U.S. patent application number 13/427054 was filed with the patent office on 2012-07-12 for heat treatment of alloys having elements for improving grain boundary strength.
Invention is credited to Winfried Esser, Dirk Goldschmidt, Christopher Hanslits, Michael Ott, Uwe Paul, Ursula Pickert, Russell G. Vogt.
Application Number | 20120175027 13/427054 |
Document ID | / |
Family ID | 40581307 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120175027 |
Kind Code |
A1 |
Esser; Winfried ; et
al. |
July 12, 2012 |
Heat Treatment of Alloys Having Elements for Improving Grain
Boundary Strength
Abstract
A method of producing a component wherein a directionally
solidified columnar grained cast superalloy material is heat
treated such that a secondary phase of the alloy is only partly
solved, thereby providing improved transverse stress rupture
strength compared to fully solved alloys.
Inventors: |
Esser; Winfried; (Bochum,
DE) ; Goldschmidt; Dirk; (Moers, DE) ; Ott;
Michael; (Mulheim, DE) ; Paul; Uwe; (Ratingen,
DE) ; Pickert; Ursula; (Muelheim A.D. Ruhr, DE)
; Hanslits; Christopher; (US) ; Vogt; Russell
G.; (US) |
Family ID: |
40581307 |
Appl. No.: |
13/427054 |
Filed: |
March 22, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10641995 |
Aug 15, 2003 |
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13427054 |
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10429950 |
May 5, 2003 |
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10641995 |
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09103097 |
Jun 23, 1998 |
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10429950 |
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Current U.S.
Class: |
148/555 ;
164/122.1; 164/122.2 |
Current CPC
Class: |
C22C 19/056 20130101;
C30B 33/02 20130101; C30B 29/52 20130101 |
Class at
Publication: |
148/555 ;
164/122.1; 164/122.2 |
International
Class: |
C22F 1/10 20060101
C22F001/10; B22D 27/04 20060101 B22D027/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2002 |
EP |
PCT/EP02/11856 |
Claims
1. A method of forming a component, comprising: casting a nickel
based alloy as a directionally solidified columnar grained or
single crystal structure comprising a secondary phase; and heat
treating the cast alloy to only partially solve the secondary
phase.
2. The method of claim 1, further comprising heat treating the cast
alloy to solve only between 30% and 90% of the secondary phase.
3. The method of claim 1, wherein the heat treating is performed at
a temperature less than a full solution temperature of the cast
alloy.
4. The method of claim 1, wherein the heat treating is performed at
a full solution temperature of the cast alloy but for only a
duration of time such that the secondary phase is not fully
solved.
5. The method of claim 1, further comprising casting the alloy to
comprise boron in an amount of about 0.003% to about 0.0175%.
6. A method of forming a component, comprising: casting a
directionally solidified nickel based superalloy consisting
essentially of, in weight %: about 11.6% to 12/70% Cr, about 8.5%
to 9.5% Co, about 1.65% to 2.15% Mo, about 3.5% to 4.10% W, about
4.8% to 5.20% Ta, about 3.4% to 3.8% Al, about 3.9% to 4.25% Ti,
about 0.05% to 0.11% C, about 0.003% to 0.0175% B, balance
essentially Ni; and heat treating the cast alloy until a .gamma.'
secondary phase of the alloy is only partially solved.
7. The method of claim 6, further comprising heat treating the cast
alloy only until the secondary phase is less than 90% solved.
8. The method of claim 7, wherein the heat treating is performed at
a temperature less than a full solution temperature of the cast
alloy.
9. The method of claim 7, wherein the heat treating is performed at
less 1250 degrees C.
10. The method of claim 7, wherein the heat treating is performed
at 1213.degree. C. for at least 1 hour.
11. The method of claim 7, wherein the heat treating is performed
at a full solution temperature of the cast alloy but for only a
duration of time such that the secondary phase is not fully
solved.
12. The method of claim 6, wherein the heat treating is performed
at 1250 degrees C. only until the secondary phase is between 30%
and 90% solved.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 10/641,995, filed 15 Aug. 2003 and incorporated by reference
herein, which is the U.S. National Stage of International
Application No. PCT/EP02/11856, file 23 Oct. 2002 and is also a
continuation-in-part of U.S. application Ser. No. 10,429,950, filed
5 May 2003 (now abandoned), which in turn is a continuation of U.S.
application Ser. No. 09/103,097, filed 23 Jun. 1998 (now
abandoned).
FIELD OF THE INVENTION
[0002] The present invention relates to a heat treatment of alloys,
especially nickel base superalloy and, more particularly, to
castings having a columnar grain microstructure.
BACKGROUND OF THE INVENTION
[0003] U.S. Pat. No. 4,597,809 describes single crystal castings
made from a nickel base superalloy having a matrix with a
composition consisting essentially of, in weight %, of 9.5% to 14%
Cr, 7% to 11% Co, 1% to 2.5% Mo, 3% to 6% W, 1% to 4% Ta, 3% to 4%
Al, 3% to 5% Ti, 6.5% to 8% Al+Ti, 0% to 1% Nb, and balance
essentially nickel with the matrix containing about 0.4 to about
1.5 volume of a phase based an tantalum carbide as a result of the
inclusion in the alloy of about 0.05% to about 0.15% C and extra Ta
in an amount equal to 1 to 17 times the C content.
[0004] Single crystal castings produced from the aforementioned
nickel base superalloy exhibit inadequate transverse grain boundary
strength. The present inventors attempted to produce directionally
solidified (DS) columnar grain castings of the nickel base
superalloy. However, the directionally solidified (DS) columnar
grain castings produced were unacceptable as DS castings as a
result of the castings exhibiting essentially no transverse grain
boundary strength and no ductility when tested at a temperature of
750 degrees C. (1382 degrees F.) and stress of 660 MPa (95.7 Ksi).
The transverse grain boundary strength and ductility were so
deficient as to render DS columnar grain castings produced from the
aforementioned nickel base superalloy unsuitable for use as turbine
blades of gas turbine engines.
[0005] WO 99/67435 discloses nickel base superalloy castings having
boron added to improve transverse stress rupture strength and
ductility of DS castings. The castings are heat treated at
1250.degree. C. for 4 h so that a full solution of the secondary
phase (.gamma.'-phase) is performed. Due to the occurrence of grain
boundary cracks after the full solution heat treatment, the
producibility is so deficient as to render DS columnar grain
castings produced from the aforementioned nickel base superalloy
unsuitable for use as turbine blades of gas turbine engines.
[0006] An object of the present invention is to provide a heat
treatment of alloys, especially of as-cast alloys, e.g. DS columnar
grain castings based on the aforementioned single crystal nickel
base superalloy, having substantially improved transverse stress
rupture strength and ductility as well as producibility to an
extent that the DS castings are acceptable for use in high
temperature applications such as turbine blades of a gas turbine
engine.
SUMMARY OF THE INVENTION
[0007] The present invention involves a novel heat treatment of
cast alloys, such as superalloys, having at least one addition,
such as boron, which improves grain boundary strength in the nickel
base superalloy. In order to significantly improve transverse
stress rupture strength and ductility of directionally solidified
(DS) columnar grain castings of such alloys, the present invention
innovatively utilizes a heat treatment which solves a secondary
phase only partly, e.g. no full solution heat treatment is
performed. Boron is often added to superalloy compositions in an
effective amount to substantially improve transverse stress rupture
strength and ductility of directionally solidified columnar grain
castings produced from the boron-modified superalloy. The boron
concentration preferably is controlled in the range of about 0.003%
to about 0.0175% by weight of the superalloy composition to this
end. In conjunction with addition of boron to the superalloy
composition, the carbon concentration preferably is controlled in
the range of about 0.05% to about 0.11% by weight of the superalloy
composition. When using such alloys to produce cast components, the
present invention innovatively processes the casting through only a
partial solution heat treatment of a secondary phase, thereby
unexpectantly providing improved producibility when compared to the
prior art process of full solution heat treating of such alloy
castings.
[0008] A preferred nickel base superalloy in accordance with an
embodiment of the present invention consists essentially of, in
weight %, of about 11.6% to 12.70% Cr, about 8.50% to 9.5% Co,
about 1.65% to 2.15% Mo, about 3.5% to 4.10% W, about 4.80% to
5.20% Ta, about 3.40% to 3.80% Al, about 3.9% to 4.25% Ti, about
0.05% to 0.11% C, about 0.003% to 0.0175% B, and balance
essentially Ni. The boron modified nickel base superalloy can be
cast as DS columnar grain castings pursuant to conventional DS
casting techniques such as the well known Bridgman mould withdrawal
technique.
[0009] DS castings produced in this manner typically have a
plurality of columnar grains extending in the direction of the
principal stress axis of the casting with the <001> crystal
axis generally parallel to the principal stress axis. DS columnar
grain castings pursuant to the present invention preferably exhibit
a stress rupture life of at least about 100 hours and elongation of
at least about 2.5% when tested at a temperature of 750 degrees C.
(1382 degrees F.) and stress of 660 MPa (95.7 Ksi) and will find
use as turbine blades, vanes, outer air seals and other components
of a industrial and aero gas turbine engines.
[0010] The above objects and advantages of the present invention
will become more readily apparent form the following detailed
description.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Exemplarily, a nickel base superalloy is chosen which
consists essentially of, in weight %, of about 9.5% to 14% Cr,
about 7% to 11% Co, about 1% to 2.5% Mo, about 3% to 6% W, about 1%
to 6% Ta, about 3$ to 4% Al, about 3% to 5% Ti, about 0% to 1% Nb,
and balance essentially Ni and B present in an amount effective to
substantially improve transverse stress rupture strength of a DS
casting as compared to a similar casting without boron present.
[0012] The inclusion of boron, as an addition, which improves the
grain boundary strength in the alloy, is chosen in an amount
effective to provide substantial transverse stress rupture strength
and ductility of a DS columnar grain casting produced from the
alloy as compared to a similar casting without boron present.
[0013] Preferably, the nickel base superalloy is modified by the
inclusion of boron B in the range of about 0.003% to about 0.0175%,
preferably 0.010% to 0.015%, by weight of the superalloy
composition to this end.
[0014] In conjunction with addition of boron to the superalloy
composition, the carbon C concentration is controlled in a
preferred range of about 0.05% to about 0.11% by weight of the
superalloy composition. Also Silizium Si, Zirkonium Zr and Hafnium
Hf can be used as addition.
[0015] Furthermore all combinations of B, C, Si, Zr, Hf are
possible.
[0016] The transverse stress rupture strength and ductility as well
as the producibility of DS castings produced from nickel base
superalloy with the modified heat treatment first described herein
are provided to an extent that the castings are rendered
commercially acceptable for use as turbine blades and other
components of gas turbine engines.
[0017] A particularly preferred boron-modified nickel base
superalloy casting composition consists essentially of, in weight
%, of about 11.6% to 12.70% Cr, about 8.5% to 9.5% Co, about 1.65%
to 2.15% Mo, about 3.5% to 4.10% W, about 4.80% to 5.20% Ta, about
3.40 to 3.80% Al, about 3.9% to 4.25% Ti, about 0.05% to 0.11% C,
about 0.003% to 0.0175% B, and balance essentially Ni and castable
to provide a DS columnar grain microstructure.
[0018] The DS microstructure of the columnar grain casting
typically includes about 0.4 to about 1.5 volume % of a phase based
an tantalum carbide.
[0019] Although not wishing to be bound by any theory, it is
thought that boron and carbon tend to migrate to the grain
boundaries in the DS microstructure to add strength and ductility
to the grain boundaries at high service temperatures, for example
816 degrees C. (1500 degrees F.) typical of gas turbine engine
blades. DS columnar grain castings produced from the above boron
modified nickel base superalloy typically have the <001>
crystal axis parallel to the principal stress axis of the casting
and exhibit a stress rupture life of at least about 100 hours and
elongation of at least about 2.5% when tested at a temperature of
750 degrees C. (1382 degrees F.). and stress of 660 MPa (95.7 Ksi)
applied perpendicular to the <001> crystal axis of the
casting.
[0020] For example, the following DS casting tests were conducted
and are offered to further illustrate, but not limit, the present
invention.
[0021] An alloy #1 having a nickel base superalloy composition in
accordance with the aforementioned U.S. Pat. No. 4,597,809 and
alloys #1A and #2 and #3 of boron modified nickel base superalloy
were prepared with the following compositions, in weight
percentages, set forth in Table I:
TABLE-US-00001 TABLE I Alloy Cr Co Mo W Ta Al Ti C B Ni #1 12.1 9.0
1.8 3.7 5.2 3.6 4.0 0.07 0.001 balance #1A 12.1 9.0 1.8 3.7 5.2 3.6
4.0 0.08 0.010 balance #2 12.1 9.0 1.8 3.7 5.2 3.6 4.0 0.09 0.011
balance #3 12.1 9.0 1.8 3.7 5.2 3.6 4.0 0.08 0.014 balance
[0022] Each alloy was cast to form DS columnar grain non-cored
castings having a rectangular shape for transverse stress rupture
testing pursuant to ASTM E-139 testing procedure.
[0023] The DS castings were produced e.g. using the conventional
Bridgman mould withdrawal directional solidification technique.
[0024] For example, each alloy was melted in a crucible of a
conventional casting furnace under a vacuum of 1 micron and
superheated to 1427 degrees C. (2600 degrees F.). The superheated
alloy was poured into an investment casting mould having a face
coat comprising zircon backed by additional slurry/stucco layers
comprising zircon/alumina. The mould was preheated to 1482 degrees
C. (2700 degrees F.) and mounted on a chill plate to effect
unidirectional heat removal from the molten alloy in the mould. The
melt-filled mould on the chill plate was withdrawn from the furnace
into a solidification chamber of the casting furnace at a vacuum of
1 micron at a withdrawal rate of 6-16 inches per hour.
[0025] The DS columnar grain castings were cooled to room
temperature under vacuum in the chamber, removed from the mould in
conventional manner using a mechanical knock-out procedure.
[0026] It is noted that the data for Alloys #1, #1A and #2
contained herein are identical to that described in prior art
International Application WO 99/67435 by inventors Winfried Esser,
et al. After being cast, Alloys #1, #1A and #2 were heat treated at
1250 degrees C. (2282 degrees F.) for 4 hours (full solution heat
treatment of the secondary .gamma.' phase) as was described in WO
99/67435. The present inventors, including said Winfried Esser,
have now recognized the benefit of using only a partial heat
treatment regiment, resulting in the data for Alloy #3 first
presented herein. The alloy for Heat #3 was heat treated at a
temperature and for a duration in such way that the solution of a
secondary phase in the matrix is only partly performed.
[0027] The nickel based superalloy has as a secondary phase the
.gamma.'-phase.
[0028] The inventive heat treatment is performed at 1213.degree. C.
for at least 1 h, which is not the solution temperature of a
secondary phase (e.g. y' phase) for this alloy.
[0029] Also the temperature of 1250.degree. C. (called the full
solution temperature), which is normally used for a full solution
treatment, can be used, but only for a shorter time than in the
prior art so that the secondary phase is not completely solved in
the matrix.
[0030] The not solubilized amount of the secondary phase in the
matrix is smaller than 90, 70, 50 or 30 vol % according to the
geometry and producibility after the heat treatment, because grain
boundary cracks are avoided, in order to increase the yield rate of
specimens and desired mechanical properties of the specimen.
[0031] The alloy can have a single crystal structure or only having
grains along one direction.
[0032] Optionally an ageing heat treatment can be performed for
this composition at 1080.degree. C. for at least 2 h after this
solution heat treatment. Optionally followed by a second ageing
heat treatment at 870.degree. C. for at least 12 h.
[0033] Especially the inventive heat treatment is used for hollow
specimen, especially blades, vanes, or liners because cracks do
appear more often in walls, especially in thin walls, than in
massive specimens after the normally used heat treatment after
casting.
[0034] The inventive heat treatment leads to an increased grain
boundary strength during this heat treatment, so that the yield
rate (components without cracks) after the heat treatment is
increased.
[0035] Also the transverse stress rupture of the component as final
product is increased during use of the component at working
conditions, because grain boundary strength is increased.
[0036] The inventive method yields also good results for massive
components, e.g. of a gas turbine.
[0037] The castings were also analysed for chemistry, and machined
to specimen configuration.
[0038] Stress rupture testing was conducted in air at a temperature
of 750 degrees C. (1382 degrees F.) and stress of 660 MPa (95.7
Ksi) applied perpendicular to the <001> crystal axis of the
specimens.
[0039] The results of stress rupture testing are set forth in TABLE
II below where LIFE in hours (HRS) indicates the time to fracture
of the specimen, ELONGATION is the specimen elongation to fracture,
and RED OF AREA is the reduction of area of the specimens to
fracture. The test data of Table II for Alloys #1, #1A, #2 and #3
correspond to Alloys #1, #1A, #2 and #3, respectively of TABLE I.
The Alloy #1 data represent an average of two stress rupture test
specimens, while the #1A, #2 and #3 data represent a single stress
rupture test specimen.
TABLE-US-00002 TABLE II Stress #of Temperature MPa Life Elonga- Red
of Alloy Tests .degree. C. (.degree. F.) (KSI) (HRS) tion (%) Area
(%) #1 2 750 (1382) 660 (95.7) 0 0 0 prior art #1A 1 750 (1382) 660
(95.7) 275 3.1 4.7 prior art #2 1 750 (1382) 660 (95.7) 182 2.6 6.3
prior art #3 1 750 (1382) 660 (95.7) 173 3.7 10.7 inven- tion
[0040] It is apparent from TABLE II that the DS columnar grain
specimens produced from heat #1 exhibited in effect essentially no
(e.g. zero hours stress rupture life) transverse grain boundary
strength when tested at a temperature of 750 degrees C. (1382
degrees F.) and stress of 660 MPa (95.7 Ksi). That is, the
specimens failed immediately to provide an essentially zero stress
rupture life. Moreover, the elongation and reduction of area data
were essentially zero. These stress rupture properties are so
deficient as to render the DS columnar grain castings produced from
heat #1 unacceptable for use as turbine blades of gas turbine
engines.
[0041] In contrast, TABLE II reveals that DS columnar grain
specimens produced from heat #1A exhibited a stress rupture life of
275 hours, an elongation of 3.1%, and a reduction of area of 4.7
and specimens from heat #2 exhibited a stress rupture life of 182
hours, an elongation of 2.6%, and a reduction of area of 6.3% when
tested at a temperature of 750 degrees C. (1382 degrees F.) and
stress of 660 MPa (95.7 Ksi).
[0042] The present invention, revealed in Alloy #3 which underwent
only a partial solutioning of the secondary phase, is effective to
provide DS columnar grain castings with substantially improved
transverse stress rupture strength and ductility; as evidenced by
the dramatically improved Elongation and Reduction of Area test
results in Table II. These properties are achieved without
adversely affecting other mechanical properties, such as tensile
strength, creep strength, fatigue strength, and corrosion
resistance of the DS castings. The present invention is especially
useful to provide large DS columnar grain industrial gas turbine
(IGT) blade castings which have the alloy composition described
above to impart substantial transverse stress rupture strength and
ductility to the castings and which have a length of about 20
centimeters to about 60 centimeters and above, such as about 90
centimeters length, used throughout the stages of the turbine of
stationary industrial gas turbine engines. The above described
boron-modified nickel base superalloy casting composition can be
cast as DS columnar grain or single crystal components.
[0043] While the invention has been described in terms of specific
embodiments thereof, it is not intended to be limited thereto but
rather only to the extent set forth in the following claims.
* * * * *