U.S. patent application number 13/918004 was filed with the patent office on 2014-12-18 for joining process for superalloys.
The applicant listed for this patent is General Electric Company. Invention is credited to Jeffrey Jon SCHOONOVER, Akane SUZUKI, David Austin WARK.
Application Number | 20140367455 13/918004 |
Document ID | / |
Family ID | 52018375 |
Filed Date | 2014-12-18 |
United States Patent
Application |
20140367455 |
Kind Code |
A1 |
SUZUKI; Akane ; et
al. |
December 18, 2014 |
JOINING PROCESS FOR SUPERALLOYS
Abstract
A method of bonding superalloys is provided. The method
includes: aligning a first superalloy subcomponent having a
gamma-prime solvus g'.sub.1 and a second superalloy subcomponent
having a gamma-prime solvus g'.sub.2, with a filler material that
includes at least 1.5 wt % boron disposed between the first and
second superalloy subcomponents; performing a first heat treatment
at a temperature T.sub.1, where T.sub.1 is above the solidus of the
filler material and below the liquidus of the filler material; and
performing a second heat treatment at a temperature T.sub.2, where
T.sub.2 is greater than T.sub.1, and where T.sub.2 is greater than
or equal to the lower of g'.sub.1 and g'.sub.2.
Inventors: |
SUZUKI; Akane; (Clifton
Park, NY) ; SCHOONOVER; Jeffrey Jon; (Albany, NY)
; WARK; David Austin; (West Sand Lake, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
52018375 |
Appl. No.: |
13/918004 |
Filed: |
June 14, 2013 |
Current U.S.
Class: |
228/231 |
Current CPC
Class: |
C22C 19/057 20130101;
B23K 35/0233 20130101; B23K 35/3033 20130101; B23K 20/22 20130101;
B23K 35/304 20130101; C22F 1/10 20130101 |
Class at
Publication: |
228/231 |
International
Class: |
B23K 20/22 20060101
B23K020/22 |
Claims
1. A method of bonding superalloys comprising: aligning a first
superalloy subcomponent having a gamma-prime solvus g'.sub.1 and a
second superalloy subcomponent having a gamma-prime solvus
g'.sub.2, with a filler material comprising at least 1.5 wt % boron
disposed therebetween; performing a first heat treatment at a
temperature T.sub.1, wherein T.sub.1 is above the solidus of the
filler material and below the liquidus of the filler material; and
performing a second heat treatment at a temperature T.sub.2,
wherein T.sub.2 is greater than T.sub.1, and wherein T.sub.2 is
greater than or equal to the lower of g'.sub.1 and g'.sub.2.
2. The method according to claim 1, wherein the first superalloy
subcomponent is the same material as the second superalloy
subcomponent.
3. The method according to claim 1, wherein the first superalloy
subcomponent is a different material than the second superalloy
subcomponent.
4. The method according to claim 1, wherein the first superalloy
subcomponent and the second superalloy subcomponent are
single-crystal materials and have less than a 10.degree. crystal
orientation deviation from each other.
5. The method according to claim 1, wherein: (a) the first
superalloy subcomponent comprises a single crystal superalloy and
the second superalloy subcomponent comprises a directionally
solidified superalloy; (b) the first superalloy subcomponent
comprises a directionally solidified superalloy and the second
superalloy subcomponent comprises a directionally solidified
superalloy; (c) the first superalloy subcomponent comprises a
single crystal superalloy and the second superalloy subcomponent
comprises a polycrystalline superalloy; (d) the first superalloy
subcomponent comprises a directionally solidified superalloy and
the second superalloy subcomponent comprises a polycrystalline
superalloy; or (e) the first superalloy subcomponent comprises a
polycrystalline superalloy and the second superalloy subcomponent
comprises a polycrystalline superalloy.
6. The method according to claim 1, wherein at least one of the
first superalloy subcomponent and the second superalloy
subcomponent is a single crystal superalloy subcomponent.
7. The method according to claim 1, wherein both the first
superalloy subcomponent and the second superalloy subcomponent are
single crystal superalloy subcomponents.
8. The method according to claim 7, wherein the first superalloy
subcomponent and the second superalloy subcomponent comprise a
single crystal cast nickel-based superalloy.
9. The method according to claim 8, wherein the first superalloy
subcomponent and the second superalloy subcomponent comprise at
least 50 wt % nickel.
10. The method according to claim 1, wherein the first superalloy
subcomponent and the second superalloy subcomponent comprise
nickel, cobalt, chromium, molybdenum, tungsten, aluminum, and
tantalum.
11. The method according to claim 1, wherein the filler material is
a foil.
12. The method according to claim 1, wherein the filler material is
a coating deposited on at least one of the first superalloy
subcomponent and the second superalloy subcomponent.
13. The method according to claim 1, wherein the filler material
comprises 1.5 to 4 wt % boron.
14. The method according to claim 1, wherein the filler material
has a thickness of 10 to 50 .mu.m.
15. The method according to claim 1, wherein the first heat
treatment is performed at a temperature T.sub.1 at least 20.degree.
C. above the solidus of the filler material.
16. The method according to claim 1, wherein the first heat
treatment is performed at a temperature T.sub.1 of 1,100 to
1,200.degree. C.
17. The method according to claim 1, wherein the second heat
treatment is performed at a temperature T.sub.2 greater than or
equal to the higher of g'.sub.1 and g'.sub.2.
18. The method according to claim 1, wherein the second heat
treatment is performed at a temperature T.sub.2 of 1,225 to
1,325.degree. C.
19. The method according to claim 1, wherein, during the first heat
treatment, the temperature is held at T.sub.1 for at least one
hour, and wherein, during the second heat treatment, the
temperature is held at T.sub.2 for at least one hour.
20. The method according to claim 1, wherein, during the first heat
treatment, 0.5 to 2 MPa pressure is applied to the first and second
superalloy subcomponents.
Description
BACKGROUND
[0001] The invention includes embodiments that relate to a method
of bonding superalloys. More particularly, the invention relates to
a semi-solid method of bonding superalloys.
[0002] Superalloy components are commonly used in various
applications, including, for example, in aircraft engine, gas
turbine, and marine turbine industries. Generally, the quality of
the superalloy components is imperative to their successful
function. To achieve the requisite quality products, even very
large superalloy components (e.g., first stage buckets of gas
turbines) are often cast so as to avoid joining (bonding)
components wherever possible. However, such large superalloy
components typically suffer from low casting yield due to the size,
complex shape, and/or presence of core. Even for smaller
components, casting a single component can be less than ideal due
to, for example, complex shapes required of the component.
[0003] Segmenting superalloy components into smaller multiple
subcomponents enables reducing the size of subcomponents,
simplifying the shape, and/or eliminating the core, thereby
allowing for improved casting yield. However, thus far, prior art
focusing on joining processes, including welding and brazing, for
superalloys has failed to produce mechanically sound joints. When
superalloy components are joined, the joint typically possesses
inferior mechanical properties (lower tensile strength, shorter
creep and fatigue life, lower ductility) due to discontinuity of
chemistry and/or microstructure across the joint. The same
drawbacks have impacted the ability to obtain hybrid components
comprising different alloys, and have plagued the art of repair
processes, which seek to replace damaged portion(s) of superalloy
components.
[0004] Thus, a need exists for an improved method of bonding
superalloys that allows for joining subcomponents, preferably in
higher-yield processes while maintaining high quality mechanical
properties.
[0005] While certain aspects of conventional technologies have been
discussed to facilitate disclosure of the invention, Applicants in
no way disclaim these technical aspects, and it is contemplated
that the claimed invention may encompass one or more of the
conventional technical aspects discussed herein.
[0006] In this specification, where a document, act or item of
knowledge is referred to or discussed, this reference or discussion
is not an admission that the document, act or item of knowledge or
any combination thereof was, at the priority date, publicly
available, known to the public, part of common general knowledge,
or otherwise constitutes prior art under the applicable statutory
provisions; or is known to be relevant to an attempt to solve any
problem with which this specification is concerned.
BRIEF DESCRIPTION
[0007] Briefly, the present invention satisfies the need for an
improved method of bonding superalloys.
[0008] More particularly, provided is a method of bonding
superalloys, which includes: aligning a first superalloy
subcomponent having a gamma-prime solvus g'.sub.1 and a second
superalloy subcomponent having a gamma-prime solvus g'.sub.2, with
a filler material comprising at least 1.5 wt % boron disposed
therebetween; performing a first heat treatment at a temperature
T.sub.1, wherein T.sub.1 is above the solidus of the filler
material and below the liquidus of the filler material; and
performing a second heat treatment at a temperature T.sub.2,
wherein T.sub.2 is greater than T.sub.1, and wherein T.sub.2 is
greater than or equal to the lower of g'.sub.1 and g'.sub.2.
[0009] The present invention may address one or more of the
problems and deficiencies of the art discussed above. However, it
is contemplated that the invention may prove useful in addressing
other problems and deficiencies in a number of technical areas.
Therefore, the claimed invention should not necessarily be
construed as limited to addressing any of the particular problems
or deficiencies discussed herein.
[0010] Certain embodiments of the presently-disclosed methods for
bonding superalloys have several features, no single one of which
is solely responsible for their desirable attributes. Without
limiting the scope of these methods as defined by the claims that
follow, their more prominent features will now be discussed
briefly. After considering this discussion, and particularly after
reading the section of this specification entitled "Detailed
Description" one will understand how the features of the various
embodiments disclosed herein provide a number of advantages over
the current state of the art. These advantages may include, without
limitation, providing methods which allow for: joining of
subcomponents, creating sound joints that are substantially free of
grain boundaries, improving casting yield of superalloy components,
obtaining joints and joined superalloys having high quality
mechanical properties, providing improved repair processes, and/or
providing improved processes allowing for the design and
manufacturing of hybrid components (which can be beneficial, for
example, where components comprising dissimilar subcomponent alloys
are desired, e.g., aircraft engine blades and gas turbine buckets
tend to see higher temperature along the leading and trailing
edges, which causes faster creep damage accumulation compared with
the remainder portion of the airfoil--hybrid joining would allow
for attaching a stronger alloy along the leading and trailing
edges, and can offer economical advantages).
[0011] These and other features and advantages of this invention
will become apparent from the following detailed description of the
various aspects of the invention taken in conjunction with the
appended claims and the accompanying drawings.
DRAWINGS
[0012] FIG. 1 is a photo micrograph showing the microstructure
change at the joint following a bonding process according to an
embodiment of the invention.
[0013] FIG. 2 is a chart showing the composition gradient of joined
superalloy subcomponents following bonding according to an
embodiment of the invention.
[0014] FIG. 3 is a photo micrograph showing the microstructure
change at the joint following bonding according to another
embodiment of the invention.
[0015] FIG. 4 depicts a chart showing the results of yield strength
testing on bonded superalloy components according to embodiments of
the present invention as compared to a non-bonded single crystal
superalloy component without a joint. The yield strength values
were normalized against the yield strength of a non-bonded
single-crystal superalloy at 1400.degree. F.
[0016] FIG. 5 depicts a chart showing the results of ultimate
tensile strength testing on bonded superalloy components according
to embodiments of the present invention as compared to a non-bonded
single crystal superalloy component without a joint. The ultimate
tensile strength values were normalized against the ultimate
tensile strength of a non-bonded single-crystal superalloy at
1400.degree. F.
[0017] FIG. 6 depicts a chart showing the results of elongation
testing on bonded superalloy components according to embodiments of
the present invention as compared to a non-bonded single crystal
superalloy component without a joint. The elongation values were
normalized against the elongation of a non-bonded single-crystal
superalloy at 1400.degree. F.
[0018] FIG. 7 is a chart depicting 1800.degree. F./30 ksi creep
test results for testing done on bonded superalloy components
according to embodiments of the present invention as compared to a
non-bonded single crystal superalloy component without a joint.
Time was normalized against the rupture life of a non-bonded
single-crystal superalloy.
[0019] FIG. 8 is a photo micrograph showing the microstructure
change at the joint for a bonded superalloy component made using a
prior art transient liquid phase bonding heat treatment.
DETAILED DESCRIPTION
[0020] The present invention is generally directed to methods of
bonding superalloys.
[0021] Although this invention is susceptible to embodiment in many
different forms, certain embodiments of the invention are shown and
described. It should be understood, however, that the present
disclosure is to be considered as an exemplification of the
principles of this invention and is not intended to limit the
invention to the embodiments illustrated.
[0022] In one aspect, the invention relates to a method of bonding
superalloys. The method comprises: aligning a first superalloy
subcomponent having a gamma-prime solvus g'.sub.1 and a second
superalloy subcomponent having a gamma-prime solvus g'.sub.2, with
a filler material comprising at least 1.5 wt % boron disposed
therebetween; performing a first heat treatment at a temperature
T.sub.1, wherein T.sub.1 is above the solidus of the filler
material and below the liquidus of the filler material; and
performing a second heat treatment at a temperature T.sub.2,
wherein T.sub.2 is greater than T.sub.1, and wherein T.sub.2 is
greater than or equal to the lower of g'.sub.1 and g'.sub.2.
[0023] Where reference is made herein to "aligning" superalloy
subcomponents (e.g., aligning a first superalloy subcomponent
having a gamma-prime solvus g'1 and a second superalloy
subcomponent having a gamma-prime solvus g'2, with a filler
material disposed therebetween), "aligning" is intended to include
arranging the superalloy subcomponents relative to one another in
any manner conducive to the joining method described herein.
[0024] While reference is made herein to a first and second
superalloy, persons having ordinary skill in the art will readily
recognize that the inventive method may be used to join two or more
(e.g., three, four, etc.) superalloy subcomponents.
[0025] The first and second superalloy subcomponents may be of any
desirable superalloy subcomponent composition.
[0026] In some embodiments, the first superalloy subcomponent is
the same material as the second superalloy subcomponent. In some
embodiments, the first and second superalloy subcomponents comprise
different materials.
[0027] In some embodiments, the first and second superalloy
subcomponents independently comprise a material selected from a
single crystal superalloy, a directionally solidified superalloy,
and a polycrystalline superalloy.
[0028] As used herein, a "single crystal superalloy" includes an
alloy formed as a single crystal, such that there are generally no
high angle grain boundaries in the material.
[0029] As used herein, a "directionally solidified superalloy"
includes an alloy having a columnar grain structure where grain
boundaries created in the solidification process are aligned
parallel to the growth direction.
[0030] As used herein, a "polycrystalline superalloy" includes an
alloy having a randomly oriented equiaxed grain structure.
[0031] In some embodiments, the first superalloy subcomponent and
the second superalloy subcomponent are selected such that:
[0032] the first superalloy subcomponent comprises a single crystal
superalloy and the second superalloy subcomponent comprises a
single crystal superalloy;
[0033] the first superalloy subcomponent comprises a single crystal
superalloy and the second superalloy subcomponent comprises a
directionally solidified superalloy;
[0034] the first superalloy subcomponent comprises a directionally
solidified superalloy and the second superalloy subcomponent
comprises a directionally solidified superalloy;
[0035] the first superalloy subcomponent comprises a single crystal
superalloy and the second superalloy subcomponent comprises a
polycrystalline superalloy;
[0036] the first superalloy subcomponent comprises a directionally
solidified superalloy and the second superalloy subcomponent
comprises a polycrystalline superalloy; or
[0037] the first superalloy subcomponent comprises a
polycrystalline superalloy and the second superalloy subcomponent
comprises a polycrystalline superalloy.
[0038] In some embodiments, at least one of the first superalloy
subcomponent and the second superalloy subcomponent is a single
crystal superalloy subcomponent.
[0039] In some embodiments, at least one of the first superalloy
subcomponent and the second superalloy subcomponent comprises a
nickel-based superalloy. In some embodiments, both the first
superalloy subcomponent and the second superalloy subcomponent
comprise a nickel-based superalloy.
[0040] In some embodiments, one or both of the first superalloy
subcomponent and the second superalloy subcomponent comprises at
least 50 wt % nickel. For example, in some embodiments, one or both
of the first superalloy subcomponent and the second superalloy
subcomponent comprises 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60,
61, 62, 63, 64, 65, 66, 67, 68, 69, or 70 wt % nickel, including
any and all ranges and subranges therein.
[0041] In some embodiments, one or both of the first superalloy
subcomponent and the second superalloy subcomponent comprises
nickel, cobalt, chromium, molybdenum, tungsten, aluminum, and/or
tantalum. In certain embodiments, one or both of the first
superalloy subcomponent and the second superalloy subcomponent may
additionally comprise rhenium, hafnium, titanium, niobium,
ruthenium, carbon, and/or boron.
[0042] According to the inventive method, the first superalloy
subcomponent has a gamma-prime (.gamma.') solvus g'.sub.1, and the
second superalloy subcomponent has a gamma-prime solvus g'.sub.2.
Above the gamma prime solvus temperature of an alloy, the gamma
prime phase is taken completely into solution in the gamma matrix
after holding for sufficient diffusion or at equilibrium
condition.
[0043] Persons having ordinary skill in the art will recognize that
the gamma prime solvus temperature is a function of actual
composition. For example, typical gamma prime solvus temperatures
for nickel-based superalloys are 1120.degree. C. to 1190.degree. C.
The Rene N5 nickel-based single crystal alloy has a reported gamma
prime solvus of about 1269.degree. C.
[0044] The filler material used in methods of the invention may be,
for example, in the form of a coating, paste or foil (produced by,
for example, melt-spinning, rolling). The filler material is
disposed between the first superalloy subcomponent and the second
superalloy subcomponent in any desirable manner. For example, where
the filler material is a coating, it may be spray-coated or
otherwise applied (e.g., by painting, ion-plasma deposition, etc.)
onto one or both of the first and second superalloy subcomponents.
Where the filler material is a paste, foil or other form, it may
also be disposed between the first and second superalloy
subcomponents in any desirable manner.
[0045] The filler material comprises at least 1.5 wt % boron, which
functions to depress the melting point of the filler material. In
some embodiments, the filler material comprises 1.5 to 4 wt %
boron. For example, in such embodiments, the filler material may
comprise 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5,
2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8,
3.9, or 4.0 wt % boron, including any and all ranges and subranges
therein (e.g., 1.5 to 4.2 wt %, 2 to 4 wt %, etc.)
[0046] Apart from the at least 1.5 wt % boron, the remaining
composition of the filler material may be selected depending upon
the desired component to be formed, and the subcomponents to be
joined. Examples of component elements which may be included in the
filler material include, without exception, Ni, Co, Cr, Mo, W, Al,
Ta, and Hf.
[0047] In some embodiments, the filler material is
nickel-based.
[0048] In some embodiments, the filler material is selected such
that its composition is similar to that of one or more superalloy
subcomponents to be joined.
[0049] In some embodiments, the filler material is applied to one
or both of the first and second superalloy subcomponents before the
subcomponents are assembled (i.e., aligned with one another, having
the filler material disposed therebetween).
[0050] The filler material may be of any desired thickness that is
consistent with the intent and purpose of the inventive method. For
example, in some embodiments, the filler material has a thickness
of 5 to 100 .mu.m, e.g., 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,
60, 65, 70, 75, 80, 85, 90, 95, or 100 .mu.m thick, including any
and all ranges and subranges therein (e.g., 10 to 50 .mu.m
thick).
[0051] A heat treatment process can be described by a curve of
temperature vs. time. In the process of the invention, T.sub.1
represents an inflection point on the curve of temperature vs. time
(i.e., the curve is not continuous). This is to be distinguished
from a process in which the substrate is heated steadily to a
temperature T.sub.n (where T.sub.n is greater than T.sub.1), in
which case the curve would show no inflection point at T1. The
purpose of the "first heat treatment at a temperature T.sub.1" is
to partially melt the filler material, and to cause boron to
diffuse out from the filler material. Thus the heat treatment is
maintained at T.sub.1 for a period of time sufficient to partially
melt the filler material, and to cause boron to diffuse out from
the filler material.
[0052] Applicants have unexpectedly found that using such a
temperature T.sub.1 in the joining process of the invention results
in a markedly improved process over prior art joining methods, such
as prior art transient liquid phase bonding processes (disclosed,
for example, in U.S. Pat. No. 6,325,871).
[0053] As the name implies, transient liquid phase bonding (TLPB)
is a bonding process that joins materials using an interlayer,
which is completely melted during heat treatment at a bonding
temperature which exceeds the liquidus of the interlayer. In fact,
"[t]he bonding temperature is usually well above the interlayer's
melting point to ensure complete melting of the interlayer and to
increase the rate of diffusion." Cook et al., "Overview of
transient liquid phase and partial transient liquid phase bonding",
J. Mater. Sci., (2011) 46:5305-5323, 5307.
[0054] While TLPB prior art requires a heat treatment corresponding
to the first heat treatment of the present invention at a
temperature exceeding the liquidus of the filler material, the
present inventive method employs a first heat treatment at a
temperature T.sub.1, wherein T.sub.1 is above the solidus of the
filler material and below the liquidus of the filler material, such
that, in the inventive method, the filler material does not fully
melt as it does in TLPB processes. Applicants have unexpectedly
found that the present method, employing a first heat treatment at
a temperature T.sub.1, yields an improved joined superalloy
structure.
[0055] During the first heat treatment, a joint is created between
the first and second superalloy subcomponents by partially melting
the filler material. Boron diffuses out from the filler material
into the first and second subcomponents, and small grains are left
along the joint. In some embodiments, grain size is smaller than
100 .mu.m, more preferably, smaller than 50 .mu.m. For example, in
certain embodiments, grain size may be, e.g., 95, 90, 85, 80, 75,
70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, or 10 .mu.m,
including any and all ranges and subranges therein.
[0056] In some embodiments, the first heat treatment is performed
at a temperature T.sub.1 at least 10.degree. C. above the solidus
of the filler material. For example, in some embodiments, T.sub.1
is performed at a temperature that is 10, 15, 20, 25, 30, 35, 40,
45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 120,
130, 140, or 150.degree. C. above the solidus of the filler
material, including any and all ranges and subranges therein (e.g.,
15-100.degree. C., 20-80.degree. C., 20-50.degree. C., etc.),
provided that T.sub.1 is below the liquidus of the filler material.
In some embodiments, the first heat treatment is performed at a
temperature T.sub.1 at least 20.degree. C. above the solidus of the
filler material.
[0057] While the temperature T.sub.1 of the first heat treatment
may be any desired temperature that is greater than the solidus of
the filler material and less than the liquidus of the filler
material, in some embodiments, the first heat treatment is
performed at a temperature T.sub.1 equal to about 1,000 to
1,200.degree. C. For example, in some embodiments, the temperature
T.sub.1 is 1,000, 1,025, 1,050, 1,075, 1,100, 1,125, 1,150, 1,175,
or 1,200.degree. C., including any and all ranges and subranges
therein (e.g., 1,100 to 1,200.degree. C.).
[0058] The duration of the first heat treatment should be
sufficient to partially melt the filler material, and to cause
boron to diffuse out from the filler material. For example, in some
embodiments, during the first heat treatment, the temperature is
held at T.sub.1 for at least 15 minutes. In other embodiments, the
temperature is held at T.sub.1 for at least 30 minutes, or for at
least one hour, and less than 10 hours.
[0059] In some embodiments, during the first heat treatment, the
temperature is held at T.sub.1 for at least one hour, and wherein,
during the second heat treatment, the temperature is held at T2 for
at least one hour.
[0060] In some embodiments, pressure is applied to the first and
second superalloy subcomponents during the first heat treatment.
For example, in some embodiments, pressure is applied to the
assembled first and second superalloy subcomponents in the
direction of the joint (i.e., from outer portions of the
subcomponents toward the filler material disposed between the
subcomponents). In some embodiments, during the first heat
treatment, 0.2 to 4 MPa pressure is applied to the first and second
superalloy subcomponents. For example, in some embodiments, 0.2,
0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8,
3.0, 3.2, 3.4, 3.6, 3.8, or 4.0 MPa pressure is applied to the
first and second superalloy subcomponents, including any and all
ranges and subranges therein (e.g., 0.5 to 2 MPa). In some
embodiments, pressure is also applied during the second heat
treatment. In other embodiments, pressure is not applied during the
second heat treatment.
[0061] In some embodiments, a fixture is used to assemble the first
and second superalloy subcomponents during the first heat
treatment. In some embodiments, the fixture is not used during the
second heat treatment, while in other embodiments, the semi-bonded
alloys (i.e., the subcomponents following the first heat treatment)
remain in a fixture during the second heat treatment.
[0062] The second heat treatment is performed subsequent to the
first heat treatment. More specifically, the second heat treatment
is performed at a temperature T.sub.2, wherein T.sub.2 is greater
than T.sub.1, and wherein T.sub.2 is greater than or equal to the
lower of g'.sub.1 and g'.sub.2.
[0063] In some embodiments, T.sub.2 is greater than or equal to the
higher of g'.sub.1 and g'.sub.2. However, T.sub.2 should not exceed
the solidus temperature of the first or second superalloy
subcomponents.
[0064] While T.sub.2 may be any temperature that is greater than
T.sub.1, and greater than or equal to the lower of g'.sub.1 and
g'.sub.2, in some embodiments, the second heat treatment is
performed at a temperature T.sub.2 of 1,200 to 1,350.degree. C. For
example, in some embodiments, T.sub.2 is 1,200, 1,225, 1,250,
1,275, 1,300, 1,325, or 1,350.degree. C., including any and all
ranges and subranges therein (e.g., 1,225 to 1,325.degree. C.).
[0065] In some embodiments, during the second heat treatment, the
temperature is held at T.sub.2 for at least 15 minutes, or at least
30 minutes, or at least 45 minutes, or at least one hour, or at
least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 hours.
[0066] In some embodiments, the second heat treatment is a
standalone treatment, insofar as the treatment at T.sub.2 may be
unaccompanied by any other immediate temporally proximate heat
treatment steps (thus, e.g., T.sub.2 is not a step in a ramped heat
treatment schedule). However, in some embodiments, the second heat
treatment may represent one step out of a multi-step heat
treatment, which may include, for example, ramped heat treatment
(e.g., ramped solution heat treatment) comprising heat treatments
at other temperatures as well.
[0067] In some embodiments (e.g., when subcomponents are
single-crystal alloys), the first superalloy subcomponent and the
second superalloy subcomponent have less than a 10.degree. crystal
orientation deviation from each other. For example, in certain
embodiments, the first superalloy subcomponent and the second
superalloy subcomponent have less than a 9.degree., 8.degree.,
7.degree., 6.degree., 5.degree., 4.degree., 3.degree., 2.degree.,
1.degree. or 0.degree. crystal orientation deviation from each
other.
[0068] In various embodiments, the inventive methods include any
other desirable steps for joining superalloy subcomponents. These
steps may include for example, solution heat treatment and/or
precipitation aging treatments of the first and/or second
superalloy subcomponents.
[0069] The methods of the invention allow for the chemistry and
microstructure of the first and second superalloy subcomponents to
be substantially reproduced within the joint.
[0070] Several embodiments of the invention are described in the
examples below.
EXAMPLES
Example A
[0071] Two Rene N5 nickel-based single crystal superalloy
subcomponents (composition shown in Table I) were prepared by
finishing with low stress grinding, such that the subcomponents had
less than 10.degree. crystal orientation deviation from each other,
had substantially flat mating surfaces, and were smooth and clean.
The Rene N5 subcomponents were aligned with a .about.2 mil thick
N5-2B foil (see Table I), which comprised 2 wt % boron, as filler
material in a fixture, and pressure was applied at about 1 MPa. In
vacuum environment, the aligned subcomponents were subjected to a
first heat treatment while in the fixture at 1150.degree. C. for
one hour, then the subcomponents were allowed to cool to room
temperature. During the first heat treatment, the filler partially
melted, and the subcomponents were metallurgically joined.
Following heating, the joint area was made up of fine grains.
[0072] The cooled joined components were removed from the fixture,
and, in the absence of pressure, were subjected to a second heat
treatment in an inert environment at 1270.degree. C. for 24 hours.
During this second heat treatment step, the fine grains along the
joint diminished in size and eventually disappeared by grain
coarsening of the single crystal grain of the subcomponents. The
chemical gradient along the joint also diminished. FIG. 1 is a
photo micrograph showing the microstructure change at the joint
following the first and second heat treatments, where the
subcomponents are represented as "SX N5". FIG. 2 is a chart showing
the composition gradient of the joined superalloy subcomponents
following the second heat treatment. As shown, consistent element
levels were observed across the subcomponents and joint, with the
exception of a slight drop in Re at the joint.
TABLE-US-00001 TABLE I (wt %) Ni Co Cr Mo W Re Al Ta Hf C B Solidus
Liquidus Rene N5 bal. 7.5 7 1.5 5 3 6.2 6.5 0.15 0.05 0.004
1344.degree. C. 1397.degree. C. N5-2B bal. 7.5 7 1.5 5 6.2 6.5 0.15
2 1110.degree. C. 1260.degree. C. MDC115 bal. 8 9 4 2 4 1 3
1035.degree. C.* 1190.degree. C.* *= calculated
Example B
[0073] Example B was prepared following the protocol set forth
above for Example A, except that for Example B, instead of using
the N5-2B foil, the Rene N5 subcomponents were aligned in a fixture
with a .about.2 mil thick MDC 115 foil (see Table I) comprising 3
wt % boron, obtained from Materials Development Corporation, as
filler material. FIG. 3 is a photo micrograph showing the
microstructure change at the joint following the first and second
heat treatments.
Analysis of Inventive Example A
[0074] High temperature tensile and creep properties of the
single-crystal Rene N5 subcomponents joined with the N5-2B foil
comprising 2 wt % boron (Example A) were measured and compared with
a single crystal Rene N5 superalloy without a joint (Counter
Example SX). The joined N5 was solution treated at 1300.degree. C.
for 2 h, followed by aging treatments at 1120.degree. C./4 h,
1080.degree. C./4 h and 900.degree. C./4 h. FIG. 4 depicts a chart
showing the results of the normalized yield strength testing. FIG.
5 depicts a chart showing the results of normalized ultimate
tensile strength testing. FIG. 6 depicts a chart showing the
results of normalized elongation testing. As shown in FIGS. 4-6,
yield strength, ultimate tensile strength and elongation of the N5
joined with the N5-2B foil comprising 2 wt % boron (Example A) were
all comparable to, and did not show any significant debit in
properties up to 2000.degree. F. compared with the single crystal
Rene N5 without joint (SX), except for elongation testing at
1800.degree. F., which was due to this Example A having large pores
along the joint, which caused the relatively low elongation
compared with the SX baseline.
[0075] FIG. 7 is a chart depicting 1800.degree. F./30 ksi creep
test results for testing done on SX and Example A. As illustrated
by the figure, the normalized time to 1% and 2% strain for the
joined components of Example A made according to the inventive
method are comparable to those of baseline data, i.e., for a single
crystal Rene N5 superalloy without joint (SX).
[0076] The foregoing results indicate that the joints produced by
the inventive process are mechanically sound.
Comparative Example C
[0077] A comparative example according to prior art transient
liquid phase bonding processes (TLPB) was also carried out. Two
Rene N5 nickel-based single crystal superalloy subcomponents were
prepared by finishing with low stress grinding, such that the
subcomponents had less than 10.degree. crystal orientation
deviation from each other, had substantially flat mating surfaces,
and were smooth and clean. The Rene N5 subcomponents were aligned
in a fixture with a .about.2 mil thick filler material of MDC115
foil comprising 3 wt % boron, obtained from Materials Development
Corporation, with applied pressure of about 1 MPa. In a vacuum
environment, the aligned subcomponents were subject to a TLPB heat
treatment while in the fixture at 1280.degree. C. for four hours,
then the subcomponents were allowed to cool to room
temperature.
[0078] FIG. 8 is a photo micrograph showing the microstructure
change at the joint for Comparative Example C following the TLPB
heat treatment. Consistent with prior art TLPB attempts, it proved
difficult to create a satisfactory joint using the prior art TLPB
process. As can be seen in FIG. 8, the resultant joint included a
mixture of areas without grains and with grains (compare to FIGS. 1
and 3, showing superior joint areas obtained with the inventive
bonding method). Due to the large size of the grains present at the
joint, it is not possible to eliminate the grains using grain
coarsening. The TLPB bonding process of the comparative example is
inferior to the inventive process that can consistently produce
sound joint without grains.
[0079] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprise" (and any form of comprise, such as
"comprises" and "comprising"), "have" (and any form of have, such
as "has" and "having"), "include" (and any form of include, such as
"includes" and "including"), and "contain" (and any form contain,
such as "contains" and "containing") are open-ended linking verbs.
As a result, a method or device that "comprises", "has", "includes"
or "contains" one or more steps or elements possesses those one or
more steps or elements, but is not limited to possessing only those
one or more steps or elements. Likewise, a step of a method or an
element of a device that "comprises", "has", "includes" or
"contains" one or more features possesses those one or more
features, but is not limited to possessing only those one or more
features. Furthermore, a device or structure that is configured in
a certain way is configured in at least that way, but may also be
configured in ways that are not listed.
[0080] As used herein, the terms "comprising" and "including" or
grammatical variants thereof are to be taken as specifying the
stated features, integers, steps or components but do not preclude
the addition of one or more additional features, integers, steps,
components or groups thereof. This term encompasses the terms
"consisting of" and "consisting essentially of".
[0081] The phrase "consisting essentially of" or grammatical
variants thereof when used herein are to be taken as specifying the
stated features, integers, steps or components but do not preclude
the addition of one or more additional features, integers, steps,
components or groups thereof but only if the additional features,
integers, steps, components or groups thereof do not materially
alter the basic and novel characteristics of the claimed
composition, device or method.
[0082] All publications cited in this specification are herein
incorporated by reference as if each individual publication were
specifically and individually indicated to be incorporated by
reference herein as though fully set forth.
[0083] Subject matter incorporated by reference is not considered
to be an alternative to any claim limitations, unless otherwise
explicitly indicated.
[0084] Where one or more ranges are referred to throughout this
specification, each range is intended to be a shorthand format for
presenting information, where the range is understood to encompass
each discrete point within the range as if the same were fully set
forth herein.
[0085] While several aspects and embodiments of the present
invention have been described and depicted herein, alternative
aspects and embodiments may be affected by those skilled in the art
to accomplish the same objectives. Accordingly, this disclosure and
the appended claims are intended to cover all such further and
alternative aspects and embodiments as fall within the true spirit
and scope of the invention.
[0086] It is to be understood that the above description is
intended to be illustrative, and not restrictive. For example, the
above-described embodiments (and/or aspects thereof) may be used in
combination with each other. In addition, many modifications may be
made to adapt a particular situation or material to the teachings
of the various embodiments without departing from their scope.
While the dimensions and types of materials described herein are
intended to define the parameters of the various embodiments, they
are by no means limiting and are merely exemplary. Many other
embodiments will be apparent to those of skill in the art upon
reviewing the above description. The scope of the various
embodiments should, therefore, be determined with reference to the
appended claims, along with the full scope of equivalents to which
such claims are entitled. In the appended claims, the terms
"including" and "in which" are used as the plain-English
equivalents of the respective terms "comprising" and "wherein."
Moreover, in the following claims, if present, the terms "first,"
"second," and "third," etc. are used merely as labels, and are not
intended to impose numerical requirements on their objects.
Further, the limitations of the following claims are not written in
means-plus-function format and are not intended to be interpreted
based on 35 U.S.C. .sctn.112, sixth paragraph, unless and until
such claim limitations expressly use the phrase "means for"
followed by a statement of function void of further structure. It
is to be understood that not necessarily all such objects or
advantages described above may be achieved in accordance with any
particular embodiment. Thus, for example, those skilled in the art
will recognize that the systems and techniques described herein may
be embodied or carried out in a manner that achieves or optimizes
one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught
or suggested herein.
[0087] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the disclosure
may include only some of the described embodiments. Accordingly,
the invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
[0088] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *