Patent Application
20080035245
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Various embodiments of this invention have been described in fulfillment of the various needs that the invention meets. It should be recognized that these embodiments are merely illustrative of the principles of various embodiments of the present invention. Numerous modifications and adaptations thereof will be apparent to those skilled in the art without departing from the spirit and scope of the present invention. Thus, it is intended that the present invention cover all suitable modifications and variations as come within the scope of the appended claims and their equivalents.
For many electrical devices and components in a variety of applications, including aerospace, wind power and electric vehicles, magnetic materials with high permeability, high saturation magnetization, low core loss, and high mechanical strength are attractive. There is a continuing need for magnetic materials with improved magnetic properties and high mechanical strength. Disclosed herein is a soft magnetic alloy having substantially high yield strength, and superior magnetic properties. In accordance with certain embodiments, certain materials (i.e., alloying additives) may be added to an iron-cobalt (Fe—Co) alloy in suitable quantities to enhance the mechanical strength, and saturation magnetization, and not significantly adversely affect coercivity to obtain high strength, high ductility, high saturation magnetization, and low coercivity magnetic materials. The details of the alloy compositions are described in the subsequent embodiments.
For example, as discussed in detail below, the soft magnetic materials may include an iron-cobalt-alloy composition, wherein cobalt (Co) is provided in the range of from about 15 atomic percent to about 60 atomic percent, or from about 20 atomic percent—to about 35 atomic percent, or from about 45 atomic percent—to about 55 atomic percent, or from about 25 atomic percent—to about 32 atomic percent. In each of these examples of Co atomic percentages, the alloy addition may include a platinum group metal, rhenium, or combinations thereof in the range of about less than 10 atomic percent, less than 5 atomic percent, less than 2 atomic percent, or between about 0.05 and 2 atomic percent. As discussed below, the alloy addition may include one or more platinum group metals, such as platinum, or palladium, or iridium, or ruthenium, or rhodium, or osmium, or combinations thereof. In certain embodiments, these alloying additions may result in magnetization of greater than about 1.8 Tesla, coercivity of less than about 100 Oersteds, and yield strength of greater than about 700 MegaPascals.
One or more of the rotor assembly 12, or the stator assembly 16, of the machine 10 may include soft magnetic alloys of the disclosed embodiments. Superior magnetic and mechanical properties of the soft magnetic alloys of the disclosed embodiments provide distinct advantages in terms of the performance of the machine. The specific composition of the alloy and its magnetic and mechanical property characterization are described in greater detail below. In the examples described herein, the machine 10 is a radial type machine where the flux flows radially through the air gap between the rotor and the stator. However, other examples of the machine 10 may operate with axial flux flow as well, where the flux flows parallel to the axis of the machine 10. Though the operation of the machine 10 is explained with a simple diagram, examples of the machine 10 are not limited to this particular simple design. Other more complicated designs are also applicable and may benefit from the soft magnetic materials discussed in detail below.
In certain embodiments, the soft magnetic alloy comprises iron, cobalt, and at least one alloying addition including a platinum group metal, rhenium, or combinations thereof. In one embodiment, cobalt is present in the alloy in the range of from about 15 atomic percent to about 60 atomic percent. In another embodiment, the alloy comprises cobalt in the range of from about 45 atomic percent to about 55 atomic percent. In one embodiment, the alloy comprises cobalt in the range of from about 20 atomic percent to about 35 atomic percent. The amount of cobalt may be chosen to optimize the magnetic properties of the alloy, reduce the material cost and enhance the material processability.
The magnetic and the mechanical properties of the alloys may be controlled by controlling the amount of alloying addition introduced. The soft magnetic alloy comprises at least one alloying addition including at least one platinum group metal, wherein the at least one platinum group metal comprises platinum, or palladium, or iridium, or ruthenium, or rhodium, or osmium, or combinations thereof. Introduction of these additions is expected to increase the yield strength of the alloy. However, the amount of the alloying addition may need to be controlled so as to limit the precipitation of intermetallic compounds, which may adversely affect the magnetic properties of the alloy. Therefore an optimum amount of alloying addition is introduced. In one embodiment, the soft magnetic alloy comprises the alloying addition in an amount less than about 10 atomic percent, or less than about 5 atomic percent. In one embodiment, the device includes alloying additions in the range of from about 0.05 atomic percent to about 2 atomic percent. In another embodiment, the soft magnetic alloy comprises alloying additions in an amount in the range of from about 0.05 atomic percent to about 1 atomic percent.
In an exemplary embodiment, the alloy comprises palladium in the amount of less than about 3 atomic percent. In another exemplary embodiment, the alloy comprises palladium in the amount of less than about 1.5 atomic percent. In one exemplary embodiment, the soft magnetic alloy comprises ruthenium less than about 3 atomic percent. In another exemplary embodiment, the soft magnetic alloy comprises ruthenium less than about 1.5 atomic percent. In another exemplary embodiment, the soft magnetic alloy comprises rhenium less than about 3 atomic percent. In another exemplary embodiment, the soft magnetic alloy comprises rhenium less than about 1.9 atomic percent.
Alloying additions may be introduced into the Fe—Co baseline alloy by a number of techniques. In some embodiments, the constituent materials are melted together and processed to obtain an alloy of desired composition. One example of such a process is vacuum induction melting. In another embodiment, all the constituent materials are subjected to mechanical alloying to obtain the alloy of desired composition.
Additional elements may be present in controlled amounts to benefit other desirable properties provided by this alloy. The amount of these additions is selected so as not to hinder the magnetic performance of the alloy. In addition, the alloy may also comprise usual impurities found in commercial grades of alloys intended for similar service or use. The levels of such impurities are controlled so as not to adversely affect the desired properties.
The alloys of the invention desirably exhibit high saturation magnetization, low coercivity, and high mechanical strength. In one embodiment, the soft magnetic material has a saturation magnetization of at least about 1.8 Tesla. In another embodiment, magnetic material has a saturation magnetization at least about 2 Tesla. In one embodiment, magnetic material has a coercivity of less than about 100 Oersteds. In another embodiment, soft magnetic material has a coercivity of less than about 50 Oersteds. The high saturation magnetization values allow the soft magnetic material to be operated at very high flux densities, enabling compact electric machine designs. In one embodiment, soft magnetic material of the disclosed embodiments has a yield strength of greater than about 500 MPa. In another embodiment, magnetic material has a yield strength of greater than about 700 MPa.
In one embodiment, a system includes a device having one or more components formed of a soft magnetic alloy. For example, the soft magnetic alloy may include iron, cobalt, and at least one alloying addition including a platinum group metal, rhenium, or combinations thereof. The composition of the soft magnetic alloy may be chosen based on the desired properties for the specific application of the device, and are similar to those described in above embodiments. Examples of the system include a generator, a motor, an alternator, or a combination thereof. In an exemplary embodiment, the device comprises a rotor of an electrical machine. In another embodiment, the device comprises a stator of an electrical machine. Non-limiting examples of the electrical machine include a generator, a motor, and an alternator. In other embodiments, the system comprises a magnetic bearing, an electromagnet pole piece for high field magnets, an actuator, an armature, a solenoid, an ignition core, or a transformer. As known to those skilled in the art of electrical machines, stator and rotor designs vary based on application, and may include one or more magnetic components. Certain embodiments of the disclosed soft magnetic materials provide performance and/or efficiency improvements for aerospace applications, due to the higher yield strength, lower magnetic core losses, and the ability to operate at relatively higher flux densities than previous magnetic alloys. In other embodiments, the soft magnetic material is incorporated into components of a machine in an electric or a hybrid vehicle, in a bearing assembly, or a wind power system.
The soft magnetic alloy of the disclosed embodiments is suitable for many electromagnetic device applications. They are especially attractive for devices comprising these alloys in a bulk monolithic structure form. These alloys may be easily processed with suitable mechanical and magnetic properties in a bulk structure form. Accordingly, in some embodiments, the device comprises a bulk monolithic structure of the alloy. The alloy comprising the device may be in the form of a sheet, a plate, or a bar. In some embodiments, the bulk monolithic structure has a thickness of at least about 100 micrometers. In another embodiment, the bulk monolithic structure has a thickness in the range of from about 500 micrometers to about 200 millimeters. In another embodiment, the bulk monolithic structure has a thickness in the range of about 400 millimeters. A sheet of the alloy may be prepared by any suitable metallurgical process including, casting, forging, extrusion, hot rolling, or cold rolling. The alloy may additionally be prepared by powder metallurgical processing. The powder may be made into a consolidated bulk structure by any known consolidation technique including hot pressing, hot isostatic pressing, blind-die compaction and extrusion, or the like. Alloys may be formed into sheets having an insulating coating thereon and overlapping the coated sheets to form a laminated article such as a stator or rotor of an electric machine.
The soft magnetic alloys of the embodiments may be prepared, worked, and formed into products using any suitable conventional technique known in the art. It may be melted in air as by means of an electric arc furnace or it may be melted using suitable vacuum melting techniques, such as vacuum induction melting (VIM) and/or vacuum arc remelting (VAR). After being melted and cast as an ingot, it may be forged into billets or slabs. It may be hot rolled to strip, and be formed into a coil while still hot. The thus-formed strip is an intermediate product substantially thicker than the finished size. The finished size may then be formed by cold rolling the strip to the desired thickness or gauge.
The following example serves to illustrate the features and advantages offered by the embodiments of the present invention, and are not intended to limit the invention thereto.
Alloys with different alloying additions were vacuum induction melted and poured into copper mold to produce 25 mm bars approximately 120 mm in length. The alloys comprised a base Fe—Co composition (with 30 atomic percent Co), then compositions to which 1.8 and 3 atomic percent of individual elements were added. The cast samples were then hot isostatically pressed at 950° C. for 4 hours at 205 MPa. Vickers hardness measurements were made on each of the alloys. The hardness values are used as an indicator of the mechanical strength of the alloys. Room temperature dc magnetic properties of each alloy were measured by vibrating sample magnetometry. High energy X-ray diffraction was used to measure the lattice parameters of each alloy and thus enable a calculation of the alloy density. The results are tabulated in Table 1 and shown in
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
