TARAKANOV, Yuri (11/122 Rav Kaniel Street, Haifa, 33139, IL)
TARAKANOV, Yuri (11/122 Rav Kaniel Street, Haifa, 33139, IL)
| CLAIMS: 1. An amorphous magnetostrictive element for use in a magnetomechanical marker, said amorphous magnetostrictive element comprising at least one amorphous ribbon made of an alloy having a composition corresponding to the formula NiaFebCocMθdCreM'mBxSiy, wherein M' corresponds to at least one surface active element from Sn, Pb, and Bi; "a" ranges from 10 to 50, "b" ranges from 20 to 60, "c" is less than 15 at.% down to 0; "d" is higher than 2 at.%; "e" is higher than 1 ; a sum (d+e) is higher than 5; "m" is higher than 0.001; "x" ranges from 10 to 25; "y" ranges from 0 to 3; and a sum of (a+b+c+d+e+m+x+y) is 100 at.%. 2. The amorphous magnetostrictive element of claim 1, wherein said alloy contains at least one of the surface active elements with the content of up to 0.4 at.%. 3. The amorphous magnetostrictive element of claim 1, wherein said alloy contains from 0.02 to 0.1 at % of at least one of Sn and Pb surface active elements. 4. The amorphous magnetostrictive element of claim 1, wherein said alloy has one of the following composition: Fe40 7Ni20 8Co149Mo3 \Cτ22Si0 ^B18Sn0 O06Pb0 004 Fe33 22Ni34 6Co8 5Mo3 3Cr2 1Si0 ^B18Sn0 Oi2Pbo O08Fe3692Ni35 3Co42Mo2 1Cr3 2Si026 008 Fe38 13Ni38 3Mo2 1Cr3 15Si025B18 \SΏQ 012Pb0 008 Fe38Ni38 5Mo3 ^r2 toSio 26Bi8Sn003Pb001 Fe37 8Ni38 7Mo4Cri 2Si025B18Sno o3Pbo 02 Fe379Ni37 95Mo4 7Cri 1Si025B18Sno O6Pb004 Fe3774Ni37 8Mo47Cri 4Si02SB18Sn005Pb003 5. The amorphous magnetostrictive element of claim 1, wherein said alloy does not contain cobalt. 6. The amorphous magnetostrictive element of claim 5, wherein said alloy has one of the following composition: Fe38 13Ni38 3Mo2 1Cr3 15Si025B18 iSnOo12Pbo oO8 Fe38Ni38 5Mo3 ]Cr2 10Sio26B18Snoo3Pb0 01 Fe37 8Ni38 7Mo4Cr! 2Si025B18Sno 03Pb0 02 Fe37 9Ni37 95Mo4 ^7Cr1 1Si025B18Sno 06Pb004 Fe3774Ni37 8Mo4 ^7Cr1 4Si0 ^B18Sn005Pb003 7. A magnetomechanical marker comprising a magnetic biasing element in the form of at least one semihard ferromagnetic strip and an amorphous magnetostrictive element, said amorphous magnetostrictive element comprising at least one amorphous ribbon made of an alloy having a composition corresponding to the formula NiaFebCθcMθdCreM'mBxSiy, wherein M' corresponds to at least one surface element from Sn, Pb, and Bi; "a" ranges from 10 to 50, "b" ranges from 20 to 60, "c" is less than 15 at.% down to 0; "d" is higher than 2 at.%; "e" is higher than 1; a sum (d+e) is higher than 5; "m" is higher than 0.001; "x" ranges from 10 to 25; "y" ranges from 0 to 3; and a sum of (a+b+c+d+e+m+x+y) is 100 at.%, said semihard ferromagnetic and magnetostrictive elements being arranged such that said magnetostrictive element is biased with a DC magnetic field created by the semihard ferromagnetic biasing element. 8. The magnetomechanical marker of claim 7, wherein the amorphous magnetostrictive element comprises two or more magnetostrictive amorphous strips. 9. The magnetomechanical marker of claim 7, wherein the magnetostrictive amorphous strip has a width ranging from 1 to 10 mm. 10. The magnetomechanical marker of claim 8, wherein the magnetostrictive amorphous strip pieces are disposed in a stack, having substantially equal widths ranging from 1 to 10 mm and having substantially equal lengths. 11. A method of manufacturing an amorphous magnetostrictive element for a magnetomechanical marker, the method comprising: - providing at least one amorphous ribbon of the composition according to claim 1, - heat-treating said amorphous ribbon under a tensile strength, in a continuous mode through consecutive hot and cold regions, and the hot region having temperature above Curie temperature of said amorphous ribbon alloy, while the cold region having temperature below Curie temperature and a predetermined length selected for cooling said ribbon down to the temperature below Curie temperature, the cold region being exposed to a DC magnetic field directed perpendicular to a longitudinal axis of the amorphous ribbon. 12. A method of manufacturing an amorphous magnetostrictive element for a magnetomechanical marker, the method comprising: - providing at least one amorphous ribbon of the composition according to claim 5, - heat-treating said amorphous ribbon under tensile strength in a continuous mode at temperature above Curie temperature of said amorphous ribbon alloy, while the ribbon cooling is carried out at room temperature in open air. 13. A method of manufacturing a magnetomechanical marker configured according to claim 7, the method comprising: - providing at least one amorphous ribbon each being of the composition according to claim 1 , - heat-treating said amorphous ribbon under a tensile strength, in a continuous mode through consecutive hot and cold regions, and the hot region having temperature above Curie temperature of said amorphous ribbon alloy, while the cold region having temperature below Curie temperature and a predetermined length selected for cooling said ribbon down to the temperature below Curie temperature, the cold region being exposed to a DC magnetic field directed perpendicular to a longitudinal axis of the amorphous ribbon, - cutting said heat treated ribbons to obtain at least one strip piece of a certain length, said at least one strip piece forming an amorphous magnetostrictive element, - disposing said at least one strip piece adjacent to at least one ferromagnetic element to thereby enable biasing of said magnetostrictive element with a DC magnetic field created by said at least ferromagnetic element. 14. A method of manufacturing a magnetomechanical marker configured according to claim 7, the method comprising: - providing at least one amorphous ribbon of the composition according to claim 5; - heat-treating said amorphous ribbon under tensile strength in a continuous mode at temperature above Curie temperature of said amorphous ribbon alloy, while the ribbon cooling is carried out at room temperature in open air, - cutting said heat treated ribbons into at least one strip piece of a certain length, - disposing said at least one strip piece and at least one ferromagnetic element to bias said at least one magnetostrictive strip piece with a DC magnetic field created by said at least one ferromagnetic element. |
FIELD OF THE INVENTION
The invention is generally in the field of magnetic markers for use in electronic article surveillance systems, and relates to a magnetomechanical marker, a magnetostrictive amorphous elements fro use therein, and a method for production of such markers.
BACKGROUND OF THE INVENTION
Magnetomechanical markers for electronic article surveillance (EAS) typically include elongated strip pieces of a magnetostrictive amorphous alloy, which are magnetically biased, by an adjacent strip of a magnetically semi-hard metal strip.
Production of magnetomechanical markers comprises several steps. These steps include selecting an alloy composition; casting the amorphous alloy in the form of a ribbon having a certain width and thickness; carrying out thermal treatment of the ribbon in presence of magnetic field; cutting the ribbons into pieces of a predetermined length to provide them with resonant properties when exposed to an AC electromagnetic field of certain frequency; and packing them into a housing together with pieces of semi-hard materials which provide magnetic bias for the amorphous strips, to form a magnetomechanical marker.
An acoustic-type magnetomechanical marker fabricated in above mentioned manner resonates at a predetermined frequency when the biasing element has been magnetized to a certain level and a suitable oscillator provides an AC magnetic field at the predetermined frequency. When a magnetostrictive material, such as an amorphous metal ribbon, is in a magnetic field (H), the ribbon's magnetic domains are caused to grow and/or rotate. This domain movement allows magnetic energy to be stored. When the field is removed, the domains return to their original orientation releasing the stored magnetic energy. Amorphous metals have high efficiency in this mode of energy storage. Since amorphous metals have no grain boundaries, their energy losses are extraordinarily low. When the ferromagnetic ribbon is magnetostrictive, additional energy storage is also possible. In the presence of a magnetic field, a magnetostrictive amorphous metal ribbon will have energy stored magnetically as described above but will also have energy stored mechanically via magnetostriction. This additional energy storage may be viewed as an increase in the effective magnetic permeability of the ribbon. When an AC magnetic field and a DC field are imposed on the magnetostrictive ribbon, energy is alternately stored and released with the frequency of the AC field. The magnetostrictive energy storage and release are maximal at the material's mechanical resonance frequency and minimal at its anti-resonance.
The transfer of magnetic and mechanical energy described above is called magnetomechanical coupling (MMC), and can be seen in all magnetostrictive materials.
The efficiency of this energy transfer is proportional to the square of a magnetomechanical coupling factor (k). It is defined as the ratio of mechanical to magnetic energy. This factor strongly depends on the ribbon surface defects.
The presence of different cavities and pins on the ribbon surface, results in additional stresses around defects and in losses of mechanical and magnetic energy.
Therefore, these surface defects reduce magnetomechanical factor and the detecting ability of the marker, so one can reduce the losses if the quality of the ribbon surface improves due to improvement of the ribbon production technology.
The efficiency of the energy transfer is also dependent on the elasticity of magnetostrictive material. Higher material elasticity results in higher efficiency of the energy transfer. Therefore, by introducing elements into the alloy composition, which increase the modulus of elasticity of magnetostrictive strips, one can improve the detection ability of the produced magnetomechanical markers. However, the alloys containing high levels of such elements like Mo and Cr have low ribbon casting ability owing to high melt viscosity and low fluidity need to be cast at high temperatures, which can result in the ribbon quality deterioration. A broad range of alloys having good elastic and magnetostrictive properties suitable for the marker material for the acousto-magnetic detection has been developed.
Typically, the main component of the marker is a magnetostrictive element made of amorphous strip, which is usually produced from amorphous alloy containing Fe, Ni and considerable amount of expensive Co.
For example, U.S. Pat. No. 4,510,489 describes magnetostrictive strip pieces produced from the amorphous alloys having a composition defined by the following formula: M a N b O c X d Y e Z f , where M is at least one of iron and cobalt, N is nickel, O is at least one of chromium and molybdenum, X is at least one of boron and phosphorous, Y is silicon, Z is carbon, "a"-"f are in atom percent, "a" ranges from about 35-85, "b" ranges from about 0-45, "c" ranges from about 0-7, "d" ranges from about 5-22, "e" ranges from about 0-15 and "f ranges from about 0-2, and the sum of d+e+f ranges from about 15-25.
As magnetostrictive strip pieces the following amorphous alloys are suggested to use: Fe 78 Si 9 B 13 , Fe 79 Si 5 Bi 6 , Fe 8 iB 13 5 Si 3 5 C 2 , Fe 67 Co 18 B 14 Si 1 , and Fe 40 Ni 38 Mo 4 B 18 .
Also, U.S. Patents Nos. RE38098, 6,171,694 and 5,728,237 by Herzer et al. describe various amorphous magnetostrictive alloys, defined by the formula Fe a Cθ b Ni c SiχB y M z wherein M denotes one or more elements of groups consisting of IV through VII of the periodic table and z lies between 0 and 5 atomic %, which are suitable for the production of magnetomechanical markers . According to these patents, the use of high content of these elements in the marker alloy results in reduced ribbon casting ability owing to the higher melting point temperature of the metal, and therefore the content of the elements improving magnetomechanical properties of the alloys is limited. U.S. Pat. Nos. 5,495,231, 5,628,840 and 6,187,112 by Hasegawa et al. disclose some other examples of amorphous magnetostrictive alloys bearing good magnetoelastic properties and containing between 12 and 45at % of cobalt. According to these techniques, magnetostrictive alloys should have a linear magnetization behavior up to a minimum applied field of at least 8 Oe, and this can be achieved by annealing the ribbon under DC magnetic field. As for the content of Mn, Mo and Cr in these alloys, this is also less than 3 atomic %. Some other metallic glasses containing up to 5 atomic % of Nb, Ta, Mo, Cr, and Mn, and exhibiting good magnetoelastic properties are disclosed in U.S. Pat. 6,359,563 by Herzer et al.
U.S. Pat. 7, 276, 128, also issued to Herzer, teaches that alloys containing a high amount of Mo of about 4 at % tend to exhibit difficulties in casting. These difficulties are largely removed when the Mo-content is reduced to about 2 at % and/or replaced by
Nb. The reduction in Mo reduces the sensitivity to the annealing stress and results e.g. in a higher slope. This may be a disadvantage if a slope of less than about 600-700
Hz/Oe is necessary for the resonator. The slope enhancement effect of a reduced Mo- content can be compensated by reducing the Fe-content toward 30 at % and below.
As it follows from the above, the content of elements from the group consisting of Nb, Ta, Mo, Cr, and Mn is limited by 5 at. %. It is due to difficulties during the casting of the amorphous ribbon, as molten alloys having in its composition high amount of Nb, Ta, Mo, Cr, and Mn are very viscous. These difficulties can be overcome by considerable increase of casting temperature; the latter however causes a decrease of ribbon surface quality. For decreasing of casting temperature it is necessary to decrease the liquid metal viscosity or to increase its fluidity. For the latter, it is recommended to add some amount of surface active elements, like Sn, Pb and Bi, into the alloy.
Amorphous alloys containing some of these elements are disclosed in International Patent Publications WO 01/50483 and WO 99/66624. Amorphous metal strips used for the production of stators have a composition defined by the formula: M 70-
S5 Y 5-20 Z 0-20 , subscripts in atom percent, where "M" is at least one of Fe, Ni and Co, "Y" is at least one of B, C and P, and "Z" is at least one of Si, Al and Ge; with the proviso that (i) up to ten (10) atom percent of component "M" can be replaced with at least one of the metallic species Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ta and W, and up to ten (10) atom percents of components (Y+Z) can be replaced by at least one of the non-metallic species In, Sn, Sb and Pb. Highest induction values at low cost are achieved for alloys wherein "M" is iron, "Y" is boron and "Z" is silicon.
The use of amorphous metal strip composed of iron-boron-silicon alloys is preferred. Most preferred is an amorphous metal strip having a composition consisting essentially of about 11 atom percent boron and about 9 atom percent silicon, the balance being iron and incidental impurities". As it is clear from the formula in both of the above indicated International Patent Publications, the "nonmetallic" species (Sn, Sb, Pb) are used in big amounts (up to 10 at.%) as glass forming components. The amorphous alloy ribbon containing such big quantity of Sn, Sb, and Pb is supposed to be brittle after high temperature annealing and cannot be used as magnetostrictive element for acoustomagnetic marker. Moreover, these alloys contain considerable amount of cobalt and are relatively thus expensive.
Amorphous alloys containing surface active elements (Sn, Pb and Bi) are disclosed in co-pending International Patent Publication WO 2008/032274 which has common inventors with the present application. Magnetostrictive amorphous strips were made of the alloys which compositions are defined by the formula: Ni a Fe b Co c M' k M" m B d Si e ; wherein M' is at least one element from the group consisting of Cr, Mo, and Mn, and M" is at least one element from the group consisting of surface active elements like Sn, Pb and Bi, and "a" ranges from 10 to 32, "b" ranges from 22 to 30, "c" ranges from 15 to 35, "d" ranges from 15 to 25, "e" ranges from 0 to 3, "k" is the sum of amount of elements of group M' and ranges from 5.1 to 10, "m" ranges from 0.001 to 0.04 and sum of "a-m" is 100. The upper level of the surface active elements is limited by 0.04 at%. As it follows from the alloy compositions described in this patent application, the amorphous alloys contain considerable amount of cobalt (15-35 at. %) as well. Amorphous alloys for magneto-acoustic markers in electronic article surveillance having reduced, low or zero Co content are discovered in U.S. Patents Nos. 6,645,314 and 7,088,247 and 7,276,128 issued to Herzer. The alloys described in these patents have composition defined by the formula: Fe a Cθ b Ni c M d CueSi x B y Z z , wherein a, b, c, d, e, x, y and z are in at %, M is at least one element from the group consisting of Mo, Nb, Ta, Cr and V, and Z is at least one element from the group consisting of C, P and Ge, and wherein a is between about 20 and about 50, b is less than or equal to about 4, c is between about 30 and about 60, d is between about 1 and about 5, e is between about 0 and about 2, x is between about 0 and about 4, y is between about 10 and about 20, z is between about 0 and about 3, and (d+x+y+z) is between about 14 and about 25, and (a+b+c+d+e+x+y+z) is equal to 100.
The above patents disclose a ferromagnetic resonator for use in a marker in a magnetomechanical electronic article surveillance system which is manufactured at reduced cost by being continuously annealed in a zone of elevated temperature with a tensile stress applied along the ribbon axis in the presence or absence of an external magnetic field applied perpendicular to the strip's length and in the plane of the strip and by providing an amorphous magnetic alloy containing iron, cobalt and nickel and in which the portion of cobalt is less than about 4 at %. The patents also summarize requirements for magneto-acoustic markers in the following way: 1. characterized by a linear B-H loop up to a minimum applied field of typically 8 Oe; 2. having a small susceptibility of the resonant frequency f r to the applied bias field H in the activated state, i.e., typically |df r /dH|<1200 Hz/Oe; and 3. characterized by a sufficiently long ring-down time of the signal i.e. high signal amplitude for a time interval of at least 1-2 ms after the exciting drive field has been switched off.
Fe-Ni based alloys used for the acoustomagnetic markers are described in U.S. Patents Nos.7,205,893 and 7,320,433 to Hasegawa; and their compositions are determined by the formula: Fe a Ni b Mo c B d , wherein a = 30 - 43 atom %, b = 35-48 atom %, c = 0 -5 atom %, d=14-20 atom % and (a+b+c+d)=100, up to 3 atom % of Mo being optionally replaced by Co, Cr, Mn and/or Nb and up to 1 atom % of B being optionally replaced by Si and/or C. Thus, these patents as well as those discussed in the previous paragraph, limit the content of elements of group (Mo, Cr, Mn and Nb) by 5 at.%.
U.S. Patent No. 5,469,140 discloses a heat treatment process in which a ribbon- shaped strip of an amorphous magnetic alloy is heat-treated, while applying a transverse saturating magnetic field. The treated strip is used in a marker for a pulsed-interrogation electronic article surveillance system.
U.S. Patent No. 5,676,767 discloses a magnetostrictive element for use in a magnetomechanical electronic article surveillance marker, which is formed by annealing a continuous ribbon of an amorphous metal alloy. The alloy ribbon is transported from reel to reel through an oven in which a transverse saturating magnetic field is applied to the ribbon. The annealed ribbon is cut into discrete strips, which are suitable for use as magnetostrictive elements.
U.S. Patent No. 5,891,270 discloses a mechanically resonant marker, which comprises a strip of magnetic glassy metal alloy that has been annealed in a furnace for a predetermined time at a plurality of temperatures. A first of the temperatures is 36O 0 C and the second of the temperatures is 33O 0 C. Annealing is carried out in the presence of an external magnetic field applied perpendicular to the strip's length and in the plane of the strip. The second of the temperatures is applied sequentially of the first temperature and is operative to induce magnetic anisotropy along the direction of the magnetic field. Annealing is continuous and the velocity of the strip passing through the annealing furnace determines the annealing time.
U.S. Patent No. 5,786,762 presents a magnetostrictive element for use in a magnetomechanical electronic article surveillance marker. Such magnetostrictive element is formed by first annealing a strip of amorphous metal alloy, said alloy comprising iron and cobalt with the proportion of cobalt being in the range of about 5 to about 45 atomic percent, in the presence of a saturating magnetic field so that said strip has a characteristic upon completion of said first annealing such that, upon application of a biasing magnetic field to said strip, said strip is mechanically resonant at a resonant frequency in response to exposure to an alternating magnetic field at said resonant frequency, said resonant frequency being subject to variation in dependence on changes in said biasing magnetic field. Subsequent to said first annealing, second annealing of said strip is done to reduce a rate at which said resonant frequency varies in dependence on changes in said biasing magnetic field.
U.S. Patent No. 5,676,767 issued to Liu describes a method of forming a magnetostrictive element for use in a magnetomechanical markers for electronic article surveillance systems. According to this method, a continuous ribbon of an amorphous metal alloy is provided, and transported through an annealing region in which heat and a saturating magnetic field are applied to anneal the ribbon; during the transportation, a curved shape is imparted to the continuous amorphous alloy ribbon. The transversely- curved active elements are provided to reduce or avoid a clamping effect that might otherwise occur when the active element is mounted in the EAS marker in proximity to a magnetic biasing element.
SUMMARY OF THE INVENTION
There exist metallic glass alloys that show linear magnetic response for an acceptable field range. These alloys, however, contain high levels of cobalt or molybdenum or chromium, resulting in increased raw material costs and/or reduced ribbon casting ability owing to the higher melting temperatures of such constituent elements as molybdenum or chromium.
The present invention provides novel alloys which provide, in combination, such properties as an extended linear magnetic response, improved mechanical resonance performance, good ribbon casting ability and economy in production of usable ribbon.
The present invention is based on the understanding of the following: As alloys containing high levels of molybdenum and chromium have reduced ribbon casting ability owing to low fluidity of liquid metal, some modifications of the alloy composition are needed to prevent reduction of the melt fluidity and therefore deterioration of the casting ability.
To improve the surface quality of the ribbon, one needs to decrease chemical interaction between the wheel surface and liquid metal during the ribbon casting. Interaction between solid and liquid metals is increased with the temperature growth. Therefore, improving the ribbon surface quality can be favored by reduction of the casting temperature to the extent possible. The commercially most significant process for amorphous materials fabrication in the form of ribbons is the rapid solidification of molten metal via melt-spinning processes, where a liquid metal is sprayed through a nozzle having very small dimensions. Accordingly, the ribbon casting temperature is mainly determined by the liquid metal fluidity. Introduction into the alloy composition of elements, which considerably increase fluidity of the molten metal, allows casting of the amorphous ribbon even with high content of Mo and Cr at relatively low temperature. This is especially important for Fe- Ni based amorphous alloys as their liquid metal viscosity is considerably higher than that of Fe-Ni-Co based alloys due to higher content of iron in Fe-Ni based alloys. Therefore, the amount of surface active elements to be introduced into a composition of the Fe-Ni based alloys is to be considerably higher than that in Fe-Ni-Co based alloys.
Magnetoelastic properties are strongly dependent on the alloy composition and tensile strength. Sensibility of Fe-Ni-Co alloys to tensile strength is decreased with an increase of cobalt content in the alloy. Moreover, as Fe- Ni based alloys are very sensitive to tensile strength and as due to the fact that during heat treatment the amorphous ribbon passes through special fixture to make curved shape ribbon, the tensile strength is not stable due to friction. So, the tensile strength should be fixed and controlled.
The present invention provides for a novel composition of a cheap alloy for magnetomechanical EAS markers, which provides improved magnetoelastic properties to the amorphous ribbon and contains low amount of cobalt or does not contains it at all. The alloy composition of the present invention allows casting at relatively low temperature in order to reduce interaction between the melt and to avoid deterioration of the casting wheel's quench surface, which result in higher quality of the ribbon surface. Also, the present provides a novel heat treatment process for the Fe-Ni based ribbon alloys, which results in improved magnetoelastic properties of the annealed material. Furthermore, the present invention provides a heat treatment process for the Fe-Ni-Co based ribbon alloy, which results in improved magnetoelastic properties of the annealed material.
The inventive amorphous metallic alloys for magnetostrictive elements have smaller content of Co and higher content of Mo and Cr (than the known alloys of the kind specified), and may be described by the following formula: Ni a Fe b Co c ModCreM' m B x Si y . Here,
M' is at least one surface active element, e.g. from Sn, Pb or Bi, and the content of the surface element(s) is defined by desired casting ability of the alloy, i.e. "m" is higher than O.OOlat.% (e.g. 0.001-0.4);
"a" ranges from 10 to 50 at.%,
"b" ranges from 20 to 60 at.%,
"c" is less than 15 at.% down to 0,
"d" is higher than 2 at.% (e.g. ranges between 2-10), and "e" is higher than 1, such that a sum (d+e) is higher than 5, e.g. up to 10,
"x" ranges from 10 to 25,
"y" ranges from 0 to 3, the entire sum (a+b+c+d+e+m+x+y) is 100 at.%.
Hence, markers comprising the magnetostrictive elements of the present invention, which contain low amount of cobalt or do not contain cobalt at all, use amorphous ribbon with higher content of such elements as Mo and Cr is needed. This improves magnetoelastic properties of the amorphous ribbon. It should be understood that Fe - Ni - Co or Fe - Ni alloys, containing large amount of Fe, Mo and Cr, have very low casting ability, and therefore it is highly desirable to introduce into these alloys appropriate amount of surface active element(s), e.g. Sn and/or Pb, which increase molten alloy fluidity and therefore improve alloy casting ability. To get a smooth surface of the amorphous ribbons, they can be cast at temperature 1320-1350° C. To get suitable fluidity of molten metal at these temperatures to produce the amorphous ribbon having smooth surface, different amounts of Sn and Pb can be introduced into the liquid metal depending on the alloy composition. The amount of surface active elements introduced into the alloy depends on the content of Fe, Mo and Cr. The higher is the content of these elements in the alloy, the larger the amounts of surface active elements that should be introduced.
In a preferred embodiment of the invention, the alloy contains both Sn and Pb such that the total content thereof ranges from 0.04 to 0.15 at % (Sn+Pb). Regarding Mo and Cr, the inventive alloys preferably contain 4.0-5.0 at % Mo and 1.0-2.0 at. % Cr.
Preferably, the alloy according to the invention has one of the following compositions:
Fe 37 74 Ni 37 8 Mo 4 - / Cr 1 4 Si 02S B 18 Sn 0 05 Pb 0 03 Fe 38 Ni 38 5 Mo 3 ^r 2 1 0Si 026 B 18 Srio 03Pb 0 01
Fe 37 8 Ni 38 - / Mo 4 Cr 1 2 Si 025 B 18 Sno 03 Pb 0 02
Also, in some other embodiments, the following compositions can be used:
Fe 4O 7 Ni 20 8 Co 14 9M03 \Cτ 2 2 Si 02 8B 18 Sn 0 ooβPbo 004
Fe 33 22 Ni 34 6 Co 8 5 Mo 3 3 Cr 2 iSio 20B 18 Sn 0 012 Pb 0 O og Fe 3692 Ni 35 3 Co 42 Mo 2 iCr 3 2 Si 020 B 18 Sn 0 012 Pb 0 008
Fe 38 13 Ni 38 3 Mo 2 1 Cr 3 15 Sio 25 B 18 !Sn 0 O i 2 Pb 0008
Fe 37 9 Ni 37 95 Mo 4 7 Cr 1 !Si 025 Bi 8 Sn 0 O6 Pb 0 04
The invention also provides a magnetomechanical marker using one or more magnetostrictive elements based on one or more of the above-described amorphous metallic alloys. Such markers can be used in theft detection systems.
The magnetomechanical marker comprises at least one magnetostrictive element and at least one ferromagnetic element. The magnetostrictive and ferromagnetic elements are arranged such that the magnetostrictive element is biased with a DC magnetic field (e.g. ranging from 3,0 to 15,0 Oe) created by the ferromagnetic element. The ferromagnetic element is a strip, continuous or segment. The width of the magnetostrictive element may be from 1 to 10mm.
In some embodiments of the invention, the marker comprises at least two magnetostrictive strip pieces disposed in a stack. The width of such strip piece preferably substantially not exceeds 10mm; and respective lengths of the magnetostrictive elements are preferably substantially equal.
The invention, in its yet other aspect, provides a method of manufacturing an amorphous magnetostrictive element for use in a magnetomechanical marker. The method comprises: providing at least one amorphous ribbon of the composition described above with small amount of Co; and applying heat-treatment to said amorphous ribbon under a tensile strength, in a continuous mode through consecutive hot and cold regions, the hot region having temperature above Curie temperature of said amorphous ribbon alloy, while the cold region having temperature below Curie temperature and a predetermined length selected for cooling said ribbon down to the temperature below Curie temperature, the cold region being exposed to a DC magnetic field directed perpendicular to a longitudinal axis of the amorphous ribbon.
For the manufacture of the amorphous magnetostrictive element from at least one amorphous ribbon of the above composition with no Co, the method comprises: heat-treating said amorphous ribbon under tensile strength in a continuous mode at temperature above Curie temperature of said amorphous ribbon alloy, while the ribbon cooling is carried out at room temperature in open air.
To manufacture a magnetomechanical marker, the heat treated ribbon is cut to obtain at least one strip piece of a certain length forming an amorphous magnetostrictive element; and said at least one strip piece is disposed adjacent to at least one ferromagnetic element to thereby enable biasing of said magnetostrictive element with a
DC magnetic field created by said at least ferromagnetic element. BRIEF DESCRIPTION OF THE DRAWINGS
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates the main components of a magnetomechanical marker according to the invention;
Fig. 2A illustrates schematic representation of the heat treatment process with exposing the ribbon to DC magnetic field;
Fig. 2B illustrates schematic representation of the heat treatment processes without exposing the ribbon to DC magnetic field;
Fig. 3 illustrates temperature distribution in two-zone heat treatment unit; Fig. 4A shows magnetoelastic properties of the amorphous ribbon made from alloy No 2 containing 14.9 at% of cobalt and heat treated without tensile stress with exposition to magnetic field; Fig. 4B shows magnetoelastic properties of the amorphous ribbon made from alloy No 2 containing 14.9 at% of cobalt and heat treated under tensile stress with exposition to magnetic field;
Fig. 5 shows magnetoelastic properties of the amorphous ribbon made from Fe - Ni alloy No 8, containing 3.1 at% of chromium and 2.1 at. % of molybdenum; Fig. 6 shows magnetoelastic properties of the amorphous ribbon made from Fe -
Ni alloy No 5, containing considerable amount chromium and reduced amount of molybdenum (< 2 at. %);
Fig. 7 shows magnetoelastic properties of the amorphous ribbon made from Fe - Ni alloy No 13, containing 1.4 at% of chromium and 4.7 at. % of molybdenum, heat treated under tensile strength without exposition to dc magnetic field.
DETAILED DESCRIPTION OF EMBODIMENTS
Referring to Fig. 1, there are schematically illustrated the main components of a magnetomechanical marker configured according to the invention. The marker includes a magnetic biasing element 12 in the form of a semihard ferromagnetic strip (continuous or segmented) and an amorphous magnetostrictive element 14. They can be placed onto a support substrate (e.g. label), for example a bottom surface of a plastic container 10 being arranged with a certain space between the biasing and amorphous magnetostrictive elements. Typically, the semihard ferromagnetic and magnetostrictive elements 12 and 14 are arranged one above the other such that the magnetostrictive element 14 is biased with a DC magnetic field (e.g. from 3,0 to 15,0 Oe) created by the semihard ferromagnetic element 12.
The amorphous magnetostrictive element 14 is configured according to the invention from an alloy having a composition corresponding to the formula Ni a Fe b Co c Mθ d Cr e M' m B x Siy, wherein M' corresponds to at least one surface active element from Sn, Pb, and Bi. The content "m" of the surface element(s) is defined by desired casting ability of the alloy to be obtained, and is higher than O.OOlat.% (e.g. 0.001-0.4). Preferably, the alloy contains both Sn and Pb surface active elements such that the total content thereof ranges from 0.04 to 0.15 at %.
In the above composition, "a" ranges from 10 to 50, "b" ranges from 20 to 60; "c" is less than 15 at.% down to 0; "d" is higher than 2, e.g. up to 10, and "e" is higher than 1, such that a sum (d+e) is higher than 5, e.g. up to 10, preferably "d" is in a range of 4.0-5.0 at. % and "e" is in a range of 1.0-2.0 at. %; "x" ranges from 10 to 25, "y" ranges from 0 to 3, the entire sum of (a+b+c+d+e+m+x+y) being 100 at.%. The magnetostrictive element 14 is prepared from a amorphous ribbon heat treated in a method which will be described more specifically further below. As indicated above, for markers comprising magnetostrictive elements which contain low amount of cobalt or do not contain cobalt at all, use of amorphous ribbon with high content of such elements as Mo and Cr is needed, which improves magnetoelastic properties of the amorphous ribbon. However, increase of the amount of Fe, Mo and Cr in the Fe - Ni - Co or Fe - Ni alloys, would result in reduction in the casting ability. Accordingly, the use of surface active elements, such as Sn and Pb, is desirable to increase molten alloy fluidity and therefore improve alloy casting ability. The amount of such surface active elements introduced into the alloy depends on the content of Fe, Mo and Cr: the higher is the content of these elements in the alloy, the larger the amounts of surface active elements that should be introduced. In this connection, reference is made to Table 1 showing examples of the magnetostrictive alloys compositions and their Curie temperatures Table 1
The inventors have conducted several experiments with the heat treatment process. Some specific but not limiting examples will now be described with reference to Figs. 2A and 2B, which schematically illustrate the principles of the heat treatment process with exposing a ribbon to DC magnetic field (Fig. 2A) and without exposure to such field (Fig. 2B).
The amorphous alloy ribbons 23 were continuously heat treated in a two-zones heat treatment unit comprising a 2 meters long tube-type oven. This was implemented by transporting the ribbon 23 from one reel 22 to another reel 21 at a certain speed selected to obtain a desired time of the ribbon heat treatment (e.g. of about 10-11 seconds). An annealing or hot zone 33 has a length of about 120 cm. A cold zone 32 has a length of 80 cm. This zone was exposed to 2.5 kOe strength DC magnetic field 31 oriented perpendicular to a longitudinal axis of the ribbon.
Fig. 3 shows the temperature distributions in a heat treatment unit. The temperatures in the cold zone were about 350°C or 60°C. The temperature of the hot zone was always above the Curie temperature of the alloy, but not lower than 400 0 C to provide transverse curved shape of the annealed ribbon. For the alloys having the Curie temperature in the range from 277°C to 332 0 C, this value of the temperature in the hot zone is considerably higher than the Curie temperature of the alloy. In the cold zone, the ribbon temperature was always below the alloy Curie temperature. Annealing of the 5 amorphous ribbons made of the alloys containing less than 15 at. % of cobalt was carried out under tensile stress. Some Fe - Ni based alloy amorphous ribbons do not containing cobalt were continuously heat treated under tensile stress without exposing it to magnetic field at all ( Fig. 2B ). The amorphous ribbons so heat-treated were then cut into 36-39 mm long pieces. Then, two 36-39 mm long strip pieces having width of 6
10 mm stacked together were exposed to a burst of an exciting signal of constant amplitude tuned to the frequency of mechanical resonance of the strip pieces material. The strip pieces responded to the exciting pulse and generated an output signal in the receiving coil. At time t o =O, excitation is terminated, and the marker starts to ring-down, reflected in the output signal which is reduced from A 0 to zero over a period of time. At time ti,
15 which is one msec after the termination of excitation, the output signal was measured, which is denoted by the quantity A 1 . Thus, A 0 ZA 1 (Krd) is a measure of the ring-down or oscillation damping. The lower value of Krd results in higher detection rate of the marker.
Examplel
20 The amorphous ribbons of 25-26 μm thickness and 6 mm width, having different amount of cobalt, were cast at temperatures 1320 -1350 0 C. They were strong and ductile. The chemical composition of cast amorphous ribbons being used is described by the formula: Ni a Fe b Co c MθdCreM' m B x Si y ; wherein M" is at least one element from Sn, Pb, and Bi; "a" ranges from 10 to 50, "b" ranges from 20 to 60, "c" is
25 less than 15 at.% down to 0; "d" is higher than 2 at.%; "e" is higher than 1 ; a sum (d+e) is higher than 5; "m" is higher than 0.001; "x" ranges from 10 to 25; "y" ranges from 0 to 3; and a sum of (a+b+c+d+e+m+x+y) is 100 at.%.
After casting, the amorphous ribbons were continuously heat treated in the tube- like two-zone heat treatment unit (Fig. 2A) by transporting the ribbon 23 from one reel 30 22 to another reel 21 at a certain speed. The first or annealing zone of the unit 33 was about 120 cm long. The annealing time was about 7.2 seconds. The second or cooling zone 32 was about 80 cm long and the cooling time was about 4.8 seconds. The heat treatment temperatures in both zones are shown in Table 2 below. The temperature distributions in the heat treatment unit is shown in Fig. 3.
In the annealing zone, the ribbon was not exposed to any DC magnetic field. The cooling zone of the heat treatment unit was exposed to 2.5 kOe strength DC magnetic field 31 oriented perpendicular to the longitudinal axis of the ribbon. The amorphous ribbons so heat-treated were then cut into 36-39 mm long pieces. Then, two 36-39 mm long strip pieces having width 6 mm stacked together were exposed to a burst of exciting signal of constant amplitude tuned to the frequency of mechanical resonance of the strip pieces material. The strip pieces responded to the exciting pulse and generated output signal in the receiving coil. At time to=O excitation is terminated and the marker starts to ring-down, reflected in the output signal which is reduced from A 0 to zero over a period of time. At time t ls which is one millisecond after the termination of excitation, the output signal of a value Ai was measured. Thus, a ratio A 0 /Ai is a measure of the ring-down or oscillation damping, K rd . The higher value of A 1 results in higher detection rate of the marker.
Typical magneto-resonant properties of the investigated resonators made from Fe-Ni based amorphous magnetostrictive strips having different cobalt content (alloys Nos. 1-4, Table 1) are shown in Table 2. Here, Ti is the annealing temperature in the first zone, T 2 is the temperature in the second zone (cooling zone), N is the tensile stress of the ribbon during annealing, A 0 is the maximum amplitude of the response signal at time t=0 at bias field of 6,5 Oe; A 1 is the amplitude of the response signal at time t=lmsec at bias field of 6,5 Oe H b ; Hk is the anisotropy field; Hp rm i n is the bias field where the resonant frequency has its minimum value; K s i or dFr/dH is the slope of Fr(H), F r is the frequency of the exciting AC magnetic field, and K rd is the ring-down coefficient.
Table 2
As can be seen from Table 2, the magnetostrictive strip pieces made from alloys containing considerable amount of Mo and Cr and reduced amount of cobalt after annealing demonstrate high amplitude signal, suitable value of the ring-down coefficient K r( j and slope value K s i.
It should be noted that a resonator made of alloy No. 1 having high content of Co (25.8 at.%) and annealed without a tensile strength produces a high amplitude signal, suitable value of the ring-down coefficient K rd , and the slope value dFr/dH as well.
At the same time, the resonators made of alloys with a reduced content of cobalt (14.9 at. %) and high content of Cr and Mo have relatively low H k , very high values of the ring-down coefficient K rt j and slope coefficient K S |, for the amorphous ribbon annealed without a tensile strength. For example, a ribbon having composition of alloy
No. 2 annealed without a tensile strength has low saturation magnetic anisotropy 6 Oe, and coefficients K r( j and K S | are very high (2.94 and 1.23 respectively). The same ribbon annealed under a tensile stress with exposition to a magnetic field has good magnetoelastic properties and suitable values of the above mentioned coefficients K r d and K s i.
In this connection, reference is also made to Figs. 4A and 4B as well. Fig. 4A shows magnetoelastic properties of the amorphous ribbon made from alloy No 2 containing 14.9 at% of cobalt and heat treated without tensile stress with exposition to DC magnetic field. Fig. 4B shows magnetoelastic properties of the amorphous ribbon made from alloy No. 2 containing 14.9 at% of cobalt and heat treated under tensile stress with the exposition to DC magnetic field. In the figures, graph Gi corresponds to the Fr as a function of the applied bias filed; and graphs G 2 and G 3 correspond to variations of the response signals Ao and Aj with the applied bias field respectively.
Thus, to obtain good magnetoelastic properties of the resonators made from inventive alloys containing cobalt of less than 15 at. %, the amorphous ribbon is to be annealed under a tensile strength with exposition to DC magnetic field in the cooling zone.
Example 2
Glassy metal alloys where prepared with no cobalt and having a composition as described by the formula: Ni a Fe b ModCreM' m B x Si y , wherein M" is at least one element from Sn, Pb, and Bi; "a" ranges from 10 to 50, "b" ranges from 20 to 60, "d" is higher than 2 at.%; "e" is higher than 1; a sum (d+e) is higher than 5; "m" is higher than 0.001; "x" ranges from 10 to 25; "y" ranges from 0 to 3; and a sum of (a+b+c+d+e+m+x+y) is 100 at.%. These samples were prepared in the same manner described above Example 1. The ribbons of 25 μm thick and 6 mm wide were cast at temperatures 1320 -1350 0 C and were strong and ductile. They were continuously heat treated under a tensile stress in the tube-like two-zones oven of Figs. 2A and 2B. In the first zone, the ribbons were annealed, without exposure to s magnetic field, at temperature 42O 0 C during 7.2 sec. The ribbon at the cooling zone was exposed to the 2.5 kOe strength magnetic field 31 (see Fig. 2A) oriented perpendicular to the longitudinal ribbon axis. The cooling time was equal to 4.8 sec. The temperature in the center of the cooling zone was kept around 60 0 C. As Curie temperatures of these types of alloys are in the range between 277-347 0 C, the annealing temperature in the first zone was chosen taking into account the capability of the ribbon to take a curved shape during its thermal treatment. The transversely-curved magnetostrictive strips have small possibility to have a clamping effect that might otherwise occur when they are mounted in an EAS marker in proximity to a magnetic biasing element.
The heat treatment process is shown schematically in Figs. 2A-2B and 3. Typical magneto-resonant properties of the inventive resonators made from the Fe-Ni based amorphous ribbons that do not containing cobalt and have different amount of molybdenum and chromium (alloys Nos. 5-8 and 9-12, Table 1) are shown in Table 3 below. Here, Ti is the annealing temperature in zone 1, T 2 is the temperature in zone 2 (cooling zone), A 0 is the maximum amplitude of a response signal at time t=0 at bias field 6,5 Oe ; A 1 is the amplitude signal at time t=lmsec at bias field 6,5 Oe Hb; H k is the anisotropy field; HFrmin is the bias field where the resonant frequency has its minimum; K s i or dFr/dH is the slope of Fr(H), F r is the frequency of the exciting AC magnetic field, K rd is the ring-down coefficient.
Table 3
As it follows from Table 3, the magnetostrictive strip pieces made from Fe - Ni alloys, containing Mo and Cr in sum more than 5 at.% and at the same time more than 2 at.% of molybdenum (alloys No8-12), after annealing demonstrate high amplitude response signal, suitable value of the ring-down K r a and slope value, Ks, coefficients. In this connection, reference is made to Fig. 5 which shows magnetoelastic properties of the amorphous ribbon made from Fe - Ni alloy No. 8, containing 3.1 at% of chromium and 2.1 at. % of molybdenum.
Quite the opposite, the magnetostrictive strip pieces made from Fe - Ni alloys Nos. 5 and 6, containing considerable amount of chromium (> 4.7 at. %) and reduced amount of molybdenum (< 2 at. %) demonstrate unsuitable magnetoelastic properties. This is illustrated in Fig. 6 showing magnetoelastic properties of the amorphous ribbon made from Fe - Ni alloy No. 5 (Table 1), containing considerable amount of chromium and reduced amount of molybdenum (< 2 at. %).
Example 3 Three amorphous alloys were prepared (cast) in a similar manner, with no cobalt and with different contents of molybdenum having compositions described by formulas: Fe 4633 Ni 302 Moo 5 Cr 47 B 18 Si 025 Sno Q 12 Pb 0008 (alloy 5) Fe 38 13 Ni 383 Mo 2 ! Cr 3 ! B 182 Si 025 Sn 0 O12 Pb 00O8 (alloy 8) Fe 3935 Ni 362 Mo 4 7 Cri 4 B 182 Si 025 Sno 06 Pb 0 M (alloy 13)
The cast amorphous ribbons were continuously heat treated in the tube-like two- zone heat treatment unit (Figs. 2A and 2B) by transporting the ribbon through the unit with a speed of 10 m/min under a tensile stress. The first or annealing zone 33 was about 120 cm long. The annealing time was about 7.2 seconds. The second or cooling zone 32 was about 80 cm long. The cooling time in the unit was about 4.8 seconds. The annealing temperature was about 42O 0 C. Distribution of temperatures in the unit is shown in Fig. 3. The temperature at the center of the cooling zone was kept around 60 0 C. The ribbons were heat treated by two ways. In the first case, the annealing and cooling of the ribbons in both zones was carried out without exposition to a magnetic field (Fig. 2B). In the second case, the ribbon annealing in the first hot zone was carried out without exposition to magnetic field, but the ribbon cooling in the cold zone was done with the exposition to the 2.5 kOe strength DC magnetic field (DCMF) 31 perpendicular oriented to the longitudinal axis of the ribbon (Fig. 2A).
The following designations were accepted: A 0 is the maximum amplitude signal at time t=0 at bias field 6,5 Oe; A 1 is the amplitude signal at time t= 1msec at bias field
6,5 Oe Hb; Hk is the anisotropy field; HFrmm is the bias field where the resonant frequency has its minimum; KsI or dFr/dH is the slope of Fr (H), Krd is the ring-down coefficient, "Yes" corresponds to the exposure of the cooling zone to the DC MF, "Not" corresponds to a condition of no exposure of the cooling zone to a DC MF. Table 4 below shows magnetoelastic properties of the two strip pieces resonators made from Fe-
Ni alloy ribbons annealed and cooled under a tensile strength with and without exposition thereof to DC magnetic field.
Table 4
The testing results shown in Table 4 indicate that magneto-elastic resonators made from amorphous ribbon not containing cobalt and having molybdenum and chromium content higher than 2 and 1 at.% respectively and a sum of their contents more than 5 at%, heat treated under tensile strength with or without exposition to DC magnetic field demonstrate good magnetoelastic properties suitable for the production of magnetomechanical markers. In this connection, reference is made to Fig. 7 showing magnetoelastic properties of the amorphous ribbon made from Fe - Ni alloy No. 13 (Table 1), containing 1.4 at% of chromium and 4.7 at. % of molybdenum, heat treated under tensile strength without exposition to DC magnetic field. As clear from Fig. 7, the resonator produced from alloy No. 13 exhibits very good magnetoelastic properties.
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