janghorban, K.; Eckert, J. DSC, XRD and TEM characterization of glassy Co40Fe22Ta8B30 alloy with very high thermal stability. Mater. Lett. 2013, 93, 322–325.
[2] Shen, B.; Inoue, A. Enhancement of the fracture strength and glass-forming ability of CoFeTaB bulk glassy alloy. J. Phys. Condens. Matter 2005, 17, 5647–5653.
[3] Shen, B.; Pang, S.; Zhang, T.; Kimura, H.; Inoue, A. Corrosion properties of Co43Fe20Ta5.5B31.5 bulk glassy alloy. J. Alloy. Compd. 2008, 460, L11–L13.
[4] Nicula, R.; Stir, M.; Ishizaki, K.; Catalá-Civera, J.M.; Vaucher, S. Nanocrystallization of amorphous alloys using microwaves: In situtime-resolved synchrotron radiation studies. J. Phys. Conf. Ser. 2009, 144, 012109.
