U.S. patent application number 10/128980 was filed with the patent office on 2003-07-24 for method for imaging inclusions in investment castings.
Invention is credited to Barrett, James R., Nikolas, Douglas G., Springgate, Mark E., Sturgis, David Howard, Yasrebi, Mehrdad.
Application Number | 20030136540 10/128980 |
Document ID | / |
Family ID | 27371571 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030136540 |
Kind Code |
A1 |
Springgate, Mark E. ; et
al. |
July 24, 2003 |
Method for imaging inclusions in investment castings
Abstract
A method for imaging inclusions in metal or metal alloy castings
is described. One embodiment of the present method first involves
casting a metal or metal alloy article using an investment casting
mold where the mold facecoat, and perhaps one or more of the mold
backup layers, comprises an imaging agent distributed substantially
uniformly throughout in amounts sufficient for imaging inclusions.
The facecoat preferably comprises an intimate mixture of a
refractory material and the imaging agent. Intimate mixtures can be
produced in a number of ways, but a currently preferred method is
to cocalcine the refractory material, such as yttria, with the
imaging agent, such as gadolinia. The facecoat also can comprise
plural mold-forming materials and/or plural imaging agents. The
difference between the linear attenuation coefficient of the
article and the linear attenuation coefficient of the imaging agent
should be sufficient to allow imaging of the inclusion throughout
the article. The metal or metal alloy article is then analyzed for
inclusions by N-ray analysis. The method also can include the step
of analyzing the metal or metal alloy by X-ray analysis. The
imaging agent, typically a metal oxide or salt, comprises a
material selected from the group consisting of boron, neodymium,
samarium, europium, gadolinium, dysprosium, holmium, erbium,
ytterbium, lutetium, iridium, physical mixtures thereof and
chemical mixtures thereof.
Inventors: |
Springgate, Mark E.;
(Portland, OR) ; Barrett, James R.; (Milwaukie,
OR) ; Sturgis, David Howard; (Boring, OR) ;
Nikolas, Douglas G.; (Battleground, WA) ; Yasrebi,
Mehrdad; (Clackamas, OR) |
Correspondence
Address: |
KLARQUIST SPARKMAN, LLP
One World Trade Center, Suite 1600
121 S.W. Salmon Street
Portland
OR
97204
US
|
Family ID: |
27371571 |
Appl. No.: |
10/128980 |
Filed: |
April 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10128980 |
Apr 23, 2002 |
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09327038 |
Jun 7, 1999 |
|
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09327038 |
Jun 7, 1999 |
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09212116 |
Dec 15, 1998 |
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6102099 |
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60069597 |
Dec 15, 1997 |
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Current U.S.
Class: |
164/4.1 ;
164/151 |
Current CPC
Class: |
G01N 23/05 20130101 |
Class at
Publication: |
164/4.1 ;
164/151 |
International
Class: |
B22D 046/00; B22D
002/00 |
Claims
We claim:
1. A method for determining whether a metal or metal alloy article
has inclusions, comprising: providing a cast metal or metal alloy
article made using a casting mold comprising ytterbium as an N-ray
imaging agent in an amount sufficient for imaging inclusions; and
determining whether the article has inclusions by N-ray
imaging.
2. The method according to claim 1 where the N-ray imaging agent is
ytterbia.
3. A method for casting a metal or metal alloy article, comprising:
providing a casting mold comprising an N-ray imaging agent which
includes a material selected from the group consisting of lithium,
boron, neodymium, samarium, europium, gadolinium, dysprosium,
holmium, ytterbium, lutetium, iridium, physical mixtures thereof
and chemical mixtures thereof; and casting a metal or metal alloy
article using the casting mold.
4. The method according to claim 3 where the N-ray imaging agent
includes a material selected from the group consisting of samarium,
gadolinium, dysprosium, physical mixtures thereof and chemical
mixtures thereof.
5. The method according to claim 3 where the N-ray imaging agent
includes gadolinium.
6. The method according to claim 5 where the N-ray imaging agent is
gadolinia.
7. The method according to claim 3 where the casting mold includes
a facecoat having a refractory material selected from the group
consisting of yttria, zirconia, alumina, calcia, silica, zirconia,
titania, tungsten, physical mixtures thereof, and chemical mixtures
thereof.
8. A method for determining whether a metal or metal alloy article
has inclusions, comprising: providing a cast metal or metal alloy
article made using a casting mold comprising an imaging agent in
amounts sufficient for imaging inclusions; and determining whether
the article has inclusions by N-ray analysis using a film image
recorder.
9. The method according to claim 8 where the film image recorder is
a camera.
10. The method according to claim 8 where the film image recorder
is a light-emitting fluorescent screen.
11. The method according to claim 8 where determining whether the
article has inclusions by N-ray analysis comprises using neutrons
selected from the group consisting of fast, epithermal, thermal and
cold neutrons, or combinations thereof.
12. The method according to claim 11 where the neutrons are cold
neutrons.
13. The method according to claim 11 where the neutrons are
epithermal neutrons.
14. The method according to claim 8 where the imaging agent is
selected from the group consisting of lithium, boron, neodymium,
samarium, europium gadolinium, dysprosium, holmium, ytterbium,
lutetium, iridium, physical mixtures thereof, and chemical mixtures
thereof, and the mold includes a facecoat refractory material
selected from the group consisting of yttria, zirconia, alumina,
calcia, silica, zircon, titania, tungsten, physical mixtures
thereof, and chemical mixtures thereof.
15. A method for real time detection of inclusions in a metal or
metal alloy article, comprising: providing a cast metal or metal
alloy article made using a casting mold comprising an imaging agent
in amounts sufficient for imaging inclusions; and determining
whether the article has inclusions by real time N-ray analysis.
16. The method according to claim 15 where determining comprises
analyzing N-ray images produced in real time using an image
displaying device.
17. The method according to claim 16 where the image displaying
device is a light-emitting fluorescent screen.
18. A method for real time detection of inclusions in a metal or
metal alloy article, comprising: casting a metal or metal alloy
article using a mold having a facecoat comprising an imaging agent
distributed substantially uniformly throughout in amounts
sufficient for imaging inclusions; and analyzing the article for
inclusions by real time N-ray analysis.
19. The method according to claim 18 where the mold is an
investment casting mold, and the imaging agent is distributed
substantially uniformly in at least a facecoat layer.
20. The method according to claim 18 where the step of analyzing
further comprises X-ray analysis.
21. The method according to claim 18 where the imaging agent
includes a material selected from the group consisting of lithium,
boron, neodymium, samarium, europium, gadolinium, dysprosium,
holmium, erbium, ytterbium, lutetium, iridium, physical mixtures
thereof and chemical mixtures thereof.
22. The method according to claim 21 where the imaging agent is a
metal salt, a metal oxide, an intermetallic, a boride, or mixtures
thereof.
23. The method according to claim 18 where the article comprises a
titanium or a titanium alloy, the facecoat comprises yttria or
zirconia, and the imaging agent is gadolinia.
24. A method for real time detection of inclusions in a metal or
metal alloy article, comprising: forming an aqueous or non-aqueous
facecoat slurry comprising an inclusion imaging agent; applying the
facecoat slurry to a pattern to form a mold facecoat comprising the
imaging agent distributed substantially uniformly throughout in
amounts sufficient for imaging inclusions; serially applying plural
backup layers to the pattern to form a mold for investment casting;
casting a metal article using the mold; and analyzing the article
for inclusions using real time N-ray analysis.
25. The method according to claim 24 where analyzing further
comprises X-ray analysis.
26. The method according to claim 24 where the imaging agent
includes a material selected from the group consisting of lithium,
boron, neodymium, samarium, europium, gadolinium, dysprosium,
holmium, erbium, ytterbium, lutetium, iridium, physical mixtures
thereof and chemical mixtures thereof.
27. The method according to claim 26 where the article comprises a
titanium or a titanium alloy and the facecoat further comprises a
refractory material selected from the group consisting of yttria,
zirconia, alumina, calcia, silica, zircon, titania, tungsten,
physical mixtures thereof, and chemical mixtures thereof.
28. The method according to claim 24 where at least a portion of
the metal or metal alloy article has a thickness of greater than
about 2 inches.
29. The method according to claim 24 where at least a portion of
the metal or metal alloy article has a thickness of greater than
about 1 inch, the imaging agent is gadolinia, and alpha case in the
article is less than or equal to that when the facecoat is
yttria.
30. A method for real-time detection of inclusions in a titanium or
titanium alloy article produced by investment casting, comprising:
forming an aqueous or non-aqueous investment casting facecoat
slurry comprising an intimate mixture of a mold-forming material
selected from the group consisting of yttria, zirconia, alumina,
calcia, silica, zircon, titania, tungsten, physical mixtures
thereof, and chemical mixtures thereof, and an imaging agent in an
amount sufficient to allow imaging of inclusions in the article,
the imaging agent including a material selected from the group
consisting of lithium, boron, neodymium, samarium, europium,
gadolinium, dysprosium, holmium, erbium, ytterbium, lutetium,
iridium, physical mixtures thereof and chemical mixtures thereof;
applying the slurry to a pattern to form a mold facecoat comprising
the intimate mixture of the mold-forming material and the imaging
agent distributed substantially uniformly throughout in amounts
sufficient for imaging inclusions wherein a linear attenuation
coefficient of the article and a linear attenuation coefficient of
the imaging agent are sufficiently different to allow imaging of
the inclusion throughout the article by real time N-ray analysis;
serially applying plural backup layers to the pattern and
thereafter firing the pattern to form a mold for investment
casting; casting a titanium or titanium alloy article using the
mold; and analyzing the article for mold inclusions by real time
N-ray analysis.
31. The method according to claim 30 where analyzing further
comprises X-ray analysis.
32. The method according to claim 30 where at least one backup
layer also comprises an imaging agent.
33. The method according to claim 30 where the mold-forming
material is yttria and the imaging agent is gadolinia.
34. The method according to claim 30 where the facecoat comprises
yttria cocalcined with gadolinia.
35. The method according to claim 30 where the facecoat comprises a
refractory material and plural imaging agents.
36. A method for detecting inclusions in investment castings,
comprising: placing a solution of at least one imaging agent inside
a cavity of an investment casting mold; allowing the solution to
remain in the cavity for a sufficient period of time to infiltrate
at least the facecoat of the mold; removing the solution from the
cavity; casting a metal or metal alloy article using the mold; and
analyzing the article for mold inclusions by N-ray imaging.
37. The method according to claim 40 where the imaging agent is
selected from the group consisting of lithium, boron, neodymium,
samarium, europium, gadolinium, dysprosium, holmium, erbium,
ytterbium, lutetium, iridium, physical mixtures thereof and
chemical mixtures thereof.
38. The method according to claim 36 where the imaging agent
comprises gadolinium, the metal or metal alloy is titanium or a
titanium alloy, and the facecoat comprises yttria.
39. The method according to claim 36 and further comprising
analyzing the article for inclusions by X-ray imaging.
40. The method according to claim 36 where the solution comprises
plural imaging agents.
41. The method according to claim 36 and further comprising placing
the mold in a chamber and reducing the pressure in the chamber to
facilitate solution infiltrating the mold.
42. A method for detecting inclusions in investment castings,
comprising forming an investment casting mold facecoat about a
pattern; infiltrating at least a portion of the facecoat using an
aqueous or non-aqueous solution of at least one imaging agent
comprising a material selected from the group consisting of
lithium, boron, neodymium, indium, samarium, europium, gadolinium,
dysprosium, holmium, erbium, ytterbium, lutetium, iridium, physical
mixtures thereof and chemical mixtures thereof; casting a metal or
metal alloy article using an investment casting mold having the
facecoat; and analyzing the article for inclusions by N-ray
imaging.
43. The method according to claim 42 and further including forming
plural mold backup layers about the pattern; and infiltrating at
least one of the plural mold backup layers with the solution of the
imaging agent.
44. The method according to claim 42 where infiltrating comprises
immersing at least a portion of the pattern having the facecoat
into an aqueous or non-aqueous solution comprising the imaging
agent for a period of time sufficient to infiltrate the facecoat
with imaging agent.
45. The method according to claim 42 where analyzing the article
comprises using moderated neutrons.
46. The method according to claim 42 where analyzing comprises real
time analysis.
47. A method for determining whether a metal or metal alloy article
has inclusions in real time, comprising: providing a cast metal or
metal alloy article made using a casting mold comprising an N-ray
imaging agent in an amount sufficient for imaging inclusions; and
determining whether the article has inclusions by real time N-ray
imaging using neutrons selected from the group consisting of fast,
epithermal, thermal and cold neutrons.
48. The method according to claim 47 where the imaging agent
comprises an intimate mixture of a refractory material and the
imaging agent.
49. The method according to claim 47 where the casting mold is
infiltrated using solutions of imaging agents.
50. The method according to claim 47 where the mold comprises a
mold-forming material selected from the group consisting of yttria,
zirconia, alumina, calcia, silica, zircon, titania, tungsten,
physical mixtures thereof, and chemical mixtures thereof, and the
imaging agent is selected from the group consisting of lithium,
boron, neodymium, samarium, europium, gadolinium, dysprosium,
holmium, erbium, ytterbium, lutetium, iridium, physical mixtures
thereof and chemical mixtures thereof.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of applicants'
prior application Ser. No. 09/327,038, filed Jun. 7, 1999, which is
a continuation of application Ser. No. 09/212,116, filed Dec. 15,
1998, which claimed priority from provisional application No.
60/069,597, filed on Dec. 15, 1997. Applicants' prior applications
are incorporated herein by reference.
FIELD
[0002] This invention concerns methods for making investment
casting molds comprising imaging agents in at least the facecoat of
the mold, and methods for imaging inclusions in metal or metal
alloy articles made using such molds.
BACKGROUND
[0003] Investment casting is a process for forming metal or metal
alloy articles (also referred to as castings) by solidifying molten
metal or alloys in molds having an internal cavity in the shape of
such articles. The molds are formed by serially applying layers of
mold-forming materials to wax patterns formed in the shape of the
desired article. The first layer applied to the pattern, referred
to as the facecoat, contacts the metal or metal alloy being cast
during the casting process. Materials used to form the facecoat,
and perhaps other "backup" layers of the mold, can flake off the
mold and become embedded in the molten metal or alloy during the
casting process. As a result, the metal or alloy article includes a
material or materials not intended to be part of the article, such
material or materials being referred to as "inclusions".
[0004] Many industries, particularly the aerospace industry, have
stringent specifications as to the acceptable content and/or size
of inclusions. The location of inclusions in castings can be
difficult, and in some cases prior to the present invention,
impossible to detect. Some inclusions, if detected, can be removed
from the metal article, and the article repaired, without
compromising its structural integrity.
[0005] Titanium has been used by the investment casting industry
primarily for casting articles having relatively small cross
sections. However, investment casting is now being considered for
producing structural components of aircrafts having significantly
larger cross sections than articles cast previously. Certain
inclusions in relatively thin articles can be detected using X-ray
analysis. For example, thorium oxide and tungsten have been used as
refractories to produce mold facecoats for investment casting. Some
thorium oxide and tungsten inclusions could be detected in titanium
castings by X-ray analysis because there is a sufficient difference
between the density of thorium oxide and tungsten and that of
titanium to allow imaging of thorium-oxide or tungsten-derived
inclusions. This also generally has proved true of articles having
relatively small cross sections cast using molds having yttria
facecoats. The difference between the density of yttria and that of
titanium is sufficient to allow detection in relatively thin parts,
such as engine components. But, X-ray detection cannot be used to
image yttria inclusions in titanium or titanium alloy articles as
the thickness of articles produced by investment casting increases
beyond some threshold thickness that is determined by various
factors, primarily the thickness of the cast part, the type of
metal or alloy being cast, the size of the inclusion and the
material or materials used to form the mold. Inclusions also cannot
be detected by X-ray if the difference between the density of the
facecoat material and the metal being cast is insufficient or if
the size of the inclusion is very small.
[0006] Thermal neutron radiography (N-ray) imaging agents have been
used in the casting industry prior to the present invention. For
example, ASTM (American Society for Testing and Materials)
publication No. E 748-95 states that "[c]ontrast agents can help
show materials such as ceramic residues in investment-cast turbine
blades." ASTM E 748-95, p. 5, beginning at about line 46. This
quote refers to the detection of ceramic residues by N-ray on
articles having an internal cavity produced by initially
solidifying metal about a ceramic core. The ceramic core is removed
to form the cavity, and thereafter a solution of gadolinium nitrate
is placed in the cavity. The gadolinium nitrate solution remains in
the cavity long enough to infiltrate porous ceramic core residues
that are on the surface of the article. The residues then can be
imaged by N-ray. However, this method does not work for imaging
inclusions.
SUMMARY
[0007] The present invention addresses the problem of imaging
inclusions embedded in relatively thick castings. One feature of
the method is the incorporation of an imaging agent into the
investment casting mold, particularly in the facecoat of the mold,
prior to casting so that inclusions can be imaged in the cast
article.
[0008] One embodiment of the present method first involves
providing a cast metal or metal alloy article made using a casting
mold comprising an imaging agent in amounts sufficient for imaging
inclusions, and thereafter determining whether the article has
inclusions by N-ray analysis. The step of providing a cast metal or
metal alloy article may comprise providing a casting mold
comprising an N-ray imaging agent, and then casting a metal or
metal alloy article using the casting mold. Typically, the mold
facecoat, and perhaps one or more of the mold backup layers,
comprises an imaging agent distributed substantially uniformly
throughout in amounts sufficient for imaging inclusions. The
article is then analyzed for inclusions by N-ray imaging. The
method also can include the step of analyzing the metal or metal
alloy by X-ray imaging. The method is particularly suitable for
detecting inclusions in relatively thick articles, such as titanium
or titanium alloy articles, where at least a portion of the article
has a thickness of greater than about 2 inches, particularly
facecoat inclusions in titanium castings. An "inclusion" can refer
to materials not desired in the casting, such as inclusions derived
from the mold facecoat. Alternatively, an "inclusion" can also
refer to materials that should be included in the casting, such as
strength-enhancing fibers, in which case the fibers can be coated
with imaging agent, or intimate mixtures of fibers and imaging
agents can be made and used. Detected deleterious inclusions are
removed by conventional means.
[0009] Simple binary mixtures comprising an imaging agent or agents
and a mold-forming material or materials can be used. The present
method preferably involves forming an intimate mixture of the
materials used to practice the present invention, such as intimate
mixtures of refractory materials, intimate mixtures of imaging
agents, and/or intimate mixtures of imaging agent or agents and a
refractory or refractory materials. Intimate mixtures can be
produced in a number of ways, but currently preferred methods are
to either calcine or fuse the mold-forming material, such as
yttria, with the imaging agent, such as gadolinia.
[0010] Alternatively, solutions of imaging agents can be used to
infiltrate the mold (as opposed to a casting) prior to casting the
metal article. For example, solutions comprising nitrate, halide,
sulfate, perchlorate salts of imaging agents can be used to form
solutions comprising such materials, and these solutions are then
used to infiltrate an investment casting mold. The infiltration
process can be enhanced by placing the mold in a chamber which can
be evacuated, at least partially. This facilitates having imaging
agent solution enter the pores of the mold.
[0011] The difference between the linear attenuation coefficient of
the article and the linear attenuation coefficient of the imaging
agent should be sufficient to allow N-ray imaging of the inclusion
throughout the article. The imaging agent typically includes a
material, usually a metal, selected from the group consisting of
lithium, boron (e.g., TiB.sub.2), neodymium, samarium, europium,
gadolinium, dysprosium, holmium, erbium, ytterbium, lutetium,
iridium, boron, physical mixtures thereof and chemical mixtures
thereof. Examples of suitable imaging agents comprising such metals
include metal oxides, metal salts, intermetallics, and borides.
Gadolinia is a currently preferred imaging agent for imaging
inclusions in titanium or titanium alloy castings.
[0012] The refractory material used to make the facecoat slurry
typically comprises from about 0.5 to about 100 weight percent
imaging agent, more typically from about 1 to about 100 weight
percent, even more typically from about 1 to about 65 weight
percent, and preferably from about 2 to about 25 weight percent,
imaging agent.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A is an N-ray image of an inclusion-containing test
bar having three facecoat-simulating inclusions, where "aa" refers
to a mixture of yttria and 2.58 weight percent gadolinia, "ab"
refers to a mixture of yttria and 25.97 weight percent gadolinia,
and "3" is a standard referring to 100 weight percent yttria.
[0014] FIG. 1B is an N-ray image of an inclusion-containing test
bar having three facecoat-simulating inclusions, where "ba" refers
to a mixture of yttria and 13.11 weight percent samaria, "bb"
refers to a mixture of yttria and 5.14 weight percent gadolinia,
and "3" is a standard referring to 100 weight percent yttria.
[0015] FIG. 1C is an N-ray image of an inclusion-containing test
bar having three facecoat-simulating inclusions, where "ca" refers
to a mixture of yttria and 56.03 weight percent samaria, "cd"
refers to a mixture of yttria and 30.8 weight percent samaria, and
"3" is a standard referring to 100 weight percent yttria.
[0016] FIG. 1D is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 45 weight percent dysprosia.
[0017] FIG. 1E is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 62 weight percent dysprosia.
[0018] FIG. 1F is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 1 weight percent dysprosia.
[0019] FIG. 2G is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 14 weight percent gadolinia.
[0020] FIG. 2H is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 60 weight percent gadolinia.
[0021] FIG. 2I is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 14 weight percent samaria.
[0022] FIG. 2J is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 27 weight percent samaria.
[0023] FIG. 2K is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 27 weight percent gadolinia.
[0024] FIG. 2L is an N-ray image of an inclusion-containing test
bar having a facecoat-simulating inclusion comprising cocalcined
yttria and 39 weight percent gadolinia.
[0025] FIG. 3 is an N-ray image of an experimental casting made
using a mold having a facecoat comprising yttria and 14 weight
percent gadolinia.
[0026] FIG. 4 is a graph of weight percent gadolinia: imaging agent
versus alpha case (thickness in inches) for a production part made
having a cross sectional thickness of 1.5 inches.
[0027] FIG. 5 is a graph of weight percent gadolinia imaging agent
versus alpha case (thickness in inches) for a production part made
having a cross sectional thickness of 1.0 inch.
[0028] FIG. 6 is an inclusion detectability graph of
cross-sectional thickness in a titanium casting versus inclusion
size detected for real time N-ray analysis versus film imaging for
N-ray and X-ray analysis.
DETAILED DESCRIPTION
[0029] The present invention concerns detecting inclusions in
investment castings using N-ray analysis, or N-ray analysis in
combination with X-ray analysis. The method is useful for detecting
inclusions in virtually all metals or metal alloys, with particular
examples being titanium metal and alloys, steel, nickel and nickel
alloys, cobalt and cobalt alloys, such as cobalt-chrome alloys,
metal matrix composites having fibers, and mixtures of these
materials. An "imaging agent" is included, preferably uniformly,
throughout at least the facecoat material of the mold so that any
inclusions derived from mold-forming materials can be detected. It
is possible that the mold-forming material of the facecoat (and
perhaps the backup layers) can function as the imaging agent. But,
most materials suitable as imaging agents are too expensive to make
this approach commercially practical. As a result, the imaging
agent generally is used in combination with a separate mold-forming
material to form slurries useful for making investment-casting
molds.
[0030] The following paragraphs discuss pertinent aspects of the
investment casting process, methods for making molds comprising
imaging agents substantially uniformly distributed throughout at
least the facecoat in amounts sufficient for imaging inclusions, as
well as methods for detecting inclusions in investment castings
made using such molds.
[0031] I. Investment Casting Process
[0032] As stated above, a first step in the investment casting
process is to provide a wax pattern (patterns made from other
polymers also can be used) in the shape of the desired article. The
pattern is serially immersed in aqueous or non-aqueous suspensions
comprising mold-forming materials, such as refractory materials.
Each layer of the mold can comprise the same mold-forming material,
a different mold-forming material can be used to form each mold
layer, or two or more mold-forming materials may be used to form
either a layer or the mold.
[0033] The facecoat is perhaps the most important mold layer
because the facecoat material contacts the metal or alloy in its
molten state during the casting process. As most metals are highly
reactive, particularly at the elevated temperatures used during
investment casting processes, it follows that the material used to
produce the facecoat must be substantially non-reactive with the
molten metal or alloy being cast under the conditions of the
casting process.
[0034] A partial list of materials useful for forming facecoats for
investment casting molds includes alumina, calcia, silica,
zirconia, zircon, yttria, titania, tungsten, physical mixtures
thereof, and chemical mixtures thereof (i.e., reaction products of
these materials). The choice of the facecoat material depends, to a
large degree, on the metal being cast. Yttria is a currently
preferred facecoat material for casting articles from titanium and
titanium alloys, primarily because it is less reactive with molten
titanium and titanium alloys than most other mold-forming
materials.
[0035] Once the facecoat is solidified about the pattern, plural
additional layers, such as from about 2 to about 25 additional
layers, typically from about 5 to about 20 additional layers, and
more typically from about 10 to about 18 additional layers, are
applied to the pattern to build up the mold. These layers are
referred to herein as "backup layers". Generally speaking,
inclusions are derived from the facecoat material, although it is
possible that inclusions may come from backup layers as well.
[0036] "Stucco" materials also generally are applied to the wet
mold layers to help form cohesive mold structures. The materials
useful as stucco materials are substantially the same as those
materials currently considered useful as mold-forming materials,
i.e., alumina, calcia, silica, zirconia, zircon, yttria, physical
mixtures thereof, and chemical mixtures thereof. A primary
difference between mold-forming materials and stuccos is particle
size, i.e., stuccos generally have larger particle sizes than other
mold-forming materials. A range of average particle sizes currently
considered suitable for use in forming investment casting slurries
comprising mold-forming materials (other than stuccos) is from
about 1 micron to about 30 microns, with from about 10 microns to
about 20 microns being a currently preferred range of average
particle size. A range of particle sizes for facecoat stucco
materials generally is from about 70 grit to about 120 grit. The
intermediate backup layers, i.e., from about layer 2 to about layer
5, generally include stuccos having a particle size of from about
30 grit to about 60 grit. The final backup layers generally include
stuccos having a particle size of from about 12 grit to about 46
grit. Stuccos, as well as mold refractory materials, can be formed
as intimate mixtures with other stucco materials and/or imaging
agents for practicing the present invention.
[0037] II. Imaging Agents Useful for Imaging Inclusions
[0038] Which imaging agent to use for a particular application
depends upon whether X-ray analysis or N-ray analysis, or the
combination of the two, is used. Also important is the impact of
the imaging agent on the quality of the titanium casting, such as
the amount of alpha case produced during the casting process when
using imaging agents. With respect to X-ray detection, primary
considerations include (1) the difference between the density of
the material being cast versus the density of the inclusion, (2)
the size, thickness, shape and orientation of the inclusion, and
(3) the thickness of the cross section being examined. If the
difference between the density of the cast material and the
inclusion is small (such as less than about 0.5 g/cc for titanium
or titanium alloy castings made using yttria facecoats and having a
cross-sectional thickness of about 2 inches; see FIG. 6) then
insufficient image contrast may be provided for suitable inclusion
detection by X-ray.
[0039] The difference between densities also has to increase for
successful imaging as the thickness of the article increases. For
example, the density of titanium is about 4.5 g/cc and that of
Ti-6A1-4V is 4.43 g/cc, whereas the density of yttria is about 5
g/cc. This difference in densities is sufficient to image
inclusions by X-ray analysis in only certain titanium articles,
depending upon the thickness of the article and the thickness and
surface area of the inclusion. Generally, X-ray analysis has proved
useful for detecting inclusions in titanium or titanium alloy
articles having maximum thicknesses at some portion of the article
of only about 2 inches or less.
[0040] The present invention has solved the problem of detecting
inclusions in relatively thick castings where X-ray analysis alone
does not suffice. An N-ray imaging agent is distributed
substantially uniformly throughout the facecoat using mixtures of
materials or solutions of materials, perhaps throughout one or more
of the backup layers, and also perhaps in stucco material used to
form the facecoat and/or one or more of the backup layers, so that
inclusions containing the imaging agent can be detected. If uniform
distribution of the imaging agent in the desired mold layer or
stucco is not achieved, then there is the possibility that the
inclusion will comprise solely mold-forming or stucco material. As
a result, the facecoat-material inclusion would not be detected,
and the casting might have an inclusion that sacrifices desired
physical attributes.
[0041] Moreover, the present invention can be used to detect the
presence of materials that are not deleterious inclusions. For
example, an imaging agent or agents can be coupled with, or form an
intimate mixture with, metal matrix composites having fibers
particles, etc. for imaging, amongst other things, the position and
orientation of the fibers.
[0042] Simple physical mixtures of mold-forming and imaging
materials generally do work to practice the present invention. But,
physical mixtures are not preferred. Instead, "intimate mixtures"
formed between the mold-forming material and the contrast agent are
preferred. "Intimate mixture" is used herein as defined in U.S.
Pat. No. 5,643,844, which patent is incorporated herein by
reference. The '844 patent teaches forming intimate mixtures of
certain dopant materials and mold-forming materials for the purpose
of reducing the rate of hydrolysis of the mold-forming materials in
aqueous investment casting slurries.
[0043] "Intimate mixtures" are different from physical binary
mixtures that result simply from the physical combination of two
components. Typically, an intimate mixture means that the imaging
agent is atomically dispersed in the mold-forming material, such as
with a solid solution or as small precipitates in the crystal
matrix of the solid mold-forming material. Alternatively, "intimate
mixture" may refer to compounds that are fused. Fused materials may
be synthesized by first forming a desired weight mixture of a
source of an imaging agent, such as gadolinium oxide (gadolinia),
and a source of a mold-forming material, particularly facecoat
materials, such as yttrium oxide (yttria). This mixture is heated
until molten and then cooled to produce the fused material. The
fused material is then crushed to form particles having desired
particle sizes for forming investment casting slurries as discussed
above. "Intimate mixture" also may refer to a coating of the
imaging agent on the external surface of the mold-forming
material.
[0044] Hence, methods for the formation of intimate mixtures
include, but are not limited to:
[0045] (1) melt fusion (heating the refractory material and the
imaging agent to a temperature above the melting point of the
mixture);
[0046] (2) solid-state sintering, referred to herein as calcination
(whereby a solid material is heated to a temperature below its
melting point to bring about a state of chemical homogeneity);
[0047] (3) co-precipitation of the refractory material with the
contrast agent, followed by calcination; and
[0048] (4) any surface coating or precipitation method by which the
imaging agent can be coated or precipitated onto an outer surface
region of the refractory material or vice versa.
[0049] Imaging agents currently considered particularly useful for
detecting inclusions in investment castings using X-ray imaging
include materials comprising metals selected from the group
consisting of erbium (e.g., Er.sub.2O.sub.3) dysprosium (e.g.,
Dy.sub.2O.sub.3), ytterbium, lutetium, actinium, and gadolinium
(e.g., Gd.sub.2O.sub.3), particularly the oxides of such compounds,
i.e., erbia, dysprosia, ytterbia, lutetia, actinia, and gadolinia.
Naturally occurring isotopes of these metals also could be used.
Materials useful as imaging agents also could be salts, hydroxides,
oxides, halides, sulfides, and combinations thereof. Materials that
form these compounds on further treatment, such as heating, also
can be used. Additional imaging agents useful for X-ray imaging can
be determined by comparing the density of the metal or alloy being
cast to that of potential imaging agents, particularly metal
oxides, and then selecting an imaging agent having a density
sufficiently greater than the density of the metal or alloy being
cast to image inclusions comprising the imaging agent throughout
the cross section of the casting.
[0050] Other factors also might be considered for the selection of
imaging agents for X-ray imaging, such as the amount of .alpha.
case produced. alpha case refers to a brittle, oxygen-enriched
surface layer on titanium and titanium alloy castings produced by
reduction of the facecoat material by the metal or alloy being
cast. alpha case thickness may vary according to the temperature at
which the mold/pattern was fired and/or cast. If the amount of
.alpha. case is too extensive for a particular cast article, then
such article may not be useable for its intended purpose. For
titanium or titanium alloys, a currently preferred imaging agent
for detecting inclusions by X-ray is gadolinia because it also is
useful for N-ray imaging, and because the density of gadolinia is
about 7.4 g/cc, whereas titanium has a density of about 4.5
g/cc.
[0051] Generally, other metals and/or alloys commonly used to
produce investment castings, such as stainless steel and the
nickel-based superalloys, have densities sufficiently different
from that of the mold-forming materials used to cast such materials
so that inclusion imaging by X-ray is not a problem. Nevertheless,
the imaging agents stated above also can be used with these
alloys.
[0052] N-ray uses neutrons as a penetrating radiation for imaging
inclusions. All energies of neutrons, e.g., fast, epithermal,
thermal and cold neutrons, can be used for N-ray imaging. N-ray
imaging using thermal neutrons is discussed in ASTM E 748-95,
entitled Standard Practices for Thermal Neutron Radiography of
Materials, which is incorporated herein by reference. N-ray imaging
is a process whereby radiation beam intensity modulation by an
object is used to image certain macroscopic details of the object.
The basic components required for N-ray imaging include a source of
fast neutrons, a moderator, a gamma filter, a collimator, a
conversion screen, a film image recorder or other imaging system, a
cassette, and adequate biological shielding and interlock systems.
See, ASTM E 748-95. A thermal neutron beam can be obtained from a
number of sources, including a nuclear reactor, a subcritical
assembly, a radioactive neutron source, or an accelerator. All
sources initially produce neutrons having high energies, and such
energies must be reduced in order to be used for imaging. The
process of reducing neutron energy, referred to herein as
moderating, can be accomplished by surrounding the source with
light materials such as water, oil, plastic, paraffin, beryllium,
or graphite. Moderated neutrons are preferable for N-ray
imaging.
[0053] Images produced by N-ray can be recorded on a film, such as
with X-ray. This is accomplished generally by placing a part to be
imaged in a neutron beam, and then recording the image on film for
each angle at which an image is desired. Whereas the number of film
images taken for a particular part may vary, working embodiments of
the method have taken 10-40 film images, which must be analyzed for
inclusions by certified personnel. Each time an image is made, an
unexposed film must be placed adjacent the part for exposure. The
film images are taken in a protected chamber. After each image is
taken, operating personnel must enter the protected chamber, place
a new film cannister adjacent the part, rotate the part, and
otherwise prepare the system for taking another film image at a
different location of the part. Each image recorded on film takes
about 15-20 minutes.
[0054] N-ray images also can be taken in real time. This is
accomplished by placing a part for analysis on a rotatable
carousel, adjacent an image recorder. The part is positioned in the
neutron beam path, and in front of an image recorder. A certain
number of frames per location are then taken, and then these frames
are digitally "integrated" to produce a composite image. The number
of frames taken can vary. Working embodiments of the method have
taken as many as 1024 frames per location to produce an image,
which is equivalent to one film shot in terms of producing an
image, although not necessarily the information conveyed by such
images. It typically has taken only about 30 seconds to produce
these 1024 frames per location on the part. These images can be
stored on standard media, such as discs. In contrast to film
imaging, real time imaging does not require that the operator enter
a protected chamber after each image is taken. Instead, the part is
rotated to another position to allow through transmission of the
neutron beam through a new portion of the part. The images produced
by this method can be displayed using an image recorder, such as a
light-emitting fluorescent screen. Real time imaging provides a
significant labor and time savings relative to film image
recording.
[0055] Whereas the selection of suitable imaging agents for X-ray
detection depends upon the difference between the density of the
imaging agent and that of the metal or alloy of the casting, the
selection of suitable imaging agents for N-ray imaging of
inclusions is determined by the linear attenuation coefficient or
the thermal neutron cross section of the material being used as an
imaging agent relative to that of the metal or alloy being cast.
The difference between the linear attenuation coefficient or the
thermal neutron cross section and that of the metal or alloy of the
casting should be sufficient so that any inclusions can be imaged
throughout the cross section of the article.
[0056] As with X-ray detection, N-ray detection can be practiced by
simply forming physical mixtures of the imaging agent or agents and
the mold-forming material or materials used to form the mold.
However, as with X-ray detection a preferred method is to form
intimate mixtures of the N-ray imaging agent or agents and the
mold-forming material or materials selected to form the facecoat
and/or the backup layers.
[0057] The materials currently deemed most useful for N-ray
detection of inclusions in investment castings include those
materials comprising metals selected from the group consisting of
lithium, boron (e.g., TiB.sub.2), neodymium, samarium, europium,
gadolinium, dysprosium, holmium, erbium, ytterbium, lutetium,
iridium, and mixtures thereof. Oxides of these metals currently are
preferred materials for N-ray imaging, although it is possible that
other materials, such as metal salts, also can be used to practice
the present inclusion imaging method. Gadolinium oxide (gadolinia)
is a currently preferred imaging agent for N-ray detection of
inclusions in titanium or titanium alloy castings. Gadolinium has
one of the highest linear attenuation coefficients of any element,
i.e., about 1483.88 cm.sup.-1, whereas the linear attenuation
coefficient of titanium is about 0.68 cm.sup.-1. Isotopes of these
elements also can be used. One example of a naturally occurring
isotope that is useful as an N-ray imaging agent is gadolinium 157,
which has a thermal neutron cross section of 254,000 barns. The
difference between the linear attenuation coefficient of titanium
or titanium alloys and the linear attenuation coefficient of
gadolinium makes gadolinia particularly suitable for N-ray imaging.
Other imaging agents for N-ray imaging of inclusions can be
selected from the group of materials having relatively large linear
attenuation coefficients. For metals and/or alloys other than
titanium, gadolinia also likely would be a preferred imaging agent,
again primarily because of the relatively large linear attenuation
coefficient of gadolinium.
[0058] Table 1 provides data concerning those materials currently
considered particularly useful for N-ray and X-ray imaging of
inclusions in investment castings. Data for titanium also is
provided for purposes of comparison.
1TABLE 1 Densities and Thermal Neutron Linear Attenuation
Coefficients Using Average Scattering and Thermal Absorption Cross
Sections for the Naturally Occurring Elements.sup.A Linear Element
Density of Attenuation Atomic Cross Section (barns).sup.a Metal
Oxides Coefficient Technique No. Symbol Scattering Absorption
(g/cc) (cm.sup.-1).sup.c used 3 Li 0.95 70.6 2.01 3.31 N-ray 5 B
4.27 767 2.46 101.79 N-ray 22 Ti 4.09 6.09 4.5 0.58 Reference 41 Nb
6.37 1.15 7.03 0.42 X-ray 49 In 2.45 193.8 6.99(In.sub.2O) 7.52
Both 7.18(In.sub.2O.sub.3) 60 Nd 16 60.6 7.24 1.89 X-ray 62 Sm 38
5670 8.3 171.86 Both 63 Eu -- 4565 7.42 94.82 Both 64 Gd 172 48890
7.4 1483.88 Both 66 Dy 105.9 940 7.81 33.13 Both 67 Ho 8.65 64.7 --
2.35 Both 68 Er 9 159.2 8.64 5.49 Both 70 Yb 23.4 35.5 9.2 1.43
X-ray 71 Lu 6.8 76.4 9.4 2.82 Both 77 Ir 14.2 425.3 11.7 30.86 Both
.sup.AASTM E 748-95 with updated data primarily from Neutron Cross
Sections: Neutron Resonance Parameters and Thermal Cross Sections,
S. F. Mughabghab, Academic Press, Inc., San Diego, Ca, 1981.
.sup.aAll cross-section values are most probable values.
.sup.cLinear attenuation coefficients were calculated using nominal
elemental atomic weights and densities.
[0059] III. Forming Molds Comprising Imaging Agents
[0060] The formation of slurries for making investment casting
molds by serial application of mold-forming and stucco materials to
patterns is known to those of ordinary skill in the art. The
present method differs from these methods by forming mold layers
that comprise an imaging agent or agents. Thus, simple physical
mixtures or intimate mixtures of the imaging agent and the
mold-forming material are used to form slurry suspensions,
typically an aqueous suspension, but perhaps also an organic-liquid
based suspension. The pattern is serially dipped into an investment
casting slurry or slurries comprising mold-forming material or
materials and an imaging agent or agents.
[0061] The following examples are intended to illustrate certain
features of the present invention, including how to make investment
casting slurries and molds therefrom for practicing the present
invention. The invention should not be limited to the particular
features exemplified.
EXAMPLE 1
[0062] This example describes the preparation of a slurry useful
for forming mold facecoats for investment castings, as well as how
to make molds comprising such facecoats. Amounts stated in this and
the following examples are percents based upon the total weight of
the slurry (weight percents), unless noted otherwise. All steps
were done with continuous mixing unless stated otherwise.
[0063] In this particular example, the facecoat refractory material
and the imaging agent were the same material, i.e., dysprosia.
Dysprosia is a good candidate for imaging inclusions by X-ray
because it has a density of about 8.2 g/cc.
[0064] A mixture was first formed by combining 2.25 weight percent
deionized water with 0.68 weight percent tetraethyl ammonium
hydroxide. 1.37 weight percent latex (Dow 460 NA), 0.15 weight
percent surfactant (NOPCOWET C-50) and 5.50 weight percent of a
colloidal silica, such as LUDOX.RTM. SM (LUDOX.RTM. SM comprises
aqueous colloidal silica, wherein the silica particles have an
average particle diameter of about 7 nms) were then added to the
mixture with continuous stirring. 90.05 weight percent dysprosia
refractory/imaging agent was added to the aqueous composition to
form a facecoat slurry. In this Example 1, and with Examples 2-3, a
trace amount of Dow 1410 antifoam was added to the slurries after
their formation. Moreover, and unless stated otherwise, the
mixtures were made by combining the materials in the order stated
in tables provided with respect to certain examples.
[0065] Wax patterns in the shape of a test bar were first immersed
in the facecoat slurry composition to form a facecoat comprising
dysprosia. Seventy grit fused alumina was used as the stucco
material for the facecoat. Two alumina slurry layers with an ethyl
silicate binder were applied over the facecoat to form the
intermediate layers. The stucco material for the second and third
intermediate layers was 46 grit fused alumina. Mold layers 4-10
were then serially applied using a zircon flour having a colloidal
silica binder. The stucco material used for mold layers 4-10 was 46
grit fused alumina. After building ten layers, the pattern was
removed in an autoclave to create a mold suitable for receiving
molten titanium alloy to cast test bars.
[0066] Molten Ti 6-4 alloy was poured into the test bar mold and
allowed to solidify. The mold was then removed from about the
casting to produce a test bar having a diameter of about 1 inch.
The test bar was then tested for the presence of .alpha. case, as
discussed in more detail below.
[0067] The test bar also was subjected to X-ray imaging to
determine the presence of inclusions. Because inclusions do not
occur every time a casting is made, and because the location of an
inclusion is difficult to predict (although software is now being
developed for such predictions), a system was developed to mimic
the presence of inclusions in samples made according to the present
examples. A small amount of facecoat flake (i.e., a facecoat
material comprising dysprosia for this example), was placed on top
of a 1-inch-thick test bar. A second 1-inch test bar was placed
over the facecoat flake. These two test bars were then welded
together to form a 2-inch thick inclusion-containing test bar. The
test bars were hot isostatically pressed (HIP) at 1650.degree. F.
and 15,000 psi to produce test bars having no detectable interface
by nondestructive detection methods.
[0068] An X-ray was taken of an inclusion-containing test bar made
in this fashion using the flake made from the facecoat slurry. The
dysprosia inclusion was clearly seen. The fact that the dysprosia
inclusions were seen clearly demonstrates that dysprosia is a good
imaging agent for imaging inclusions in titanium and titanium-alloy
castings using X-ray imaging techniques.
EXAMPLE 2
[0069] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and titanium test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the imaging agent in the facecoat. In contrast to Example 1,
this example used a physical mixture of a refractory material,
i.e., yttria, with an imaging agent, i.e., dysprosia, to form the
facecoat. Otherwise, the facecoat slurry and mold were produced in
a manner substantially identical to that of Example 1. The
materials used to produce the facecoat slurry are provided below in
Table 2.
2 TABLE 2 MATERIALS WEIGHT PERCENT deionized water 2.64 tetraethyl
ammonium hydroxide 0.79 titanium dioxide 3.22 latex (Dow 460 NA)
1.63 surfactant (NOPCOWET C-50) 0.18 colloidal silica (Ludox SM)
6.48 yttria 32.17 dysprosia 52.89
[0070] As in Example 1, a test bar was produced from Ti 64 alloy
using molds with facecoats having the composition stated in Table
2. This test bar was also tested for alpha case and the alpha case
data is provided by Table 5.
[0071] An inclusion-containing test bar was made using a flake
comprising a physical mixture of yttria and dysprosia. The test bar
made in this manner was then subjected to X-ray imaging to
determine whether the inclusion could be detected. The X-ray image
clearly showed the presence of the facecoat-simulated inclusion in
the center of the inclusion-containing test bar.
EXAMPLE 3
[0072] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
these molds to determine the amount of .alpha. case produced in
such test bars. As with Example 1, the refractory material and the
imaging agent were the same material, i.e., erbia. Otherwise, the
facecoat slurry and mold were produced in a manner substantially
identical to that of Example 1. The materials used to produce the
facecoat slurry are provided below in Table 3.
3 TABLE 3 MATERIALS WEIGHT PERCENT deionized water 2.13 tetraethyl
ammonium hydroxide 0.64 latex (Dow 460 NA) 1.30 surfactant
(NOPCOWET C-50) 0.14 colloidal silica (Ludox SM) 5.21 erbia
90.58
[0073] As in Example 1, Ti 6-4 test bars having a diameter of about
1 inch were cast using molds having a facecoat produced using the
composition provided in Table 3. The amount of alpha case detected
in test bars made according to this Example 3 is provided below in
Table 5.
[0074] An inclusion-containing test bar was made using a flake
comprising erbia as the refractory and the imaging agent. The test
bar made in this manner was then subjected to X-ray imaging to
determine whether the inclusion could be detected. The X-ray image
clearly showed the presence of the facecoat-simulated inclusion in
the center of the inclusion-containing test bar.
EXAMPLE 4
[0075] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the facecoat material. As with Example 2, the facecoat slurry
comprised a physical mixture of a mold-forming material, i.e.,
yttria, and an imaging agent, i.e., erbia. Otherwise, the facecoat
slurry and mold were produced in a manner substantially identical
to that of Example 1. The materials used to produce the facecoat
slurry are provided below in Table 4.
4 TABLE 4 MATERIALS WEIGHT PERCENT Deionized water 2.25 Tetraethyl
ammonium hydroxide 0.83 Titanium dioxide 3.27 Latex (Dow 460 NA)
1.65 surfactant (NOPCOWET C-50) 0.19 colloidal silica (Ludox SM)
6.57 yttria 32.67 erbia 52.57
[0076] An inclusion-containing test bar was made using a flake
comprising a physical mixture of yttria and erbia. The test bar
made in this manner was then subjected to X-ray imaging to
determine whether the inclusion could be detected. The X-ray image
clearly showed the presence of the facecoat-simulated inclusion in
the center of the inclusion-containing test bar.
[0077] The amount of alpha case in test bars produced as stated
above in Examples 1-4 is provided below in Table 5. Because yttria
has been found to minimize alpha case in titanium and titanium
alloy castings, it is used as a control for comparing the alpha
case results of the other materials considered useful as imaging
agents.
5TABLE 5 Example No. alpha case, inches Left Top Right 1. a.
Continuous a. 0.007 a. 0.007 a. 0.003 b. Total b. 0.016 b. 0.017 b.
0.012 2. a. Continuous a. 0.003 a. 0.003 a. 0.003 b. Total b. 0.010
b. 0.012 b. 0.012 3. a. Continuous a. 0.009 a. 0.008 a. 0.002 b.
Total b. 0.014 b. 0.019 b. 0.004 4. a. Continuous a. 0.002 a. 0.002
a. 0.003 b. Total b. 0.009 b. 0.004 b. 0.019 5. Yttria a.
Continuous a. 0.002 a. 0.002 a. 0.002 facecoat as a b. Total b.
0.004 b. 0.005 b. 0.003 control.
[0078] Table 5 shows that castings made according to the present
invention may have slightly more alpha case than occurs by simply
using yttria as a refractory material, as would be expected.
Castings having a continuous alpha case of about 0.020 inch or
less, preferably about 0.015 inch or less, and a total alpha case
of about 0.035 inch or less, and preferably about 0.025 inch or
less, are still considered useful castings. As a result, Table 5
shows that articles made according to the present invention are
acceptable even though such castings may have slightly more .alpha.
case than castings made using molds having yttria facecoats
comprising no imaging agent.
[0079] However, if normal casting procedures result in too much
alpha case using molds made in accordance with the present
invention, then other procedures may be used in combination with
the process of the present invention to decrease the alpha case.
For example, the mold might be cooled from the normal casting
temperature of about 1,800.degree. F. to a lower temperature, such
as a temperature of about 700.degree. F. See the alpha case results
provided below for Examples 11-17, and 19-20.
[0080] Alternatively, delay pour techniques might be used. This
method comprises delaying pouring molten metals or alloys,
particularly reactive metals or alloys, from a crucible and into an
investment casting mold for a delay period of 1 second to 120
seconds. The delay period is increased as the quantity of material
to be poured increases. The delay period is measured from the time
the electrode clears the crucible to permit tipping of the crucible
and the commencement of tipping of the crucible for pouring molten
metal or alloy from the crucible and into an investment casting
mold. Castings produced by this method have substantially less
facecoat contamination and less alpha case than castings produced
without using a delay period. Furthermore, the variability of
casting contamination levels is substantially reduced by
instituting a delay period.
EXAMPLE 5
[0081] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 step-wedge test bars
cast using such molds to determine the effectiveness of inclusion
imaging using the facecoat material, as well as the amount of alpha
case produced by casting such test bars. As with Example 2, this
example used a physical mixture of a refractory material, i.e.,
yttria, and an imaging agent, i.e., gadolinia, for the production
of the facecoat slurry. Otherwise, the facecoat slurry and mold
were produced in a manner substantially identical to that of
Example 1. The materials used to produce the facecoat slurry are
provided below in Table 6.
6 TABLE 6 MATERIALS WEIGHT PERCENT deionized water 4.10 tetraethyl
ammonium hydroxide 1.00 titanium dioxide 4.00 latex (Dow 460 NA)
1.96 surfactant (NOPCOWET C-50) 0.21 ludox SM (colloidal silica)
7.80 yttria 78.58 gadolinia 2.25 antifoaming agent (Dow 1410)
0.10
[0082] Step-wedge test castings (1.5 inches; 1 inch; 0.5 inch; 0.25
inch and 0.125 inch) were cast from Ti 6-4 alloy metal using molds
having a facecoat produced using the composition provided in Table
6. Alpha case test results for these step-wedge castings are
provided below in Table 7. C indicates continuous alpha case while
T indicates total alpha case.
7TABLE 7 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" refractory flour is
C T C T C T C T C T 100% yttria 0.004 0.009 0.003 0.006 0.003 0.006
0.002 0.007 0.001 0.003 refractory flour is C T C T C T C T C T
yttria plus 2.25 wt. 0.003 0.007 0.009 0.019 0.004 0.009 0.002
0.004 0.001 0.003 % gadolinia
[0083] FIG. 1A is an N-ray image of a 2-inch-thick
inclusion-containing test bar made having three facecoat-simulating
inclusions sandwiched between two 1-inch thick plates, including
one inclusion made from yttria and acting as a control where no
inclusion is seen (the inclusion labeled "3" in FIG. 1A), and one
inclusion labeled "aa" comprising a physical mixture of yttria and
2.25 weight percent (slurry basis)/2.58 weight percent (dry basis)
gadolinia. The inclusion comprising the yttria-gadolinia imaging
composition is clearly seen in FIG. 1A. Hence, FIG. 1A demonstrates
that inclusions can be detected using N-ray imaging of castings
made from molds comprising imaging agents physically mixed with
other refractory materials according to the method of the present
invention.
EXAMPLE 6
[0084] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the facecoat material, as well as the amount of alpha case
produced by casting such test bars. As with Example 2, this example
used a physical mixture of a refractory material, i.e., yttria, and
an imaging agent, i.e., gadolinia, for the production of the
facecoat slurry. Otherwise, the facecoat slurry and mold were
produced in a manner substantially identical to that of Example 1.
The materials used to produce the facecoat slurry are provided
below in Table 8.
8 TABLE 8 MATERIALS WEIGHT PERCENT deionized water 3.84 tetraethyl
ammonium hydroxide 0.94 titanium dioxide 3.75 latex (Dow 460 NA)
1.84 surfactant (NOPCOWET C-50) 0.20 colloidal silica (Ludox SM)
7.33 yttria 60.71 gadolinia 21.30 antifoaming agent (Dow 1410)
0.09
[0085] FIG. 1A is the N-ray image discussed above in Example 5
where the sample marked "ab" is an inclusion comprising a physical
mixture of yttria and 21.30 weight percent (slurry basis)/25.97
weight percent (dry basis) gadolinia that was made using the
facecoat slurry composition stated in Table 8. The inclusion made
having 25.97 weight percent gadolinia is the inclusion most clearly
seen in FIG. 1A. Hence, FIG. 1A not only demonstrates that facecoat
inclusions in the interior of the titanium-alloy casting are
readily detected using N-ray imaging and gadolinia imaging agents
according to the method of the present invention, but further that
the clarity of the N-ray image can be adjusted by the amount of the
imaging agent used. This suggests that inclusions may be detected
in castings having cross sections of greater than two inches by
increasing the amount of imaging agent used. One possible method
for determining the maximum amount of a particular imaging agent
that can be used for forming a casting is to determine the amount
of imaging agent that can be used to generally obtain a casting
having a continuous a case of about 0.020 inch or less and a total
alpha case of about 0.035 inch or less.
EXAMPLE 7
[0086] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the facecoat material, as well as the amount of alpha case
produced by casting such test bars. As with Example 2, this example
used a physical mixture of a refractory material, i.e., yttria, and
an imaging agent, i.e., samaria, for the production of the facecoat
slurry. Otherwise, the facecoat slurry and mold were produced in a
manner substantially identical to that of Example 1. The materials
used to produce the facecoat slurry are provided below in Table
9.
9 TABLE 9 MATERIALS WEIGHT PERCENT deionized water 4.04 tetraethyl
ammonium hydroxide 0.97 titanium dioxide 3.85 latex (Dow 460 NA)
1.93 surfactant (NOPCOWET C-50) 0.21 colloidal silica (Ludox SM)
7.71 yttria 69.74 samaria 11.45 antifoaming agent (Dow 1410)
0.1
[0087] FIG. 1B is an N-ray image of an inclusion-containing test
bar having three facecoat-simulating inclusions. The inclusion in
FIG. 1B marked "ba" comprised a physical mixture of yttria and
11.45 weight percent (slurry basis)/13.11 weight percent (dry
basis) samaria that was made using the slurry composition of Table
9, and the inclusion marked "3" being yttria as a control. The
inclusion made having 13.11 weight percent samaria clearly can be
seen in FIG. 1B, indicating that samaria can be used as an imaging
agent for N-ray imaging of inclusions according to the method of
the present invention.
EXAMPLE 8
[0088] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the facecoat material, as well as the amount of alpha case
produced by casting such test bars. As with Example 2, this example
used a physical mixture of a refractory material, i.e., yttria, and
an imaging agent, i.e., gadolinia, for the production of the
facecoat slurry. Otherwise, the facecoat slurry and mold were
produced in a manner substantially identical to that of Example 1.
The materials used to produce the facecoat slurry are provided
below in Table 10.
10 TABLE 10 MATERIALS WEIGHT PERCENT deionized water 4.06
tetraethyl ammonium hydroxide 0.99 titanium dioxide 3.97 latex (Dow
460 NA) 1.94 surfactant (NOPCOWET C-50) 0.21 colloidal silica
(Ludox SM) 7.76 yttria 76.48 gadolinia 4.49 antifoaming agent (Dow
1410) 0.10
[0089] FIG. 1B is the N-ray image discussed in Example 7 where the
inclusion marked "bb" comprises a physical mixture of yttria and
4.49 weight percent (slurry basis)/5.14 weight percent (dry basis)
gadolinia made using the facecoat slurry composition stated in
Table 10. Inclusion "bb", made having 5.14 weight percent
gadolinia, is clearly seen in FIG. 1B, and is as distinguishable as
inclusion "ba" in FIG. 1B made from the slurry having 11.95 weight
percent samaria.
EXAMPLE 9
[0090] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the facecoat material, as well as the amount of alpha case
produced by casting such test bars. As with Example 2, this example
used a physical mixture of a refractory material, i.e., yttria, and
an imaging agent, i.e., samaria, for the production of the facecoat
slurry. Otherwise, the facecoat slurry and mold were produced in a
manner substantially identical to that of Example 1. The materials
used to produce the facecoat slurry are provided below in Table
11.
11 TABLE 11 MATERIALS WEIGHT PERCENT deionized water 3.52
tetraethyl ammonium hydroxide 0.85 titanium dioxide 3.36 latex (Dow
460 NA) 1.68 surfactant (NOPCOWET C-50) 0.18 colloidal silica
(Ludox SM) 6.71 yttria 33.75 samaria 49.86 antifoaming agent (Dow
1410) 0.09
[0091] FIG. 1C is an N-ray image of an inclusion-containing test
bar having three facecoat-simulating inclusions. The inclusion in
FIG. 1C marked "ca" comprised a physical mixture of yttria and
49.86 weight percent (slurry basis)/56.03 weight percent (dry
basis) samaria that was made using the slurry composition of Table
11. The inclusion in FIG. 1C marked "3" is yttria, which was used
as a control. The inclusion made having, 56.03 weight percent
samaria can be clearly seen as "ca" in FIG. 1C.
EXAMPLE 10
[0092] This example concerns the production of a facecoat slurry,
molds made having such facecoat, and Ti 6-4 test bars cast using
such molds to determine the effectiveness of inclusion imaging
using the facecoat material, as well as the amount of alpha case
produced by casting such test bars. As with Example 2, this example
used a physical mixture of a refractory material, i.e., yttria, and
an imaging agent, i.e., samaria, for the production of the facecoat
slurry. Otherwise, the facecoat slurry and mold were produced in a
manner substantially identical to that of Example 1. The materials
used to produce the facecoat slurry are provided below in Table
12.
12 TABLE 12 MATERIALS WEIGHT PERCENT deionized water 3.83
tetraethyl ammonium hydroxide 0.92 titanium dioxide 3.65 latex (Dow
460 NA) 1.82 surfactant (NOPCOWET C-50) 0.20 colloidal silica
(Ludox SM) 7.30 yttria 55.07 samaria 27.11 antifoaming agent (Dow
1410) 0.10
[0093] FIG. 1C is the N-ray image discussed in Example 9 where the
inclusion marked "cd" comprises a physical mixture of yttria and
27.11 weight percent (slurry basis)/30.80 weight percent (dry
basis) samaria made using the facecoat slurry composition stated in
Table 12. The inclusion of labeled "cd", made having 30.8 weight
percent samaria, is clearly seen in FIG. 1C.
EXAMPLE 11
[0094] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made having such facecoat, and Ti 6-4 test
bars cast using such molds to determine the effectiveness of
inclusion imaging using the facecoat material, as well as the
amount of alpha case produced by casting such test bars at two
different temperatures, namely 700.degree. F. and 1800.degree. F.
This Example 11 concerns a facecoat slurry comprising an intimate
mixture of calcined erbia/yttria. Otherwise, the facecoat slurry
and mold were produced in a manner substantially identical to that
of Example 1. The materials used to produce the facecoat slurry are
provided below in Table 13.
13 TABLE 13 MATERIALS WEIGHT PERCENT deionized water 3.67
tetraethyl ammonium hydroxide 0.87 titanium dioxide 3.50 latex (Dow
460 NA) 1.75 surfactant (NOPCOWET C-50) 0.17 colloidal silica
(Ludox SM) 6.99 calcined erbia/yttria (36%/64%) 82.96 antifoaming
agent (Dow 1410) 0.09
[0095] Alpha case data is provided below in Table 14 for test bars
cast at 1,800.degree. F. and 700.degree. F. using shells having the
composition discussed in Example 11.
14TABLE 14 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 11 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.005 0.009 0.009 0.028 0.003 0.010 0.002 0.004 0.001 0.003
refractory flour was C T C T C T C T C T yttria plus 36 wt. % 0.003
0.006 0.006 0.016 0.003 0.014 0.002 0.009 0.001 0.004 erbia Example
11 - 700.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.002 0.006 0.002 0.004 0.002 0.007 0.002 0.005 0.001 0.003
refractory flour was C T C T C T C T C T yttria plus 36 wt. % 0.003
0.010 0.003 0.013 0.003 0.010 0.001 0.005 0.001 0.003 erbia
[0096] The alpha case data provided by Table 14 shows that parts
cast using shells made as described in Example 11 had acceptable a
case, i.e., less than about 0.020 inch continuous alpha case, and
less than about 0.035 inch total alpha case. The alpha case data
also shows, as would be expected, that reducing the mold
temperature also reduces the amount of alpha case. This is best
illustrated by comparing the total alpha case at the two different
temperatures for castings of a particular thickness. For example,
the 1 inch test bar had a total alpha case of about 0.016 inch at
1,800.degree. F., and 0.013 inch at 700.degree. F.
EXAMPLE 12
[0097] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made having such facecoat, and Ti 6-4 test
bars cast using such molds to determine the effectiveness of
inclusion imaging using the facecoat material, as well as the
amount of alpha case produced by casting such test bars. This
Example 12 concerns a facecoat slurry comprising calcined
erbia/yttria. Otherwise, the facecoat slurry and mold were produced
in a manner substantially identical to that of Example 1. The
materials used to produce the facecoat slurry are provided below in
Table 15.
15 TABLE 15 MATERIALS WEIGHT PERCENT deionized water 3.26
tetraethyl ammonium hydroxide 0.78 titanium dioxide 3.10 latex (Dow
460 NA) 1.55 surfactant (NOPCOWET C-50) 0.16 colloidal silica
(Ludox SM) 6.20 calcined erbia/yttria (63%/37%) 84.88 antifoaming
agent (Dow 1410) 0.07
[0098] Alpha case data at 1,800.degree. F. and 700.degree. F. for
test bars made using shells having the composition discussed in
Example 11 is provided below in Table 16.
16TABLE 16 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 12 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.004 0.009 0.004 0.005 0.002 0.009 0.004 0.010 0.003 0.009
refractory flour was C T C T C T C T C T yttria plus 62 wt. % 0.004
0.007 0.004 0.009 0.003 0.009 0.004 0.012 0.001 0.003 erbia Example
12 - 700.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.001 0.004 0.005 0.010 0.003 0.005 0.00 0.00 0.00 0.00
Refractory flour was C T C T C T C T C T yttria plus 62 wt. % 0.001
0.003 0.002 0.008 0.002 0.002 0.00 0.00 0.003 0.010 erbia
[0099] Information provided by Table 16 shows that parts cast using
shells made as described in Example 12 had acceptable alpha case,
and that reducing the mold temperature also generally reduces the
amount of alpha case.
EXAMPLE 13
[0100] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made having that facecoat, and Ti 6-4 test
bars cast using such molds to determine the effectiveness of
inclusion imaging using the facecoat material, as well as the
amount of alpha case produced by casting such test bars. This
Example 13 concerns a facecoat slurry comprising calcined
dysprosia/yttria. Otherwise, the facecoat slurry and mold were
produced in a manner substantially identical to that of Example 1.
The materials used to produce the facecoat slurry are provided
below in Table 17.
17 TABLE 17 MATERIALS WEIGHT PERCENT deionized water 3.60
tetraethyl ammonium hydroxide 0.86 titanium dioxide 3.43 latex (Dow
460 NA) 1.71 surfactant (NOPCOWET C-50) 0.17 colloidal silica
(Ludox SM) 6.86 calcined dysprosia/yttria (45%/55%) 83.28
antifoaming agent (Dow 1410) 0.09
[0101] FIG. 1D is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 1D shows the
presence of the inclusion.
[0102] Alpha case data at 1,800.degree. F. and 700.degree. F. for
parts made using shells having the composition discussed in Example
13 is provided below in Table 18.
18TABLE 18 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 13 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.006 0.009 0.003 0.007 0.001 0.004 0.001 0.003 <0.001
0.002 refractory flour C T C T C T C T C T was yttria plus 45 0.004
0.006 0.012 0.032 0.003 0.014 0.003 0.010 <0.001 0.002 wt. %
dysprosia Example 13 - 700.degree. F. refractory flour was C T C T
C T C T C T 100% yttria 0.003 0.004 0.003 0.014 0.001 0.004 0.001
0.002 0.001 0.001 refractory flour was C T C T C T C T C T yttria
plus 45 wt. % 0.003 0.005 0.002 0.004 0.003 0.010 0.001 0.004 0.001
0.004 dysprosia
EXAMPLE 14
[0103] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made using such facecoat, and Ti 6-4 test bars
cast using such molds to determine the effectiveness of inclusion
imaging using the facecoat material, as well as the amount of alpha
case produced by casting such test bars. This Example 14 concerns a
facecoat slurry comprising calcined dysprosia/yttria. Otherwise,
the facecoat slurry and mold were produced in a manner
substantially identical to that of Example 1. The materials used to
produce the facecoat slurry are provided below in Table 19.
19 TABLE 19 MATERIALS WEIGHT PERCENT deionized water 3.35
tetraethyl ammonium hydroxide 0.80 titanium dioxide 3.19 latex (Dow
460 NA) 1.59 surfactant (NOPCOWET C-50) 0.16 colloidal silica
(Ludox SM) 6.38 calcined dysprosia/yttria (62%/38%) 84.46
antifoaming agent (Dow 1410) 0.07
[0104] FIG. 1E is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 1E shows the
presence of the inclusion.
[0105] Alpha case data for test bars cast using shell temperatures
of 1,800.degree. F. and 700.degree. F. and using shells having the
composition discussed in Example 14 is provided below in Table
20.
20TABLE 20 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 14 -
1800.degree. F. refractory flour was C T C T C T C T C T was 100%
yttria 0.004 0.007 0.006 0.020 0.001 0.005 0.002 0.009 <0.001
0.003 refractory flour C T C T C T C T C T was yttria plus 62 0.004
0.007 0.008 0.027 0.002 0.007 0.002 0.010 0.001 0.004 wt. %
dysprosia Example 14 - 700.degree. F. refractory flour was C T C T
C T C T C T flour was 0.002 0.004 0.002 0.004 0.001 0.004 0.001
0.003 <0.001 <0.001 100% yttria refractory C T C T C T C T C
T flour was 0.003 0.005 0.003 0.011 0.002 0.005 <0.001 0.004
<0.001 <0.001 yttria plus 62 wt. % dysprosia
EXAMPLE 15
[0106] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made having such facecoat, and Ti 6-4 test
bars cast using such molds to determine the effectiveness of
inclusion imaging using the facecoat material, as well as the
amount of alpha case produced by casting such test bars. This
Example 15 concerns a facecoat slurry comprising calcined
gadolinia/yttria. Otherwise, the facecoat slurry and mold were
produced in a manner substantially identical to that of Example 1.
The materials used to produce the facecoat slurry are provided
below in Table 21.
21 TABLE 21 MATERIALS WEIGHT PERCENT deionized water 4.19
tetraethyl ammonium hydroxide 1.00 titanium dioxide 3.99 latex (Dow
460 NA) 1.99 surfactant (NOPCOWET C-50) 0.20 colloidal silica
(Ludox SM) 7.97 calcined gadolinia/yttria (01%/99%) 80.56
antifoaming agent (Dow 1410) 0.10
[0107] FIG. 1F is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 1F shows the
presence of the inclusion.
[0108] Alpha case data for test bars cast using shells having the
composition discussed in Example 15 is provided below in Table
22.
22TABLE 22 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 15 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.005 0.009 0.003 0.006 0.009 0.028 0.002 0.003 0.00 0.00
refractory flour was C T C T C T C T C T yttria plus 1 wt. % 0.007
0.012 0.002 0.005 0.003 0.007 0.002 0.003 0.00 0.00 gadolinia
Example 15 - 700.degree. F. refractory flour was C T C T C T C T C
T 100% yttria 0.002 0.005 0.001 0.003 0.00 0.00 0.00 0.00 0.00 0.00
refractory flour was C T C T C T C T C T yttria plus 1 wt. % 0.002
0.003 0.002 0.003 0.00 0.00 0.00 0.00 0.00 0.00 gadolinia
EXAMPLE 16
[0109] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made using such facecoat, and Ti 6-4 test bars
cast using such molds to determine the effectiveness of inclusion
imaging using the facecoat material, as well as the amount of alpha
case produced by casting such test bars. This Example 16 concerns a
facecoat slurry comprising calcined gadolinia/yttria. Otherwise,
the facecoat slurry and mold were produced in a manner
substantially identical to that of Example 1. The materials used to
produce the facecoat slurry are provided below in Table 23.
23 TABLE 23 MATERIALS WEIGHT PERCENT deionized water 4.04
tetraethyl ammonium hydroxide 0.96 titanium dioxide 3.85 latex (Dow
460 NA) 1.93 surfactant (NOPCOWET C-50) 0.19 colloidal silica
(Ludox SM) 7.70 calcined gadolinia/yttria (14%/86%) 81.22
antifoaming agent (Dow 1410) 0.14
[0110] FIG. 2G is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2G shows the
presence of the inclusion.
[0111] Alpha case data for test bars cast as discussed in Example
16 is provided below in Table 24.
24TABLE 24 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 16 -
1800.degree. F. Refractory flour was C T C T C T C T C T 100%
yttria 0.005 0.009 0.005 0.009 0.005 0.010 0.002 0.003 0.001 0.004
Refractory flour was C T C T C T C T C T yttria plus 14 wt. % 0.005
0.009 0.004 0.011 0.002 0.005 0.002 0.005 0.00 0.00 gadolinia
Example 16 - 700.degree. F. Refractory flour was C T C T C T C T C
T 100% yttria 0.003 0.007 0.003 0.005 0.001 0.003 0.00 0.00 0.00
0.00 Refractory flour was C T C T C T C T C T yttria plus 14 wt. %
0.003 0.004 0.001 0.005 0.00 0.00 0.00 0.00 0.00 0.00 gadolinia
EXAMPLE 17
[0112] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds that have been made using such facecoat, and
Ti 6-4 test bars cast using such molds to determine the
effectiveness of inclusion imaging using the facecoat material, as
well as the amount of alpha case produced by casting such test
bars. This Example 17 concerns a facecoat slurry comprising
calcined gadolinia/yttria. Otherwise, the facecoat slurry and mold
were produced in a manner substantially identical to that of
Example 1. The materials used to produce the facecoat slurry are
provided below in Table 25.
25 TABLE 25 MATERIALS WEIGHT PERCENT deionized water 3.53
tetraethyl ammonium hydroxide 0.84 titanium dioxide 3.36 latex (Dow
460 NA) 1.68 surfactant (NOPCOWET C-50) 0.17 colloidal silica
(Ludox SM) 6.72 calcined gadolinia/yttria (60%/40%) 83.62
antifoaming agent (Dow 1410) 0.08
[0113] FIG. 2H is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2H shows the
presence of the inclusion.
[0114] Alpha case data for test bars cast as discussed in Example
17 is provided below in Table 26.
26TABLE 26 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 17 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.004 0.008 0.004 0.007 0.003 0.007 0.001 0.003 0.0 0.00
refractory flour was C T C T C T C T C T yttria plus 60 wt. % 0.012
0.014 0.005 0.010 0.003 0.007 0.001 0.004 0.00 0.00 gadolinia
Example 17 - 700.degree. F. refractory flour was C T C T C T C T C
T 100% yttria 0.005 0.009 0.002 0.007 0.002 0.007 0.002 0.004 0.00
0.00 refractory flour was C T C T C T C T C T yttria plus 60 wt. %
0.004 0.006 0.002 0.003 0.003 0.003 0.002 0.003 0.00 0.00
gadolinia
EXAMPLE 18
[0115] This example concerns producing facecoat slurries comprising
gadolinia as both the mold-forming material and the imaging agent
and molds having such facecoat. The facecoat slurry and mold are
produced in a manner substantially identical to that of Example 1.
The materials for producing the facecoat slurry are provided below
in Table 27.
27 TABLE 27 MATERIALS WEIGHT PERCENT deionized water 3.04
tetraethyl ammonium hydroxide 0.72 titanium dioxide 2.90 latex (Dow
460 NA) 1.45 surfactant (NOPCOWET C-50) 0.14 colloidal silica
(Ludox SM.sub.-- 5.79 gadolinia (100%) 85.88 antifoaming agent (Dow
1410) 0.08
[0116] Molds produced according to this Example 18 are not deemed
suitable for casting parts. This apparently is due to the increased
aqueous solubility of gadolinia relative to yttria. The problems
encountered with this Example 18 however, likely can be addressed
by taking into consideration the enhanced aqueous solubility of
pure gadolinia as compared to other imaging materials, and mixtures
of mold-forming agents and imaging agents.
EXAMPLE 19
[0117] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made using such facecoat, and Ti 6-4 test bars
cast using such molds to determine the effectiveness of inclusion
imaging using the facecoat material, as well as the amount of alpha
case produced by casting such test bars. This Example 19 concerns a
facecoat slurry comprising calcined samaria/yttria. Otherwise, the
facecoat slurry and mold were produced in a manner substantially
identical to that of Example 1. The materials used to produce the
facecoat slurry are provided below in Table 28.
28 TABLE 28 MATERIALS WEIGHT PERCENT deionized water 4.04
tetraethyl ammonium hydroxide 0.96 titanium dioxide 3.85 latex (Dow
460 NA) 1.93 surfactant (NOPCOWET C-50) 0.19 colloidal silica
(Ludox SM) 7.70 calcined samaria/yttria (14%/86%) 81.22 antifoaming
agent (Dow 1410) 0.11
[0118] FIG. 2I is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2I shows the
presence of the inclusion.
[0119] Alpha case data for test bars cast at shell temperatures of
1,800.degree. F. and 700.degree. F. using shells made from the
composition discussed in Example 19 is provided below in Table
29.
29TABLE 29 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 19 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.004 0.010 0.006 0.019 0.003 0.014 0.002 0.012 <0.001
0.002 refractory flour was C T C T C T C T C T yttria plus 14 wt. %
0.003 0.005 0.006 0.019 0.003 0.012 0.002 0.005 0.001 0.004 samaria
Example 19 - 700.degree. F. refractory flour was C T C T C T C T C
T was 100% 0.003 0.007 0.004 0.007 0.003 0.004 0.002 0.005
<0.001 0.001 yttria refractory flour C T C T C T C T C T was
yttria plus 0.003 0.012 0.003 0.006 0.003 0.012 <0.001 0.004
<0.001 <0.001 14 wt. % samaria
EXAMPLE 20
[0120] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds that have been made using such facecoat, and
Ti 6-4 test bars cast using such molds to determine the
effectiveness of inclusion imaging using the facecoat material, as
well as the amount of alpha case produced by casting such test
bars. This Example 20 concerns a facecoat slurry comprising
calcined samaria/yttria. Otherwise, the facecoat slurry and mold
were produced in a manner substantially identical to that of
Example 1. The materials used to produce the facecoat slurry are
provided below in Table 30.
30 TABLE 30 MATERIALS WEIGHT PERCENT deionized water 3.90
tetraethyl ammonium hydroxide 0.93 titanium dioxide 3.71 latex (Dow
460 NA) 1.86 surfactant (NOPCOWET C-50) 0.19 colloidal silica
(Ludox SM) 7.43 calcined samaria/yttria (27%/73%) 81.89 antifoaming
agent (Dow 1410) 0.09
[0121] FIG. 2J is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2J shows the
presence of the inclusion.
[0122] Alpha case data for test bars cast as discussed in Example
20 is provided below in Table 31.
31TABLE 31 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 20 -
1800.degree. F. refractory flour was C T C T C T C T C T 100%
yttria 0.005 0.010 0.004 0.005 0.003 0.005 0.002 0.005 0.001 0.00
refractory flour was C T C T C T C T C T yttria plus 27 wt. % 0.003
0.005 0.005 0.010 0.003 0.016 0.003 0.009 0.00 0.00 samaria Example
20 - 700.degree. F. refractory flour was C T C T C T C T C T flour
was 0.003 0.005 0.004 0.021 0.002 0.005 0.001 0.003 0.001 0.002
100% yttria refractory C T C T C T C T C T flour was 0.003 0.009
0.003 0.005 0.002 0.011 <0.001 0.004 <0.001 0.003 yttria plus
27 wt. % samaria
EXAMPLE 21
[0123] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made having such facecoat, and Ti 6-4 test
bars cast using such molds to determine the effectiveness of
inclusion imaging using the facecoat material, as well as the
amount of alpha case produced by casting such test bars. This
Example 21 concerns a facecoat slurry comprising calcined
gadolinia/yttria. Otherwise, the facecoat slurry and mold were
produced in a manner substantially identical to that of Example 1.
The materials used to produce the facecoat slurry are provided
below in Table 32.
32 TABLE 32 MATERIALS WEIGHT PERCENT deionized water 3.90
tetraethyl ammonium hydroxide 0.93 titanium dioxide 3.71 latex (Dow
460 NA) 1.86 surfactant (NOPCOWET C-50) 0.19 colloidal silica
(Ludox SM) 7.43 calcined gadolinia/yttria (27%/73%) 81.89
antifoaming agent (Dow 1410) 0.09
[0124] FIG. 2K is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2K shows the
presence of the inclusion.
EXAMPLE 22
[0125] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds that have been cast using such facecoat, and
Ti 6-4 test bars cast using such molds to determine the
effectiveness of inclusion imaging using the facecoat material, as
well as the amount of alpha case produced by casting such test
bars. This Example 22 concerns a facecoat slurry comprising
calcined gadolinia/yttria. Otherwise, the facecoat slurry and mold
were produced in a manner substantially identical to that of
Example 1. The materials used to produce the facecoat slurry are
provided below in Table 33.
33 TABLE 33 MATERIALS WEIGHT PERCENT deionized water 3.77
tetraethyl ammonium hydroxide 0.90 titanium dioxide 3.59 latex (Dow
460 NA) 1.80 surfactant (NOPCOWET C-50) 0.18 colloidal silica
(Ludox SM) 7.18 calcined gadolinia/yttria (39%/61%) 82.49
Antifoaming agent (Dow 1410) 0.09
[0126] FIG. 2L is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2L shows the
presence of the inclusion.
EXAMPLE 23
[0127] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made having such facecoat, and Ti 6-4
structural castings made using such molds to determine the
effectiveness of inclusion imaging agents using the facecoat
material, as well as the amount of .alpha. case produced by casting
such a part. This Example 23 concerns a facecoat slurry comprising
calcined gadolinia/yttria. Otherwise, the facecoat slurry and molds
were produced in a manner substantially identical to that of
Example 1. The materials used to produce the facecoat slurry are
provided in Table 23. Alpha case results from four locations are
shown in Table 34.
34TABLE 34 Location C I 1 0.004 0.004 2 0.002 0.006 3 0.004 0.006 4
0.008 0.015
[0128] Non-destructive testing using N-ray analysis revealed the
presence of two inclusions (FIG. 3) in a section thickness of about
1 inch, the inclusions having observed lengths of about 0.025 inch
and 0.050 inch. Standard production techniques for inspection using
both X-ray analysis and ultrasonic inspection did not reveal these
inclusions. This example therefore demonstrates (1) the ability of
the gadolinia-doped facecoat to produce castings having acceptable
alpha case levels, and (2) the benefits of using N-ray analysis to
detect inclusions, which otherwise would go undetected using
conventional techniques developed prior to the present
invention.
EXAMPLE 24
[0129] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made using such facecoat, and Ti 6-4 parts
cast using such molds to determine the effectiveness of inclusion
imaging using the facecoat material, as well as the amount of alpha
case produced by casting such test bars. This Example 24 concerns a
facecoat slurry comprising calcined gadolinia/yttria. Otherwise,
the facecoat slurry and mold were produced in a manner
substantially identical to that of Example 1. The materials used to
produce the facecoat slurry are provided below in Table 35.
35 TABLE 35 MATERIALS WEIGHT PERCENT deionized water 4.04
tetraethyl ammonium hydroxide 0.96 titanium dioxide 3.85 latex (Dow
460 NA) 1.93 surfactant (NOPCOWET C-50) 0.19 colloidal silica
(Ludox SM) 7.70 calcined gadolinia/yttria (14%/86%) 81.22
antifoaming agent (Dow 1410) 0.14
[0130] FIG. 2G is an N-ray image of a test bar made from a mold
having the facecoat composition described above. FIG. 2G shows the
presence of the inclusion.
[0131] Alpha case data for test bars cast as discussed in Example
16 is provided below in Table 36.
36TABLE 36 Face-coat 1.5" 1.0" 0.5" 0.25" 0.125" Example 24 -
1800.degree. F. Refractory flour was C T C T C T C T C T 100%
yttria 0.005 0.009 0.005 0.009 0.005 0.010 0.002 0.003 0.001 0.004
Refractory flour was C T C T C T C T C T yttria plus 14 wt. % 0.005
0.009 0.004 0.011 0.002 0.005 0.002 0.005 0.00 0.00 gadolinia
EXAMPLE 25
[0132] This example concerns the production of facecoat slurries
comprising an intimate mixture of a mold-forming material and an
imaging agent, molds made using such facecoat, and Ti 6-4
developmental parts that were cast using such molds to determine
the effectiveness of inclusion imaging using the facecoat material,
as well as the amount of alpha case produced by casting such parts.
This Example 25 concerns a facecoat slurry comprising calcined
gadolinia/yttria. Otherwise, the facecoat slurry and mold were
produced in a manner substantially identical to that of Example 1.
The materials used to produce the facecoat slurry are provided
below in Table 37. The molds were heated to 1800.degree. F. prior
to pouring.
37 TABLE 37 MATERIALS WEIGHT PERCENT deionized water 4.04
Tetraethyl ammonium hydroxide 0.96 titanium dioxide 3.85 latex (Dow
460 NA) 1.93 surfactant (NOPCOWET C-50) 0.19 colloidal silica
(Ludox SM) 7.70 calcined gadolinia/yttria (14%/86%) 81.22
antifoaming agent (Dow 1410) 0.14
[0133]
38TABLE 38 PRODUCTION PART ALPHA CASE COMPARISON FOR PURE YTTRIA
FACECOATS VS. FACECOATS COMPRISING YTTRIA AND 14 WEIGHT PERCENT
GADOLINIA YTTRIA + GADOLINIA YTTRIA FACECOAT FACECOAT Alpha case
Alpha case Location Thickness (in.) Thickness (in.) 1 Continuous
0.010 Continuous 0.004 Total 0.013 Total 0.010 2 Continuous 0.008
Continuous 0.004 Total 0.018 Total 0.011 3 Continuous 0.003
Continuous 0.002 Total 0.005 Total 0.005 4 Continuous 0.006
Continuous 0.002 Total 0.009 Total 0.008 5 Continuous 0.006
Continuous 0.004 Total 0.017 Total 0.010 6 Continuous 0.008
Continuous 0.005 Total 0.020 Total 0.011 7 Continuous 0.006
Continuous 0.002 Total 0.011 Total 0.006 8 Continuous 0.005
Continuous 0.002 Total 0.012 Total 0.007
[0134] Table 38 compares the amount of alpha case in production
parts cast using molds comprising gadolinia imaging agent to the
same parts cast using yttria, a known facecoat material
particularly useful for investment casting titanium and titanium
alloy parts. A person skilled in the art of investment casting
might conclude that the addition of imaging agent to a yttria
facecoat would increase the amount of alpha case. Surprisingly,
little detrimental effects have been demonstrated with respect to
substituting imaging agent for known facecoat materials and the
quality of the part shown.
[0135] FIGS. 4 and 5 are graphs of alpha case thickness, in inches,
for production parts cast having cross sectional thicknesses of 1.5
inches and 1.0 inch, respectively. Surprisingly, FIG. 4 shows that
as the percent gadolinia increases from an initial amount of about
1% to between about 20% and 40% the alpha case decreases. As stated
above, this is unexpected as a person of ordinary skill in the art
likely would expect that increasing the percent imaging agent would
increase the alpha case. The data plotted on FIG. 5 supports the
conclusion that, at least for parts having a cross sectional
thickness of 1 inch or greater, substituting imaging agent does not
seem to increase the alpha case. For parts having cross sectional
thicknesses of 1 inch or greater, increasing the percent of
gadolinia imaging agent up to about 40 weight percent has the
positive effect of decreasing the alpha case relative to parts made
using molds having pure yttria facecoats.
EXAMPLE 26
[0136] This example concerns the real-time analysis and
detectability of inclusions by N-ray analysis. For this example, Ti
6-4 material having a 0.25 inch cross sectional thickness was
obtained. Samples of this material were stacked in 0.25 inch
increments from 0.25 inch up to 4 inches. Flakes of facecoat
material 0.007 inch thick and of varying cross sectional area were
placed on top of the stack. For each thickness of titanium, an
N-ray film was obtained. Moreover, for each thickness, a real-time
image was obtained having 1024 frames of data, and then such data
was integrated to provide an electronic image. The film and
electronic images were then compared to determine the sensitivity
of the real time imaging relative to the film imaging method.
[0137] With reference to FIG. 6, the smallest inclusion that was
detected by both film and real time for a part having a cross
sectional thickness of less than one inch was an 0.007-inch thick
flake having a length of 0.003 inch. For titanium thicknesses of
about 1.25 inches, the minimum thickness for N-ray film is still a
0.007-inch thick flake having a length of 0.003 inch. For real time
N-ray imaging the inclusion size that can be imaged increased to
about 0.007-inch thick inclusions having a length of 0.016 inch.
Thus, the minimum inclusion size that can be seen in real time for
a titanium part having a thickness of about 1.25 inch has increased
relative to that of parts having smaller cross sectional
thicknesses, but only from about 0.003 inch to about 0.016 inch.
This holds true for parts having cross sectional thicknesses of up
to about 2.5 inches in cross section. For parts having cross
sectional thicknesses of 2.75 inches, N-ray film can still detect
0.007-inch thick flakes having a length of 0.003 inch, whereas real
time analysis can detect a 0.007-inch thick inclusions having a
length of 0.038 inch. FIG. 6 demonstrates that real time N-ray
analysis is sufficiently capable of imaging inclusions that it can
be used instead of film recording for detecting inclusions.
Moreover, FIG. 6 shows that both real time and film recording N-ray
techniques are much more sensitive than X-ray techniques for
imaging inclusions in titanium castings.
[0138] IV. Infiltration Method for Forming Molds Comprising Imaging
Agents
[0139] The method described above involves forming a mold having at
least a facecoat that includes one or more imaging agents. An
alternative method for forming investment casting molds comprising
imaging agents might be to first form a mold substantially as
described above, and thereafter infiltrate the mold with a suitable
imaging agent. In this method all particles, including stucco would
be coated with the imaging agent.
[0140] One method for infiltrating the mold would be to form the
mold in the conventional manner to have an internal cavity in the
shape of the desired article. A solution, typically but not
necessarily an aqueous solution, of an imaging agent would then be
placed inside the cavity for a sufficient period of time to
substantially uniformly infiltrate the desired portion of the mold.
For example, a solution of a gadolinium salt, such as a nitrate,
sulfate or halide salt, would be placed inside the cavity.
[0141] A second method for infiltrating the mold would be to
immerse a pattern having at least a facecoat applied thereto into
an aqueous or non-aqueous solution comprising an imaging agent to
infiltrate at least the facecoat with the imaging agent. The
pattern could be immersed in imaging agent solutions after
application of only the facecoat, after application of the facecoat
and then again after application of at least one backup layer,
after the facecoat and then again plural times after each
application of subsequent backup layers, or after application of
each and every layer of the mold. The infiltration process is
facilitated by using a vacuum chamber to at least partially
evacuate the pores of the mold, thereby allowing imaging agent
solution enter such pores. Infiltrating molds is described in more
detail in U.S. Pat. No. 5,927,379, which is incorporated herein by
reference.
[0142] The "infiltration" should provide suitable results. However,
it currently is believed that forming molds comprising an intimate
mixture of a mold-forming material or materials and an imaging
agent or agent in at least the facecoat provides a preferred
process.
[0143] The present invention has been described with respect to
certain preferred embodiments. However, the present invention
should not be limited to the particular features described.
Instead, the scope of the invention should be determined by the
following claims.
* * * * *