EP0329704B1

EP0329704B1 - Near-zero magnetostrictive glassy metal alloys for high frequency applications

Info

Publication number: EP0329704B1
Application number: EP87907699A
Authority: EP
Inventors: Ryusuke Hasegawa
Original assignee: AlliedSignal Inc
Current assignee: Honeywell International Inc
Priority date: 1986-11-03
Filing date: 1987-10-27
Publication date: 1992-01-02
Anticipated expiration: 2007-10-27
Also published as: JP2697808B2; EP0329704A1; JPH02500788A; WO1988003699A1; JPH0625399B2; JPH0693392A; DE3775778D1

Abstract

A glassy metal alloy has a value of magnetostriction near-zero and the composition CoaFebNicMdBeSif, where ''a'' ranges from about 65.5 to 70.5 atom percent, ''b'' ranges from about 3.8 to 4.5 atom percent, ''c'' ranges from about 0 to 3 atom percent, ''d'' ranges from about 1 to about 2 atom percent, ''e'' ranges from about 10 to about 12 atom percent and ''f'' ranges from about 14 to 15 atom percent when M is selected from vanadium, chromium, molybdenum, niobium and tungsten, when M is manganese, ''a'' ranges from about 68.0 to 70.0 atom percent, ''b'' ranges from about 2.5 to 4.0 atom percent, ''c'' ranges from 0 to 3 atom percent, ''d'' ranges from 1 to about 4 atom percent, ''e'' ranges from about 10 to 12 atom percent and ''f'' ranges from about 14 to about 15 atom percent. The alloy has a saturation magnetostriction value ranging from about -1x10-6 to +1x10-6, a saturation induction ranging from about 0.65 to about 0.80 Tesla and a Curie temperature ranging from about 245 to 310°C.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to glassy metal alloys with near-zero magnetostriction which are especially suited for use in high frequency applications.

2. Description of the Prior Art

Saturation magnetostriction λ_s is related to the fractional change in length of Δℓ/ℓ that occurs in a magnetic material on going from the demagnetized to the saturated, ferromagnetic state. The value of magnetostriction, a dimensionless quantity, is often given in units of microstrains (i.e., a microstrain is a fractional change in length of one part per million).
Ferromagnetic alloys of low magnetostriction are desirable for several interrelated reasons:

1. Soft magnetic properties (low coercivity, high permeability) are generally obtained when both the saturation magnetostriction λ_s and the magnetocrystalline anisotropy K approach zero. Therefore, given the same anisotropy, alloys of lower magnetostriction will show lower dc coercivities and higher permeabilities. Such alloys are suitable for various soft magnetic applications.
2. Magnetic properties of such zero magneto-strictive materials are insensitive to mechanical strains. When this is the case, there is little need for stress-relief annealing after winding, punching or other physical handling needed to form a device from such material. In contrast, magnetic properties of stress-sensitive materials, such as the crystalline alloys, are seriously degraded by such cold working and such materials must be carefully annealed.
3. The low dc coercivity of zero magnetostrictive materials carries over to ac operating conditions where again low coercivity and high permeability are realized (provided the magneto-crystalline anisotropy is not too large and the resistivity not too small). Also because energy is not lost to mechanical vibrations when the saturation magnetostriction is zero, the core loss of zero magnetostrictive materials can be quite low. Thus, zero magnetostrictive magnetic alloys (of moderate or low magnetocrystalline anisotropy) are useful where low loss and high ac permeability are required. Such applications include a variety of tape-wound and laminated core devices, such as power transformers, signal transformers, magnetic recording heads and the like.
4. Finally, electromagnetic devices containing zero magnetostrictive materials generate no acoustic noise under AC excitation. while this is the reason for the lower core loss mentioned above, it is also a desirable characteristic in itself because it eliminates the hum inherent in many electromagnetic devices.

There are three well-known crystalline alloys of zero magnetostriction (in atom percent, unless otherwise indicated):

(1) Nickel-iron alloys containing approximately 80% nickel ("80 nickel permalloys");
(2) Cobalt-iron alloys containing approximately 90% cobalt; and
(3) Iron-silicon alloys containing approximately 6 wt. % silicon.

Also included in these categories are zero magneto-strictive alloys based on the binaries but with small additions of other elements such as molybdenum, copper or aluminum to provide specific property changes. These include, for example, 4% Mo, 79% Ni, 17% Fe (sold under the designation Moly Permalloy) for increased resistivity and permeability; permalloy plus varying amounts of copper (sold under the designation Mumetal) for magnetic softness and improved ductility; and 85 wt. % Fe, 9 wt. % Si, 6 wt. % Al (sold under the designation Sendust) for zero anisotropy.
The alloys included in category (1) are the most widely used of the three classes listed above because they combine zero magnetostriction with low anisotropy and are, therefore, extremely soft magnetically; that is they have a low coercivity, a high permeability and a low core loss. These permalloys are also relatively soft mechanically and their excellent magnetic properties, achieved by high temperature (above 1000°C) anneal, tend to be degraded by relatively mild mechanical shock.
Category (2) alloys such as those based on Co₉₀Fe₁₀ have a much higher saturation induction (B_s about 1.9 Tesla) than the permalloys. However, they also have a strong negative magnetocrystalline anisotropy, which prevents them from being good soft magnetic materials. For example, the initial permeability of Co₉₀Fe₁₀ is only about 100 to 200.
Category (3) alloys such as Fe/6 wt% Si and the related ternary alloy Sendust (mentioned above) also show higher saturation inducations (B_s about 1.8 Tesla and 1.1 Tesla, respectively) than the permalloys. However these alloys are extremely brittle and have, therefore, found limited use in powder form only. Recently both Fe/6.5 wt.% Si [IEEE Trans. MAG-16, 728 (1980)] and Sendust alloys (IEEE Trans. MAG-15 1149 (1970)] have been made relatively ductile by rapid solidification. However, compositional dependence of the magnetostriction is very strong in these materials, difficult precise tayloring of the alloy composition to achieve near-zero magnetostriction.
It is known that magnetocrystalline anisotropy is effectively eliminated in the glassy state. It is therefore desirable to seek glassy metal alloys of zero magnetostriction. Such alloys might be found near the compositions listed above. Because of the presence of metalloids which tend to quench the magnetization by the transfer of charge to the transition-metal d-electron states, however, glassy metal alloys based on the 80 nickel permalloys are either non-magnetic at room temperature or have unacceptably low saturation inductions. For example, the glassy alloy Fe₄₀Ni₄₀P₁₄B₆ (the subscripts are in atom percent) has a saturation induction of about 0.8 Tesla, while the glassy alloy Ni₄₉Fe₂₉P₁₄B₆Si₂ has a saturation induction of about 0.46 Tesla and the glassy alloy Ni₈₀P₂₀ is non-magnetic. No glassy metal alloys having a saturation magnetostriction approximately equal to zero have yet been found near the iron-rich Sendust composition. A number of near-zero magnetostrictive glassy metal alloys based on the Co-Fe crystalline alloy mentioned above in (2) have been reported in the literature. These are, for example, Co₇₂Fe₃P₁₆B₆AL₃ (AIP Conference Proceedings, No. 24, pp. 745-746 (1975)) Co_70.5Fe_4.5Si₁₅B₁₀ (Vol. 14, Japanese Journal of Applied Physics, pp. 1077-1078 (1975)) Co_31.2Fe_7.8Ni_39.0B₁₄SI₈ [proceedings of 3rd International Conference on Rapidly Quenched metals, p. 183, (1979)] and Co₇₄Fe₆B₂₀ [IEEE Trans. MAG-12, 942 (1976)]. Table I lists some of the magnetic properties of these materials.

Table I

Saturation induction (B_s), Curie temperature (^ϑf), the first crystallization temperature (T_cl), ascast dc coercivity (H_C), and dc coercivity and permeability ( µ )in the annealed states of some of the prior art zero magnetostrictive glassy alloys.

The saturation induction (B_s) of these alloys ranges between 0.6 and 1.2 Tesla. The glassy alloys with B_s close to 0.6 T show low coercivities and high permeabilities comparable to crystalline supermalloys. However, these alloys tend to be magnetically unstable at relatively low (150°C) temperatures. On the other hand, the glassy alloys with B_s ∼ 1.2 Tesla tend to have their ferromagnetic Curie temperatures ( ϑ_f ) near or above their first crystallization temperatures (T_cl). This makes heat-treatment of these materials very difficult to achieve desired soft magnetic properties because such annealing is most effective when carried out at temperatures near ϑ_f.
A recent prior art (Journal of Applied Physics 53, 7819 (1983)] discloses near-zero magnetostrictive glassy alloys with excellent soft magnetic properties and magnetic stability. These glassy alloys were designed with the idea of a saturation induction as high as possible. Recent trends in the applied magnetics do not necessarily require high saturation inductions but a high squareness ratio, a low ac core loss and a high permeability at high frequencies. In view of this, glassy metal alloys exhibiting these features are desirable.
EP-A-84 138 describes a new series of glassy metal alloys with near-zero magnetostriction is disclosed. The glassy alloys have the composition CO_aFe_bNi_cMo_dB_eSi_f, where a ranges from about 58 to 70 atom percent, b ranges from about 2 to 7.5 atom percent, c ranges from about 0 to 8 atom percent, d ranges from about 1 to 2 atom percent, e ranges from about 11 to 15 atom percent and f ranges from about 9 to 14 atom percent with the proviso that the sum of a, b, c ranges from about 72 to 76 atom percent and the sum of e and f ranges from about 23 to 26 atom percent. The magnetostriction of these alloys ranges from about -1 × 10⁻⁶ to +1 × 10⁻⁶ and the saturation induction is between about 0.6 and 0.8 Tesla. The transition metal content is responsible for the low magnetostriction in these alloys. The metalloid content strongly affects the saturation induction. Curies temperature, and magnetic stability. Magnetostriction is mildly affected by the metalloid composition and a particular range of Si/B ratio for certain iron, cobalt containing alloys wherein the magnetostriction is near-zerao and relatively insensitive to the Si/B ratio. The same Si/B ratios also provide high magnetic stability.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a magnetic alloy that is at least 70% glassy, and which has a near-zero magnetostriction, high magnetic and thermal stability and excellent soft magnetic properties at high frequencies. The glassy metal alloy has the composition Co_aFe_bNi_cM_dB_eSi_f, where subscripts are in atom percents and "a" ranges from 65.5 to 70.5, "b" ranges from 3.8 to 4.5, "c" ranges from 0 to 3, "d" ranges from 1 to 2, "e" ranges from 10 to 12 and "f" ranges from 14 to 15 when M is selected from a group consisting of vanadium, chromium, molybdenum, niobium and tungsten; when M is manganese, "a" ranges from 68.0 to 70.0, "b" ranges from 2.5 to 4.0, "c" ranges from 0 to 3, "d" ranges from 1 to 4, "e" ranges from 10 to 12 and "f" ranges from 14 to 15. The glassy alloy has a value of saturation magnetostriction ranging from -1 x 10⁻⁶ to + 1 x 10⁻⁶, a saturation induction of at least 0.65 Tesla, a Curie temperature ranging from 245 to 310°C and the first crystallization temperature ranging from 530 to 575°C.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, there is provided a magnetic alloy that is at least 70% glassy and which has an outstanding combination of properties, including a near-zero magnetostriction, high magnetic and thermal stability and such soft magnetic properties as high permeability, low ac core loss and low coercivity.
The purity of the above composition is that found in normal commercial practice. However, it will be appreciated that up to about 2 atom percent of (Si + B) may be replaced by carbon, aluminum or germanium without significantly degrading the desirable magnetic properties of these alloys.
Examples of essentially zero magnetostrictive glassy metal alloys of the invention include
Co_65.7Fe_4.4Ni_2.9Mo₂B₁₁Si₁₄ and
Co_68.13Fe_4.0Ni_1.37Mo_1.5B₁₀Si₁₅. These glassy alloys possess saturation induction between about 0.65 and 0.70 Tesla, Curie temperature of about 270°C and the first crystallization temperature of about 530°C. Some magnetic and thermal properties of other near-zero magnetostrictive glassy alloys of the present invention are listed in Table II.
The presence of the metal element M is to increase T_cl and hence the thermal stability of the alloy system. The content of M beyond 2 atom percent, however, reduces the Curies temperature to a level lower than 245°C, which is undesirable in conventional magnetic devices.
For some applications, it may be desirable or acceptable to use a material with a small positive or a small negative magnetostriction. When this is the case, all of the glassy alloys of Table II exhibiting the saturation magnetostriction value ranging from -1 x 10⁻⁶ to + 10⁻⁶ may qualify. The value of the magnetostriction is essentially determined by the ratio of Fe/(Co+Fe) or (Fe+Mn)/(Co+Fe+Mn). These ratios are about 0.06 and 0.07-0.09 respectively. The small amount of the element Ni and the metal M excepting Mn which is present in the glassy alloys of the present invention is relatively ineffective to alter the magnetostriction of these alloys.
The glassy alloy of the invention are conveniently prepared by techniques readily available elsewhere; see, e.g., U.S. Patent 3,845,805, issued November 5, 1974 and 3,856,513, issued December 24, 1974. In general, the glassy alloys, in the form of continuous ribbon, wire, etc., are rapidly quenched from a melt of the desired composition at a rate of at least about 10⁵K/sec.
A metalloid content of boron and silicon in the range of about 24 to 27 atom percent of the total alloy composition is sufficient for glass formation, with boron ranging from about 10 to 12 atom percent and silicon ranging from about 14 to about 15 atom percent.
Tables III and IV give ac core loss (L), exciting power (P₈) and permeability ( µ ) at 0.1 Tesla induction and at 50 kHz of the near-zero magnetostrictive glassy alloys of the present invention annealed at different temperature (T_o). Summarizing, by water quenching subsequent to the heat-treatments given in Table III, the glassy alloys of the present invention exhibit, on the average, L=4W/kg,P₈=6VA/kg and µ =28,000. One of them, namely, Co_68.13Fe_4.0Ni_1.37Mo_1.5B₁₀Si₁₅, can attain L=3.0 W/kg,P₈=4.2VA/kg and µ =38,000. Slower cooling after the heat-treatments generally results in higher value for the loss and the exciting power, and lower permeabilities. Some of the glassy alloys of the present invention, when cooled slowly subsequent to the heat-treatments, however, show results comparable to or better than those exhibited by the materials quenched rapidly after the heat-treatments. One such example is shown by a glassy Co_68.75Fe_4.25W₂B₁₀Si₁₅, which gives L=2.7W/kg, P₈=4.6VA/kg and µ =34,100 at 50 kHz and 0.1 Tesla induction when heat-treated at 400°C for 15 min. without a field and cooled slowly at a rate of about -4°C/min. Compared with these values, a prior art crystalline non-magnetostrictive supermalloy of the similar thickness (25 µm ) given L=BW/kg, P₈=10VA/kg and µ = 19,000 at 0.1 Tesla and 50 kHz. Examples of glassy alloys outside the scope of the invention are set forth in Table V. The advantageous combination of properties provided by the alloys of the present invention cannot be achieved in prior art nonmagnetostrictive glassy alloys with high saturation induction, such as Co₇₄Fe₆B₂₀, because their Curie temperatures are higher than the first crystallization temperatures and the heat-treatment to improve their properties are not so effective as in those with lower saturation inductions. The above properties, achieved in the glassy alloys of the present invention, may be obtained in low induction glassy alloys of the prior art. However, these alloys of the prior art such as Co_31.2Fe_7.8-Ni_39.0-B₁₄Si₈ tend to be magnetically unstable at relatively low temperature of about 150°C as pointed out earlier. The best combined properties of another glassy alloy of a prior art were L=4W/kg, P₈=7 VA/kg and µ =23,000 obtained for a glassy Co_67.4Fe_4.1Ni_3.0Mo_1.5-B_12.5Si_11.5 annealed at 380°C for 15 min. and cooled rapidly. It is again clear that the glassy alloys of the present invention are generally superior to this class of glassy alloys.
Table V shows the magnetic properties of some of the representative glassy alloys of the composition Co_aFe_bNi_cM_dB_eSi_f (M is selected from the group consisting of V, Cr, Mn, Mo, Nb and W), in which at least one of a, b, c, d, e and f is outside the composition range defined in the present invention. The table indicates that the alloys with at least one of the constituents outside the defined ranges exhibit either Curie temperature or saturation induction too low to be practical in many magnetic applications
The following examples are presented to provide a more complete understanding of the invention. The specific techniques, conditions, materials, proportions and reported data set forth to illustrate the principles and practice of the invention are exemplary and should not be construed as limiting the scope of the invention.

EXAMPLES

1. Sample Preparation

The glassy alloys listed in Tables II-VII were rapidly quenched (about 10⁶ K/sec) from the melt following the techniques taught by Chen and Polk in U.S Patent 3,856,513. The resulting ribbons, typically 25 to 30 µm thick and 0.5 to 2.5 cm wide, were determined to be free of significant crystallinity by x-ray diffractometry (using CuK radiation) and scanning calorimetry. Ribbons of the glassy metal alloys were strong, shiny, hard and ductile.

2. Magnetic Measurements

Continuous ribbons of the glassy metal alloys prepared in accordance with the procedure described in Example I were wound onto bobbins (3.8 cm O.D.) to form closed-magnet-path toroidal samples. Each sample contained from 1 to 3 g of ribbon. Insulated primary and secondary windings (numbering at least 10 each) were applied to the toroids. These samples were used to obtain hysteresis loops (coercivity and remanence) and initial permeability with a commercial curve tracer and core loss (IEEE Standard 106-1972).
The saturation magnetization, M_s, of each sample, was measured with a commercial vibrating sample magnetometer (Princeton Applied Research). In this case, the ribbon was cut into several small squares (approximately 2 mm x 2 mm). These were randomly oriented about their normal direction, their plane being parallel to the applied field (0 to 720 kA/m. The saturation induction R_s (=4 π 4M_sD) was then calculated by using the measured mass density D.
The ferromagnetic Curie temperature ( ϑ_f ) was measured by inductance method and also monitored by differential scanning calorimetry, which was used primarily to determine the crystallization temperatures. The first or primary crystallization temperature (T_cl) was used to compare the thermal stability of various glassy alloys of the present and prior art inventions.
Magnetic stability was determined from the reorientation kinetics of the magnetization, in accordance with the method described in Journal of Applied Physics, Vol. 49, p. 6510 (1978), which method is incorporated herein by reference thereto.
Magnetostriction measurements employed metallic strain gauges (BLH Electronics), which were bonded (Eastman - 910 Cement) between two short lengths of ribbon. The ribbon axis and gauge axis were parallel. The magnetostriction was determined as a function of applied field from the longitudinal strain in the parallel ( Δℓ/ℓ ) and perpendicular ( Δℓ/ℓ) in-plain fields, according to the formula λ =2/3[( Δℓ/ℓ) - Δℓ/ℓ)].

Claims

1. A magnetic alloy that is at least 70% glassy, having the formula Co_aFe_bNi_cM_dB_eSi_f where the subscripts are in atom percent and "a" ranges from 65.5 to 70.5, "b" ranges from 3.8 to 4.5, "c" ranges from 0 to 3, "d" ranges from 1 to 2, "e" ranges from 10 to 12 and "f" ranges from 14 to 15 when M is selected from the group consisting of vanadium, chromium, molybdenum, niobium and tungsten; when M is manganese, "a" ranges from 68.0 to 70.0, "b" ranges from 2.5 to 4.0, "c" ranges from 0 to 3, "d" ranges from 1 to 4, "e" ranges from 10 to 12 and "f" ranges from 14 to 15, said alloy having a value of the saturation magnetostriction between - 1x10⁻⁶ to +1x10⁻⁶, a Curie temperature ranging from 245°C to 310°C, a first crystallization temperature ranging from 530°C to 575°C and a saturation induction of at least 0.65 Tesla.

2. The magnetic alloy of claim 1 having the formula Co_65.7Fe_4.4Ni_2.9Mo₂B₁₁Si₁₄.

3. The magnetic alloy of claim 1 having the formula Co_68.13Fe_4.0Ni_1.37Mo_1.5B₁₀Si₁₅.

4. The magnetic alloy of claim 1 having the formula Co_69.6Fe_4.4Mo₁B₁₀Si₁₅.

5. The magnetic alloy of claim 1 having the formula Co_68.75Fe_4.25Mo₂B₁₀Si₁₅.

6. The magnetic alloy of claim 1 having the formula Co_69.6Fe_4.4Cr₁B₁₀Si₁₅.

7. The magnetic alloy of claim 1 having the formula Co_68.75Fe_4.25Cr₂B₁₀Si₁₅.

8. The magnetic alloy of claim 1 having the formula Co_68.2Fe_3.8Mn₁B₁₂Si₁₅.

9. The magnetic alloy of claim 1 having the formula Co_67.7Fe_3.3Mn₂B₁₂Si₁₅.

10. The magnetic alloy of claim 1 having the formula Co_70.0Fe_4.0Mn₁B₁₀Si₁₅.

11. The magnetic alloy of claim 1 having the formula Co_69.5Fe_3.5Mn₂B₁₀Si₁₅.

12. The magnetic alloy of claim 1 having the formula Co_69.0Fe_3.0Mn₃B₁₀Si₁₅.

13. The magnetic alloy of claim 1 having the formula Co_68.5Fe_2.5Mn₄B₁₀Si₁₅.

14. The magnetic alloy of claim 1 having the formula Co_69.6Fe_4.4V₁B₁₀Si₁₅.

15. The magnetic alloy of claim 1 having the formula Co_68.75Fe_4.25V₂B₁₀Si₁₅.

16. The magnetic alloy of claim 1 having the formula Co_69.6Fe_4.4Nb₁B₁₀Si₁₅.

17. The magnetic alloy of claim 1 having the formula Co_68.75Fe_4.25Nb₂B₁₀Si₁₅.

18. The magnetic alloy of claim 1 having the formula Co_69.6Fe_4.4W₁B₁₀Si₁₅.

19. The magnetic alloy of claim 1 having the formula Co_68.75Fe_4.25W₂B₁₀Si₁₅.