Patent Grant
7786393
An element for making an electric contact to a contact member for enabling an electric current to flow between said element and said contact member. The element comprising a body having at least a contact surface thereof coated with a contact layer to be applied against said contact member. The contact layer comprises a continuous or discontinuous film comprising a multielement material.
Recent studies has shown that compounds having the general formula Mn+1AXn exhibit unusual and exceptional mechanical properties as well as advantageous electrical thermal and chemical properties. Despite having high stiffness these compounds are readily machinable, resistant to thermal shock, unusually damage tolerant, have low density and are thermodynamically stable at high temperatures (up to 2300° C. in vacuum). M is a transition metal or a combination of transition metals, n is 1, 2, 3 or higher, A is a group A element or a combination of a group A element, and X is Carbon, Nitrogen or both. Group A element is any of a list: Aluminium Al, Silicon Si, Phosphor P, Sulfur S, Gallium Ga, Germanium Ge, Arsenic As, Cadmium Cd, Indium I, Tin Sn, Thallium Tl, Lead Pb. Transition metal M is any of a list: Scandium Sc, Titanium Ti, Vanadium V, Chromium Cr, Zirconium Zr, Niobium Nb, Molybdenum Mo, Hafnium Hf, Tantalum Ta. Mn+1AXn compounds have layered and hexagonal structures with Mn+1Xn layers interleaved with layers of pure A and this is an anisotropic structure which has exceptionally strong M-X bonds together with weaker M-A bonds, which gives rise to their unusual combination of properties.
Mn+1AXn compounds are characterized according to the number of transition metal layers separating the A-group element layers: in 211 compounds there are two such transition metal layers, on 312 compounds there are three and on 413 compounds there ore four. 211 compounds are the most predominant, these comprise Ti2AlC, Ti2AlN, Hf2PbC, Nb2AlC, (NB,Ti)2AlC, Ti2AlN0,5C0,5, Ti2GeC, Zr2SnC, Ta2GaC, Hf2SnC, Ti2SnC, Nb2SnC, Zr2PbC and Ti2PbC. The only known 312 compounds are Ti3AlC2, Ti3GeC2 and Ti3SiC2. Ti4AlN3 and Ti4SiC3 are the only 413 compounds known to exist at present. A large number of solid solution permutations and combinations are also conceivable as it is possible to form solid solutions on the M-sites, the A-sites and the X-sites of these different phases.
The Mn+1AXn compounds can be in ternary, quaternary or higher phases. Ternary phases has three elements, i.e. Ti3SiC2, quaternary phases has four elements i.e. Ti2AlN0.5C0.5, and so on. Thermally, elastically, chemically and electrically the ternary phases, quaternary phases or higher phases share many of the attributes of the binary phases.
Michel Barsoum has synthesized, characterized and published data on the Mn+1AXn phases named above in bulk form [“The Mn+1AXn Phases: A New class of Solids”, Progressive Solid State Chemistry, Vol. 28 pp 201-281, 2000]. His measurements on Ti3SiC2 show that it has a significantly higher thermal conductivity and a much lower electrical resistivity than titanium and, like other Mn+1AXn phases, it has ability to contain and confine damage to small areas thus preventing/limiting crack propagation through the material. Its layered structure and the fact that bonding between the layers is weaker than along the layers (as in graphite) give rise to a very low friction coefficient, even after six months exposure to atmosphere.
The research groups of Prof. Lars Hultman at Linköping University and Prof. Ulf Jansson at Uppsala University have demonstrated that magnetron sputtering process (a sort of Physical Vapor Deposition, PVD) can be used to deposit coatings of Ti3SiC2 and other Mn+1AXn phases onto various substrates at relatively low temperatures (approximately 750-1000° C.) [Palmquist, J.-P., et al., “Magnetron sputtered epitaxial single-phase Ti3SiC2 thin films”. Applied Physics Letters, 2002. 81: p. 835; Seppänen, T., et al. “Structural characterization of epitaxial Ti3SiC2 FILM”, in Proc. 53rd Annual Meeting of the Scandinavian Society for Electron Microscopy, Tampere, Finland 12-15 Jun., 2002 (Ed. J. Keränen and K. Sillanpää, University of Tampere, Finland, ISSN 1455-4518, 2002), p. 142-143.]
A contact element in an electrical contact arrangement may have many different applications. The contact element is used for making an electric contact to a contact member for enabling an electric current to flow between said element and said contact member. The contact element comprises a body having at least a contact surface thereof coated with a contact layer to be applied against said contact member. A sliding electric contact arrangement comprising two contact surfaces adapted to be applied to each other for establishing an electric contact may slide with respect to each other when establishing and/or interrupting and/or maintaining the contact action. Such electric contact elements, which may establish sliding contacts or stationary contacts has preferably a body made of for instance copper or aluminum.
The contact layer is arranged for establishing a contact to the contact member with desired properties, such as a low contact resistance and low friction coefficient with respect to the material of the contact member to be contacted etc. Such applications are for instance for making contacts to semiconductor devices for establishing and interrupting electric contact, in mechanical disconnections and breakers and for establishing and interrupting electric contacts in contact arrangements of plug-in type. Such electric contact elements, which may establish sliding contacts or stationary contacts has preferably a body made of for instance copper or aluminium.
An example of a contact element including a contact layer, such as a continuous film of a multielement material having strong bonds, such as covalent or metallic bonds, within each atomic layer and weaker bonds, through longer bonding distance or for example as van der Waals bonds or hydrogen bonds, between at least some adjacent atomic layers thereof is given in WO01/41167. The multielement material is MoS2, WS2 or of any layered ternary carbides and layered nitrides that can be described as M3AX2. A problem with the described multielement material is that methods to produce the material are carried out at high temperatures (700-1400° C.). This means that an electrical electric contact element, which has a body made of a material that is not shape resistant at high temperatures, for instance copper or aluminum cannot be made use of.
The object of the present invention is to provide an electric contact element having a contact layer with a low friction without the disadvantages mentioned above of such layers already known in connection with use and/or manufacture thereof.
This object is obtained by providing an element for making an electric contact to a contact member for enabling an electric current to flow between said element and said contact member, said element comprising a body having at least a contact surface thereof coated with a contact layer applied against said contact member, and that said contact layer comprises a film comprising a multielement material comprising a nanocomposite of M-X, M-A-X nanocrystals and amorphous regions with M, A, X elements in one or several phases, such as M-A, A-X, M-A-X, or X. The multielement material comprises material with equal or similar composition as at least one of a carbide and nitride that can be described as Mn+1AXn, where M is a transition metal or a combination of a transition metals, n is 1, 2, 3 or higher, A is an group A element or a combination of a group A element, and X is Carbon, Nitrogen or both. The multielement material also comprise at least one nanocomposite comprising single elements, binary phases, ternary phases, quaternary phases or higher order phases based on the atomic elements in the corresponding Mn+1AXn compound.
A nanocomposite is a composite comprising crystals, regions or structures with a characteristic length scale above 0.1 nm and below 1000 nm.
According to a preferred embodiment of the invention the Mn+1AXn compound is a layered carbide or layered nitride.
A preferred Mn+1AXn phase is Ti3SiC2, where the resulting film deposited at low temperature is a nanocomposite of TiC nanocrystals and an amorphous phase with Si—C, Ti—Si—C, Ti—Si and C. This film posses good mechanical, chemical, temperature and contact properties.
It has been found that low temperature deposition of the multielement laminated structure results in nanocomposite compounds, with single elements, binary phases and ternary phases or a higher order phase depending of the number of atomic elements, with good chemical and contact properties. The composition of the compounds on an average should be equal or similar to the composition of the Mn+1AXn phases, such as A-X, M-A-X and X phases. The nanocomposite compounds shows also the desired ductile behaviour, posses non welding properties, shock resistance, chemical inertness, low contact resistance and good high temperatures properties which are all desired properties in electrical contact arrangement. Single phase crystalline microstructure forms large grains structure forms grains from 700° C.
In an embodiment of the invention the multielement material is equal or similar to any of a layered carbide and nitride that can be described as Mn+1AXn. The multielement material is in an amorphous state or nanocrystalline (0.5-500 nm grain size) state. The Mn+1AXn compound has a composition MxAyXx where {0≦x, y, z≦1; x+y+z=1} or both.
TixSiyCz with x=0.5 and 0.1<y<0.3 made by magnetron sputtering onto substrates kept at low temperature, Ts≦700° C., exhibit contact resistance against Ag of 6 μohm at a force of 800 N, which is comparable with Ag—Ag contacts. At the same time many useful mechanical properties are comparable in terms of friction, wear, and hardness to the previously known binary metal containing any metal Me and diamond-like carbon compound C, Me-C.
Unlike the diamond-like carbon compound that is designed for high hardness and thus typically exhibit brittle fracture, the material comprising compounds with equal or similar composition as any of carbide and nitride that can be described as Mn+1AXn and nanocomposites are ductile as seen by wear, scraping, scratching and indenting tests.
The A group element to M-X compounds improves the afore mentioned properties. The nanocomposite comprising compounds with equal or similar composition as at least one of a layered carbide and nitride that can be described as Mn+1AXn, such as M-X, M-A-X nanocrystals and amorphous regions with M, A, X elements in one or several phases, such as M-A, A-X, M-A-X, X. The nanocomposites have metallic or ceramic or mixed character type depending on the composition and processing of the film.
The deposited coatings comprising nanocomposites may form a transfer layer of nanolaminated crystalline Mn+1 AXn phases or carbon graphite during mechanical wear of an electrical contact. The phase transformation is driven by the thermo-mechanical energy generated in the contact zone. This layer may exhibit ultralow friction due to easy basal plane slip if the Mn+1AXn phase or graphite phase becomes textured parallel to the coating surface. Thus, the coating would not only be functional, but also self-adapting for the application.
PVD, CVD and other deposition processes involving co-deposition of elemental, precursor or compound sources which can be used to make thin films consisting of multielement material equal or similar to Mn+1AXn compound, said multielement material comprising a nanocomposite of M-X or M-A-X nanocrystals and amorphous regions with M, A, X elements in one or several phases, such as M-A, A-X, M-A-X, X. Preferably the depositions are made at low substrate temperatures such as in the demonstrated example. Finally, we note the possibility to design a coating with the widest possible range of properties compared to other materials as function of composition x, y, z and to make gradient material in one deposition run by varying the compositions from different sources.
It has turned out that a nanocomposite comprising said multielement material, and/or a metallic layer is excellent as a contact layer on a contact element in question for many reasons. A contact layer comprising such a multielement material, and/or a metallic layer according to the invention used as a contact has low contact resistance. The friction coefficient thereof is typically 0.1-0.6. The metallic layer provides the low contact resistance. Furthermore, in regions where the contact has a high friction said metallic layer can be worn and the said underlying multielement material comprising a nanocomposite of M-X, M-A-X nanocrystals and amorphous regions with M, A, X elements in one or several phases, such as M-A, A-X, M-A-X, X appears on the surface and reduces the friction.
According to another preferred embodiment of the invention the thickness of the metallic layer is in the range 1 nm to 1000 μm.
According to another preferred embodiment of the thickness of the metallic layer is in the range of a fraction of an atomic layer to 5 μm. This reduce the use of metal without effect the wear properties and friction properties.
According to another preferred embodiment of the invention said metallic layer is any of Au, Ag, Pd, Pt, and Rh. This is an advantage because the noble metals do not form oxides or thermal instable oxides. This is an advantage when used as coatings in high-efficient electrical contacts.
According to another preferred embodiment of the invention said metallic layer is an alloy with at least one of any of the afore mentioned metals.
According to another preferred embodiment of the invention the said metallic layer is any metal or a metal alloy.
According to another preferred embodiment of the invention the said metallic layer is any metal or metal composite where the composite can be an oxide, carbide, nitride or boride. It is an advantage to dope the metal to improve the properties of the layer, for instance the structure of the material.
According to another preferred embodiment of the invention said metallic layer is any metal or metal composite, said composite comprising a polymer, an organic material or a ceramic material such as an oxide, carbide, nitride or boride.
It is an advantage to incorporate a polymer, an organic material or a ceramic material to improve the properties of the layer for instance,
According to another preferred embodiment of the invention said the multielement material is coated with a metallic layer sufficiently thick to be able to wire-bond or solder a surface in a bonding to establish a non-separable electrical bond at the surface. The metal film act as a bonding layer by wire-bonding.
Furthermore, said underlying multielement material provides a low friction and wear resistance. Furthermore, said underlying multielement material also is a mechanical load carrying structure with ductile properties under the thin metallic film. The multielement material as low temperature films are showing equal properties compared to films that possesses a layered crystalline structure. The chemical inertness and the smoothness of the multielement compound also contribute to a low friction. The low friction is also due to grain rotation of the nanocomposite phases, and grain boundary phases or carbon. The multielement material are relatively chemical inert and stable at temperatures exceeding 400° C. Furthermore, said materials have low tendency to form oxides, which prevent degradation of electric contact to said contact member. Furthermore said multielement material coated or combined with a metallic layer show a ductile performance.
Said multielement material with equal or similar composition as a Mn+1AXn compound, will have a morphology varying from amorphous or nanocrystalline to pure crystalline, and the morphology may be selected in accordance with the particular use of the contact element and the costs for producing the multielement material.
According to a preferred embodiment of the invention the multielement material of said film coated or combined with a metallic layer is in the range 0.001 μm to 1000 μm, and in a very preferred embodiments is less then 5 μm. Said film of metallic layer is in the range of a fraction of an atomic layer to 1 mm. Such coatings may have a lifetime being nearly indefinite thanks to the very low friction and wear resistance of this material, so that in closed systems the result aimed at will be achieved through a thin film having low costs of material and manufacturing process as a consequence thereof.
According to another a preferred embodiment of the invention the multielement material coated or combined with a metallic layer is above 5 μm. Such a thickness is preferred in the case of using such a film on a contact element in a contact arrangement where the contact element and the contact member are going to be moved with respect to each other, such as in a sliding contact, and accordingly not only moved by different coefficients of thermal expansion upon thermal cycling, such as when used on a slip ring in an electric rotating machine.
According to another preferred embodiment of the invention the nanocomposite multielement film is a blend of different Mn+1AXn compounds where the resulting phases and atomic ratio of the elements are depended on the atomic elements in the Mn+1AXn phases and the ratio between the materials.
According to another preferred embodiment of the invention the body deeper under said contact surface is made of material being non-resistant to corrosion, and the material last mentioned is coated by a corrosion resistant material such as nickel, adapted to receive said film on top thereof. It is preferred to proceed in this way, since the multielement material film may have pores with a risk of corrosion of the underlying body material therethrough.
Another object of the present invention is to provide sliding electric contact arrangement of the type defined in the introduction allowing a movement of two contact surfaces applied against each other while reducing the inconveniences discussed above to a large extent.
This object is according to the invention obtained by providing such an arrangement with a contact element according to the present invention with said film arranged to form a dry contact with a friction coefficient, below 0.6, preferably below 0.2, to a contact member.
In another preferred embodiment of the invention such an arrangement with a contact element according to the present invention is provided with said film arranged to form a dry contact with a friction coefficient below 0.1.
The basic features and advantages of such a contact arrangement are associated with the characteristics of the contact element according to the present invention and appear from the discussion above of such a contact element. However, it is pointed out that a “sliding electric contact” includes all types of arrangements making an electric contact between two members, which may move with respect to each other when the contact is established and/or interrupted and/or when the contact action is maintained. Accordingly, it includes not only contacts sliding along each other by action of an actuating member, but also so called stationary contacts having two contact elements pressed against each other and moving with respect to each other in the contacting state as a consequence of magnetostriction, thermal cycling and materials of the contact elements with different coefficients of thermal expansion or temperature differences between different parts of the contact elements varying over the time.
A contact arrangement of the type last mentioned constitutes a preferred embodiment of the present invention, and the contact elements may for instance be pressed with a high pressure, preferably exceeding 1 MPa against each other without any mechanical securing means, but the contact elements may also be forced against each other by threaded screws or bolts.
According to another preferred embodiment of the invention said contact arrangement is adapted to be arranged in an electric rotating machine, where the film comprising multielement material will result in a number of advantages. It is in particular possible to benefit from the low friction coefficient of the multielement material when arranging the contact element and the contact member of the contact arrangement on parts of the rotating machine moving with respect to each other, such as for instance the slip ring as a contact element and a contact element sliding thereupon. It will in this way be possible to replace the carbon brushes used in the electric rotating machines by a contact element according to the present invention and a film of said type is then also preferably arranged on the moving part, such as a slip ring. Said carbon brushes have a number of disadvantages, such as a restricted lifetime, since the carbon is consumed. Furthermore, carbon dust is spread out on the windings and other parts of the machine, which may disturb the function thereof. It is preferred to have a thickness of the film of multielement material exceeding 10 μm for such a contact element, since also the film of multielement material will be consumed, but comparatively slowly, in this application thereof.
Electrical contacts arrangements according to other preferred embodiments of the invention are different kinds of contacts having contact surfaces moving while bearing against each other in establishing and/or interrupting an electric contact, such as plug-in contacts or different types of spring-loaded contacts, in which it is possible to take advantage of the very low friction coefficient of a multielement material resulting in a self-lubricating dry contact without the problems of lubricants such as oils or fats while making it possible to reduce the operation forces and save power consumed in actuating members.
Electrical contacts arrangements according to other preferred embodiments of the invention are included in tap changers on transformers, where a low friction is a great advantage when the contact elements are sliding with their contact surfaces against each other, and in mechanical disconnectors and breakers and in relays.
The invention also relates to a use of the contact arrangement, in which a probe for measuring and testing an integrated circuit is covered with said multielement material film, a contact layer is coated/combined with a metallic layer, avoiding chemical degradation and metal cladding on the probe. It is self evident that this use according to the invention is very favourable, since it will make it possible to carry out measurements and testing without any interruptions for replacing or cleaning the probe.
The invention also relates to a use of the contact arrangement, in which a contact for enabling contact to an electronic device, such as an integrated circuit is covered with a said multielement material film enabling electrical contact to the device.
Further advantages as well as advantageous features appear from the following description.
With reference to the appended drawings, below follows a specific description of preferred embodiments of the invention. In the drawings;
In another preferred embodiment of the invention the multielement material may comprise ternary phases and/or higher order phases for example 211, 312, 413 compounds. The multielement material has at least one carbide and/or nitride that can be described as Mn+1AXn component. In order to improve friction, thermal properties, mechanical properties or electrical properties the multielement material may comprise one or a combination of compounds any of a list: a single group A element, a combination of a group A elements, X is Carbon, X is Nitrogen, X is both Carbon and Nitrogen, a nanocomposite of M-X, a nanocomposite of M-A-X, nanocrystals and/or amorphous regions with M, A, X elements in one or several phases, such as M-A, A-X, M-A-X. The proportions of the included compounds may vary within a range of 0.0001-90% of the weight of the film. Different proportions of the compounds will strengthen the mechanical, physical, and chemical properties. In a preferred embodiment of the invention the proportions of the included compounds should not exceed 50% of the weight of the film, and in another preferred embodiment of the invention less then 20%. For instance compounds of Ag exceed the surface conductibility.
Another preferred embodiment according to the invention is a multielement material with excess of the M, A, X element. The multielement material for instance comprise the compound Tin+1SiCn+Cm. The compound Tin+1SiCn+Cm is a multielement material with excess carbon. That means that the film contains free carbon elements. The excess carbon X are transported to the surface and may function as a friction lower surface termination that provides electrical contact and protect the electrical surface from oxidation. The compound Ti3SiC2+Cm has a low contact resistance. The material may also have groups of M-A, M-A-X, A-X in various proportions.
In another preferred embodiment according to the invention the multielement material comprises the compound Ti3Si0.5Sn0.5C2. If the A group element is tin, Sn, the film may be too hydroscopic. If the A group element is silicon, Si, the film may react with oxygen and form a coating of an isolating oxide on the surface. These disadvantages are avoided if a combination of A element, in this case Sn and Si are used.
An arrangement for making a good electric contact to a semiconductor component 14 is illustrated in
A sliding contact arrangement according to another preferred embodiment of the invention is schematically illustrated in
A contact element and a sliding electric contact arrangement according to the present invention may find many other preferred applications, and such applications would be apparent to a man with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.
It would for example be possible to dope the thin friction film for improving friction, thermal, mechanical or electrical properties by one or several compounds or elements. However, the amount of doping should not exceed 20% of the weight of the film. It is then also possible to have different films on different contact surfaces of the contact elements and the contact member, for instance some doped and others not or some formed by at least two sub-layers and others having only one layer.
Another example of a contact arrangement according to the invention is to cover a probe for measuring and testing an integrated circuit (IC) with said film, comprising a multielement material and a metal layer, avoiding chemical degradation and metal cladding on the probe.
Furthermore, the contact elements and arrangements of the invention are not restricted to any particular system voltages, but may be used on low, intermediate and high voltage applications.
The multielement material of the contact layer according to the invention may form a solid film together with 50-90% of metal, for instance of Ti or Au, for improving the conductivity. This may take place by forming a homogeneous dispersion of the metal in the material, inhomogeneous dispersion with metallic regions and multielement regions, such as a composite or by arranging a layer of the multielement chemical compound and a layer of the metal alternating.
This application claims priority to U.S. provisional patent applications 60/511,424 and 60/511,430 filed 16 Oct. 2003 and is the national phase under 35 U.S.C. §371 of PCT/IB2004/003390 filed 18 Oct. 2004.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2004/003390 | 10/18/2004 | WO | 00 | 12/22/2006 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2005/038985 | 4/28/2005 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6747291 | Lu et al. | Jun 2004 | B1 |
| 6838627 | Isberg et al. | Jan 2005 | B1 |
| 20020000598 | Kang et al. | Jan 2002 | A1 |
| 20020068488 | Tuller et al. | Jun 2002 | A1 |
| Number | Date | Country |
|---|---|---|
| WO 03046247 | Jun 2003 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20070111031 A1 | May 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60511424 | Oct 2003 | US | |
| 60511430 | Oct 2003 | US |
