Co-based Glassy Alloys Research Articles

Formation and ultrahigh mechanical strength of multicomponent Co-based bulk glassy alloys

A glassy phase with glass transition (GT) was formed in a wide B content range of 12–31 at% for (Co0.75Cr0.125Mo0.125)100-xBx alloys. The appearance of GT at the low metalloid content of 12%B among Co-, Fe- and Ni-based alloys is the first, in contrast to the absence of GT for (Fe0.75Cr0.125Mo0.125)88B12 and (Ni0.75Cr0.125Mo0.125)88B12 alloys. The Co-based 12%B glassy alloy crystallized through unique three stages, i.e., glass (G) → [G + hcp + fcc] → [G + fcc] → [fcc + M23B6]. The appearance of GT is due to the necessity of long-range rearrangement of constituent elements for the simultaneous precipitation of hcp and fcc phases from glassy phase. The glass transition temperature, crystallization temperature, Vickers hardness (Hv) and Young's modulus for the Co-based glassy alloys increase linearly with increasing B content and reach 904 K, 946 K, 1566 and 188 GPa, respectively, at 31%B. The good bending plasticity is retained up to 29%B. The crystallization of the 27–29%B alloy occurs through G → [G + M23B6] → [M23B6 + M2B] and the ultrahigh Hv above 2000 is attained for the metastable [G + M23B6] phase state. The glassy alloy rod with a diameter of 1 mm was prepared for the 27%B alloy and exhibited ultrahigh yield strength of 4700 MPa, plastic strain of 1% and high oxidation resistance up to about 1200 K. The Co-based bulk glassy alloy with simultaneously high strength, ultrahigh hardness and high oxidation resistance, is promising for the future high hardness and heat-resistance materials.

Crystallization kinetics of Co40Fe22Ta8B30 glassy alloy with high thermal stability and soft magnetic properties

In this paper, the thermal stability, the crystallization kinetics and magnetic properties of the melt-spun Co40Fe22Ta8B30 glassy alloy were investigated. The results show that the present alloy has a wide supercooled liquid region of 74K and a high incubation time prior to crystallization upon isothermal annealing above the glass transition temperature compared to the well-known Co43Fe20Ta5.5B31.5 glassy alloy. The crystallization kinetics was systematically investigated by the Kissinger, Ozawa and isoconversional approaches under the isochronal condition, and Johnson–Mehl–Avrami (JMA) model under the isothermal situation, respectively. It was found that the Co40Fe22Ta8B30 metallic glass indicated an apparent activation energy of 520±5kJ/mol corresponding to the first crystallization event, which is higher than many other Fe-based and Co-based glassy alloys. The Avrami exponent calculated based on the JMA approach lies in the range of 2.13–1.58 for different isothermal annealing temperatures, revealing that the crystallization is governed by the three-dimensional diffusion-controlled growth with a decreasing nucleation rate. In addition, Co40Fe22Ta8B30 metallic glass exhibits good soft magnetic properties, i.e. a very low coercivity of 0.8A/m and a magnetization of 42Am2/kg. The influence of the devitrification on the evolution of the coercivity, magnetization and thermomagnetic behavior of Co40Fe22Ta8B30 glassy alloy was investigated.

Effect of Nb Addition on the Glass-Forming Ability, Soft-Magnetic Properties and Mechanical Properties of CoFeNiBSiNb Bulk Glassy Alloys

The effect of Nb addition on the glass-forming ability (GFA), soft-magnetic properties and mechanical properties of [(Co0.65Fe0.35)0.9Ni0.1]73-xB21.9Si5.1Nbx(x=36) alloy system were investigated. The results showed that by adjusting the content of Nb, the thermal stability of the supercooled liquid and the GFA increased effectively. With increasing the amount of Nb, the supercooled liquid region (ΔTx) increased from 45 to 65 K and the reduced glass transition temperature (Trg=Tg/Tl) was located in the range of 0.5840.644. As a result, the [(Co0.65Fe0.35)0.9Ni0.1]73-xB21.9Si5.1Nbx bulk glassy alloys (BGAs) with diameters up to 5.0 mm were produced by copper mold casting. In addition to the high GFA, the Co-based glassy alloys exhibited excellent soft-magnetic properties, i.e., saturation magnetization of 0.530.81 T, low coercive force of 0.511.75 A/m, and high effective permeability of (1.522.53)×104 at 1 kHz under a field of 1 A/m. Besides, the Co-based BGAs also exhibited super high fracture strength of 42704490 MPa and vickers hardness of 11271182.

(Co1−xFex)68B21.9Si5.1Nb5 bulk glassy alloys with high glass-forming ability, excellent soft-magnetic properties and superhigh fracture strength

The glass-forming ability (GFA), soft-magnetic properties and mechanical properties of (Co1−xFex)68B21.9Si5.1Nb5 (x = 0.1–0.5) glassy alloys were investigated. The (Co1−xFex)68B21.9Si5.1Nb5 glassy alloys exhibit a wide supercooled liquid region of over 40 K, and high reduced glass transition temperatures between 0.603 and 0.648. As a result, the (Co1−xFex)68B21.9Si5.1Nb5 bulk glassy alloys (BGAs) with diameters up to 5.5 mm were produced by copper mold casting. In addition to high GFA, this Co-based glassy alloys exhibit excellent soft-magnetic properties, i.e., saturation magnetization of 0.49–0.91 T, low coercive force of 0.71–1.58 A/m, and high effective permeability of (2.21–3.25) × 104 at 1 kHz under a field of 1 A/m. Besides, this Co-based BGAs also exhibit superhigh fracture strength of 4250–4450 MPa and plastic strain of 0.6–1.3%.

Effects of B and Si contents on glass-forming ability and soft-magnetic properties in (Co0.89Fe0.057Nb0.053)100−x(B0.8Si0.2)x glassy alloys

The effects of B and Si contents on the glass-forming ability (GFA) and soft-magnetic properties of (Co0.89Fe0.057Nb0.053)100−x(B0.8Si0.2)x (x=22–30) alloys were investigated. The thermal stability of the supercooled liquid increased with increasing the B and Si contents from x=24 to 28, and accompanying the decreases of liquidus temperature of alloys. As a result, The (Co0.89Fe0.057Nb0.053)100−x(B0.8Si0.2)x bulk glassy alloys with diameters up to 3.5 mm were synthesized in the composition range of x=24–28. In addition to high GFA, the Co-based glassy alloys exhibit excellent soft-magnetic properties as well, i.e., moderate saturation magnetization of 0.51–0.72 T, low coercive force of 0.4–1.5 A/m, and high initial permeability of 22 340–29 570 at 1 kHz under a field of 1 A/m.

Effect of B to Si concentration ratio on glass-forming ability and soft-magnetic properties in (Co0.705Fe0.045B0.25−xSix)96Nb4 glassy alloys

The effect of B to Si concentration ratio on the glass-forming ability (GFA) and soft-magnetic properties of (Co0.705Fe0.045B0.25−xSix)96Nb4 (x=0.02–0.1) alloys was investigated. The (Co0.705Fe0.045B0.25−xSix)96Nb4 bulk glassy alloys with diameters up to 2mm were synthesized in the composition range of x=0.02–0.06. In addition to high GFA, the Co-based glassy alloys exhibit excellent soft-magnetic properties as well, i.e., rather high saturation magnetization of 0.62T, low coercive force of 0.6–1A∕m, and superhigh initial permeabilities of 37 100–53 700 at 1kHz under a field of 1A∕m. The alloys with Si contents of x=0.05 and 0.06 exhibit high initial permeabilities of 29 300 and 24 300, respectively, even at 100kHz.

Formation, Mechanical and Magnetic Properties of (Fe,Co)-B-Si-Nb Bulk Glassy Alloys

Fe- and Co-based bulk glassy alloys (BGAs) with diameters up to 5 and 4 mm were formed respectively in (Fe,Co)-B-Si-Nb system by copper mold casting. The Fe-based glassy alloys in [(Fe1-xCox)0.75B0.2Si0.05]96Nb4 system exhibit saturation magnetization (Is) of 0.84-1.13 T and low coercive force (Hc) of 1.5-2.7 A/m. Its BGAs exhibit superhigh strength ( σ f) of 3900-4250 MPa, Young’s modulus (E) of 190-210 GPa, elastic strain (εe) of 0.02 and plastic strain (εp) of 0.0025. For the Co-based glassy alloys in [(Co1-xFex)0.75B0.2Si0.05]96Nb4 system, in addition to superhigh σ f of 3980-4170 MPa, they also exhibit excellent soft magnetic properties, i.e., Is of 0.71-0.97 T, Hc of 0.7-1.8 A/m, high effective permeability (μe) of 1.48-3.25×104 at 1 kHz under a field of 1 A/m, and extremely low saturation magnetostriction (λs) of 0.55-5.76×10-6.

Syntheses and Applications of Fe-, Co-, Ni- and Cu-Based Bulk Glassy Alloys

This paper reviews our recent results of the formation, fundamental properties, workability and applications of late transition metal (LTM) base bulk glassy alloys (BGAs) developed since 1995. The BGAs were obtained in Fe-(Al,Ga)-(P,C,B,Si), Fe-(Cr,Mo)-(C,B), Fe-(Zr,Hf,Nb,Ta)-B, Fe-Ln-B(Ln=lanthanide metal), Fe-B-Si-Nb and Fe-Nd-Al for Fe-based alloys, Co-(Ta,Mo)-B and Co-B-Si-Nb for Co-based alloys, Ni-Nb-(Ti,Zr)-(Co,Ni) for Ni-based alloys, and Cu-Ti-(Zr,Hf), Cu-Al-(Zr,Hf), Cu-Ti-(Zr,Hf)-(Ni,Co) and Cu-Al-(Zr,Hf)-(Ag,Pd) for Cu-based alloys. These BGAs exhibit useful properties of high mechanical strength, large elastic elongation and high corrosion resistance. In addition, Fe- and Co-based glassy alloys have good soft magnetic properties which cannot be obtained for amorphous and crystalline type magnetic alloys. The Feand Ni-based BGAs have already been used in some application fields. These LTM base BGAs are promising as new metallic engineering materials.

Fabrication, properties and applications of bulk glassy alloys in late transition metal-based systems

This paper reviews our recent results of the formation, fundamental properties, workability and applications of late transition metal (LTM)-based bulk glassy alloys (BGAs) developed since 1995. The BGAs were obtained in Fe–(Al,Ga)–(P,C,B,Si), Fe–(Cr,Mo)–(C,B), Fe–(Zr,Hf,Nb,Ta)–B, Fe–Ln–B (Ln = lanthanide metal), Fe–B–Si–Nb and Fe–Nd–Al for Fe-based alloys, Co–(Ta,Mo)–B and Co–B–Si–Nb for Co-based alloys, Ni–Nb–(Ti,Zr)–(Co,Ni) for Ni-based alloys, and Cu–Ti–(Zr,Hf), Cu–Al–(Zr,Hf), Cu–Ti–(Zr,Hf)–(Ni,Co) and Cu–Al–(Zr,Hf)–(Ag,Pd) for Cu-based alloys. These BGAs exhibit useful properties of high mechanical strength, large elastic elongation and high corrosion resistance. In addition, Fe- and Co-based glassy alloys have good soft magnetic properties which cannot be obtained for amorphous and crystalline type magnetic alloys. The Fe- and Ni-based BGAs have already been used in some application fields. These LTM-based BGAs are promising as new metallic engineering materials.

Enhancement of the fracture strength and glass-forming ability of CoFeTaB bulk glassyalloy

Co43Fe20Ta5.5B31.5 bulk glassy alloy has the best glass-forming ability (GFA) among the Co-basedglassy alloys, and the highest strength (the compressive true strengthσf = 5185 MPa) among all known bulk crystalline and glassy alloys. With the aim of synthesizingnew Co-based bulk glassy alloys with much higher strength and much largerGFA, we investigated the effect of Mo and Si additions on the enhancement ofσf and GFA in the Co–(Fe, Mo, Ta)–(B, Si) system. The small amount of2 at.% Mo added to the Co–Fe–Ta–B glassy alloy resulted in obtaining anultrahigh true fracture strength of 5545 MPa and high Young’s modulus(E) of 282 GPa. By further adding 1 and 2 at.% Si, Co–(Fe, Mo, Ta)–(B, Si) bulk glassyalloys were synthesized in the diameter range up to 3 mm, and they exhibitedσf of over4450 MPa and E of over 227 GPa. In addition, the ultrahigh-strength glassy alloys simultaneously exhibited excellentsoft magnetic properties, i.e., saturation magnetization of 0.32–0.35 T, low coercive force of0.7–1.1 A m−1, and high effectivepermeability of 3.9–4.77 × 104 at 1 kHz. The improvement of GFA andσf is interpreted to result from the enhanced atomic bonding nature by adding Mo and Si.

Magnetic hardening in gradually devitrified Co-based glassy alloys

It is shown that gradual devitrifiation of non-magnetostrictive Co-based metallic glass leads to a giant, five orders of magnitude, increase of its coercivity. This magnetic hardening is due to the pinning of domain walls by growing fine crystallites much smaller than the domain wall width, the number and size of which increase with an increase of the annealing temperature.