AU2002220245A1 - Refining and casting apparatus and method - Google Patents

Description

REFINING AND CASTING APPARATUS AND METHOD

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to an apparatus and a method for refining

and casting metal and metal alloy ingots and other preforms. The present invention

more particularly relates to an apparatus and a method useful for refining and casting

large diameter ingots and other preforms of metals and metal alloys prone to

segregation during casting, and wherein the preforms formed by the apparatus and

method may exhibit minimal segregation and lack significant melt-related defects.

The apparatus and method of the invention find particular application in, for example,

the refinement and casting of complex nickel-based superalloys, such as alloy 706 and alloy 718, as well as certain titanium alloys, steels, and cobalt-base alloys that are

prone to segregation when cast by conventional, state-of-the-art methods. The present

invention is also directed to preforms and other articles produced by the method

and/or apparatus of the present invention.

DESCRIPTION OF THE INVENTION BACKGROUND

In certain critical applications, components must be manufactured from

large diameter metal or metal alloy preforms exhibiting minimal segregation and

which are substantially free of melt-related defects such as white spots and freckles.

(For ease of reference, the tenn "metallic material" is used herein to refer collectively

to unalloyed metals and to metal alloys.) These critical applications include use of

metal components as rotating components in aeronautical or land-based turbines and

in other applications in which metallurgical defects may result in catastrophic failure

of the component. So that preforms from which these components are produced are

free of deleterious non-metallic inclusions, the molten metallic material must be

appropriately cleaned or refined before being cast into a preform. If the metallic

materials used in such applications are prone to segregation when cast, they are

typically refined by a "triple melt" technique which combines, sequentially, vacuum

induction melting (VIM), electroslag remelting (ESR), and vacuum arc remelting

(VAR). Metallic materials prone to segregation, however, are difficult to produce in

large diameters by VAR melting, the last step in the triple melt sequence, because it is

difficult to achieve a cooling rate that is sufficient to minimize segregation. Although

solidification microsegregation can be minimized by subjecting cast ingots to lengthy homogenization treatments, such treatments are not totally effective and may be

costly. In addition, VAR often will introduce macro-scale defects, such as white

spots, freckles, center segregation, etc., into the ingots. In some cases, large diameter

ingots are fabricated into single components, so VAR-introduced defects cannot be

selectively removed prior to component fabrication. Consequently, the entire ingot or

a portion of the ingot may need to be scrapped. Thus, disadvantages of the triple melt

technique may include large yield losses, lengthy cycle times, high materials

processing costs, and the inability to produce large-sized ingots of segregation-prone

metallic materials of acceptable metallurgical quality.

One known method for producing high quality preforms from melts of

segregation prone metallic materials is spray forming, which is generally described in,

for example, United States Patent Nos. 5,325,906 and 5,348,566. Spray forming is

essentially a "moldless" process using gas atomization to create a spray of droplets of

liquid metal from a stream of molten metal. The process parameters of the spray

forming technique are adjusted such that the average fraction of solid within the

atomized droplets at the instant of impact with a collector surface is sufficiently high

to yield a high viscosity deposit capable of assuming and maintaining a desired

geometry. High gas-to-metal mass ratios (one or greater) are required to maintain the

heat balance critical to proper solidification of the preform.

Spray forming suffers from a number of disadvantages that make its

application to the formation of large diameter preforms problematic. An unavoidable

byproduct of spray forming is overspray, wherein the metal misses the developing

preform altogether or solidifies in flight without attaching to the preform. Average yield losses due to overspray in spray forming can be 20-30%. Also, because

relatively high gas-to-metal ratios are required to maintain the critical heat balance

necessary to produce the appropriate solids fraction within the droplets on impact with

the collector or developmg preform, the rapid solidification of the material following

impact tends to entrap the atomizing gas, resulting in the formation of gas pores

within the preform.

A significant limitation of spray forming preforms from segregation

prone metallic materials is that preforms of only limited maximum diameter can be

formed without adversely affecting microstructure and macrostracture. Producing

larger spray formed preforms of acceptable quality requires increasingly greater

control of the local temperature of the spray to ensure that a semi-liquid spray surface

layer is maintained at all times. For example, a relatively cooler spray may be

desirable near the center of the preform, while a progressively warmer spray is desired

as the spray approaches the outer, quicker cooling areas of the preform. The effective

maximum diameter of the preform is also limited by the physics of the spray forming

process. With a single nozzle, the largest preforms possible have a maximum

diameter of approximately 12-14 inches. This size limitation has been established

empirically due to the fact that as the diameter of the preform increases, the rotational

speed of the surface of the preform increases, increasing the centrifugal force

experienced at the semi-liquid layer. As the diameter of the preform approaches the

12 inch range, the increased centrifugal force exerted on the semi-liquid layer tends to

cause the layer to be thrown from the preform face. Accordingly, there are significant drawbacks associated with certain

known techniques applied in the refining and casting of preforms, particularly large

diameter preforms, from segregation prone metallic materials. Thus, a need exists for

an improved apparatus and method for refining and casting segregation prone metals

and metal alloys.

BRIEF SUMMARY OF THE INVENTION

In order to address the above-described need, the present invention

provides a method of refining and casting a preform including the steps of providing a

consumable electrode of a metallic material and then melting and refining the

electrode to provide a molten refined material. At least a portion of the molten refined

material passes through a passage that is protected from contamination by contact

with oxygen in the ambient air. The passage preferably is constructed of a material

that will not react with the molten refined material. A droplet spray of the molten

refined material is formed by impinging a gas on a flow of the molten refined material

emerging from the passage. The droplet spray is deposited within a mold and

solidified to a preform. The preform may be processed to provide a desired article

such as, for example, a component adapted for rotation in an aeronautical or land-

based turbine.

The step of melting and refining the consumable electrode may consist

of at least one of electroslag remelting the consumable electrode and vacuum arc

remelting the consumable electrode to provide the molten refined material. The

passage through which the molten refined material then passes may be a passage

formed through a cold induction guide. At least a portion of the molten refined alloy passes through the cold induction guide and is inductively heated within the passage.

In less demanding applications, e.g., applications in which some small level of oxide

contaminants in the alloy can be tolerated, a cold induction guide need not be used.

Components used in such less demanding applications include, for example, static

components of aircraft turbine engines. In cases in which a cold induction guide is

not used, the passage may be an unheated passage protected from the atmosphere and

including walls composed of a refractory material. The passage may be adapted to

protect the molten refined material from undesirable impurities. The molten refined

material emerging from the passage is then solidified to a preform as noted above.

The present invention also addresses the above-described need by

providing an apparatus for refining and casting an alloy. The apparatus includes a

melting and refining apparatus that includes: at least one of an electroslag remelting

apparatus and a vacuum arc remelting apparatus; a transfer apparatus (such as, for

example, a cold induction guide) in fluid communication with the melting and

refining apparatus; and a nucleated casting apparatus in fluid communication with the

transfer apparatus. A consumable electrode of a metallic material introduced into the

melting and refining apparatus is melted and refined, and the molten refined material

passes to the nucleated casting apparatus via a passage formed through the transfer

apparatus. In the case where the transfer apparatus is a cold induction guide, at least a

portion of the refined material is retained in molten form in the passage of the cold

induction guide by inductive heating.

When casting a metallic material by certain embodiments of the

method of the present invention, the material need not contact the oxide refractories used in the melting crucibles and pouring nozzles utilized in conventional casting

processes. Thus, the oxide contamination that occurs on spalling, erosion, and

reaction of such refractory materials may be avoided.

The electroslag remelting apparatus that may be a part of the refining

and casting apparatus of the present invention includes a vessel having an aperture

therein, an electric power supply in contact with the vessel, and an electrode feed

mechanism configured to advance a consumable electrode into the vessel as material

is melted from the electrode during the electroslag remelting procedure. A vacuum

arc remelting apparatus differs from an electroslag remelting apparatus in that the

consumable electrode is melted in a vessel by means of a DC arc under partial

vacuum, and the molten alloy droplets pass to the transfer apparatus of the apparatus

of the invention without first contacting a slag. Although vacuum arc remelting does

not remove microscale inclusions to the extent of electroslag remelting, it has the

advantages of removing dissolved gases and minimizing high vapor pressure trace

elements in the electrode material.

The cold induction guide that may be a part of the casting and refining

apparatus of the invention generally includes a melt collection region that is in direct

or indirect fluid communication with the aperture of the vessel of the melting and

refining apparatus. The cold induction guide also includes a transfer region defining

the passage, which terminates in an orifice. At least one electrically conductive coil

may be associated with the transfer region and may be used to inductively heat

material passing through the passage. One or more coolant circulation passages also may be associated with the transfer region to allow for cooling of the inductive coils

and the adjacent wall of the passage.

The nucleated casting apparatus of the casting and refining apparatus

of the invention includes an atomizing nozzle in direct or indirect fluid

communication with the passage of the transfer apparatus. An atomizing gas supply is

in communication with the nozzle and forms a droplet spray from a flow of a melt

received from the transfer apparatus. A mold, which includes a base and side wall to

which the preform conforms, is disposed adjacent to the atomizing nozzle, and the

position of the mold base relative to the atomizing nozzle may be adjustable.

The method and apparatus of the invention allow a refined melt of a

metallic material to be transferred to the nucleated casting apparatus in molten or

semi-molten form and with a substantially reduced possibility of recontamination of

the melt by oxide or solid impurities. The nucleated casting technique allows for the

formation of fine grained preforais lacking substantial segregation and melt-related

defects associated with other casting methods. By associating the refining and casting

features of the invention via the transfer apparatus, large or multiple consumable

electrodes may be electroslag remelted or vacuum arc remelted to form a continuous

stream of refined molten material that is nucleation cast into a fine grained preform,

h that way, preforms of large diameter may be conveniently cast from metallic

materials prone to segregation or that are otherwise difficult to cast by other methods.

Conducting the method of the invention using large and/or consumable electrodes also

makes it possible to cast large preforms in a continuous manner. Accordingly, the present invention also is directed to preforms

produced by the method and/or apparatus of the invention, as well as articles such as,

for example, components for aeronautical or land-based turbines, produced by

processing the preforms of the present invention. The present invention also is

directed to preforms and ingots of segregation prone alloys of 12 inches or more in

diameter and which lack significant melt-related defects. Such preforms and ingots of

the invention may be produced by the method and apparatus of the present invention

with levels of segregation characteristic of smaller diameter NAR or ESR ingots of

the same material. Such segregation prone alloys include, for example, alloy 706,

alloy 718, alloy 720, Rene 88, and other nickel-based superalloys.

The reader will appreciate the foregoing details and advantages of the

present invention, as well as others, upon consideration of the following detailed

description of embodiments of the invention. The reader also may comprehend such

additional advantages and details of the present invention upon carrying out or using

the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention may be better

understood by reference to the accompanying drawings in which:

Figure 1 is a block diagram of an embodiment of the refining and

casting method according to the present invention;

Figure 2 is a schematic representation of an embodiment of a refining

and casting apparatus constructed according to the present invention; Figures 3(a) and (b) are graphs illustrating parameters calculated for a

simulated casting of a melt of alloy 718 using a refining and casting apparatus

constructed as shown schematically in Figure 2, and operated with a mass flow rate of

8.5 lbs./minute;

Figures 4(a) and (b) are graphs illustrating parameters calculated for a

simulated casting of a melt of alloy 718 using a refining and casting apparatus

constructed as shown schematically in Figure 2, and operated with a mass flow rate of

25.5 lbs./minute;

Figure 5 depicts the embodiment of the apparatus of the invention used

in the trial castings of Example 2;

Figure 6 is an as-sprayed center longitudinal micrograph

(approximately 5 OX magnification) of an ingot cast using an apparatus constructed

according to the present invention, and demonstrating an equiaxed ASTM 4.5 grain

structure; and

Figure 7 is an as-cast micrograph taken from a 20-inch diameter NAR

ingot (approximately 5 OX magnification).

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In one aspect, the present invention provides a novel process for

refining a metallic material and casting the material to a preform. The preform may

be processed to provide a finished article. The process of the invention includes

melting and refining the metallic material and subsequently casting the material to a

preform by a nucleated casting technique. Melting and refining the material may be accomplished by, for example, electroslag remelting (ESR) or vacuum arc remelting

(VAR). The process of the invention also includes transferring the molten refined

material to a nucleated casting apparatus through a passage so as to protect it from

contamination. The passage may be that formed through a cold induction guide (CIG)

or another transfer apparatus.

The present invention also provides an apparatus combining at least an

apparatus for melting and refining the metallic material, an apparatus for producing

the preform from the molten refined material by nucleated casting, and a transfer

apparatus for transferring the molten refined material from the melting and refining

apparatus to the nucleated casting apparatus. As further described below, the

apparatus and method of the invention are particularly advantageous when applied in

the production of large diameter, high purity preforms from metallic materials prone

to segregation during casting. For example, large diameter (12-14 inches or more)

preforms may be produced from segregation prone and other difficult to cast metallic

materials by the present apparatus and method which are substantially free from melt-

related defects and exhibit minimal segregation.

One embodiment of the apparatus and method of the present invention

is depicted in Figure 1. In a first step, a consumable electrode of a metallic material is

subjected to ESR, in which a refined heat of the material is generated by passage of

electric current through the electrode and an electrically conductive slag disposed

within a refining vessel and in contact with the electrode. The droplets melted from

the electrode pass through and are refined by the conductive slag, are collected by the

refining vessel, and may then be passed to a downstream apparatus. The basic components of an ESR apparatus typically include a power supply, an electrode feed

mechanism, a water cooled copper refining vessel, and the slag. The specific slag

type used will depend on the particular material being refined. The ESR process is

well known and widely used, and the operating parameters that will be necessary for

any particular electrode type and size may readily be ascertained by one having

ordinary skill in the art. Accordingly, further detailed discussion of the manner of

construction or mode of operation of an ESR apparatus or the particular operating

parameters used for a particular material and/or electrode type and size is unnecessary.

As further indicated in Figure 1, the embodiment also includes a CIG

in fluid communication, either directly or indirectly, with the ESR apparatus. The

CIG is used to transfer the refined melt produced in the ESR to a nucleated casting

apparatus. The CIG maintains the molten refined material produced by ESR in a

molten form during transfer to the nucleated casting apparatus. The CIG also

maintains the purity of the melt achieved through ESR by protecting the molten

material from the atmosphere and from the recontamination that can result from the

use of a conventional nozzle. The CIG preferably is directly coupled to both the ESR

apparatus and the nucleated casting apparatus so as to better protect the refined molten

material from the atmosphere, preventing oxides from forming in and contaminating

the melt. Properly constructed, the CIG also may be used to meter the flow of the

molten refined material from the ESR apparatus to the nucleated casting apparatus.

The construction and manner of use of a CIG, also variously referred to as a cold

finger or cold wall induction guide, is well known in the art and is described in, for

example, United States Patent Nos. 5,272,718, 5,310,165, 5,348,566, and 5,769,151, the entire disclosures of which are hereby incorporated herein by reference. A CIG

generally includes a melt container for receiving molten material. The melt container

includes a bottom wall in which is formed an aperture. A transfer region of the CIG is

configured to include a passage, which may be generally funnel-shaped, constructed

to receive molten material from the aperture in the melt container. In one

conventional construction of a CIG, the wall of the funnel-shaped passage is defined

by a number of fluid-cooled metallic segments, and the fluid-cooled segments define

an inner contour of the passage that generally decreases in cross-sectional area from

an inlet end to an outlet end of the region. One or more electrically conductive coils

are associated with the wall of the funnel-shaped passage, and a source of electrical

current is in selective electrical connection with the conductive coils.

During the time that the molten refined material is flowing from the

melt container of the CIG through the passage of the CIG, electrical current is passed

through the conductive coils at an intensity sufficient to inductively heat the molten

material and maintain it in molten form. A portion of the molten material contacts the

cooled wall of the funnel-shaped passage of the CIG and may solidify to form a skull

that insulates the remainder of the melt flowing through the CIG from contacting the

wall. The cooling of the wall and the formation of the skull assures that the melt is

not contaminated by the metals or other constituents from which the inner walls of the

CIG are formed. As is known in the art, the thickness of the skull at a region of the

funnel-shaped portion of the CIG may be controlled by appropriately adjusting the

temperature of the coolant, the flow rate of the coolant, and/or the intensity of the

current in the induction coils to control or entirely shut off the flow of the melt though the CIG; as the thickness of the skull increases, the flow through the transfer region is

correspondingly reduced. With regard to that feature, reference is made to, for

example, United States Patent No. 5,649,992, the entire disclosure of which is hereby

incorporated herein by reference.

CIG apparatuses may be provided in various forms, but each such CIG

typically includes the following: (1) a passage is provided utilizing gravity to guide a

melt; (2) at least a region of the wall of passage is cooled so as to allow formation of a

skull of the melt on the wall; and (3) electrically conductive coils are associated with

at least a portion of the passage, allowing inductive heating of molten material passing

through the passage. Persons having ordinary skill in the art may readily provide an

appropriately designed CIG having any one or all of the forgoing three features for

use in an apparatus constructed according to the present invention without further

discussion herein.

The CIG is in direct or indirect fluid communication with the nucleated

casting apparatus and transfers the refined molten material from the ESR apparatus to

the casting apparatus. Nucleated casting is known in the art and is described in, for

example, United States Patent Nos. 5,381,847 and in D. E. Tyler and W. G. Watson,

Proceedings of the Second International Spray Forming Conference (Olin Metals

Research Labs., September 1996), each of which is hereby incorporated herein by

reference, hi nucleated casting, a liquid stream of metallic material is disrupted or

broken into a cone of sprayed droplets by an impinging gas flow. The resultant cone

of droplets is directed into a casting mold having bottom and side walls, where the

droplets accumulate to provide a preform having a shape that conforms to the mold. The gas flow rate used to generate the droplets in the nucleated casting process is

adjusted to provide a relatively low fraction of solid (relative to the spray forming

process) within the individual droplets. This produces a low viscosity material that is

deposited in the mold. The low viscosity semi-solid material fills and may conform to

the contour of the mold. The impinging gas and impacting droplets create turbulence

at the semi-solid surface of the casting as it is deposited, enhancing the uniform

deposition of the casting within the mold. By depositing a semi-solid material into

the mold with a gas flowing over the surface of the material as it is deposited, the

solidification rate of the material is enhanced and a fine grain structure results.

As incorporated in the present invention in conjunction with the

melting/refining apparatus and the transfer apparatus, the nucleated casting apparatus

may be used to form relatively large cast preforms, preforms of 16 inches or more in

diameter. Consumable feed electrodes cast through the apparatus of the invention

may be of a size adequate to provide a continuous stream of molten material exiting

from the outlet of the transfer apparatus over a prolonged period to deliver a large

volume of molten material to the nucleated casting apparatus. Preforms that may be

successfully cast by the nucleated casting process include alloys that otherwise are

prone to segregation such as, for example, complex nickel-based superalloys,

including alloy 706, alloy 718, alloy 720, Rene' 88, titanium alloys (including, for

example Ti(6-4) an Ti(17)), certain steels, and certain cobalt-base alloys. Other

metallic materials that are prone to segregation upon casting will be readily apparent

to those of ordinary skill. Preforms of such metallic materials may be formed to large

diameters by nucleated casting without casting-related defects such as white spots, freckles, beta flecks, and center segregation. Of course, the apparatus of the invention

also may be applied to cast preforms of metallic materials that are not prone to

segregation.

As is the case with ESR and CIG, nucleated casting is well known in

the art and one of ordinary skill may, without undue experimentation, after having

considered the present description of the invention, construct a nucleated casting

apparatus or adapt an existing apparatus to receive a melt from a transfer apparatus as

in the present invention. Although nucleated casting and spray forming both use a gas

to atomize a molten stream to form a plurality of molten alloy droplets, the two

processes differ in fundamental respects. For example, the gas-to-metal mass ratios

(which may be measured as kilograms of gas/kilograms of metal) used in each process

differ. In the nucleated casting process incorporated in the present invention, the gas-

to-metal mass ratio and the flight distance are selected so that before impacting the

collection surface of the mold or the surface of the casting being formed up to about

30 volume percent of each of the droplets is solidified. In contrast, the droplets

impacting the collection surface in a typical spray forming process, such as that

described in, for example, United States Patent No. 5,310,165 and European

application no. 0 225 732, include about 40 to 70 volume percent of solid. To ensure

that 40 to 70 percent of the spray droplets are solid, the gas-to-metal mass ratio used

to create the droplet spray in spray forming typically is one or greater. The lower

solids fractions used in nucleated casting are selected to ensure that the deposited

droplets will conform to the casting mold and voids will not be retained within the

casting. The 40-70 volume percent solids fraction used in the spray forming process is selected to form a free-standing preform and would not be suitable for the nucleated

casting process.

An additional distinction of spray forming is that although both spray

forming and nucleated casting collect the atomized droplets into a solid preform, in

spray forming the preform is deposited on a rotating collector that lacks side walls to

which the deposited material conforms. Significant disadvantages associated with

that manner of collection include porosity in the preform resulting from gas

entrapment and significant yield losses resulting from overspray. Although porosity

may be reduced in spray formed ingots during hot working, the porosity may reappear

during subsequent high temperature heat treatment. One example of that phenomenon

is porosity resulting from argon entrapment in superalloys, which can appear during

thermally induced porosity (TIP) testing and may act as nucleating sites for low cycle

fatigue fractures.

Spray forming also has limited utility when forming large diameter

preforms. In such cases a semi-liquid layer must be maintained on the sprayed surface

at all times to obtain a satisfactory casting. This requires that any given segment of a

surface being spray formed must not solidify between the time that it exits the spray

cone, rotates with the collector about the rotational axis of the collector, and reenters

the spray cone. That restriction (in combination with the limitation on rotational

speed imposed by the centrifugal forces) has limited the diameter of preforms that

may be spray formed. For example, spray forming devices with a single spray nozzle

may only form preforms having a diameter no larger than about 12 inches. In the

present invention, the inventors have found that the use of nucleated casting greatly increases the size of castings that may be formed from molten metallic materials

prepared by the melting and refining apparatus/transfer apparatus combination.

Because, relative to spray forming, the nucleated casting process may be configured to

evenly distribute the droplets supplied to the mold and solidification may ensue

rapidly thereafter, any residual oxides and carbonitrides in the preform will be small

and finely dispersed in the preform microstructure. An even distribution of droplets

may be achieved in the nucleated casting process by, for example, rastering the one or

more droplet spray nozzles and/or translating and/or rotating the mold relative to the

droplet spray in an appropriate pattern.

A schematic representation of a refining and casting apparatus 10

constructed according to the present invention is shown in Figure 2. The apparatus 10

includes a melting and refining apparatus in the form of an ESR apparatus 20, a

transfer apparatus in the form of CIG 40, and a nucleated casting apparatus 60. The

ESR apparatus 20 includes an electric power supply 22 which is in electrical contact

with a consumable electrode 24 of the metallic material to be cast. The electrode 24 is

in contact with a slag 28 disposed in an open bottom, water-cooled vessel 26 that may

be constructed of, for example, copper or another suitable material. The electric

power supply 22 provides a high amperage, low voltage current to a circuit that

includes the electrode 24, the slag 28, and the vessel 26. The power supply 22 may be

an alternating or direct current power supply. As current passes tlirough the circuit,

electrical resistance heating of the slag 28 increases its temperature to a level

sufficient to melt the end of the electrode 24 in contact with the slag 28. As the

electrode 24 begins to melt, droplets of molten material form, and an electrode feed mechanism (not shown) is used to advance the electrode 24 into the slag 28 as the

electrode melts. The molten material droplets pass through the heated slag 28, and the

slag 28 removes oxide inclusions and other impurities from the material. After

passing through the slag 28, the refined molten material 30 pools in the lower end of

the vessel 26. The pool of refined molten material 30 then passes to a passage 41

within the CIG 40 by force of gravity.

The CIG 40 is closely associated with the ESR apparatus 20 and, for

example, an upper end of the CIG 40 may be directly connected to the lower end of

the ESR apparatus 20. In the apparatus 10, the vessel 26 forms both a lower end of

the ESR apparatus 20 and an upper end of the CIG 40. Thus, it is contemplated that

the melting and refining apparatus, transfer apparatus, and nucleated casting apparatus

of the refining and casting apparatus of the invention may share one or more elements

in common. The CIG 40 includes a funnel-shaped transfer portion 44 surrounded by

current carrying coils 42. Electrical current is provided to the coils 42 by an

alternating current source (not shown). The coils 42 serve as induction heating coils

and are used to selectively heat the refined molten material 30 passing through the

transfer portion 44. The coils 42 are cooled by circulating a suitable coolant such as

water through conduits associated with the transfer portion 44. The cooling effect of

the coolant also causes a skull (not shown) of solidified material to form on the inner

wall of the transfer portion 44. Control of the heating and/or cooling of the transfer

portion 44 may be used to control the rate of, or to interrupt entirely, the flow of

molten material 30 through the CIG 40. Preferably, the CIG 40 is closely associated

with the ESR apparatus 20 so that the molten refined material exiting the ESR apparatus 20 is protected from the atmosphere and does not, for example, undergo

oxidation.

Molten material exits a bottom orifice 46 of the CIG 40 and enters the

nucleated casting apparatus 60. In the nucleated casting apparatus 60, a supply of

suitably inert atomizing gas 61 is delivered to an atomizing nozzle 62. The flow of

gas 61 exiting the atomizing nozzle 62 impinges the stream of molten material 30 and

breaks the stream into droplets 64. The resulting cone of droplets 64 is directed into a

casting mold 65 including a side wall 66 and abase 67. As the material is deposited

into the mold 65, the base 67 may rotate to better ensure uniform deposition of the

droplets. The droplets 64 produced by the apparatus 10 are larger than those of

conventional spray casting. The larger droplets 64 are an advantage over conventional

spray casting in that they exhibit reduced oxygen content and require less gas

consumption for atomization. Also, the gas-to-metal ratio of the droplets produced by

the nucleated casting apparatus 60 may be less than one-half that conventionally used

in spray forming. The flow rate of gas 61 and the flight distance of the droplets 64 are

adjusted to provide a semi-solid material of a desired solid to liquid ratio in the

casting mold 66. The desired solid to liquid ratio is in the 5% - 40% range, volume

per volume. The relatively low solids fraction of the droplets directed into the casting

mold 66 results in the deposit of a low viscosity semi-solid material 68 that conforms

to the shape of the casting mold 66 as it is filled.

The impact of the spray of droplets 64 creates a turbulent zone at the

uppermost surface 70 of the preform 72. The depth of the turbulent zone is dependent

upon the velocity of the atomization gas 61 and the size and velocity of the droplets 64. As the droplets 64 begin to solidify, small particles of solid form in the liquid

having the lattice structure characteristic of the given material. The small particle of

solid which begins to form in each of the droplets then acts as a nucleus onto which

other atoms in the vicinity tend to attach themselves. During solidification of the

droplets 64, many nuclei form independently at various locations and have random

orientation. The repetitive attachment of succeeding atoms results in the growth of

crystals composed of the same basic patterns that extend outward from the respective

nuclei until the crystals begin to intersect with one another. In the present invention,

sufficient nuclei are present as fine dendritic structures within each of the droplets 64

so that the resulting preform 72 formed will consists of a uniform equiaxed grain

structure.

To maintain the desired solids fraction in the material deposited in the

casting mold 66, the distance between the point of atomization and the upper surface

70 of the preform 72 is controlled. Thus, the apparatus 10 of the present invention

may also include a means for adjusting this distance comprising a retractable stalk 75

attached to the base 67 of the mold 65. As the material is deposited and conforms to

the side wall 66, the base 67 is continuously retracted downward so that the distance

between the atomizing nozzle 62 and the surface 70 of the preform 72 is maintained.

Retraction of the base 67 downward exposes a portion of the walls of the solidified

preform below the wall 66 of the mold 65.

Although only a single combination of a CIG and nucleated casting

apparatus is included in the apparatus 10, it is contemplated that multiple atomizing

spray apparatuses or multiple combinations of a melting and refining apparatus (such as an ESR apparatus) with an atomizing spray apparatus feeding a single casting mold

may be advantageous. For example, a system employing multiple transfer

apparatus/atomizing nozzle combinations downstream of a single ESR apparatus

would permit ingots of greater diameters to be manufactured because the multiple

atomized sprays may cover a greater area in the mold. In addition, process rates

would increase and costs would be reduced. Alternatively, a single or multiple ESR

or other melting and refining apparatuses may feed multiple atomizing nozzles

directed at several molds so as to create multiple preforms from a single feed

electrode supplied to the melting and refining apparatus.

Other possible modifications to the above-described apparatus 10 of

the invention include: adapting the nucleated casting apparatus 60 so as to rotate the

nucleated casting cast preform 72 during processing to give a more even distribution

of the droplet spray over a large surface; the use of multiple atomizing nozzles to feed

a single mold; and equipping the apparatus 10 so that the one or more atomizing

nozzles can oscillate. As noted above, a VAR apparatus is one melting and refining

apparatus that may be used in place of the ESR apparatus 20 to melt the consumable

electrode 24. In VAR, the consumable electrode is melted by application of DC

current and does not pass through a conductive slag.

Another possible modification to the apparatus 10 is to incorporate a

member having a passage therethrough and constructed with walls of ceramic or other

suitable refractory material as the transfer apparatus in place of the CIG 40 to transfer

the material melted in the ESR apparatus 20 (or other melting and refining apparatus)

to the nucleated casting apparatus 60. In such case, the passage within the transfer apparatus would not be associated with means to heat the material passing

therethrough and, accordingly, there would be less flexibility in regulating the flow of

the molten material to the nucleated casting apparatus 60.

The apparatus 10 also may be adapted to modify the manner of

withdrawal of the preform 72 and to maintain acceptable surface finish on the preform

72. For example, the apparatus 10 may be constructed so that the casting mold 65

reciprocates (i.e., the mold moves up and down), the casting mold 65 oscillates, and/or

the preform 72 reciprocates in a manner similar to that used in conventional

continuous casting technology. Another possible modification is to adapt the

apparatus such that the one or more atomizing nozzles move to raster the spray and

increase coverage on the surface of the preform. The apparatus may be programmed

to move the one or more nozzles in any suitable pattern.

Also, to better ensure minimizing porosity in the preform, the chamber

in which the nucleated casting occurs may be maintained at partial vacuum such as,

for example, 1/3 to 2/3 atmosphere. Maintaining the chamber under partial vacuum

also has the advantage of better maintaining the purity of the material being cast. The

purity of the material also may be maintained by conducting the casting in a protective

gas atmosphere. Suitably protective gases include, for example, argon, helium,

hydrogen, and nitrogen.

Although the foregoing description of the casting apparatus 10 refers to

the (ESR apparatus 20), transfer apparatus (CIG 40), and nucleated casting apparatus

60 as relatively discrete apparatuses associated in series, it will be understood that the

apparatus 10 need not be constructed in that way. Rather than being constructed of discrete, disconnectable melting/refining, transfer, and casting apparatuses, the

apparatus 10 may incorporate the essential features of each of those apparatuses

without being capable of deconstruction into those discrete and individually operable

apparatuses. Thus, reference in the appended claims to a melting and refining

apparatus, a transfer apparatus, and a nucleated casting apparatus should not be

construed to mean that such distinct apparatuses may be disassociated from the

claimed apparatus without loss of operability.

The following computer simulations and actual examples confirm

advantages provided by the apparatus and method of the present invention.

Example 1 - Computer simulation

Computer simulations show that preforms prepared by the apparatus 10

of the invention will cool significantly faster than ingots produced by conventional

processing. Figure 3 (mass flow rate to caster of 0.065 kg/sec. or about 8.5 lb/min.)

and Figure 4 (mass flow rate to caster of 0.195 kg/sec.) illustrate the calculated effects

on the temperature and liquid volume fraction of a preform cast by the apparatus 10 of

the present invention using the parameters shown in Table 1 below.

Table 1 - Parameters of Simulated Castings

Preform Geometry • Cylindrical 20 inch (508 mm) preform diameter

• Inflow region constitutes entire top surface of preform Nucleated Casting Apparatus Operating Conditions • Mass flow rates of 0.065 kg/sec. (as reported in the reference of footnote 1 below for a comparable VAR process) (Figure 3) and 0.195 kg/sec. (Figure 4) 324° K (51°C) average temperature of the cooling water in the mold. • 324° K (51°C) effective sink temperature for radiation heat loss from the ingot top surface.

• Alloy flowing into the mold is at the liquidus temperature of the alloy.

• Heat loss coefficients due to convection from the top surface of preform as per E. J. Lavernia and Y. Wu., "Spray Atomization and

Deposition" (John Wiley & Sons., 1996), pp. 311-314, with gas- to-metal ratio of 0.2, and side surface 0 W/m²K. The disclosure of the Lavernia and Wu reference is hereby incorporated herein by reference. Preform Material and Thermophysical Properties

• Alloy 718.

• Liquidus and solidus temperatures of 1623°K and 1473°K, respectively (as reported in the reference of footnote 1 below).

• Emmissivities of 0.05 (top surface) and 0.2 (side surface). Model for Heat Transfer to Mold

• The model for heat transfer to the mold is that described in the reference of n. 1, wherein the heat transfer boundary condition transitions linearly from a full contact condition for surface preform temperatures greater than the liquidus temperature to a gap heat transfer condition for surface temperatures less than the solidus temperature.

L. A. Bertram et al., "Quantitative Simulations of a Superalloy VAR Ingot at the Macroscale", Proceedings of the 1997 International Symposium on Liquid Metal processing and Casting, A. Mitchell and P. Auburtin, eds. (Am. Vac. Soc, 1997). The reference is hereby incorporated herein by reference. • 20 inc (508 mm) diameter mold. The isotherm data provided graphically in Figures 3 and 4 demonstrates

that the surface temperature of the preform produced in the simulations is below the

liquidus temperature of the alloy. The maximum preform temperatures calculated for

Figures 3 and 4 are 1552°K and 1600°K, respectively. Therefore, the pool under the

spray will be semi-solid, and the semi-solid nature of the pool is shown by the liquid

fraction data that is graphically shown in Figures 3 and 4.

Table 2 below compares certain results of the computer simulations with

typical results of a VAR casting of a perform of similar size reported in the reference

of n. 1. Table 2 shows that the pool of material on the surface of a preform prepared

by the apparatus 10 of the present invention may be semi-solid, while that produced

by conventional VAR processing is fully liquid up to 6 inches below the surface.

Thus, for a given preform size, there is substantially less latent heat to be removed

from the region of solidification of a preform cast by an apparatus constructed

according to the present invention. That, combined with the semi-solid nature of the

pool, will minimize microsegregation and the possibility of freckle formation, center

segregation, and other forms of detrimental macrosegregation. In addition, the present

invention also completely eliminates the possibility of white spot defect formation, a

defect inherent in the VAR process.

Table 2 - Comparison Of Invention With VAR Cast Ingot

Example 2 - Trial Casting A trial casting using an apparatus constructed according to the invention

was performed. The apparatus 100 is shown schematically in Figure 5 and, for

purposes of understanding its scale, was approximately thirty feet in overall height.

The apparatus 100 generally included ESR head 110, ESR furnace 112, CIG 114,

nucleated casting apparatus 116, and material handling device 118 for holding and

manipulating the mold 120 in which the casting was made. The apparatus 100 also

included ESR power supply 122 supplying power to melt the electrode, shown as 124,

and CIG power supply 126 for powering the induction heating coils of CIG 114.

ESR head 110 controlled the movement of the electrode 124 within ESR

furnace 112. ESR furnace 124 was of a typical design and was constructed to hold an electrode of approximately 4 feet in length by 14 inches in diameter. In the case of

the alloy used in the trial casting, such an electrode weighed approximately 2500

pounds. ESR furnace 112 included hollow cylindrical copper vessel 126 having view

ports 128 and 130. View ports 128 and 130 were used to add slag (generally shown as

132) to, and to assess the temperature within, ESR furnace 112. CIG 114 was about

10" in vertical length and was of a standard design including a central bore for

passage of molten material surrounded by copper walls including coolant circulation

passages. The copper walls were, in turn, surrounded by induction heating coils for

regulating the temperature of the material passing through CIG 114.

Nucleated casting apparatus 116 included chamber 136 surrounding mold

120. Chamber 136 enclosed mold 120 in a protective nitrogen atmosphere in which

the casting was carried out. The walls of chamber 136 are shown transparent in

Figure 5 for purposes of viewing mold 120 and its associated equipment within

chamber 136. Mold 120 was held at the end of robot arm 138 of material handling

device 118. Robot arm 138 was designed to support and translate mold 120 relative

to the spray of molten material, shown generally as 140, emanating from the nozzle of

nucleated casting apparatus 116. In the trial casting, however, robot arm 138 did not

translate the mold 120 during casting. An additional advantage of chamber 136 is to

collect any overspray generated during casting.

The supplied melt stock was a cast and surface ground 14 inch diameter

VIM electrode having a ladle chemistry shown in Table 3. The electrode was

electroslag remelted at a feed rate of 33 lbs./minute using apparatus 100 of Figure 5.

The slag used in the ESR furnace 112 had the following composition, all components shown in weight percentages: 50% CaF₂, 24% CaO, 24% Al₂O₃, 2% MgO. The melt

refined by the ESR treatment was passed through CIG 114 to nucleated casting

apparatus 116. CIG 114 was operated using gas and water recirculation to regulate

temperature of the molten material within the CIG 114. Argon gas atomization was

used to produce the droplet spray within nucleated casting apparatus 116. The

minimum 0.3 gas-to-metal ratio that could be used with the atomizing nozzle

incorporated into the nucleated casting apparatus 116 was employed. The atomized

droplets were deposited in the center of mold 120, which was a 16 inch diameter, 8

inch depth (interior dimensions) uncooled 1 inch thick steel mold with Kawool

insulation covering the mold baseplate. As noted above, mold 120 was not rastered,

nor was the spray cone rastered as the preform was cast.

Centerline plates were cut from the cast preform and analyzed. In

addition, a 2.5 X 2.5 X 5 inch section from the mid-radius position was upset forged

from 5 inches to 1.7 inches height at 1950°F to enhance etch inspectability for

macrosegregation. The chemistry of the cast preform at two positions is provided in

Table 3.

Table 3 - Ladle and Cast Preform Chemistry

A tin addition was made to the molten ESR pool at the fourteenth minute

of the fifteen-minute spraying run to mark the liquidus pool depth. The tin content

was measured every 0.25 inch after deposition. The measured distance between the

liquidus and solidus boundaries was estimated to be 4-5 inches. This confirmed the shallow melt pool predicted by the model described in Example 1. Visual inspection

of the preform revealed certain defects indicating that the deposited material required

additional fluidity to fill the entire mold. No attempt was made to "hot top" the

preform by reducing the gas-to-metal ratio or pouring the stream of metallic material

without atomization. Suitable adjustment to the deposition process may be made in

order to inhibit formation of defects within the preform.

The as-sprayed structure of the preform produced by the above nucleated

casting process and an as-cast micrograph from a 20 inch diameter VAR ingot of the

same material are shown in Figures 6 and 7, respectively. The nucleation cast (NC)

preform (Figure 6) possesses a uniform, equiaxed ASTM 4.5 grain structure with

Laves phase present on the grain boundaries, δ phase also appears at some grain

boundaries, but probably precipitated during a machining anneal conducted on the

cast preform material. The VAR ingot includes a large grain size, greater Laves phase

volume, and larger Laves particles than the spray cast material (>40μm for VAR vs.

<20μm for spray cast).

Macrosegregation-related defects such as white spots and freckles were not

observed in the preform. A mult was upset forged to refine grain structure and aid in

detection of defects. A macro plate from the forging did not reveal any

macrosegregation defects. The oxide and carbide dispersions of the preform material

were refined relative to VAR ingot material and were similar to that found in spray

formed material. Carbides were less than 2 micrometers and oxides were less 10

micrometers in size in the preform. Typically, 20 inch diameter preforms of alloy 718

cast by conventional VAR have carbides of 6-30 microns and oxides of 1-3 microns up to 300 microns in the microstructure. The carbides and oxides seen in material cast

by the present invention are typical of those seen in spray forming, but are finer

(smaller) than those seen in other melt processes such as VAR. These observations

confirm that more rapid solidification occurs in the method of the invention than in

conventional VAR ingot melting of comparably sized ingots, even though the method

of the invention typically uses a much higher casting rate than VAR.

The chemistry analyses shown in Table 3 do not reveal any elemental

gradients. In particular, no niobium gradient was detected in the preform. Niobium is

of particular interest because migration of that element from the preform surface to the

center has been detected in spray formed ingots. Table 3 does demonstrate

differences between the ladle chemistry and ingot chemistry for the preform. Those

differences are attributed to porosity in the preform samples used in the XRF

procedure rather than actual difference in chemistry.

Based on the results of the experimental casting, a lower gas-to-metal ratio

is desirable to enhance mold fill and inhibit porosity problems. Use of a more fluid

spray may increase microsegregation to some extent, but the wide beneficial margin

exhibited in the trial over VAR should accommodate any increase. Grain size also

may increase with increasing fluidity, but the constant impingement of new droplets

provides a high density of grain nucleation sites to inhibit formation of large or

columnar grains within the preform. Greater spray fluidity would significantly

enhance the ability of the droplets to fill the mold, and a more fluid impingement zone

would reduce sidewall rebound deposition. An additional advantage of a more fluid

impingement zone is that the atomizing gas will more readily escape the material and a reduction in porosity will result. To enhance outgassing of the atomizing gas from

the preform surface, the casting may be performed in a partial vacuum such as, for

example £ atmosphere. Any increase in size of carbides and oxides resulting from

reducing the gas-to-metal ratio is expected to be slight. Thus, an advantageous

increase in fluidity of the droplet spray is expected to have only minor effects on grain

structure and second phase dispersion.

Accordingly, the apparatus and method of the present invention address

significant deficiencies of current methods of casting large diameter preforms from

alloys prone to segregation. The melting and refining apparatus provides a source of

refined molten alloy that is essentially free from deleterious oxides. The transfer

apparatus provides a method of transferring the refined molten alloy to the nucleated

casting apparatus with a reduced possibility of oxide recontamination. The nucleated

casting apparatus may be used to advantageously form small grained, large diameter

ingots from segregation prone alloys without the casting-related defects associated

with VAR and/or spray casting.

It is to be understood that the present description illustrates those

aspects of the invention relevant to a clear understanding of the invention. Certain

aspects of the invention that would be apparent to those of ordinary skill in the art and

that, therefore, would not facilitate a better understanding of the invention have not

been presented in order to simplify the present description. Although the present

invention has been described in connection with certain embodiments, those of

ordinary skill in the art will, upon considering the foregoing description, recognize

that many modifications and variations of the invention may be employed. All such variations and modifications of the invention are intended to be covered by the

foregoing description and the following claims.

Claims (45)

CLAIMSWe claim:

1. A method of producing a preform, the method comprising:

providing a consumable electrode of a metallic material;

melting and refining the consumable electrode to provide a molten refined

material;

passing at least a portion of the molten refined material through a passage in

which the molten refined material is protected from contamination by oxygen in the

ambient air;

forming a droplet spray of the molten refined material by impinging a gas on a

flow of the molten refined material from the passage, wherein the gas is supplied to the

flow of molten refined material in a ratio less than 1 on a unit mass of gas per unit mass

of molten refined material basis; and

depositing and solidifying the droplet spray of the molten refined material within

a mold to form the preform.

2. The method of claim 1 wherein melting and refining the consumable electrode

comprises one of:

electroslag remelting the consumable electrode to provide the molten refined

material; and

vacuum arc remelting the consumable electrode to provide the molten refined

material.

3. The method of claim 2, wherein electroslag remelting the consumable electrode

comprises:

providing an open-bottomed vessel containing a slag;

contacting the consumable electrode with the slag within the open-bottomed

vessel;

passing electric current through a circuit including the consumable electrode, the

slag, and the vessel to cause resistance heating of the slag resulting in melting of material

from the consumable elecfrode at the electrode's contact point with the slag, thereby

forming droplets of molten material; and

allowing the droplets of the molten material to pass through the heated slag.

4. The method of claim 3, wherein the electroslag remelting the consumable electrode

further comprises:

controlling the delivery of the consumable electrode into the vessel to maintain

contact between the electrode and the heated slag.

5. The method of claim 2, wherein vacuum arc remelting the consumable electrode

comprises:

contacting the consumable electrode with a DC arc under partial vacuum to heat

the electrode, thereby forming droplets of molten material.

6. The method of claim 1 , wherein passing at least a portion of the molten refined

material through a passage comprises:

providing a cold induction guide;

collecting the molten refined material in the cold induction guide; and

passing at least a portion of the molten refined material through a passage in the

cold induction guide while inductively heating the molten refined material within the

passage.

7. The method of claim 6, wherein the cold induction guide comprises:

a molten material collection region;

a transfer region including a passage terminating in an orifice;

at least one electrically conductive coil associated with the transfer region; and

at least one coolant circulation passage associated with the transfer region.

8. The method of claim 7, wherein passing at least a portion of the molten refined

material through a passage comprises:

receiving the molten refined material in the molten material collection region; and

passing at least a portion of the molten refined material tlirough the passage in the

transfer region while maintaining an electric current through the electrically conductive

coil and passing coolant through the coolant circulation passage.

9. The method of claim 1 , wherein passing at least a portion of the molten refined

material through a passage comprises passing at least a portion of the molten refined material through a passage having

walls lined with a refractory material and lacking an inductive heating source.

10. The method of claim 1, wherein depositing and solidifying the droplet spray

comprises:

generating a turbulent zone on a surface of the preform by the impact of

droplets of the molten refined material and the impinging gas.

11. The method of claim 1, wherein depositing and solidifying the droplet spray

comprises:

depositing and solidifying the droplet spray of the molten refined material within

a mold under at least one of a partial vacuum and a protective gas atmosphere.

12. The method of claim 1, wherein the gas-to-metal mass ratio is less than 0.3.

13. The method of claim 1 , wherein in forming a droplet spray the droplets of molten

refined material are partially solid such that, on average, from 5 to 40 percent by volume

of each droplet is solid.

14. The method of claim 1 , wherein the metallic material is one of a nickel-based

superalloy, a titanium alloy, a steel, and a cobalt-base alloy.

15. The method of claim 1 , wherein the metallic material is a nickel-based superalloy

selected from the group consisting of alloy 706, alloy 718, alloy 720, and Rene 88.

16. The method of claim 1, wherein the metallic material is a titanium alloy selected

from the group consisting of Ti(6-4) and Ti(17).

17. The method of claim 1, wherein the preform is at least 12 inches in diameter.

18. A method for producing a preform, the method comprising:

providing an apparatus comprising

a melting and refining apparatus selected from an electroslag

remelting apparatus and a vacuum arc remelting apparatus,

a transfer apparatus including a passage therethrough terminating

in an orifice, the transfer apparatus in fluid communication with the

melting and refining apparatus, and

a nucleated casting apparatus comprising a mold, the nulcleated

casting apparatus in fluid communication with the transfer apparatus;

providing a consumable electrode of a metallic material;

melting and refining the consumable electrode in the melting and refining

apparatus to provide a molten refined material;

passing the molten refined material through the transfer apparatus;

providing the moltend refined material to the nucleated casting apparatus and

forming a droplet spray of the molten refined material by impinging a gas on a flow of the molten refined material from the passage, wherein the gas is supplied to the flow of

molten refined material in a ratio less than 1 on a unit mass gas per unit mass molten

refined material basis; and

depositing and solidifying the droplet spray of the molten refined material within

the mold to form the preform.

19. An apparatus for providing a preform of a metallic material, the apparatus

comprising:

a melting and refining apparatus selected from an electroslag remelting apparatus

and a vacuum arc remelting apparatus;

a transfer apparatus including a passage therethrough terminating in an orifice,

said transfer apparatus in fluid communication with said melting and refining apparatus;

and

a nucleated casting apparatus in fluid communication with said transfer apparatus.

20. The apparatus of claim 19, wherein said electroslag remelting apparatus comprises:

an open-bottomed vessel having an aperture therein;

an electric power supply in contact with said vessel;

a conductive slag within said vessel; and

a feed mechanism adapted to feed a consumable electrode into said vessel.

21. The apparatus of claim 19, wherein said vacuum arc remelting apparatus comprises:

a vacuum chamber; an open-bottomed vessel within said vacuum chamber and having an aperture

therein; and

an electric power supply associated with said chamber.

22. The apparatus of claim 19, wherein said transfer apparatus comprises a cold

induction guide.

23. The apparatus of claim 22, wherein said cold induction guide comprises:

a melt collection region in fluid communication with said aperture of said open-

bottomed vessel;

a transfer region including a passage terminating in an orifice;

at least one electrically conductive coil associated with said transfer region; and

at least one coolant circulation passage associated with said transfer region.

24. The apparatus of claim 19, wherein said transfer apparatus comprises:

a passage having walls lined with a refractory material and lacking an inductive

heating source, said passage terminating in an orifice.

25. The apparatus of claim 19, wherein said nucleated casting apparatus comprises:

an atomizing nozzle in fluid communication with said orifice of said internal void;

an atomizing gas supply in communication with said nozzle; and

a mold including side walls and a base disposed under said atomizing nozzle, a

position of said base relative to the atomizing nozzle being adjustable.

26. An article produced by a method comprising:

providing a consumable electrode of a metallic material;

melting and refining the consumable electrode to provide a molten refined

material;

passing at least a portion of the molten refined material through a passage

protected from contact with the atmosphere;

forming a droplet spray of the molten refined material by impinging a gas on a

flow of the molten refined material from the passage, wherein the gas is supplied to the

flow of molten refined material in a ratio less than 1 on a unit mass gas per unit mass

volume of molten refined material basis; and

depositing and solidifying the droplet spray of the molten refined material within

a mold.

27. The article of claim 26, wherein melting and refining the consumable electrode

comprises one of:

electroslag remelting the consumable electrode to provide the molten refined

material; and

vacuum arc remelting the consumable electrode to provide the molten refined

material.

28. The article of claim 27, wherein electroslag remelting the consumable electrode

comprises: providing an open-bottomed vessel containing a slag;

contacting the consumable electrode with the slag within the open-bottomed

vessel;

passing electric current through a circuit including the consumable electrode, the

slag, and the vessel to cause resistance heating of the slag resulting in melting of material

from the consumable electrode at the electrode's contact point with the slag, thereby

forming droplets of molten material; and

allowing the droplets of the molten material to pass through the heated slag.

29. The article of claim 28, wherein electroslag remelting the consumable electrode

further comprises:

controlling the delivery of the consumable electrode into the vessel to maintain

contact between the electrode and the heated slag.

30. The article of claim 27, wherein vacuum arc remelting the consumable electrode

comprises:

contacting the consumable electrode with a DC arc under vacuum to heat the

electrode, thereby forming droplets of molten material.

31. The article of claim 26, wherein passing at least a portion of the molten refined

material through a passage comprises:

providing a cold induction guide;

collecting the molten refined material in the cold induction guide; and passing at least a portion of the molten refined material through a passage in the

cold induction guide while inductively heating the molten refined material witliin the

passage.

32. The article of claim 31, wherein the cold induction guide comprises:

a molten material collection region;

a transfer region including a passage terminating in an orifice;

at least one electrically conductive coil associated with the transfer region; and

at least one coolant circulation passage associated with the transfer region.

33. The article of claim 32, wherein passing at least a portion of the molten refined

material through a passage comprises:

receiving the molten refined material in the molten material collection region; and

passing at least a portion of the molten refined material through the passage in the

fransfer region while maintaining an electric current through the electrically conductive

coil and passing coolant tlirough the coolant circulation passage.

34. The article of claim 26, wherein passing at least a portion of the molten refined

material through a passage comprises:

passing at least a portion of the molten refined material through a passage having

walls lined with a refractory material and lacking an inductive heating source.

35. The article of claim 26, wherein depositing and solidifying the droplet spray

comprises:

generating a turbulent zone on a surface of the preform by the impact of droplets

of the molten refined material and the impinging gas.

36. The article of claim 26, wherein depositing and solidifying the droplet spray

comprises:

depositing and solidifying the droplet spray of the molten refined material within

a mold under at least one of a partial vacuum and a protective gas atmosphere.

37. The article of claim 26, wherein the gas-to-metal mass ratio is less than 0.3.

38. The article of claim 26, wherein in forming a droplet spray the droplets of molten

refined material are partially solid such that, on average, from 5 to 40 percent by volume

of each droplet is solid.

39. The article of claim 25, wherein the metallic material is one of a nickel-based

superalloy, a titanium alloy, a cobalt-bas alloy, and a steel.

40. The article of claim 26, wherein the metallic material is a nickel-based superalloy

selected from the group consisting of alloy 706, alloy 718, alloy 720, and Rene 88.

41. The method of claim 26, wherein the metallic material is a titanium alloy selected

from the group consisting of Ti(6-4) and Ti(17).

42. The article of claim 26, wherein the article is a preform of at least 12 inches in

diameter.

43. The article of claim 26, wherein:

the article is a rotating components adapted for use in one of an aeronautical and a

land-based turbine;

depositing and solidifying the droplet spray of the molten refined material within a

mold provides a preform,; and

the method further comprises processing the preform to provide the component.

44. An article provided by a method comprising:

providing an apparatus comprising

a melting and refining apparatus selected from an electroslag

remelting apparatus and a vacuum arc remelting apparatus,

a transfer apparatus including a passage therethrough terminating

in an orifice, the transfer apparatus in fluid communication with the

melting and refining apparatus, and

a nucleated casting apparatus comprising a mold, the nulcleated

casting apparatus in fluid communication with the transfer apparatus;

providing a consumable electrode of a metallic material; melting and refining the consumable electrode in the melting and refining

apparatus to provide a molten refined material;

passing the molten refined material through the transfer apparatus;

providing the molten refined material to the nucleated casting apparatus and

forming a droplet spray of the molten refined material by impinging a gas on a flow of

the molten refined material from the passage, wherein the gas is supplied to the flow of

molten refined material in a ratio less than 1 on unit mass gas per unit mass molten

refined material basis; and

depositing and solidifying the droplet spray of the molten refined material within

the mold.

45. The article of claim 44, wherein the article is one of a preform of at least 12

inches in diameter and a rotating component adapted for use in one of an aeronautical and

a land-based turbine.