SINGLE PIECE CASTING OF REACTIVE ALLOYS

Abstract

A method of vacuum induction melting a charge of material includes preheating a mold; inserting the charge into the mold; placing the mold into a chamber; reducing an operating pressure within the chamber; induction melting the charge within the mold; allowing material of the charge to fill a cavity defined within the mold; applying electromagnetic pressure to the charge within the mold; and applying an electromagnetic field to material of the charge positioned within the cavity defined within the mold.

Description

1. CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/635,963, attorney docket no. FSPT.00001, filed on Apr. 20, 2012, the disclosure of which is incorporated herein by reference.

This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/651,620 attorney docket no. FSPT.00002, filed on May 25, 2012, the disclosure of which is incorporated herein by reference

2. BACKGROUND

This disclosure relates to systems for investment casting parts using materials that are heated to a molten state using an induction heating system to permit the materials to then fill a mold that defines one or more cavities for defining the shape of a finished part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are flow chart illustrations of an exemplary system for induction melting.

FIG. 2a is an illustration of an exemplary embodiment of a mold having a cup and defining one or more cavities in communication with the cup.

FIG. 2b is an illustration of an exemplary embodiment of the mold of FIG. 2a having a reactive charge of material positioned within the cup of the mold.

FIG. 2c is an illustration of the mold of FIG. 2b positioned within as chamber having an induction heating coil.

FIG. 2d is a graphical illustration of an exemplary embodiment of a thermal profile of a charge of material during operation of the method of FIGS. 1a and 1b.

FIG. 3a is a photograph of an exemplary experimental embodiment of the microstructure of the blade of a turbine wheel provided using the method of FIGS. 1a and 1b.

FIG. 3b is a photograph of an exemplary experimental embodiment of the microstructure of the blade root of a turbine wheel provided using the method of FIGS. 1a and 1b.

FIG. 3c is a photograph of an exemplary experimental embodiment of the microstructure of the hub of a turbine wheel provided using the method of FIGS. 1a and 1b.

FIG. 4a is a photograph of an exemplary experimental embodiment of the microstructure of the blade root of a turbine wheel provided using the method of FIGS. 1a and 1b.

FIG. 5a is a photograph of an exemplary experimental embodiment of a casting of a turbine wheel generated using the method of FIGS. 1a and 1b.

FIG. 5b is a photograph of an exemplary experimental embodiment of a casting of a turbine wheel generated using a VAR method of casting.

FIG. 6a is a photograph of a cross section of an exemplary experimental embodiment of a casting of a turbine wheel generated using the method of FIGS. 1a and 1b.

FIG. 6b is a photograph of a cross section of a casting of a turbine wheel generated using a VAR method of casting.

FIG. 7a is a photomicrograph of a cross section of an exemplary experimental embodiment of a casting of a turbine wheel generated using the method of FIGS. 1a and 1b.

FIG. 7b is a photomicrograph of a cross section of a casting of a turbine wheel generated using a VAR method of casting.

DETAILED DESCRIPTION

In the drawings and description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawings are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings.

Referring to FIGS. 1a and 1b, an exemplary embodiment of a method 100 for induction melting of titanium aluminide includes, in 102, providing a conventional ceramic mold having a cup in communication with a cavity defined within the mold for defining a shape of a part.

Referring to FIG. 2a, in an exemplary embodiment, 102, the mold 102a includes a cup 102b in communication with a cavity 102c defined within the mold for defining a shape of a part. As will be recognized by persons having ordinary skill in the art, the cavity 102c defined within the ceramic mold 102a may define one or more cavities permitting molten materials to fill therein and thereby define the shape of a part. In an exemplary embodiment, the cavity 102c of the mold 102a defines a turbine or a compressor wheel.

Referring again to FIGS. 1a and 1b, in an exemplary embodiment a reactive alloy charge is then provided in a conventional manner in 104. In an exemplary embodiment, the reactive alloy charge comprises a reactive alloy such as, for example, a titanium alloy which may, for example, be titanium aluminide.

Then, in 106, in an exemplary embodiment, the mold 102a may be preheated in a conventional manner.

Then, in 108, in an exemplary embodiment, referring to FIGS. 1a, 1b and 2b, the reactive alloy charge 108a is then placed within the cup 102b of the preheated mold 102a in a conventional manner, in 108. In an exemplary embodiment, before, during or after preheating the mold in 106, the charge 108a may also be preheated.

Then, in 110, in an exemplary embodiment, referring to FIGS. 1a, 1b, and 2c, the mold 102a is placed into a conventional chamber 110a having a conventional high frequency alternating current induction heating coil 110b such that the mold 102a is surrounded by the coil in a conventional manner. In an exemplary embodiment, chamber 110a comprises a quartz chamber.

Then, in 112, in an exemplary embodiment, the operating pressure within the chamber 110a is reduced in a conventional manner. In an exemplary embodiment, in 112, the operating pressure within the chamber 110a is reduced to less than about 100 millitorr.

Then, in 114, in an exemplary embodiment, the induction coil 110b is operated, in a conventional manner, to apply a time dependent electromagnetic field to mold 102a. In an exemplary embodiment, as will be recognized by persons having ordinary skill in the art, the operation of the induction coil 110b to apply a time dependent electromagnetic field to mold 102a will thereby induce eddy currents within the reactive alloy charge 108a thereby heating, and eventually melting and rendering molten, the reactive alloy charge. Furthermore, as will be recognized by persons having ordinary skill in the art, the operation of the induction coil 110b to apply a time dependent electromagnetic field to mold 102a will thereby also generate an electromagnetic field which is opposed to the applied time dependent electromagnetic field and creating repulsive pressures on the reactive alloy charge 108a.

In an exemplary embodiment, during the operation of the method 100, the application of the time dependent electromagnetic field in 114 is provided in multiple stages in which the intensity of the time dependent electromagnetic field is increased. For example, as illustrated in FIG. 2d, in an exemplary embodiment, the application of the time dependent electromagnetic field in 114 is provided such that the operating temperature of the charge 108a is increased in multiple stages until melting of the charge 108a is completed. Then, the intensity of the time dependent electromagnetic field is continually decreased following complete melting of charge 108a.

Then, in an exemplary embodiment, in 116, the induction coil 110b is operated to manipulate the time dependent applied electromagnetic field to apply greater magnetic pressure on a top portion of the reactive alloy charge 108a relative to a bottom portion of the reactive alloy charge. The general manner of manipulating a time dependent applied electromagnetic field to apply different magnetic pressures at different locations is considered well known in the art. For example, manipulating a time dependent applied electromagnetic field to apply different magnetic pressures at different locations, may be provided by using a non-constant diameter induction coil, or providing an additional induction coil disposed around a portion of the first induction coil.

In an exemplary, in 116, the application of a greater magnetic pressure to the a top portion of the reactive alloy charge 108a relative to the bottom portion of the reactive alloy charge acts to apply a force to the charge that injects the charge into the cavity 102c of the mold 102a.

Then, in 118, the operations of 114 and 116 are then continued until the reactive charge 108a is completely melted and injected into the cavity 102c of the mold 102a by operation of the induction coil 110b.

In an exemplary embodiment, during the operation of the method 100, initially, the upper portion of the charge 108a is melted first, due to the greater electromagnetic field applied to that portion of the charge. Then, in an exemplary embodiment, during the operation of the method 100, the melting of the upper portion of the charge 108a is then followed by melting of the bottom portion of the charge due to a combination of electromagnetic induced heating and convection. In an exemplary embodiment, during the operation of the method 100, the melting of the bottom portion of the charge 108a is then followed by the injection of the melted portion of the charge 108a due to the application of the magnetic pressures onto the charge 108a in 116. Thus, it is important to maintain a seal between the cup 102b and the cavity 102c until the charge 108a is completely melted.

As will be recognized by persons having ordinary skill in the art, the operation of the induction coil 110b in 114 will also electromagnetically stir the melted portion of the reactive alloy charge 108a.

In an exemplary embodiment, operation of the induction coil 110b in 114 will also apply an electromagnetic field to the melted and/or solidified portions of the reactive alloy charge within the cavity 102c of the mold 102a. As a result, filling of the cavity 102c of the mold 102a is improved, thereby permitting thinner parts to be formed and defects may be contained and limited to an off part, or non-critical, section. Furthermore, in an exemplary embodiment, application of an electromagnetic field to the melted and/or solidified portions of the reactive alloy charge 108a within the cavity 102c of the mold 102a permits controlling and modifying a structure of the solidified portion of the reactive alloy 108a within the cavity 102c of the mold 102a. Furthermore, in an exemplary embodiment, application of an electromagnetic field to the melted and/or solidified portions of the reactive alloy charge 108a within the cavity 102c of the mold 102a permits the portion of the reactive alloy charge 108a within the cavity 102c of the mold 102a to remain controllably molten such that the operator may control and determine which portion of the reactive alloy charge 108a within the cavity 102c of the mold 102a is the last portion to solidify.

In several exemplary embodiments, one or more elements of the mold 102a may be fabricated from a graphite material. For example, in an exemplary embodiment, the mold 102a may include a graphite cup 102b and/or a graphite cup liner. Furthermore, in an exemplary embodiment, at least a portion of the mold 102a that defines the cavity 102c may also include a graphite material. In an exemplary embodiment, where at least portions of the mold 102a include a graphite material, since graphite can be an electrical conductor, during operation of the method 100, the graphite portions of the mold 102a are inductively heated thereby and provide additional heating of the casting of the reactive alloy charge within the cup 102b and/or cavity 102c.

In several exemplary experimental embodiments of the method 100, castings of turbine wheels were provided using a reactive titanium alloy charges having the following nominal compositions: 1) titanium with 28% by weight aluminum, 9% by weight niobium, and 2% by weight molybdenum, 2) titanium with 33% by weight aluminum, 5% by weight niobium and 2% by weight chromium, and 3) titanium with 6% by weight aluminum and 4% by weight vanadium.

In some exemplary experimental embodiments, the following results were observed: 1) there was no centerline shrinkage; 2) the macrostructure was a symmetric and columnar solidification structure; and 3) using conventional x-ray testing, there was no detectable gas porosity or inclusions.

Referring to FIG. 3a, in the exemplary experimental embodiment, the microstructure of the blade of the turbine wheel was lamellar gamma titanium aluminide with generally uniform grain and lamellae size.

Referring to FIG. 3b, in the exemplary experimental embodiment, the microstructure of the blade root of the turbine wheel was lamellar gamma titanium aluminide with uniform grain & lamellae sizes which were consistent with those of the blade microstructure.

Referring to FIG. 3c, in the exemplary experimental embodiment, the microstructure of the hub of the turbine wheel was lamellar gamma titanium aluminide with slightly larger grain and lamellae sizes than found at the root and blade.

Referring to FIG. 4a, in the exemplary experimental embodiment, the microstructure of the blade root of the turbine wheel was lamellar gamma titanium aluminide with generally uniform grain and lamellae size.

In several exemplary experimental comparative embodiments, the operation and results of the method 100 was compared with operation and results of a conventional vacuum arc remelting (“VAR”) investment casting process. In all of these exemplary comparative embodiments, the investment cast article was a compressor wheel.

In the exemplary experimental embodiments of the methods 100 and VAR, the final dimensions of the cast compressor wheels were within acceptable manufacturing tolerances for both processes.

As illustrated in FIG. 5a, the gating ratio for the exemplary experimental embodiments of the method 100 was 1.5:1. As will be recognized by persons having ordinary skill in the art, the gating ratio is equal to the ratio of the mass of the charge to the mass of the resulting cast part. The lower the gating the ratio, the more efficient the casting process.

As illustrated in FIG. 5b, the gating ratio for the exemplary experimental embodiments of the method VAR was 3.35:1.

A tabular summary of the mechanical properties of investment cast turbine wheels provided by the exemplary experimental embodiments of the methods 100 and VAR is provided below:

		Ultimate Tensile	Yield Strength
	Specimen	Strength (Ksi)	@0.2% Offset (Ksi)
	Method 100 - No. 1	145.8	133.0
	Method 100 - No. 2	143.4	133.6
	VAR Average*	137.4	126.2

As illustrated in FIG. 6a, exemplary experimental embodiments of the method 100 included centerline shrinkage.

As illustrated in FIG. 6b, exemplary experimental embodiments of the method VAR included centerline shrinkage.

As illustrated in FIG. 7a, exemplary experimental embodiments of the method 100 exhibited the illustrated microstructure at 50× magnification.

As illustrated in FIG. 7b, exemplary experimental embodiments of the method VAR exhibited the illustrated microstructure at 50× magnification.

The results of the comparative exemplary experimental embodiments of the methods 100 and VAR demonstrated that the method 100 was and is capable of producing parts virtually identical to those provided using the conventional VAR process on every level, and in some cases the method 100 produces better results than the method VAR. This was an unexpected result. For example, with respect to the dimensional and chemical results, the methods 100 and VAR processes produce similar parts. All dimensions and elements measured from the parts made through the method 100 process were within specification and capability. As far as advantages, for example, a major advantage of the method 100 is the capability to reduce the gating ratio versus that required for the method VAR. Thus, the method 100 can produce the same amount of cast parts as the VAR process while using less than half the amount of metal. This was an unexpected result. Furthermore, as demonstrated by the exemplary comparative experimental results, the mechanical properties of the parts produced using the method 100 had a greater ultimate and yield strength than those produced using the method VAR. This was an unexpected result. In addition, the method 100 was also capable of significantly reducing the amount of centerline shrink that is developed during casting versus that produced by the VAR method. This was an unexpected result. Furthermore, the method 100 was capable of controlling the microstructure of the cast parts by controlling the cooling rates. This is possible because of the single piece process of the method 100, and this result allows for uniform and consistent cooling throughout the part. Comparing the parts cast in Ti6-4, the grains structures between the methods 100 and VAR were virtually identical. Thus, the method 100 provided superior results to that for the VAR method. A tabular summary of the results provided by the methods 100 and VAR is provided below:

	Method 100	VAR
	Dimensions	In Spec. and Comparable
	Chemistry	In Spec., Capable, and Comparable
	Gating Ratio	1.5:1	3.35:1
	Mechanical Properties	~144 Ksi (UTS)	~137 Ksi (UTS)
		~133 Ksi (YS)	~126 Ksi (YS)
	Centerline Shrink	Minimal	Large
	Ti 6-4 Microstructure	In Spec. and Comparable
	TiAl Microstructure	Controllable	Incapable

A method of vacuum induction melting a charge of material and casting an article includes preheating a mold; inserting the charge into the mold; placing the mold into a chamber; reducing an operating pressure within the chamber; induction melting the charge within the mold; applying electromagnetic pressure to the charge within the mold; allowing material of the charge to fill a cavity defined within the mold; and applying an electromagnetic field to material of the charge positioned within the cavity defined within the mold. In an exemplary embodiment, the charge of material is preheated. In an exemplary embodiment, the mold includes a ceramic material. In an exemplary embodiment, the charge includes a reactive alloy. In an exemplary embodiment, the charge includes a titanium alloy. In an exemplary embodiment, the charge includes a titanium aluminide alloy. In an exemplary embodiment, the chamber includes a quartz chamber. In an exemplary embodiment, applying magnetic pressure includes manipulating a time dependent electromagnetic field. In an exemplary embodiment, applying magnetic pressure includes manipulating a time dependent electromagnetic field during a melting of the charge. In an exemplary embodiment, applying magnetic pressure includes manipulating a time dependent electromagnetic field during a flowing of the charge into the cavity. In an exemplary embodiment, applying magnetic pressure includes manipulating a time dependent electromagnetic field during a solidification of the charge. In an exemplary embodiment, applying magnetic pressure includes manipulating electromagnetic field gradients. In an exemplary embodiment, applying electromagnetic pressure includes applying a stronger electromagnetic field to an upper portion of the charge than to a lower portion of the charge. In an exemplary embodiment, applying electromagnetic pressure includes locating the charge within a non uniform electromagnetic field. In an exemplary embodiment, the method further includes allowing the material of the charge to solidify within the cavity in the presence of an applied electromagnetic field. In an exemplary embodiment, the solidified material includes a symmetrical structure. In an exemplary embodiment, the solidified material includes an asymmetrical structure. In an exemplary embodiment, the solidified material does not include detectable gas porosity using conventional gas porosity detection methods. In an exemplary embodiment, the solidified material does not include inclusions using conventional inclusion detection methods. In an exemplary embodiment, the solidified material includes a fully lamellar microstructure. In an exemplary embodiment, the material includes titanium aluminide. In an exemplary embodiment, the solidified material includes a hub and one or more blades that extend in a radial direction from the hub. In an exemplary embodiment, the solidified material includes a turbine wheel. In an exemplary embodiment, the solidified material includes a compressor wheel.

A system for vacuum induction melting a charge of material and casting an article includes means for preheating a mold; means for inserting the charge into the mold; means for placing the mold into a chamber; means for reducing an operating pressure within the chamber; means for induction melting the charge within the mold; means for allowing material of the charge to fill a cavity defined within the mold; means for applying electromagnetic pressure to the charge within the mold; and means for applying an electromagnetic field to material of the charge positioned within the cavity defined within the mold. In an exemplary embodiment, the system includes means for preheating the charge of material. In an exemplary embodiment, the mold includes a ceramic material. In an exemplary embodiment, the charge includes a reactive alloy. In an exemplary embodiment, the charge includes a titanium alloy. In an exemplary embodiment, the charge includes a titanium aluminide alloy. In an exemplary embodiment, the chamber includes a quartz chamber. In an exemplary embodiment, the means for applying magnetic pressure includes means for manipulating a time dependent electromagnetic field. In an exemplary embodiment, the means for applying magnetic pressure includes means for manipulating a time dependent electromagnetic field during a melting of the charge. In an exemplary embodiment, the means for applying magnetic pressure includes means for manipulating a time dependent electromagnetic field during a flowing of the charge into the cavity. In an exemplary embodiment, the means for applying magnetic pressure includes means for manipulating a time dependent electromagnetic field during a solidification of the charge. In an exemplary embodiment, the means for applying magnetic pressure includes means for manipulating electromagnetic field gradients. In an exemplary embodiment, the means for applying electromagnetic pressure includes means for applying a stronger electromagnetic field to an upper portion of the charge than to a lower portion of the charge. In an exemplary embodiment, the means for applying electromagnetic pressure includes means for locating the charge within a non uniform electromagnetic field. In an exemplary embodiment, the system further includes: means for allowing the material of the charge to solidify within the cavity in the presence of an applied electromagnetic field. In an exemplary embodiment, the solidified material includes a symmetrical structure. In an exemplary embodiment, the solidified material includes an asymmetrical structure. In an exemplary embodiment, the solidified material does not include detectable gas porosity using conventional gas porosity detection methods. In an exemplary embodiment, the solidified material does not include inclusions using conventional inclusion detection methods. In an exemplary embodiment, the solidified material comprises a fully lamellar microstructure. In an exemplary embodiment, the material comprises titanium aluminide. In an exemplary embodiment, the solidified material includes a hub and one or more blades that extend in a radial direction from the hub. In an exemplary embodiment, the solidified material includes a turbine wheel. In an exemplary embodiment, the solidified material includes a compressor wheel.

A method for vacuum induction melting a charge of material and casting an article includes providing a ceramic mold which comprises a cup which communicates with a cavity defined within the mold for defining a shape of a part; providing a reactive alloy charge; preheating the mold; placing the charge of material within the preheated cup of the mold; applying a time dependent electromagnetic field to the mold; inducing electrical eddy currents within the reactive alloy charge; generating an electromagnetic field which is opposed to the applied time dependent electromagnetic field and creating repulsive pressures on the reactive alloy charge; manipulating the time dependent applied electromagnetic field and applying greater magnetic pressure on a top portion of the reactive alloy charge relative to a bottom portion of the reactive alloy charge; melting at least a portion of the reactive alloy charge; electromagnetically stirring the melted portion of the reactive alloy charge; forcing the melted portion of the reactive alloy charge into at least a portion of the cavity of the mold using the magnetic pressures; and applying an electromagnetic field to the melted portion of the reactive alloy charge within the cavity of the mold. In an exemplary embodiment, the method includes preheating the charge of material. In an exemplary embodiment, the method further includes allowing the melted portion of the reactive alloy charge to solidify within the cavity of the mold. In an exemplary embodiment, the method further includes applying an electromagnetic field to the solidified portion of the reactive alloy charge within the cavity of the mold. In an exemplary embodiment, the method further includes controlling and modifying a structure of the solidified portion of the reactive alloy within the cavity of the mold. In an exemplary embodiment, applying the electromagnetic field to the solidified portion of the reactive alloy charge within the cavity of the mold includes heating treating the solidified portion of the reactive alloy within the cavity of the mold.

A system for vacuum induction melting a charge of material and casting an article includes means for providing a ceramic mold which comprises a cup which communicates with a cavity defined within the mold for defining a shape of a part; means for providing a reactive alloy charge; means for preheating the mold; means for placing the charge of material within the preheated cup of the mold; means for applying a time dependent electromagnetic field to the mold; means for inducing electrical eddy currents within the reactive alloy charge; means for generating an electromagnetic field which is opposed to the applied time dependent electromagnetic field and means for creating repulsive pressures on the reactive alloy charge; means for manipulating the time dependent applied electromagnetic field and means for applying greater magnetic pressure on a top portion of the reactive alloy charge relative to a bottom portion of the reactive alloy charge; means for melting at least a portion of the reactive alloy charge; means for electromagnetically stirring the melted portion of the reactive alloy charge; means for forcing the melted portion of the reactive alloy charge into at least a portion of the cavity of the mold using the magnetic pressures; and means for applying an electromagnetic field to the melted portion of the reactive alloy charge within the cavity of the mold. In an exemplary embodiment, the system further includes means for allowing the melted portion of the reactive alloy charge to solidify within the cavity of the mold. In an exemplary embodiment, the system further includes means for applying an electromagnetic field to the solidified portion of the reactive alloy charge within the cavity of the mold. In an exemplary embodiment, the system further includes means for controlling and modifying a structure of the solidified portion of the reactive alloy within the cavity of the mold. In an exemplary embodiment, the means for applying the electromagnetic field to the solidified portion of the reactive alloy charge within the cavity of the mold includes means for heating treating the solidified portion of the reactive alloy within the cavity of the mold.

It is understood that variations may be made in the above without departing from the scope of the invention. While specific embodiments have been shown and described, modifications can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments as described are exemplary only and are not limiting. Many variations and modifications are possible and are within the scope of the invention. Furthermore, one or more elements of the exemplary embodiments may be omitted, combined with, or substituted for, in whole or in part, one or more elements of one or more of the other exemplary embodiments. Accordingly, the scope of protection is not limited to the embodiments described, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Claims

1. A method of vacuum induction melting a charge of material and casting an article, comprising:

preheating a mold;

inserting the charge into the mold;

placing the mold into a chamber;

reducing an operating pressure within the chamber;

induction melting the charge within the mold;

applying electromagnetic pressure to the charge within the mold;

allowing material of the charge to fill a cavity defined within the mold to form the article; and

applying an electromagnetic field to material of the charge positioned within the cavity defined within the mold.

2. The method of claim 1, further comprising preheating the charge.

3. The method of claim 1, wherein the mold comprises a ceramic material.

4. The method of claim 1, wherein the mold comprises a graphite material.

5. The method of claim 1, wherein the mold comprises a ceramic and a graphite material.

6. The method of claim 1, wherein the charge comprises a reactive alloy.

7. The method of claim 6, wherein the charge comprises a titanium alloy.

8. The method of claim 6, wherein the charge comprises a titanium aluminide alloy.

9. The method of claim 1, wherein the chamber comprises a quartz chamber.

10. The method of claim 1, wherein applying magnetic pressure comprises manipulating a time dependent electromagnetic field.

11. The method of claim 10, wherein applying magnetic pressure comprises manipulating a time dependent electromagnetic field during a melting of the charge.

12. The method of claim 10, wherein applying magnetic pressure comprises manipulating a time dependent electromagnetic field during a flowing of the charge into the cavity.

13. The method of claim 10, wherein applying magnetic pressure comprises manipulating a time dependent electromagnetic field during a solidification of the charge.

14. The method of claim 1, wherein applying magnetic pressure comprises manipulating electromagnetic field gradients

15. The method of claim 1, wherein applying electromagnetic pressure comprises applying a stronger electromagnetic field to an upper portion of the charge than to a lower portion of the charge.

16. The method of claim 1, wherein applying electromagnetic pressure comprises locating the charge within a non uniform electromagnetic field.

17. The method of claim 1, further comprising:

allowing the material of the charge to solidify within the cavity in the presence of an applied electromagnetic field

18. The method of claim 17, wherein the solidified material comprises a symmetrical structure.

19. The method of claim 17, wherein the solidified material comprises an asymmetrical structure.

20. The method of claim 17, wherein the solidified material does not include detectable gas porosity using conventional gas porosity detection methods.

21. The method of claim 17, wherein the solidified material does not include inclusions using conventional inclusion detection methods.

22. The method of claim 17, wherein the solidified material comprises a fully lamellar microstructure.

23. The method of claim 22, wherein the material comprises a titanium aluminide alloy.

24. The method of claim 17, wherein the solidified material comprises a hub and one or more blades that extend in a radial direction from the hub.

25. The method of claim 17, wherein the solidified material comprises a turbine wheel.

26. The method of claim 17, wherein the solidified material comprises a compressor wheel.

27. A method for vacuum induction melting a charge of material and casting an article, comprising:

providing a ceramic mold which comprises a cup which communicates with a cavity defined within the mold for defining a shape of a part;

providing a reactive alloy charge;

preheating the mold;

placing the charge of material within the preheated cup of the mold;

applying a time dependent electromagnetic field to the mold;

inducing electrical eddy currents within the reactive alloy charge;

generating an electromagnetic field which is opposed to the applied time dependent electromagnetic field and creating repulsive pressures on the reactive alloy charge;

manipulating the time dependent applied electromagnetic field and applying greater magnetic pressure on a top portion of the reactive alloy charge relative to a bottom portion of the reactive alloy charge;

melting at least a portion of the reactive alloy charge;

electromagnetically stirring the melted portion of the reactive alloy charge;

forcing the melted portion of the reactive alloy charge into at least a portion of the cavity of the mold using the magnetic pressures to form the article; and

applying an electromagnetic field to the melted portion of the reactive alloy charge within the cavity of the mold.

28. The method of claim 27, further comprising allowing the melted portion of the reactive alloy charge to solidify within the cavity of the mold.

29. The method of claim 28, further comprising applying an electromagnetic field to the solidified portion of the reactive alloy charge within the cavity of the mold.

30. The method of claim 29, further comprising controlling and modifying a structure of the solidified portion of the reactive alloy within the cavity of the mold.

31. The method of claim 29, wherein applying the electromagnetic field to the solidified portion of the reactive alloy charge within the cavity of the mold comprises heat treating the solidified portion of the reactive alloy within the cavity of the mold.