U.S. patent application number 10/097478 was filed with the patent office on 2003-09-18 for system and filter for filtering hard alpha inclusions from reactive metal alloys.
This patent application is currently assigned to The Boeing Company. Invention is credited to Cotton, James D..
Application Number | 20030173394 10/097478 |
Document ID | / |
Family ID | 27788312 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030173394 |
Kind Code |
A1 |
Cotton, James D. |
September 18, 2003 |
System and filter for filtering hard alpha inclusions from reactive
metal alloys
Abstract
A system for filtering hard alpha inclusions from a reactive
metal alloy, such as titanium, is provided. The system includes a
vessel, a receptacle and a filter. The vessel is capable of holding
the reactive metal alloy in a molten form, and can pour the molten
reactive metal alloy. The receptacle is for receiving the molten
reactive metal alloy poured from the vessel. And to prevent at
least some hard alpha inclusions from entering the receptacle, the
filter is disposed between the vessel and the receptacle such that
the molten reactive metal alloy passes therethrough before being
received by the receptacle. The filter includes a frame, and a
porous surface that is disposed within the frame. The porous
surface defines openings that are sized to permit the reactive
metal alloy in molten form to pass therethrough while capturing
hard alpha inclusions.
Inventors: |
Cotton, James D.; (Issaquah,
WA) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
The Boeing Company
Seattle
WA
|
Family ID: |
27788312 |
Appl. No.: |
10/097478 |
Filed: |
March 14, 2002 |
Current U.S.
Class: |
228/101 |
Current CPC
Class: |
Y02P 10/20 20151101;
C22B 34/1295 20130101; B01J 10/005 20130101; C22B 9/20 20130101;
Y02P 10/234 20151101; C22B 9/023 20130101; B01D 39/2051
20130101 |
Class at
Publication: |
228/101 |
International
Class: |
B23K 001/00 |
Goverment Interests
[0001] This invention was made with government support under
Contract No. F33657-97-C-0030 awarded by Department of the Air
Force. The government may have certain rights in this invention.
Claims
What is claimed is:
1. A system for filtering hard alpha inclusions from a reactive
metal alloy, said system comprising: a vessel capable of holding
the reactive metal alloy in a molten form, wherein said vessel is
capable of pouring the molten reactive metal alloy; a receptacle
for receiving the molten reactive metal alloy poured from said
vessel; and a filter disposed between said vessel and said
receptacle through which the molten reactive metal alloy passes
before being received by said receptacle for preventing at least
some hard alpha inclusions from entering said receptacle, said
filter comprised of a material having a melting point that exceeds
a melting point of the reactive metal alloy and is at least
partially insoluble in the molten reactive metal alloy.
2. A system according to claim 1 further comprising: a heating
element in thermal contact with said filter, wherein said heating
element is capable of preheating said filter so as to limit
solidifying of the molten reactive metal alloy on said filter as
the molten reactive metal alloy passes therethrough.
3. A system according to claim 2 further comprising: a chamber
defining an internal cavity within which said vessel, receptacle
and filter are disposed, wherein the internal cavity is isolated
from an external environment, and wherein said heating element is
capable of preheating said filter by passing current through said
filter.
4. A system according to claim 2, wherein said filter comprises a
porous surface defining a plurality of openings, and wherein said
heating element preheats said filter to thereby limit the
solidifying of the molten reactive metal alloy within the openings
defined by said porous surface of said filter.
5. A system according to claim 1, wherein at least a portion of
said filter comprises a refractory metal alloy including at least
one of niobium, molybdenum, tantalum, rhenium and tungsten.
6. A system according to claim 1, wherein said filter includes a
porous surface defining a plurality of openings, and wherein the
porous surface comprises a refractory metal.
7. A system according to claim 6, wherein the refractory metal is
selected from a group consisting of niobium, molybdenum, tantalum,
rhenium and tungsten.
8. A system according to claim 1, wherein the reactive metal alloy
with a solvus temperature displaying a positive slope comprises
titanium.
9. A system according to claim 1, wherein said filter comprises: a
frame; and a porous surface disposed within said frame such that
said frame extends peripherally about said porous surface, wherein
said porous surface defines a plurality of openings that are sized
to permit the reactive metal alloy in molten form to pass
therethrough.
10. A system according to claim 1, wherein said filter comprises a
material having a solubility less than a predetermined percent by
weight in the molten reactive metal alloy.
11. A system according to claim 10, wherein the material of said
filter has a solubility less than twenty-five percent by weight in
the molten reactive metal alloy.
12. A system according to claim 1, wherein said filter comprises a
material having a melting point greater than a melting point of the
reactive metal alloy by at least a predetermined amount.
13. A system according to claim 12, wherein the material of said
filter has a melting point greater than a melting point of the
reactive metal alloy by at least 500 degrees Celsius.
14. A filter for filtering hard alpha inclusions from a reactive
metal alloy, said filter comprising: a frame; and a porous surface
disposed within said frame such that said frame extends
peripherally about said porous surface, wherein said porous surface
defines a plurality of openings that are sized to permit the
reactive metal alloy in molten form to pass therethrough while
separating at least some hard alpha inclusions therefrom, said
porous surface comprised of a material having a melting point that
exceeds a melting point of the reactive metal alloy and is at least
partially insoluble in the molten reactive metal alloy.
15. A filter according to claim 14, wherein said filter is formed
of a thermally conductive material that is capable of being
preheated so as to limit solidifying of the molten reactive metal
alloy on the filter as the molten reactive metal alloy passes
through said porous surface.
16. A filter according to claim 14, wherein said porous surface
comprises a refractory metal alloy including at least one of
niobium, molybdenum, tantalum, rhenium and tungsten.
17. A filter according to claim 14, wherein said porous surface
comprises a refractory metal.
18. A filter according to claim 17, wherein the refractory metal is
selected from a group consisting of niobium, molybdenum, tantalum,
rhenium and tungsten.
19. A filter according to claim 14, wherein said porous surface
comprises a material having a solubility less than a predetermined
percent by weight in the molten reactive metal alloy.
20. A filter according to claim 19, wherein the material of said
porous surface has a solubility less than twenty-five percent by
weight in the molten reactive metal alloy.
21. A filter according to claim 14, wherein said porous surface
comprises a material having a melting point greater than a melting
point of the reactive metal alloy by at least a predetermined
amount.
22. A filter according to claim 21, wherein the material of said
porous surface has a melting point greater than a melting point of
the reactive metal alloy by at least 500 degrees Celsius.
Description
FIELD OF THE INVENTION
[0002] The present invention relates generally to manufacturing
components from reactive metal alloys and, more particularly, to
filtering hard alpha inclusions from reactive metal alloys during
casting of components from the same.
BACKGROUND OF THE INVENTION
[0003] In many industries today, such as the biomedical and
aerospace industries, components experience severe service
conditions and, thus, are often made from titanium alloys or
superalloys. For example, turbine-powered aircraft contain critical
rotating components in the engine, such as the fan, compressor and
the turbine sections, that are made from titanium alloys and/or
superalloys. Generally, such alloys are manufactured by secondary
remelting processes, such as plasma arc cold hearth melting (PAM),
electron beam cold hearth melting (EBM), vacuum arc remelting
(VAR), and electroslag remelting (ESR). During the manufacturing of
the components, quality control takes a significant role because
failure of such components can lead to catastrophic loss of the
complex system as well as other losses.
[0004] In quality control, one of the most important quality issues
for titanium alloys and superalloys is melt-related inclusions. In
this regard, inclusions can consist of unusually coarse segregated
phases formed in the melt, or as exogenous materials having origins
outside the deliberate alloy constituents. In the case of exogenous
materials for investment castings, one type of inclusion is mold
shell fragments. Mold shell fragments are inadvertently released
from the ceramic shell mold during casting as a result of high
thermal stresses and erosion of the mold by the molten metal. The
ceramic mold innermost layer (that faces the molten metal)
typically contains rare earth metal oxide(s), such as erbia, that
are utilized because of their high melting point and chemical
compatibility with the reactive titanium melt. Upon release, the
mold shell fragments may be incorporated into the body of the
casting itself, and thereby become inclusion defects.
[0005] Another type of exogenous inclusion, peculiar to titanium
and other reactive metal alloys with solvus temperatures that rise
with interstitial oxygen, nitrogen or carbon content, is "hard
alpha", also known as Type I inclusions. Hard alpha inclusions
originate within such alloys during process operations, such as
welding, flame cutting, grinding, cutting and even furnace air
leaks, that expose the molten alloy to elements in air,
particularly oxygen, nitrogen, and carbon. When such exposure
occurs, the alloy takes the elements into solution where the
elements simultaneously stabilize and embrittle the alpha phase of
the alloy. By stabilizing and embrittling the alpha phase, a defect
is created within the alloy that is very similar in most other
respects to the base alloy. Particulate debris from such operations
can inadvertently migrate to the casting furnace and enter the
ceramic shell mold as the casting pour takes place. Because hard
alpha inclusions have a melting point exceeding that of the clean
alloy, hard alpha inclusions can survive exposure to the melt,
enter the mold and become a brittle inclusion. Additionally, hard
alpha inclusions can enter the primary metal supply stream and
unknowingly become part of the melt stock.
[0006] As stated, hard alpha inclusions originate during certain
process operations within titanium and other reactive metal alloys
with solvus temperatures displaying a positive slope as oxygen,
nitrogen or carbon are added. Such process operations are integral
to other process streams at the foundry where the components are
manufactured and, as such, the process operations cannot be totally
eliminated or isolated from the casting activity. As a result,
detailed contamination control plans are typically implemented to
prevent the generation and introduction of hard alpha debris into
the foundry. Such contamination control plans, however, have a
number of drawbacks. While contamination control plans aid in
preventing the generation and introduction of hard alpha debris,
such control plans generally do not remove hard alpha debris that
actually do form or become introduced from operations external to
the foundry. Also, contamination control plans typically add cost
to the manufacture of the components, and add time required in the
production schedule of the components. Additionally, such
contamination control plans are generally difficult to enforce
among manufacturers, and cannot be easily validated. In this
regard, because of the limitations of contamination control plans
and the associated risk of component failure, the design of
components made from such alloys still typically accounts for the
presence of hard alpha inclusions.
SUMMARY OF THE INVENTION
[0007] In light of the foregoing background, the present invention
provides a system and filter for filtering hard alpha inclusions
from reactive metal alloys. In contrast to conventional
contamination control plans, the system and filter of the present
invention remove hard alpha debris that forms or becomes introduced
into the foundry. As such, the design of components made from
relevant alloys manufactured according to the present invention
need not account for the presence of hard alpha inclusions. Also,
the system and filter add relatively little cost to the manufacture
of components, when compared to the cost to develop and implement a
conventional detailed contamination control plan. Utilizing the
system and filter of the present invention does not add any
appreciable time to the production schedule of components. Further,
because the system and filter of the present invention remove hard
alpha inclusions as opposed to attempting to control or limit the
formation of such contaminants, no need exists to enforce or
validate implementation of the filter as required by conventional
contamination control plans.
[0008] According to one embodiment, the present invention provides
a system for filtering hard alpha inclusions from a reactive metal
alloy, such as titanium. The system includes a vessel that is
capable of holding the reactive metal alloy in a molten form, and
can pour the molten reactive metal alloy. The system also includes
a receptacle for receiving the molten reactive metal alloy poured
from the vessel. And to prevent at least some hard alpha inclusions
from entering the receptacle, the system includes a filter disposed
between the vessel and the receptacle through which the molten
reactive metal alloy passes before being received by the
receptacle.
[0009] The filter includes a frame, and a porous surface that is
disposed within the frame such that the frame extends peripherally
about the porous surface. The porous surface defines a plurality of
openings that are sized to permit the reactive metal alloy in
molten form to pass therethrough. The filter is comprised of a
material having a melting point that exceeds a melting point of the
reactive metal alloy and is at least partially insoluble in the
molten reactive metal alloy. The material of the filter can have a
solubility less than a predetermined percent by weight in the
molten reactive metal alloy, such as less than twenty-five percent
by weight. Also, the material of the filter can have a melting
point greater than a melting point of the reactive metal alloy by
at least a predetermined amount, such as at least 500 degrees
Celsius. For example, the filter can comprise an alloy including at
least one of niobium, molybdenum, tantalum, rhenium and
tungsten.
[0010] Further, to limit solidifying of the molten reactive metal
alloy on the filter as the molten reactive metal alloy passes
through the filter, the system can include a heating element in
thermal contact with the filter. More specifically, the heating
element can preheat the filter to thereby limit the solidifying of
the molten reactive metal alloy within the openings defined by the
porous surface of the filter. And in another embodiment, the system
further includes a chamber defining an internal cavity within which
the vessel, receptacle and filter are disposed. In this embodiment,
the internal cavity is isolated from an external environment. Also,
the heating element is capable of preheating the filter by passing
current through the filter.
[0011] The system and filter of the present invention, therefore,
filter hard alpha inclusions from reactive metal alloys with solvus
temperatures displaying a positive slope. In contrast to
conventional contamination control plans, the system and filter of
the present invention add relatively little cost to the manufacture
of components, and do not add any appreciable time to the
production schedule of components. Further, in contrast to
conventional contamination control plans, the system and filter of
the present invention filter out hard alpha inclusions as opposed
to attempting to control or limit the formation of such
contaminants. And as such, no need exists to enforce or validate
implementation of the filter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0013] FIG. 1 is a block diagram of a system for filtering hard
alpha inclusions from a reactive metal alloy, according to one
embodiment of the present invention;
[0014] FIG. 2 is a schematic front view of a filter according to
one embodiment of the present invention with an exploded inset of a
portion of the filter;
[0015] FIG. 3 is a graph illustrating the solubility per weight at
the melting temperature of several refractory metals in accordance
with one embodiment of the present invention; and
[0016] FIG. 4 is a schematic view of a vacuum arc skull melting and
casting furnace system including a filter in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0018] Referring to FIG. 1, a system 10 for filtering hard alpha
inclusions from reactive metal alloys includes a vessel 12, a
receptacle 14 and a filter 16. The reactive metal alloys can
comprise any of a number of alloys that are susceptible to hard
alpha inclusions, such as titanium. In this regard, hard alpha
inclusions originate within alloys during process operations that
expose the molten reactive metal alloy to elements in air,
particularly oxygen, nitrogen, and carbon. When such exposure
occurs, the alloy takes the elements into solution where the
elements simultaneously stabilize and embrittle the alpha phase of
the alloy. In this regard, reactive metal alloys that are
susceptible to hard alpha inclusions generally include those alloys
with solvus temperatures that rise with interstitial oxygen,
nitrogen or carbon content. These reactive metal alloys include
those metal alloys that experience an increase in melting point as
the oxygen, nitrogen or carbon content of the alloy increases, thus
allowing local regions of high oxygen, nitrogen or carbon content
to persist during melting of the alloy. For example, the reactive
metal alloy can comprise any alloy including elements such as
zirconium, hafnium, and yttrium. But in a preferred embodiment, the
reactive metal alloy comprises titanium.
[0019] The vessel 12 is capable of holding the reactive metal alloy
in molten form 18, and is capable of pouring the molten reactive
metal alloy. The vessel can comprise any of a number of different
materials so long as the vessel is capable of maintaining the
vessel's mechanical strength and rigidity, and as long as the
vessel does not react with or contaminate the molten reactive metal
alloy. To allow the vessel to hold the molten reactive metal alloy
without reacting with the metal alloy, the vessel can include an
alloy "skull" layer of solidified reactive metal alloy on the
inside surface of the vessel between the vessel and the molten
reactive metal alloy, as such is known to those skilled in the art.
For example, when the reactive metal alloy comprises titanium, the
vessel can comprise a copper crucible with a titanium skull layer
on the inside surface of the crucible between the molten titanium
and the crucible.
[0020] The receptacle 14 is capable of receiving the molten
reactive metal alloy poured from the vessel 12. The receptacle can
comprise any of a number of different materials but, similar to the
vessel, the receptacle is capable of maintaining the receptacle's
mechanical strength and rigidity at high temperatures, and does not
react with the molten reactive metal alloy 18. For example, the
receptacle can comprise a ceramic mold for a component of a complex
system, such as a fan for an aircraft engine. Also similar to the
vessel, the receptacle can include a layer of material on the inner
surface of the receptacle to allow the receptacle receive the
molten reactive metal alloy without reacting therewith. For
example, when the molten reactive metal alloy comprises titanium,
the innermost layer of the receptacle (that faces the molten metal)
can include a layer of rare earth metal oxide(s), such as erbia,
that has a high melting point and chemical compatibility with the
reactive molten titanium.
[0021] As previously stated, particular molten reactive metal
alloys can develop hard alpha inclusions when the molten reactive
metal alloy is exposed to elements in air, such as oxygen and
nitrogen. As such, to filter hard alpha inclusions from the molten
reactive metal alloy 18 poured from the vessel 12 into the
receptacle 14, the system 10 includes the filter 16. The filter is
disposed between the vessel and the receptacle and can be mounted
in any manner therebetween. For example, the filter can be mounted
directly over the opening of the vessel such that the molten
reactive metal alloy passes through the filter as the vessel pours
the molten reactive metal alloy into the receptacle. Alternatively,
the filter can be mounted directly over the opening of the
receptacle such that the molten reactive metal alloy poured from
the vessel passes through the filter before the receptacle receives
the molten reactive metal alloy.
[0022] As shown in FIG. 2, the filter 16 includes a frame 20, and a
porous surface 22 disposed within the frame such that the frame
extends peripherally about the porous surface. The porous surface
defines a plurality of openings 24 that allow the molten reactive
metal alloy 18 to pass through the porous surface. In one
embodiment, the porous surface comprises a plurality of metal
strands, such as wires, that extend across the frame in different
directions and cross one another to thereby define the plurality of
openings. As described below, the openings have a square shape, but
it should be understood that the openings can be any shape without
departing from the spirit and scope of the present invention.
[0023] The openings 24 of the filter 16 should be designed with a
sufficient area such that the molten reactive metal alloy 18 can
pass through the filter at a desired flow rate without accumulating
on the porous surface 22 of the filter. But the area of the
openings should also be small enough that the porous surface
maintains the filter's mechanical strength and rigidity as the
molten reactive metal alloy passes therethrough. Additionally, the
area of the openings should be small enough so that solid
contaminants, particularly hard alpha inclusions, do not pass
through the filter. In this regard, the area of the openings can be
selected to thereby select the maximum size of the hard alpha
inclusions allowed through the filter. For example, the openings
can be selected to have dimensions x and y, that equal one another
and are equal to 0.070 inches. Also, the thickness, t, of the
porous surface between the openings (or diameter of the wires if
the porous surface comprises such) can be selected to equal 0.0050
inches. Thus, the porous surface would define a plurality of
openings that are 87% open (i.e.,
0.070.sup.2/[0.070+0.0050].sup.2). As another example, the porous
surface can define openings that are selected to be 90% open, with
the thickness, t, selected to be between 0.005 and 0.010 inches,
and the x and y dimensions determined accordingly.
[0024] Again referring to FIG. 1, to limit the solidification of
the molten reactive metal alloy on the porous surface 22 of the
filter 16 and, particularly, within the openings 24, the system 10
can further include a heating element 26. The heating element is
capable of preheating the filter prior to and/or during pouring of
the molten reactive metal alloy from the vessel 12. The heating
element can comprise any of a number of different devices as such
are known. The heating element is capable of preheating the filter
to a temperature sufficient to limit the amount of molten reactive
metal alloy that solidifies on the filter to as little as possible.
In one embodiment, the system further includes a chamber 28, such
as a vacuum chamber, that defines an internal cavity within which
the vessel, receptacle 14 and filter are disposed. In this
embodiment, the heating element can preheat the filter by passing
current through the filter sufficient to preheat the filter to a
desired temperature.
[0025] Referring now to FIG. 3, the porous surface 22 of the filter
16 can comprise any of a number of different refractory metals or
refractory metal alloys. Similarly, the frame 20 can comprise any
of a number of different refractory metals or refractory metal
alloys. In a preferred embodiment, the frame comprises the same
material as the porous surface, although the frame and porous
surface can comprise different materials without departing from the
spirit and scope of the present invention. The refractory metal or
refractory metal alloy is selected such that the refractory metal
or refractory metal alloy has a melting point that exceeds a
melting point of the reactive metal alloy and is at least partially
insoluble in the molten reactive metal alloy 18. In this regard,
the refractory metal or refractory metal alloy may be selected to
have a solubility less than a predetermined percent by weight in
the molten reactive metal alloy, and a melting point greater than
the melting point of the reactive metal alloy by at least a
predetermined amount. By so selecting the refractory metal or
refractory metal alloy, the material of the filter has the least
chance of contaminating the molten reactive metal alloy as the
molten reactive metal alloy passes therethrough, and the material
is the least susceptible to creep or deflection.
[0026] Therefore, with respect to titanium, the materials located
in the lower right region of the graph of FIG. 3 include those
refractory metals that have a sufficiently low solubility in molten
titanium at a sufficiently high melting temperature from which the
porous surface 22 and/or the frame 20 of the filter 16 can be made.
As is known, titanium has a melting point of approximately 1660
degrees Celsius (designated in FIG. 3 by the broken line). As an
example, the material can be selected to have a melting point at
least 500 degrees Celsius more than the melting point of titanium.
Also, the material may be selected to have a solubility less than
twenty-five percent by weight at the melting point of the material.
It should also be understood, however, that the material of the
porous surface and/or the frame can be selected with other
differences in melting temperature and other amounts of
insolubility if so desired. As shown, for example, in the preferred
embodiment where the molten reactive metal alloy 18 comprises
molten titanium, the porous surface comprises tungsten, W. It
should be understood, however, that the porous surface and/or the
frame can also comprise niobium, Nb, tantalum, Ta, molybdenum, Mo,
and/or rhenium, Re. Alternatively, the porous surface and/or the
frame can comprise a refractory metal alloy that includes at least
one refractory metal selected from W, Nb, Ta, Mo and Re, as well as
vanadium, V, rhodium, Rh and hafnium Hf.
[0027] Referring to FIG. 4, one type of system that would benefit
from the filtering of the present invention is depicted. As shown,
a vacuum arc skull melting and casting furnace 30 generally
includes a vacuum-tight chamber 32 in which molten metal alloy 34
is driven down into a crucible 36 (i.e., vessel). A power supply 38
provides current to strike an electric arc between a consumable
electrode 40 and the crucible to thereby melt the reactive metal
alloy in the crucible. The crucible can be water cooled and, as
such, a solidified metal alloy skull can form on the inner surface
of the crucible thereby shielding the crucible from direct contact
with the molten metal alloy. Once a specified amount of molten
metal alloy 34 is contained within the crucible 36, the electrode
40 can be retracted. Thereafter, the crucible is tilted to pour the
molten metal alloy into an investment casting mold 42 (i.e.,
receptacle) positioned beneath the crucible. Before the molten
metal alloy reaches the investment casting mold, however, the
molten metal alloy can pass through a filter 44 designed in
accordance with the present invention. The filter is disposed
between the crucible and the investment casting mold. And by
passing the molten metal alloy through the filter, solid
contaminants, particularly hard alpha inclusions, can be removed
from the molten metal alloy.
[0028] It will be appreciated that the system and filter of the
present invention can be utilized in many different applications,
of which the vacuum arc skull melting and casting furnace used in
investment casting is one example. The system and filter of the
present invention would benefit any system or process where molten
reactive metal alloy that is susceptible to hard alpha inclusions
or other contaminants. For example, the system and filter of the
present invention can be used to purify molten reactive metal alloy
by removing hard alpha inclusions and other contaminants from
molten reactive metal alloy supply stock for forging, extrusions or
the like.
[0029] Therefore, the present invention provides a system and
filter that adds relatively little cost to the manufacture of
components, when compared to the cost to develop and implement a
conventional detailed contamination control plan. Also, no need
exists to enforce or validate implementation of the system and
filter of the present invention, in contrast to conventional
contamination control plans. In this regard, the design of
components made from relevant alloys manufactured according to the
present invention need not account for the presence of hard alpha
inclusions larger than the size of the openings of the filter.
Systems utilizing such improved components will benefit from
improved reliability and safety, and reduced cost, due to extended
safe operating life and reduced inspection.
[0030] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation
* * * * *