Patent Application
20070235445
The drawings accompanying and forming part of this specification are included to depict certain embodiments of the invention. A clearer concept of embodiments of the invention, and of components combinable with embodiments of the invention, and operation of systems provided with embodiments of the invention, will be readily apparent by referring to the exemplary, and therefore nonlimiting, embodiments illustrated in the drawings (wherein identical reference numerals (if they occur in more than one view) designate the same elements). Embodiments of the invention may be better understood by reference to one or more of these drawings in combination with the following description presented herein. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale.
Embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components and equipment are omitted so as not to unnecessarily obscure the embodiments of the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.
Within this application several publications are referenced by Arabic numerals, or principal author's name followed by year of publication, within parentheses or brackets. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims after the section heading References. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference herein for the purpose of indicating the background of embodiments of the invention and illustrating the state of the art.
The invention can include non-contact ultrasonic treatment of metals via induction heating in a high magnetic field. This method can be combined with other high-field magnetic processing of materials, but can be used to advantage in circumstances where only high intensity ultrasonic treatment is beneficial. A specific advantage of this method is that the ultrasonic energy is coupled directly to the sample, and no direct contact is required. The ability to couple acoustic energy directly via a non-contacting method overcomes a huge technological barrier to the more widespread use of ultrasonic processing. The invention can include a superior ultrasonic processing method for producing enhanced material properties in metallic alloys.
The invention can include a synergistic combination of high surface current density (induced via induction heating) in a high-field magnet, which is a very effective method for creating a high energy density acoustic environment. This provides a non-contact method for applying high-intensity ultrasonic energy to the processing of metals. Furthermore, the applied ultrasonic excitation can be uniformly distributed over most of the surface of the metal sample.
Using this method, non-contacting ultrasonic treatment can be applied to the processing of metal alloys in the solid and/or melt phase(s). Molten metals can be contained in a non-metallic ceramic crucible of a type that is readily penetrated by the induction heating fields. Ultrasonic treatment in the solid phase can be achieved either at near-ambient temperatures, or at elevated temperature. When applied under high temperature conditions, temperature control can readily be achieved via the induction heating process, whereas at ambient temperatures, active cooling would be required to remove the heat deposited by the inductive heating system.
A method is described for non-contact ultrasonic treatment of metals via induction heating in a high magnetic field. The method can be coupled with high-field magnetic processing of materials, but can also be used to advantage in circumstances where only high intensity ultrasonic treatment is beneficial. A specific advantage of the method is that the ultrasonic energy is coupled directly to the sample, and no direct contact is required. Generally this approach eliminates the elevated temperature problems associated with the use of the more conventional probe/horn ultrasonic applicator.
In the discussion that follows, the high intensity EMAT effect created by induction heating in a high-field magnet is described in greater detail. The amplitude of the resulting ultrasonic excitation is compared with the much weaker EMAT effect that is intrinsic to all induction heating systems. The latter effect is discussed first.
Referring to
The surface current, Jθ, as it flows perpendicularly to the axial magnetic field, experiences a force −J×B that acts on the surface of the sample, as shown in
If the time dependence of the induction field is given by Hz=Ho sin(2 πft) where f=300 kHz and Ho=35 kA/m, then the induced surface current density is given by Jθ=Ho sin(2 πft). In this case, the time dependence of the radial force (i.e., pressure) is given by Fr=−μo(H0)2 sin2(2 πft). Note that the pressure does not reverse direction, and is always directed inward (i.e., in the −r direction). From the trigonometric identity 2 sin2×=1−cos(2×), it can be seen that the pressure includes two contributions, 1) a time-averaged component given by −(½)μo(Ho)2, and an oscillatory component, (½)μo(Ho)2 cos(4 πft), of the same amplitude that oscillates at twice the induction heating frequency, i.e., at a frequency of 600 kHz. [Note that the pressure can equivalently be attributed to the discontinuity in the energy density (or pressure) of the magnetic field, μoHo2, at the surface of the conductor, due to the fact that the magnetic field is excluded from the metal by the skin effect.]
In summary, induction heating by itself results in the direct application of an oscillatory pressure to the heated surface at an ultrasonic frequency that is twice the induction heating frequency. This is essentially an electromagnetic acoustical transducer (EMAT), and this rather weak effect is intrinsic to the induction heating process. If the surface current density in the heating coil is 35 kA/m, then the pressure amplitude is about 750 Pa, which is 1500 Pa peak-to-peak, or about 1/60th of atmospheric pressure. For other values of surface current density, the pressure varies as the square of the current density.
Referring to
For the previous induction heating example, the B-field produced by the induction current density of 35 kA/m was just 0.044 Tesla. When induction heating is performed inside a high-field magnet, as shown in
In this case, the magnet field strength has a constant value of Bz=30 T, while the induced surface current density is the same as for the previous example, as give by Jθ=Ho sin(2 πft). The time dependence of the radial force (i.e., pressure) is then given by Fr=Jθ×Bz=HoBz sin(2 πft), which alternates in direction whenever the surface current changes direction (i.e., at the induction heating frequency). The magnitude (amplitude) of the pressure is given by Fr=Jθ×Bz=(35 kA/m)(30 T)=1,050,000 nt/m2=1.05 MPa, or 2 MPa peak-to-peak. To put this in perspective, note that this amplitude is approximately twice the pressure amplitude needed to produce cavitation in molten metals depending on the gas content of the melt.
In summary, induction heating in a high-field magnet greatly enhances the acoustic stimulation of the heated surface, and does so at an ultrasonic frequency that is exactly equal to the induction heating frequency. The acoustic driving force is bi-directional, alternatively compressing and stretching the sample. In liquids, the later leads to cavitation, which can be very beneficial for ultrasonic processing of the melt phase. Note that the static field provided by the high-field magnet greatly enhances the efficiency of the EMAT (electromagnetic acoustical transducer). For the specific example given, the amplitude of the acoustic pressure generated by induction heating within the high-field magnetic is at least 1000 times greater than the pressure generated by the intrinsic self-field of the induction heating by itself. If the surface current density of the heating coil is 35 kA/m, in a 30 T magnet, then the resulting acoustic pressure amplitude is 1 MPa, or about 10 atmospheres. For other values of induced surface current density, the pressure amplitude varies just linearly with the current density.
The effectiveness of acoustical excitation can be greatly enhanced if the frequency happens to coincide with a natural resonant frequency of the sample. Because of the large mismatch in the acoustic impedance at a material-air interface, most of the acoustic energy will be trapped within the sample and the sample container, forming an acoustical resonator. If the acoustic drive frequency is chosen to match a natural resonant frequency of the sample/holder, then the peak acoustic pressure in the resonator is enhanced by a factor that is equal to the quality factor of the resonator. Quality factors for liquid metal columns with large length-to-diameter ratios are expected to be in the range of 10-100. Although a somewhat smaller quality factor might be expected for the proposed experimental configuration, due consideration will be given to take advantage of acoustical resonances.
Referring to
Referring to
The invention can include feedback control of frequencies. The control of frequencies for induction heating carrier and for ultrasonic modulation may be configured as a part of a feedback control system so that those frequencies track shifts in resonance due to thermal effects and mechanical changes.
For the large external field, preferred embodiments of the invention include a substantially static (e.g., homogeneous) magnetic field. Alternative embodiments of the invention can include a large magnetic field generated and applied by an alternating current source or by a large single (or multiple) magnetic pulse. (Pulsed magnets at the National High Magnetic Field Laboratory at Los Alamos National Laboratory (LANL) are capable of up to 100 T.) For pulse durations long enough to include a significant number of ultrasonic cycles, the magnetically enhanced EMAT effect can produce enormously intense ultrasonic compression. Similarly, an alternating high magnetic field can also be used with an induction heating source to produce intense ultrasonic energy. The most likely uses of an alternating B-field would be for reasons other than an ultrasonic effect; however, ultrasonic processing using the enhanced J×B forces could be effectively used with an alternating field. The J×B forces would be calculated in the same way as static systems only the B-field would be time varying.
Preferred embodiment of the invention include a configuration of the work piece and an induction coil immersed inside a large static magnet field from a solenoid-type magnet. Naturally, in this case the “work piece” (such as a casting) would be inside the bore of the magnet either with the induction coil surrounding the work piece or inside of it. Alternative embodiments of the invention can include the magnet, work piece, and induction coil configured in reverse order, i.e., a large magnet is surrounded by the work piece and the induction coil is either between the work piece and the magnet or surrounds the work piece. This system configuration could be used for processing inside a large diameter tube for example. The J×B forces would be calculated the same as other systems although the B-field might not be as intense as inside the magnet's bore. Generically, the inter-relationship of the fields in these configurations can be termed confocal.
Specific embodiments of the invention will now be further described by the following, nonlimiting examples which will serve to illustrate in some detail various features. The following examples are included to facilitate an understanding of ways in which an embodiment of the invention may be practiced. It should be appreciated that the examples which follow represent embodiments discovered to function well in the practice of the invention, and thus can be considered to constitute preferred mode(s) for the practice of the embodiments of the invention. However, it should be appreciated that many changes can be made in the exemplary embodiments which are disclosed while still obtaining like or similar result without departing from the spirit and scope of an embodiment of the invention. Accordingly, the examples should not be construed as limiting the scope of the invention.
An embodiment of a non-contact, ultrasonic, ohmically decoupled insert inside a nine Tesla superconducting magnet is shown in
An embodiment for continuous work piece processing is shown in
An embodiment is shown in
An embodiment is shown in
A practical application of an embodiment of the invention that has value within the technological arts can be melt degassing prior to or during solidifications processes (this has significant ramifications for aluminum alloys). A practical application of the invention can be grain refinement (via enhanced nucleation, growth, and fragmentation processes) during solidification. A practical application of the invention can be reduction or elimination of macro- and micro-segregation during solidification. (i.e., development of more homogeneous microstructures by reducing or eliminating coring and banding during solidification). A practical application of the invention can be enhanced nucleation and growth during fusion (solidification) and solid-state phase transformations. A practical application of the invention can be development of more equiaxed microstructures that are less dendritic. A practical application of the invention can be refinement of inclusion particle size for a given volume fraction of impurities (inclusions) to improve performance as smaller particles initiate fracture by void initiation and coalescence at higher strains than larger inclusions. A practical application of the invention can be reduction of grain refining alloy additions (such as titanium diboride in aluminum alloys) by ultrasonically enhancing grain refinement resulting in production cost reduction. A practical application of the invention can be residual stress reduction or elimination. A practical application of the invention can be fatigue life enhancement. A practical application of the invention can be enhanced metal deformation processing as a result of a more homogeneous microstructure. A practical application of the invention can be ultrasonic atomization processing to produce uniform powders (via liquid microdroplets) for powder metallurgy applications or flame spraying coating processes. A practical application of the invention can be enhancement of catalytic reactions as ultrasonic irradiation can increase reactivities by nearly a million-fold (through the process of acoustic cavitation since during bubble collapsing phase intense heating of the bubbles occurs which can increase the local temperature and pressure significantly). A practical application of the invention can be production of more homogeneous aluminum alloys with low solubility (1-3%) and low melting (Pb, Bi, Sn, etc.) alloy additions for the purpose of enhancing machinability (this can be accomplished by the emulsification and dispersion of these elements in the molten alloy. A practical application of the invention can be enhanced semi-solid (thixotropic or rheocast alloy processing) deformation processing by producing more equiaxed semi-solid microstructures that can be shape cast or forged into components requiring higher strains than possible with irregular semi-solid microstructures. The more equiaxed microstructure will facilitate using lower deformation loads for a given amount of strain. A practical application of the invention can be production of hypereutectic Al—Si alloys which normally contain coarse primary silicon particles by ultrasonically facilitating the development of fine primary silicon particles which in turn increases the plasticity of the cast metal and allows for ingot deformation using conventional deformation processing equipment and techniques. A practical application of the invention can be the adoption of ultrasonic processing approaches for grain refinement during continuous casting (e.g., for bar & rod or strip production) or shape casting (e.g., die casting, semi-solid melt forging) operations as no probe needs to be in contact directly with the melt or crucible/mold. A practical application of the invention can be elimination of retained austenite by ultrasonically eliminating (or enhancing mobility of) defect structures that pin phase transformation front interfaces. A practical application of the invention can be enhancement of diffusion processes by locally enhancing the mobility of diffusing species. A practical application of the invention can be coupling with magnetic processing to amplify the high magnetic field processing effects such as accelerated transformation kinetics or development of metastable microstructures for enhanced performance. A practical application of the invention can be accelerating phase transformation processes such as the aging process of precipitation hardening alloys (e.g., Al, Ti, Ni, Fe, Mg alloys) or the tempering of ferrous materials. A practical application of the invention can be modification of the volume fractions of the various constituents in the microstructure evolving during phase decomposition (e.g., the volume fraction of austenite in a steel during elevated temperature processing). A practical application of the invention can be enhancement of general processes that have any threshold activation energy. A practical application of the invention can be enhanced activation of carbon nanotube precursor materials containing appropriate catalysts for the formation and growth of desired nanostructures such as single walled (SWNT) and multi-walled (MWNT) carbon nanotubes, especially when the induction field is preferentially activating in some manner [e.g., locally higher temperatures] relative to one or some of a set of constituents (e.g., the catalyst particle(s) in the nanotube precursor material(s)). The invention can be utilized in conjunction with magnetic processing to amplify the high magnetic field processing effects such as accelerated transformation kinetics or development of metastable microstructures for enhanced performance. There are virtually innumerable uses for embodiments of the invention, all of which need not be detailed here.
Embodiments of the non-contact process invention include at least the followings benefits over conventional contact ultrasonic processing methods for both the melt-phase and also the solid-state phase. Embodiments of the invention obviate the need for the utilization of some form of probe or horn that has the precise length measurements (usually determined experimentally and needs to be some multiple of one-half wavelength) at the specific temperature of use to produce the acoustic waves associated with conventional contact processing. Embodiments of the invention obviate the material compatibility/corrosion problems involved with the use of conventional contact processing in the context of molten metal applications which limits the survivability and usefulness of the transducer/horn. Contact methods using these probes/horns have a temperature gradient that can be a function of time that makes it extremely difficult to achieve an appropriate length ultrasonic wave in the probe/horn. Embodiments of the invention can substantially eliminate the elevated temperature problems associated with the probe/horn. Embodiments of the invention improve quality and/or reduce costs compared to previous approaches.
The phrase high magnetic field is intended to mean a magnetic field greater than or equal to 1 Tesla (e.g., 2 T, 3 T, 4 T, 5 T, 6 T, 7 T, 8 T, 9 T, 10 T, . . . , 30 T, 31 T, 32 T, 33 T, etc.). The phrase bi-directional vibration is intended to mean oscillatory motion along two directions of an axis, the difference in magnitudes of which are less than or equal to 10% (e.g., 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, . . . , 0.4%, 0.3%, 0.2%, 0.1% etc.) of one another. The phrase ohmically decoupled is intended to mean that a decrease in induced surface current due to a decrease in inductive coil current can be compensated for (traded off), with respect to vibration, with an increase in a static magnetic field while ohmic heating from the induced surface current is reduced as the square of the decreased inductive coil current. The term program and/or the phrase computer program are intended to mean a sequence of instructions designed for execution on a computer system (e.g., a program and/or computer program, may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer or computer system). The phrase ultrasonic frequency is intended to mean frequencies greater than or equal to approximately 10 KHz. The phrase radio frequency is intended to mean frequencies less than or equal to approximately 300 GHz
The term substantially is intended to mean largely but not necessarily wholly that which is specified. The term approximately is intended to mean at least close to a given value (e.g., within 10% of). The term generally is intended to mean at least approaching a given state. The term coupled is intended to mean connected, although not necessarily directly, and not necessarily mechanically. The term proximate, as used herein, is intended to mean close, near adjacent and/or coincident; and includes spatial situations where specified functions and/or results (if any) can be carried out and/or achieved. The term distal, as used herein, is intended to mean far, away, spaced apart from and/or non-coincident, and includes spatial situation where specified functions and/or results (if any) can be carried out and/or achieved. The term deploying is intended to mean designing, building, shipping, installing and/or operating.
The terms first or one, and the phrases at least a first or at least one, are intended to mean the singular or the plural unless it is clear from the intrinsic text of this document that it is meant otherwise. The terms second or another, and the phrases at least a second or at least another, are intended to mean the singular or the plural unless it is clear from the intrinsic text of this document that it is meant otherwise. Unless expressly stated to the contrary in the intrinsic text of this document, the term or is intended to mean an inclusive or and not an exclusive or. Specifically, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). The terms a and/or an are employed for grammatical style and merely for convenience.
The term plurality is intended to mean two or more than two. The term any is intended to mean all applicable members of a set or at least a subset of all applicable members of the set. The phrase any integer derivable therein is intended to mean an integer between the corresponding numbers recited in the specification. The phrase any range derivable therein is intended to mean any range within such corresponding numbers. The term means, when followed by the term “for” is intended to mean hardware, firmware and/or software for achieving a result. The term step, when followed by the term “for” is intended to mean a (sub)method, (sub)process and/or (sub)routine for achieving the recited result.
The terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The terms “consisting” (consists, consisted) and/or “composing” (composes, composed) are intended to mean closed language that does not leave the recited method, apparatus or composition to the inclusion of procedures, structure(s) and/or ingredient(s) other than those recited except for ancillaries, adjuncts and/or impurities ordinarily associated therewith. The recital of the term “essentially” along with the term “consisting” (consists, consisted) and/or “composing” (composes, composed), is intended to mean modified close language that leaves the recited method, apparatus and/or composition open only for the inclusion of unspecified procedure(s), structure(s) and/or ingredient(s) which do not materially affect the basic novel characteristics of the recited method, apparatus and/or composition.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.
The described embodiments and examples are illustrative only and not intended to be limiting. Although embodiments of the invention can be implemented separately, embodiments of the invention may be integrated into the system(s) with which they are associated. All the embodiments of the invention disclosed herein can be made and used without undue experimentation in light of the disclosure. Although the best mode of the invention contemplated by the inventor(s) is disclosed, embodiments of the invention are not limited thereto. Embodiments of the invention are not limited by theoretical statements (if any) recited herein. The individual steps of embodiments of the invention need not be performed in the disclosed manner, or combined in the disclosed sequences, but may be performed in any and all manner and/or combined in any and all sequences. The individual components of embodiments of the invention need not be formed in the disclosed shapes, or combined in the disclosed configurations, but could be provided in any and all shapes, and/or combined in any and all configurations. The individual components need not be fabricated from the disclosed materials, but could be fabricated from any and all suitable materials.
It can be appreciated by those of ordinary skill in the art to which embodiments of the invention pertain that various substitutions, modifications, additions and/or rearrangements of the features of embodiments of the invention may be made without deviating from the spirit and/or scope of the underlying inventive concept. All the disclosed elements and features of each disclosed embodiment can be combined with, or substituted for, the disclosed elements and features of every other disclosed embodiment except where such elements or features are mutually exclusive. The spirit and/or scope of the underlying inventive concept as defined by the appended claims and their equivalents cover all such substitutions, modifications, additions and/or rearrangements.
The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” and/or “step for.” Subgeneric embodiments of the invention are delineated by the appended independent claims and their equivalents. Specific embodiments of the invention are differentiated by the appended dependent claims and their equivalents.
This invention was made with United States Government support under prime contract No. DE-AC05-00OR22725 to UT-Battelle, L.L.C. awarded by the Department of Energy. The Government has certain rights in this invention.
