U.S. patent application number 13/266276 was filed with the patent office on 2012-07-26 for nickel base superalloy with multiple reactive elements and use of said superalloy in complex material systems.
Invention is credited to Magnus Hasselqvist.
Application Number | 20120189488 13/266276 |
Document ID | / |
Family ID | 40793022 |
Filed Date | 2012-07-26 |
United States Patent
Application |
20120189488 |
Kind Code |
A1 |
Hasselqvist; Magnus |
July 26, 2012 |
Nickel base superalloy with multiple reactive elements and use of
said superalloy in complex material systems
Abstract
A nickel-base y/y' superalloy with a blend of at most moderate
cost, high oxidation resistance, high hot corrosion resistance,
moderate strengthening, adequate allow stability and comparatively
good weldability is provided. The alloy includes up to 20 wt % of
the sum of Co and Fe, between 17 and 21 wt % Cr, between 0.5 and 3
wt % of the sum of Mo and W, at most 2 wt % Mo, between 4.8 and 6
wt % Al, between 1.5 and 5 wt % Ta, between 0.01 and 0.2 wt % of
the sum of C and B, between 0.01 and 0.2 wt % Zr between 0.05 and
1.5 wt % Hf, between 0.05 and 1.0 wtz % Si, and between 0.01 and
0.5 wt % of the sum of rare earths such as Sc, Y, the actinides and
the lanthanides, such that at least two of these rare earths are
present in the alloy, and no more than 0.3 wt % of any of these
rare earths.
Inventors: |
Hasselqvist; Magnus;
(Finspong, SE) |
Family ID: |
40793022 |
Appl. No.: |
13/266276 |
Filed: |
April 7, 2010 |
PCT Filed: |
April 7, 2010 |
PCT NO: |
PCT/EP2010/054593 |
371 Date: |
January 16, 2012 |
Current U.S.
Class: |
420/443 |
Current CPC
Class: |
F02C 7/232 20130101;
C22C 19/055 20130101; C22C 19/051 20130101; F01D 5/288 20130101;
B23K 35/304 20130101; C22C 19/056 20130101 |
Class at
Publication: |
420/443 |
International
Class: |
C22C 19/05 20060101
C22C019/05 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2009 |
EP |
09005851.2 |
Claims
1-23. (canceled)
24. A nickel base .gamma./.gamma.' superalloy, comprising: up to 20
wt % of a first sum of Co and Fe; between 17 and 21 wt % Cr;
between 0.5 and 3 wt % of a second sum of Mo and W; at most 2 wt %
Mo; between 4.8 and 6 wt % Al; between 1.5 and 5 wt % Ta; between
0.01 and 0.2 wt % of a third sum of C and B; between 0.01 and 0.2
wt % Zr; between 0.05 and 1.5 wt % Hf; between 0.05 and 1.0 wt %
Si; and between 0.01 and 0.5 wt % of a fourth sum of rare earths of
which at least two are present in the alloy, and at most 0.3 wt %
of any rare earth.
25. A nickel base .gamma./.gamma.' superalloy consisting of: up to
20 wt % of a first sum of Co and Fe; between 17 and 21 wt % Cr;
between 0.5 and 3 wt % of a second sum of Mo and W; at most 2 wt %
Mo; between 4.8 and 6 wt % Al; between 1.5 and 5 wt % Ta; between
0.01 and 0.2 wt % of a third sum of C and B; between 0.01 and 0.2
wt % Zr; between 0.05 and 1.5 wt % Hf; between 0.05 and 1.0 wt %
Si; between 0.01 and 0.5 wt % of a fourth sum of rare earths of
which at least two are present in the alloy, and at most 0.3 wt %
of any rare earth; and remainder Ni and unavoidable impurities.
26. The nickel base .gamma./.gamma.' superalloy according to claim
25, wherein Y is present only as an unavoidable impurity.
27. The nickel base .gamma./.gamma.' superalloy according to claim
25, further comprising: between 4.5 and 5.5 wt % Co, between 18.2
and 19 wt % Cr, between 1.4 and 1.8 wt % W, between 5.2 and 5.5 wt
% Al, between 2.8 and 3.6 wt % Ta, between 0.015 and 0.025 wt % C,
between 0.04 and 0.07 wt % Zr, between 0.25 and 0.4 wt % Hf,
between 0.07 and 0.13 wt % Si, between 0.05 and 0.15 wt % the
fourth sum of La and Y, at least 0.02 wt % La, and at least 0.02 wt
% Y.
28. The nickel base .gamma./.gamma.'' superalloy according to claim
26, further comprising: between 4.5 and 5.5 wt % Co, between 18.2
and 19 wt % Cr, between 1.4 and 1.8 wt % W, between 5.2 and 5.5 wt
% Al, between 2.8 and 3.6 wt % Ta, between 0.015 and 0.025 wt % C,
between 0.04 and 0.07 wt % Zr, between 0.25 and 0.4 wt % Hf,
between 0.07 and 0.13 wt % Si, and between 0.05 and 0.5 wt % of the
fourth sum of rare earths, at most 0.3 of any rare earth, and La
and Y present only as impurities.
29. The nickel base .gamma./.gamma.' superalloy according to claim
28, further comprising: about 5 wt % Co, about 18.5 wt % Cr, about
1.6 wt % W, about 5.3 wt % Al, about 3.2 wt % Ta, about 0.02 wt %
C, about 0.05 wt % Zr, about 0.3 wt % Hf, about 0.1 wt % Si, about
0.05 wt % Ce, and about 0.05 wt % Gd.
30. The nickel base .gamma./.gamma.' superalloy according to claim
26, further comprising: between 4.5 and 5.5 wt % Co, between 18.2
and 19 wt % Cr, between 0.8 and 1.2 wt % Mo, between 5.2 and 5.5 wt
% Al, between 2.8 and 3.6 wt % Ta, between 0.015 and 0.025 wt % C,
between 0.04 and 0.07 wt % Zr, between 0.25 and 0.4 wt % Hf,
between 0.07 and 0.13 wt % Si, between 0.05 and 0.5 wt % of the
fourth sum of Ce and Gd, at least 0.02 wt % Ce, at least 0.02 wt %
Gd, and at most 0.3 wt % of Ce or Gd.
31. The nickel base .gamma./.gamma.' superalloy according to claim
26, further comprising: between 4.5 and 5.5 wt % Co, between 20.2
and 20.8 wt % Cr, between 0.8 and 1.2 wt % W, between 4.8 and 5.2
wt % Al, between 1.8 and 2.2 wt % Ta, between 0.015 and 0.025 wt %
C, between 0.04 and 0.07 wt % Zr, between 0.25 and 0.4 wt % Hf,
between 0.3 and 0.5 wt % Si, between 0.05 and 0.5 wt % of the
fourth sum of rare earths, and wherein La and Y present only as
impurities.
32. The nickel base .gamma./.gamma.' superalloy according to claim
31, further comprising: about 5 wt % Co, about 20.5 wt % Cr, about
1 wt % W, about 5 wt % Al, about 2 wt % Ta, about 0.02 wt % C,
about 0.05 wt % Zr, about 0.3 wt % Hf, about 0.4 wt % Si, about
0.05 wt % Ce, and about 0.05 wt % Gd.
33. A component to be used in a hot environment, comprising: a
nickel base .gamma./.gamma.' superalloy according to claim 25.
34. The component according to claim 33, wherein the component is a
filler alloy for repair welding of such hot components.
35. The component according to claim 33, wherein the component is a
filler alloy for cladding of such hot components.
36. The component according to claim 33, wherein the component is a
protective coating and/or bond coat in TBC systems on such hot
components.
37. The component according to claim 33, wherein the component is
in dual use as coating and/or bond coat in a TBC system, and, as a
filler alloy for repair welding on such hot components.
38. The component according to claim 33, wherein the component is
in dual use as coating and/or bond coat in a TBC system, and, as a
filler alloy for cladding on such hot components.
39. The component according to claim 33, wherein the component is
an intermediate layer between the base alloy and a coating and/or a
bond coat in a TBC system on such hot components.
40. The component according to claim 33, wherein the nickel base
.gamma./.gamma.' superalloy is in equiaxed form.
41. The component according to claim 33, wherein the nickel base
.gamma./.gamma.' superalloy is in directionally solidified
form.
42. The component according to claim 33, wherein the nickel base
.gamma./.gamma.' superalloy is in single crystal form.
43. The component according to claim 33, wherein the nickel base
.gamma./.gamma.' superalloy is produced by a production process
resulting in an S content below 10 ppmw in the alloy.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2010/054593, filed Apr. 7, 2010 and claims
the benefit thereof. The International Application claims the
benefits of European Patent Office application No. 09005851.2 EP
filed Apr. 27, 2009. All of the applications are incorporated by
reference herein in their entirety.
FIELD OF INVENTION
[0002] The present invention relates to a nickel-base
.gamma./.gamma.' superalloy with multiple reactive elements and use
of the superalloy in complex materials.
TECHNICAL BACKGROUND
[0003] Nickel-base .gamma./.gamma.' superalloys are essential for
critical components in aero and land based gas turbines, but are
used also in other applications. The difference between said
superalloys depend on the level of knowledge and production
technology available at the time they were developed, and, on
different relative emphasis on properties such as cost, oxidation
resistance, corrosion resistance, strengthening, alloy stability,
ductility, weldability and compatibility with other alloys in
complex material systems.
[0004] Nickel-base .gamma./.gamma.' superalloys are used in single
crystal, directionally solidified or equiaxed form. In each crystal
there is a y matrix which is essentially Ni with elements like Co,
Cr, Mo, W and Re in solid solution, and, .gamma.' particles which
are essentially Ni3Al with elements like Ta, Ti, Nb and V in solid
solution. Grain boundaries, if present, are usually decorated by
carbides and/or borides which provide cohesive strength. Zr also
contributes to grain boundary cohesion. Grain boundaries in
directionally solidified components are usually protected by
significant additions of Hf. Zr and Hf can also contribute to the
reactive element effect for improved cyclic oxidation resistance.
Reactive element effects can also be obtained from Si and rare
earths.
[0005] Elements like Mo, W and Re provide solution strengthening of
the y matrix, and, Ta, Ti, Nb and V provide solution strengthening
of the .gamma.' particles. Al provides strengthening as it
increases the amount of .gamma.' particles, and increases the
concentration of Mo, W and Re in the .gamma. matrix.
[0006] Nickel-base .gamma./.gamma.' superalloys can seldom be
regarded as low cost, but, if the levels of expensive elements such
as W and Ta are kept moderate, and the levels of very expensive
elements such as Re, Ru and noble metals like Pt are kept very low
or are excluded, the cost can be regarded as moderate in
context.
[0007] In the context of hot components in e.g. gas turbines it is
generally accepted that excellent oxidation resistance require the
ability to form a very adherent and continuous low permeability
AL2O3 scale.
[0008] [Barrett] teaches that the ability to form a continuous
Al2O3 scale is provided by Al, enhanced by Cr and Ta, somewhat
reduced by Mo and W, and significantly reduced by Ti, Nb and V.
This implies that less Al is needed to form such an Al2O3 scale if
the levels of Cr and Ta are increased, or, the levels of Ti, Nb and
V are reduced.
[0009] [Sarioglu] teaches that the scale adherence is severely
reduced by tramp elements, especially S, but, that this effect can
be neutralized by a combination of clean casting and addition of
small measured levels of reactive elements such as Hf, Zr and rare
earths. He also teaches that a detrimental effect of S is
associated with its tendency to diffuse to the metal/scale
interphase which is then weakened.
[0010] [Pint 1] underlines the importance of S, and further teaches
the beneficial RE effects when small levels of Hf and the rare
earth Y are combined.
[0011] [Harris] teaches that the combination of the two rare earths
La and Y provide more cyclic oxidation resistance than when Y or La
are used separately. He also teaches that while Y is the most
commonly used rare earth, it may not always be the most efficient,
and that Ce can be very efficient.
[0012] [Pint 2] teaches that Ce, Gd, Sm, Tb, Nd and La were more
effective than e.g. Hf, Zr and Y for improvement of oxide scale
adherence at the same level of concentration.
[0013] [Caron 1] teaches the beneficial reactive element effects
when small levels of Hf and Si are combined.
[0014] [Pint 3] teaches that excellent reactive element effects can
be obtained when multiple reactive elements are used, one example
being the excellent cyclic oxidation resistance seen in tests on
Haynes-214 which contained small measured levels of Zr, Si and Y.
Excellent cyclic oxidation resistance was also seen in Rene-N5
which contained small levels of Hf, Zr, Si and Y.
[0015] [Aimone] teaches that only about 10% of the rare earth
additions are typically retained during master heat casting, due to
evaporation or reaction with surrounding materials. He further
teaches that addition of 20 ppm Y was not effective, additions in
the 200-500 ppm range very effective, and additions in the
1000-2000 ppm range less effective, implying that retained Y levels
in the alloy in the 20-50 ppm range were very effective, and, that
too high retained levels of rare earths are not optimal.
[0016] One conclusion is that surprisingly low levels of Al are
needed to form a continuous Al2O3 scale when supported by adequate
levels of elements such as Cr, Ta and Si, provided that too high
levels of deleterious elements like Ti and Nb are avoided. Another
conclusion is that excellent scale adherence requires a combination
of a low S production process and multiple reactive elements from
the group of Hf, Zr, Si and rare earths. The rare earths should be
used at small retained measured levels and it is advantageous to
use at least two. Also, the initial rare earth composition must be
chosen on the basis of the retention for the particular production
process used.
[0017] Corrosion resistance is provided by Cr. Less than 12 wt % Cr
is regarded as poor, at least 12 wt % Cr as moderate, at least 16
wt % Cr as good, and at least 20 wt % Cr as excellent.
[0018] [Goldschmidt] teaches that the hot corrosion resistance of
the alloy SC16 with 16 wt % Cr and 3 wt % Mo is significantly
inferior to the well-known alloy IN738LC with 16 wt % Cr and 1.8 wt
% Mo. IN738LC is generally recognized as having a good corrosion
resistance. Therefore a restriction to at most 2 wt % Mo in a new
alloy seems prudent, and we would like to have at least 16 wt % Cr,
preferably with some margin as we are possibly entering an era
where relatively corrosive fuels, e.g. certain bio-fuels, will be
utilized.
[0019] High strength base alloys typically use in the order of 4 to
10 wt % Mo+W+Re for matrix strengthening, and in the order of 4-10
wt % Ti+Ta+Nb for strengthening of the .gamma.' particles, and
contain between 40 and 70 vol % .gamma.' particles. IN738LC
contains about 43 vol % particles, 4.4 wt % Mo+W and 6.2 wt %
Ti+Ta+Nb. In contrast, low strength alloys such as Haynes-214,
which is still equivalent in strength to traditional weld filler
alloys such as IN625, contain no strengthening of the matrix or the
particles, and the .gamma.' particle content is small or zero at
high service temperatures. In this context, a moderate
strengthening level is taken to be a .gamma.' content in the 30-50
vol % range and in the range of 2 to 8 wt % of the sum of matrix
and particle strengthening elements.
[0020] If the concentration of Cr, Mo, W and Re in the y matrix is
too high, phases like a Cr, or, topologically close packed phases
will folio directly or in service. Thus, an increased .gamma.'
content, or, increased Mo, W or Re levels, must be accompanied by a
reduction in Cr content if extensive precipitation of such phases
is to be avoided. One particular effect of such phase precipitation
is a reduction in creep strength, and phase stability has therefore
been an important subject for base alloy design. In addition,
extensive phase precipitation may cause loss of ductility, said
phases are often known as brittle phases. It should be noted that
stability may be even more important for alloys in complex
materials systems due to the interdiffusion which might locally
increase the concentration of alloy additions as described
above.
[0021] [Caron 2] teaches that the risk for precipitation of brittle
phases for an alloy can be estimated through comparison of the Md
value for this alloy and a relatively similar alloy with known TCP
risks. For the alloys discussed here, the Md value can be
calculated from
Md=0.717aNi+0.777aCo+1.142aCr+1.267aRe+1.55aMo+1.655aW+1.9aAl+1.9aSi+2.1-
17aNb+2.224aTa+2.271aTi+3.02aHf
wherein a Co is the content of Co in atom % etc. In context, good
stability is taken to be better than for IN738LC as calculated by
this formula
[0022] [Yeh] teaches that Si partitions preferably to the .gamma.'
phase such that the .gamma.' content is increased, implying that
any addition of significant levels of Si to an initially stable
alloy must be balanced by a reduction in the levels of Al, Cr or
the strengthening elements to avoid significant brittle phase
precipitation.
[0023] Classical coating alloys tend to be based on .beta. and
.gamma./.beta. phase structures which provide high Al reservoirs.
The .beta. phase is essentially NiAl. The problem with these alloys
is that their brittleness implies that they are normally only used
as a thin layer. Therefore, they are sensitive to interdiffusion
with the base alloy, e.g. through loss of Al due to diffusion to
low Al base alloys and/or reduction of oxidation resistance due to
interdiffusion of Ti from the base alloy into the coating.
Recently, strengthening elements have been added to these classical
coatings alloys to retard the interdiffusion rates, typically using
Re, Ru and Ta additions. [Subramanian] teaches that the Re
additions in SiCoat2464 significantly increases the oxidation
resistance thanks to a reduced rate of Al interdiffusion.
[0024] In comparison with classical coating alloys, almost all
.gamma./.gamma.'' superalloys will provide good ductility, provided
extensive levels of e.g. brittle phases, eutectics, casting
porosity and weld-cracking are avoided.
[0025] It should also be mentioned that some overlay coating alloys
based on the .gamma./.gamma.' structure have been developed, often
with emphasis on corrosion resistance using high Cr and Si levels,
and, recent developments also include some strengthening element
additions.
[0026] It should also be mentioned that coating alloys based on the
.gamma./.gamma. structure with noble elements like Pt added for
strengthening and oxidation resistance have been developed, see
e.g. [Zhang].
[0027] Whenever an alloy may be used in a material system which
includes an aluminide, it is important for the alloy to be
compatible with said aluminide.
[0028] [Vedula] teaches that small additions of Hf to NiAl result
in significantly improved creep strength. [Tolpygo] teaches that Hf
in the base alloy will diffuse into an applied aluminide coating
and reduce the rumpling of the coating surface such that the oxide
scale adherence is increased, which can be interpreted as an effect
of the improved creep strength when Hf is added to NiAl.
[0029] It should also be mentioned that rumpling increases the
surface roughness, and hence also the heat transfer coefficient of
a surface, and that this can also lead to accelerated oxidation
attack.
[0030] Welding and cladding of hot components has typically been
done using y based alloys or IN625 as fillers. Technology such as
laser welding then enabled e.g. the use of IN738LC based filler
alloys for the IN738LC base alloy. Recently, filler alloys based on
high Al, high strength, high .gamma.' content alloys have been
introduced for e.g. repair of oxidation damage. [Fujita] teaches
that a filler alloy based on Rene-142 could be used for laser weld
repair of CMSX-4 such that the single crystal structure of the
latter was preserved. Both alloys have .gamma.' contents in the
60-70 vol % range.
[0031] In the context of filler alloys with high oxidation
resistance, we therefore regard an alloy with 40-50 vol % .gamma.'
and moderate strengthening as having good weldability, and it
should be obvious to those skilled in the art that the use of such
filler alloys would be less difficult and costly as the use of
alloys such as Rene-142.
[0032] It should also be mentioned that internal work has shown
that many typical damage cases do not require repair using filler
alloys with Rene-142 level strength. Simulations were e.g.
performed on a first stage blade made in CMSX-4, with increased hot
gas temperatures relative to real engine conditions to simulate
future upgrades. Further, to simulate weld-repair of oxidation
damage on this particular squealer tip, the creep rate (for given
levels of stress and temperature) was increased by a factor of 100
on said tip relative to CMSX-4, but no excessive creep resulted
thanks to the low creep loads on said tip.
[0033] The dual use of an alloy for coating and repair would make
the repair and refurbishment process easier and less costly. More
of the coating alloy would be added where needed, including where
the coating has been consumed and some of the substrate lost, in
which case the coating alloy is used to rebuild the component to
produce the necessary geometry.
[0034] Consider also a hot component such as a gas turbine first
stage vane made in a [low Al high Ti] alloy like IN939. A common
problem is local overheating on the platforms, and classical
coating systems tend to provide a quite limited life due to
interdiffusion with the [low Al high Ti] substrate. The ability to
increase the thickness from standard levels to, say, 2 mm in the
locally hot area, i.e. to apply cladding, would significantly
increase the component life. Application of e.g. a PtAl coating on
top could then be used to further increase this component life. In
such areas, the full creep strength of the substrate is not
necessary, but, some creep strength is still useful to resist
erosion and rumpling of the surface due to the high velocity hot
gas stream, because increased surface roughness implies higher heat
transfer into the component, and thus an accelerated oxidation
process.
STATE OF THE ART
[0035] Early development of .gamma./.gamma.' superalloys resulted
in alloys such as U-700 which has a composition, in wt %, given by
Ni-17Co-15Cr-4.5Mo-4.3Al-3.5Ti-0.07Zr-0.08C. U-700 can form a
continuous Al2O3 scale with 4.3 wt % Al thanks to 15 wt % Cr and
despite 3.5 wt % Ti. These alloys have less hot corrosion
resistance than suggested by their Cr levels due to their high
levels of Mo, the main strengthening element in use at the time
they were developed. Their .gamma. contents are in the 45 to 55 vol
% range.
[0036] One line of subsequent alloy development led to alloys such
as IN939, IN738LC and IN792, and this class of alloys remains the
norm in land based gas turbines to this day. IN939 has a
composition, in wt %, given by
Ni-19Co-22Cr-2W-2A1-3.7Ti-1.4Ta-1Nb-0.1Zr-0.15C-0.01B. That of
IN738LC is
Ni-8.5Co-16Cr-1.8Mo-2.6W-3.4Al-3.4Ti-1.8Ta-0.9Nb-0.09Zr-0.08C-0.01B.
That of IN792 is
Ni-9Co-12.5Cr-1.8Mo-4.2W-3.4A1-4.2Ti-4.2Ta-0.08C-0.015B.
[0037] Compared to alloys such as U-700, Mo is partly replaced by W
for improved corrosion resistance, and, Al is partly replaced by
Ti, Nb and Ta for improved creep strength through increased
strengthening of the .gamma.' particles. In particular, these
alloys contain high Ti levels.
[0038] Their hot corrosion resistance range from excellent in
IN939, good in IN738LC to moderate in IN792 depending on their Cr
contents. These alloy do not have the capability to form a
continuous Al2O3 scale, thus they do not provide good oxidation
resistance. The .gamma.' particle contents are typically in the
30-55 vol % range. Improved knowledge allowed alloy designers to
handle phase stability better than for the old alloys above. The
creep strength varies from moderate in alloys like IN939 to high in
alloys like IN792.
[0039] Another line of subsequent alloy development led to alloys
such as Mar M-247 which has a composition, in wt %, given by
Ni-10Co-8Cr-0.7Mo-10W-5.65Al-1Ti-3Ta-1.5Hf-0.15C. The introduction
of directional solidification led to derivative alloys such as
CM247DS, and single crystal casting led to derivative alloys such
as Rene N5 and CMSX-4 which have compositions, in wt %, given by
Ni-7.5Co-7Cr-1.5Mo-5W-3Re-6.1Al-6.5Ta-0.1Hf-0.05C and
Ni-9Co-6.5Cr-0.6Mo-6.5W-3Re-5.65Al-1Ti-6.5Ta-0.1Hf
respectively.
[0040] The corrosion resistance in this class of alloys is poor due
to their very low Cr levels. Their high Al levels supported by
moderate to high Ta levels, allow them to form continuous Al2O3
scales despite their very low Cr levels. Recently, significant work
has been done to enhance their oxidation resistance and coating
compatibility via clean casting and use of reactive element
effects. Their weldability is poor due to their very high .gamma.'
contents in the 60 to 75 vol % range. Care has been taken to
achieve good alloy stability to avoid reduction of creep strength.
Their creep strengths range from high in alloys such as Mar M-247
to very high in alloys such as Rene N5 and CMSX-4
[0041] Outside these three main classes, there are some specialized
alloys of interest. Haynes-214 has a basic composition in wt %
given by Ni-3Fe-16Cr-4.5Al and also contains small levels of Zr, Si
and Y to provide reactive element effects. It combines good
corrosion resistance, excellent oxidation resistance and high
weldability. The creep strength is comparatively poor because it
contains no strengthening elements.
[0042] Two patent applications have recently been disclosed. These
alloys can to some extent be viewed as derivatives of U-700 in
which Mo has been at least partly replaces by W, and Ti has been at
least partly replaced by Ta:
[0043] Patent application EP 1914327A1 discloses an alloy with at
least 12 wt % Cr, at least 4 wt % Al, at least 7.5 wt % Ta and at
least 3 wt % of the sum of matrix strengthening elements Mo+W+Re.
This implies that it is a high strength alloy, and, consequently we
cannot assume good weldability in the sense described above.
[0044] Patent application WO 2009109521 discloses an alloy with
between 17 and 21 wt % Cr, between 4.0 and 4.7 wt % Al, and
moderate levels of matrix and particle strengthening elements. This
is likely to have most of the properties of the present invention,
but even a moderate loss of Al would reduce an oxidation resistance
which otherwise might have been excellent. A typical embodiment is
STAL18 with a composition, in wt %,
Ni-5Co-18Cr-0.8Mo-2.5W-4.4Al-4.4Ta-0.03C-0.03Zr-0.005B-0.1Hf-0.1Si-0.02Ce
[0045] One typical example of .gamma./.gamma.'' based coatings is
SV-20 with a nominal composition, in wt %, of
Ni-25Cr-2.7Si-5.5A1-0.5Y-1Ta. Because of the high Cr content and
the relatively high .gamma.' content caused by these Al and Si
levels, the .gamma./.gamma.' structure is not stable. Patent
EP1426759 teaches that SV-20 has an equilibrium content of
.about.20 vol % .alpha.-Cr below 900.degree. C., and that thermal
cycling between room temperature and temperatures above 900.degree.
C. will result in solutioning, re-precipitation, and some levels of
non-equilibrium products.
DESCRIPTION OF THE INVENTION
[0046] The objective with the present invention is to provide a
nickel-base .gamma./.gamma.'' superalloy with a unique blend of
moderate cost, excellent oxidation resistance, good corrosion
resistance, moderate strength, good stability, good ductility, good
weldability, good compatibility with aluminide coatings, and a
margin against moderate loss of Al in complex material systems.
[0047] A further objective is its use in hot components such as,
but not restricted to, blades, vanes, heat shields, sealings and
combustor parts in gas turbines. A further objective is its use as
filler alloy for repair welding and/or cladding of such hot
components. A further objective is its use as protective coating
and/or as bond coat in a TBC system on such hot components. A
further objective is its dual use as coating and/or bond coat, and,
for repair and/or cladding on such hot components. A further
objective is its use as intermediate layer between the base alloy
and another coating and/or bond coat on such hot components. A
further objective is its use in polycrystalline, directionally
solidified or single crystal form in such components. A further
objective is its production by processes such as, but not
restricted to, precision casting, laser welding/cladding, hot box
welding, laser sintering, cold spraying, explosion welding and
vacuum plasma spraying. A further objective is its production by
low S processing. A further objective is its use as part of
material systems as exemplified above produced by low S
processing.
[0048] While the alloy disclosed in this invention does not have
the strength necessary for its use as base alloy in highly loaded
areas of hot components, as needed to e.g. avoid excessive
elongation of gas turbine blades, its strength is sufficient for
many hot components, and, for large areas of most hot components,
e.g. on platforms and blade tips. The alloy is therefore useful for
e.g. manufacturing of many hot components and cladding or repair of
most hot components, thanks to the range of other properties
described above.
[0049] The composition of this invention is based on the following
idea: Good corrosion resistance and stability require at most a
moderate level of .gamma.' particles and at most moderate levels of
strengthening elements to allow for a high Cr content without
extensive brittle phase precipitation. This also implies good
ductility and weldability. At the same time, excellent oxidation
resistance require formation of a continuous and very adherent
Al2O3 scale, and this must be achieved despite the restriction on
the .gamma.' content, and therefore on the Al content, and the fact
that there must be at least some strengthening of the .gamma.'
particles which also adds to the .gamma.' content. The solution is
to rely on Ta which is beneficial for the oxidation resistance
rather than the deleterious elements Ti, Nb or V for strengthening
of the .gamma.' particles, and, to utilize clean production
methodology and multiple reactive elements, to make up for a
comparatively moderate Al level.
[0050] The dual use as coating and filler alloy is possible thanks
to the comparatively good ductility associated with the
.gamma./.gamma.' structure. This is likely to be significantly more
difficult with classical .beta. phase based brittle coating alloys.
It could in theory be done with .gamma./.gamma.' coatings
strengthened by noble elements, but the cost would be significantly
higher. It might be possible with .gamma./.gamma.' coatings such as
SV-20, but, we would prefer to avoid the uncertainties associated
with the lack of alloy stability in such coating alloys, especially
as there may be further enrichment of brittle phase forming
elements due to interdiffusion in complex material systems.
DETAILED DESCRIPTION OF THE INVENTION
[0051] Cobalt levels up to 20 wt % are generally utilized in
nickel-base .gamma./.gamma.' superalloys, and it seems reasonable
to allow for the same variation to e.g. allow for embodiments
matched against different base alloys. Fe additions are less
common, but moderate Fe additions are used in e.g. the highly
oxidation resistant alloy Haynes-214.
[0052] It should be clear to those skilled in the art through
comparison with e.g. IN738LC that 17 to 21 wt % Cr should be
sufficient to provide good hot corrosion resistance considering
that the levels of deleterious elements in general, and Mo in
particular, are restricted.
[0053] Moderate strengthening of the matrix elements is provided by
between 0.5 and 3 wt of Mo+W, with a limit to at most 2 wt % Mo to
preserve the good hot corrosion resistance provided by the high Cr
content.
[0054] The oxidation resistance is based on 4.8 to 6 wt % Al.
[0055] While 4.8 wt % Al is low compared to e.g. .beta. phase based
coating alloys and oxidation resistant blade alloys like e.g.
CM247CC, Haynes-214 shows that 4.5 wt % can be sufficient for
excellent cyclic oxidation resistance when supported by high levels
of Cr and an appropriate multiple reactive element recipe. The
lower Al limit is set a bit above the 4.5 wt % used in Haynes-214
to provide some margin against interdiffusion effects when the
alloy is used in material systems as described above. More than 6
wt % Al is not compatible with the Cr levels needed for good hot
corrosion resistance given the requirement on adequate phase
stability.
[0056] Moderate strengthening of the .gamma.' particles is provided
by between 1.5 and 5 wt % Ta.
[0057] C+B levels of up to 0.2 wt % are commonly used for grain
boundary strengthening, and even when the alloy is used in single
crystal form it is advantageous to include at least 0.01 wt % for
low angle boundary tolerance.
[0058] The Zr content should be at least 0.01 wt % to contribute to
multiple reactive element doping, and can be up to 0.2 wt % to e.g.
contribute to grain boundary strengthening.
[0059] The Hf content should be at least 0.05 wt % to contribute to
multiple reactive element doping, and can be up to 1.5 wt % to
contribute to e.g. rumpling resistance of an applied aluminide
coating, or, for grain boundary strengthening when the alloy is
used in directionally solidified form.
[0060] The Si content should be at least 0.05 wt % to contribute to
multiple reactive element doping, but can be up to 1.0 wt % to e.g.
improve the corrosion resistance. A limit on 1 wt % is set to avoid
unstable alloy behavior.
[0061] The sum of rare earths should be at least 0.01 wt % to
provide an appropriate level of retained rare earths after the
production process when said production process has a high degree
of rare earth retention. The sum of rare earths may have to be up
to 0.5 wt % to provide an appropriate level of retained rare earths
after the production process when said production process has a low
degree of rare earth retention.
[0062] The compositions disclosed here relates to the stage in the
production chain prior to the actual application, which could be
e.g. casting of a component from bar stock, vacuum plasma spraying
from powder, or laser welding from powder, except in the case of
cold spraying and similar non-melting processes in which it relates
to the stage before the last melting prior to said cold spraying or
a similar process.
[0063] According to one embodiment of the invention the alloy may
include up to 20 wt % of Co+Fe, between 17 and 21 wt % Cr, between
0.5 and 3 wt % of Mo+W, at most 2 wt % Mo, between 4.8 and 6 wt %
Al, between 1.5 and 5 wt % Ta, between 0.01 and 0.2 wt % of C+B,
between 0.01 and 0.2 wt % Zr, between 0.05 and 1.5 wt % Hf, between
0.05 and 1.0 wt % Si, and between 0.01 and 0.5 wt % of the sum of
rare earths such that at least two rare earths are present, and at
most 0.3 wt % of any rare earth is present.
[0064] Additionally, the alloy may include up to 20 wt % of Co+Fe,
between 17 and 21 wt % Cr, between 0.5 and 3 wt % of Mo+W, at most
2 wt % Mo, between 4.8 and 6 wt % Al, between 1.5 and 5 wt % Ta,
between 0.01 and 0.2 wt % of C+B, between 0.01 and 0.2 wt % Zr,
between 0.05 and 1.5 wt % Hf, between 0.05 and 1.0 wt % Si, and
between 0.01 and 0.5 wt % of the sum of rare earths such that at
least two rare earths are present, and at most 0.3 wt % of any rare
earth is present, and Y present only as an unavoidable
impurity.
[0065] Alternatively, the alloy may include between 2 and 8 wt %
Co, between 17 and 19 wt % Cr, between 1 and 2.2 wt % W, between
4.8 and 5.8 wt % Al, between 2 and 4.5 wt % Ta, between 0.01 and
0.1 wt % of C+B, between 0.02 and 0.08 wt % Zr, between 0.1 and 0.5
wt % Hf, between 0.05 and 0.4 wt % Si, and between 0.02 and 0.2 wt
% of the sum of rare earths of which at least two are present.
[0066] Additionally, the alloy may include between 4.5 and 5.5 wt %
Co, between 18.2 and 19 wt % Cr, between 1.4 and 1.8 wt % W,
between 5.2 and 5.5 wt % Al, between 2.8 and 3.6 wt % Ta, between
0.015 and 0.025 wt % C, between 0.04 and 0.07 wt % Zr, between 0.25
and 0.4 wt % Hf, between 0.07 and 0.13 wt % Si, and between 0.05
and 0.15 wt % (La+Y), at least 0.02 La, at least 0.02 Y.
[0067] In a preferred embodiment called STAL185W1, the alloy may
include about 5.0 wt % Co, about 18.5 wt % Cr, about 1.6 wt % W,
about 5.3 wt % Al, about 3.2 wt % Ta, about 0.02 wt % C, about 0.05
wt % Zr, about 0.3 wt % Hf, about 0.1 wt % Si, about 0.05 wt % Y
and about 0.05 wt % La.
[0068] Alternatively, the alloy may include between 2 and 8 wt %
Co, between 17 and 19 wt % Cr, between 1 and 2.2 wt % W, between
4.8 and 5.8 wt % Al, between 2 and 4.5 wt % Ta, between 0.01 and
0.1 wt % of C+B, between 0.02 and 0.08 wt % Zr, between 0.1 and 0.5
wt % Hf, between 0.05 and 0.4 wt % Si, and between 0.05 and 0.5 wt
% of the sum of rare earths, at most 0.3 of any rare earth, and Y
present only as unavoidable impurity.
[0069] Additionally, the alloy may include between 4.5 and 5.5 wt %
Co, between 18.2 and 19 wt % Cr, between 1.4 and 1.8 wt % W,
between 5.2 and 5.5 wt % Al, between 2.8 and 3.6 wt % Ta, between
0.015 and 0.025 wt % C, between 0.04 and 0.07 wt % Zr, between 0.25
and 0.4 wt % Hf, between 0.07 and 0.13 wt % Si, and between 0.05
and 0.5 wt % of the sum of Ce+Gd, at least 0.02 wt % Ce, at least
0.02 wt % Gd, and at most 0.3 wt % of Gd or Ce.
[0070] In a preferred embodiment called STAL185W2, the alloy may
include about 5 wt % Co, about 18.5 wt % Cr, about 1.6 wt % W,
about 5.3 wt % Al, about 3.2 wt % Ta, about 0.02 wt % C, about 0.05
wt % Zr, about 0.3 wt % Hf, about 0.1 wt % Si, about 0.05 wt % Ce
and about 0.05 wt % Gd.
[0071] Alternatively, the alloy may include between 2 and 8 wt %
Co, between 17 and 19 wt % Cr, between 0.5 and 1.5 wt % Mo, between
4.8 and 5.8 wt % Al, between 2 and 4.5 wt % Ta, between 0.01 and
0.1 wt % of C+B, between 0.02 and 0.08 wt % Zr, between 0.1 and 0.5
wt % Hf, between 0.05 and 0.4 wt % Si, and between 0.02 and 0.2 wt
% of the sum of rare earths of which at least two are present in
the alloy.
[0072] Additionally, the alloy may include, measured in wt %,
between 4.5 and 5.5 wt % Co, between 18.2 and 19 wt % Cr, between
0.8 and 1.2 wt % Mo, between 5.2 and 5.5 wt % Al, between 2.8 and
3.6 wt % Ta, between 0.015 and 0.025 wt % C, between 0.04 and 0.07
wt % Zr, between 0.25 and 0.4 wt % Hf, between 0.07 and 0.13 wt %
Si, and between 0.05 and 0.15 wt % (La+Y), at least 0.02 wt % La,
at least 0.02 wt % Y.
[0073] In a preferred embodiment called STAL185Mo1, the alloy may
include about 5.3 wt % Co, about 18.5 wt % Cr, about 1.0 wt % Mo,
about 5.3 wt % Al, about 3.2 wt % Ta, about 0.02 wt % C, about 0.05
wt % Zr, about 0.3 wt % Hf, about 0.1 wt % Si, about 0.05 wt % Y
and about 0.05 wt % La.
[0074] Alternatively, the ally may include between 2 and 8 wt % Co,
between 17 and 19 wt % Cr, between 0.5 and 1.5 wt % Mo, between 4.8
and 5.8 wt % Al, between 2 and 4.5 wt % Ta, between 0.01 and 0.1 wt
% of C+B, between 0.02 and 0.08 wt % Zr, between 0.1 and 0.5 wt %
Hf, between 0.05 and 0.4 wt % Si, and between 0.02 and 0.5 wt % of
the sum of rare earths of which at least two are present in the
alloy, at most 0.3 wt % of any rare earth, and Y present only as an
unavoidable impurity.
[0075] Additionally, the alloy may include, measured in wt %,
between 4.8 and 5.8 wt % Co, between 18.2 and 19 wt % Cr, between
0.8 and 1.2 wt % Mo, between 5.2 and 5.5 wt % Al, between 2.8 and
3.6 wt % Ta, between 0.015 and 0.025 wt % C, between 0.04 and 0.07
wt % Zr, between 0.25 and 0.4 wt % Hf, between 0.07 and 0.13 wt %
Si, and between 0.05 and 0.5 wt % (Ce+Gd), at least 0.02 wt % Ce,
at least 0.02 wt % Gd, at most 0.3 wt % Ce or Gd.
[0076] In a preferred embodiment called STAL185Mo2, the alloy may
include about 5.3 wt % Co, about 18.5 wt % Cr, about 1.0 wt % Mo,
about 5.3 wt % Al, about 3.2 wt % Ta, about 0.02 wt % C, about 0.05
wt % Zr, about 0.3 wt % Hf, about 0.1 wt % Si, about 0.05 wt % Ce
and about 0.05 wt % Gd.
[0077] Alternatively, for increased hot corrosion resistance, the
alloy may include, measured in wt %, between 2 and 8 wt % Co,
between 20 and 21 wt % Cr, between 0.5 and 1.5 wt % W, between 4.7
and 5.3 wt % Al, between 1.5 and 2.5 wt % Ta, between 0.01 and 0.1
wt % of C+B, between 0.02 and 0.08 wt % Zr, between 0.1 and 0.5 wt
% Hf, between 0.1 and 0.7 wt % Si, and between 0.02 and 0.2 wt % of
the sum of rare earths of which at least two are present in the
alloy.
[0078] Additionally, the alloy may include, measured in wt %,
between 4.5 and 5.5 wt % Co, between 20.2 and 21.8 wt % Cr, between
0.8 and 1.2 wt % W, between 4.8 and 5.2 wt % Al, between 1.8 and
2.2 wt % Ta, between 0.015 and 0.025 wt % C, between 0.04 and 0.07
wt % Zr, between 0.25 and 0.4 wt % Hf, between 0.3 and 0.5 wt % Si,
and between 0.05 and 0.15 wt % (La+Y), at least 0.02 wt % La, at
least 0.02 wt % Y.
[0079] In a preferred embodiment called STAL205W1, the alloy may
include about 5 wt % Co, about 20.5 wt % Cr, about 1 wt % W, about
5 wt % Al, about 2 wt % Ta, about 0.02 wt % C, about 0.05 wt % Zr,
about 0.3 wt % Hf, about 0.4 wt % Si, about 0.05 wt % Y and about
0.05 wt % La.
[0080] Alternatively, the alloy may include between 2 and 8 wt %
Co, between 20 and 21 wt % Cr, between 0.5 and 1.5 wt % W, between
4.7 and 5.3 wt % Al, between 1.5 and 2.5 wt % Ta, between 0.01 and
0.1 wt % of C+B, between 0.02 and 0.08 wt % Zr, between 0.1 and 0.5
wt % Hf, between 0.1 and 0.7 wt % Si, between 0.02 and 0.5 wt % of
the sum of rare earths such that at least two rare earths are
present in the alloy, Y present only as an unavoidable impurity, at
most 0.3 wt % of any rare earth.
[0081] Additionally, the alloy may include, measured in wt %,
between 4.5 and 5.5 wt % Co, between 20.2 and 20.8 wt % Cr, between
0.8 and 1.2 wt % W, between 4.8 and 5.2 wt % Al, between 1.8 and
2.2 wt % Ta, between 0.015 and 0.025 wt % C, between 0.04 and 0.07
wt % Zr, between 0.25 and 0.4 wt % Hf, between 0.3 and 0.5 wt % Si,
and between 0.05 and 0.5 wt % (Ce+Gd), at least 0.02 wt % Ce, and
at least 0.02 wt % Gd, at most 0.3 wt % Ce or Gd.
[0082] In a preferred embodiment called STAL205W2, the alloy may
include about 5 wt % Co, about 20.5 wt % Cr, about 1 wt % W, about
5 wt % Al, about 2 wt % Ta, about 0.02 wt % C, about 0.05 wt % Zr,
about 0.3 wt % Hf, about 0.4 wt % Si, about 0.05 wt % Ce and about
0.05 wt % Gd.
[0083] Using our in-house alloy design system, we calculate a
.gamma.' particle content of 45 vol %, and a Md value of 0.9580 for
STAL185W1 and the figures are similar for STAL185W2, STAL185Mo1 and
STAL185Mo2. For STAL205 we calculate a .gamma.' particle content of
about 41 vol % and a Md value of 0.9563. For comparison, we
calculate a .gamma.' particle content of 43 vol % and a Md value of
0.9818 for IN738LC. All particle contents relate to a reference
temperature of 900 degree Celsius. These values indicate
comparatively good alloy stability and weldability.
[0084] The superalloy according to the invention should be
processed with a clean production process to produce an alloy with
at most 10 ppmw S, preferably less than 2 ppmw S. Additionally,
each part of a complex material system in which the superalloys
according to the invention is included should be processed with a
clean production process which results in at most 10 ppmw S,
preferably less than 2 ppmw S.
[0085] We do not expect any of the embodiments above to be optimal
for all materials systems and conditions of interest within the
scope of the present invention. Mo will e.g. reduce the solvus
temperature whereas W increases it, and while the difference in may
only be a few degree Celsius, this might enable or prevent a heat
treatment aimed at one of the alloys within a complex material
system. The choice of reactive elements may need to be adjusted to
the reactive elements used in other alloys in a complex material
system. Consequently, more than one embodiment is needed, and
further embodiments can be designed to optimize compatibility with
e.g. specific base alloys or for specific corrosive
environments.
COMPARISON WITH STATE-OF-THE-ART
[0086] If we make a restriction to alloys forming Al2O3 scales, the
class of classical alloys similar to IN939, IN738LC and IN792 is
excluded.
[0087] If we further make a restriction to alloys with at least 16
wt % Cr for good corrosion resistance, the class of alloys similar
to CMSX-4 and Rene N5 is excluded.
[0088] If we further make a restriction to alloys with at most 2 wt
% Mo to avoid degradation of the corrosion resistance, the class of
old alloys similar to U-700 is excluded.
[0089] If we further make a restriction to alloys with good
ductility, all .beta. phase based alloys are excluded.
[0090] If we further make a restriction to alloys having at least
two wt % of the sum of matrix strengthening elements like Mo, W and
Re, and, particle strengthening elements like Ti, Ta, Nb and V,
alloys such as Haynes 214 are excluded.
[0091] If we further make a restriction to alloys which do not
contain noble elements or elements such as Re and Ru, the class of
Pt containing .gamma./.gamma.'coating alloys as well as some novel
Re and Re+Ru strengthened coating alloys are excluded.
[0092] If we further make a restriction to alloys with good
weldability, high strength alloys such as the alloy disclosed in EP
1914327A1 are excluded.
[0093] If we further make a restriction to alloys with good alloy
stability, alloys such as SV-20 are excluded.
[0094] Patent application WO 2009109521 is in many ways similar to
the present invention. The difference is that it has less Al than
in the invention, and therefore less margin against loss of Al in a
complex material system before it starts to loose it's initially
good to excellent oxidation resistance.
REFERENCES
[0095] [Barrett] C. A. Barrett A Statistical Analysis of Elevated
Temperature Gravimetric Cyclic Oxidation Data of 36 Ni- and Co-base
Superalloys based on an Oxidation Attack Parameter NASA TM
105934
[0096] [Sarioglu] C. Sarioglu, et al. The Control of Sulfur Content
in Nickel-Base Single Crystal Superalloys and its Effect on Cyclic
Oxidation Resistance Proceedings `Superalloys 1996`
[0097] [Pint 1] B. A. Pint et al Effect of Cycle Frequency on
High-Temperature Oxidation Behavior of Alumina- and Chromia-Forming
Alloys Oxidation of Metals, 58 (1/2), 73-101 (2002)
[0098] [Harris] K. Harris et al. Improved Performance CMSX-4 Alloy
Turbine Blades Utilising PPM Levels of Lanthanum and Yttrium
Proceedings `Materials for Advanced Power Engineering, 5-7 Oct.,
1998, Liege, Belgium`
[0099] [Pint 2] Progress in Understanding the Reactive Element
Effect since the Whittle and Stringer Literature Review `Proc. of
the J. Stringer Symposium, November 2001`
[0100] [Caron 1] P. Caron et al. Improvement of the Cyclic
Oxidation Behaviour of Uncoated Nickel Based Single Crystal
Superalloys Proceedings `Materials for Advanced Power Engineering
1994`
[0101] [Pint 3] B. A. Pint et al. The use of Two Reactive Elements
to Optimize Oxidation Performance of Alumina-Forming Alloys
Materials at High Temperature 20(3) 375-386, 2003
[0102] [Aimone] P. R. Aimone, R. L. McCormick The Effects of
Yttrium and Sulphur on the Oxidation Resistance of an Advanced
Single Crystal Nickel Base Superalloy Proceedings `Superalloys
1992`
[0103] [Goldschmidt] D. Goldschmidt Single-Crystal Blades Proc.
from Materials for Advanced Power Engineering 1994, Part I,
p.661-674
[0104] [Caron 2] P. Caron High Gamma Prime Solvus New Generation
Nickel-Based Superalloys for Single Crystal Turbine Blade
Applications Proceedings `Superalloys 2000`
[0105] [Yeh] Yeh et al. Development of Si-Bearing 4th Generation
Ni-Base Single Crystal Superalloys Proceedings `Superalloys
2008`
[0106] [Subramanian] R. Subramanian Advanced Multi-Functional
Coatings for Land-Based Industrial Gas Turbines Proceedings `ASME
Turbo Expo 2008, Berlin, Germany, GT2008-51532`
[0107] [Zhang] Y. Zhang et al. A Platinum-Enriched
.quadrature.+.quadrature.' Two-Phase Bond Coat on Ni-Based
Superalloys Surface and Coatings Technology. Volume 200. Issues
5-6. 21 Nov. 2005. Pp. 1259-1263
[0108] [Vedula] K. Vedula et al. Alloys based on NiAl for High
Temperature Applications Proceedings `High-Temperature Ordered
Intermetallic Alloys, Vol. 39 Materials Research Society Symposia
Proceedings, 1984`
[0109] [Tolpygo] V. K. Tolpygo Effect of Hf, Y and C in the
underlying superalloy on the rumpling of diffusion aluminide
coatings Acta Materialia, v 56, n 3, February, 2008, p 489-499
[0110] [Fujita] Y. Fujita et al Laser Epitaxial Cladding of Ni-Base
Single Crystal Superalloy Materials Science Forum, Vols. 580-582
(2008), pp. 67-70
* * * * *