U.S. patent application number 09/735767 was filed with the patent office on 2002-08-08 for niobium-silicide based composites resistant to high temperature oxidation.
This patent application is currently assigned to General Electric Company. Invention is credited to Bewlay, Bernard Patrick, Jackson, Melvin Robert, Zhao, Ji-Cheng.
Application Number | 20020104594 09/735767 |
Document ID | / |
Family ID | 24957097 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020104594 |
Kind Code |
A1 |
Jackson, Melvin Robert ; et
al. |
August 8, 2002 |
Niobium-silicide based composites resistant to high temperature
oxidation
Abstract
A niobium-silicide refractory metal intermetallic composite
adapted for use in a turbine component. The niobium-silicide
refractory metal intermetallic composite comprises: between about
19 atomic percent and about 24 atomic percent titanium; between
about 1 atomic percent and about 5 atomic percent hafnium; up to
about 7 atomic percent tantalum; between about 16 atomic percent
and about 22 atomic percent silicon; up to about 6 atomic percent
germanium; up to about 5 atomic percent boron; between about 7
atomic percent and about 14 atomic percent chromium; up to about 4
atomic percent iron; up to about 4 atomic percent aluminum; up to
about 3 atomic percent tin; up to about 3 atomic percent tungsten;
up to about 3 atomic percent molybdenum; and a balance of niobium.
A ratio of the sum of atomic percentages of niobium and tantalum
present in said niobium silicide refractory intermetallic composite
to the sum of atomic percentages of titanium and of hafnium present
in said niobium silicide refractory intermetallic composite has a
value between about 1.4 and about 2.2. Chromium and iron together
comprise between about 7 atomic percent and about 15 atomic percent
of the niobium silicide refractory intermetallic composite, and
silicon, germanium, and boron together comprise between about 16
atomic percent and about 22 atomic percent of the niobium silicide
refractory intermetallic composite.
Inventors: |
Jackson, Melvin Robert;
(Niskayuna, NY) ; Bewlay, Bernard Patrick;
(Schenectady, NY) ; Zhao, Ji-Cheng; (Niskayuna,
NY) |
Correspondence
Address: |
General Electric Company
CRD Patent Docket Rm 4A59
P.O. Box 8, Bldg. K-1 - Salamone
Schenectady
NY
12301
US
|
Assignee: |
General Electric Company
|
Family ID: |
24957097 |
Appl. No.: |
09/735767 |
Filed: |
December 13, 2000 |
Current U.S.
Class: |
148/422 |
Current CPC
Class: |
C22C 27/02 20130101;
Y02T 50/672 20130101; F05D 2200/11 20130101; F01D 5/28 20130101;
Y02T 50/60 20130101; C22C 29/18 20130101 |
Class at
Publication: |
148/422 |
International
Class: |
C22C 027/02 |
Goverment Interests
[0001] This invention was made with Government support under
Contract No. F33615-98-C-5215, awarded by the United States Air
Force, Department of Defense, and the United States Government
therefore has certain rights in the invention.
Claims
What is claimed is:
1. A turbine component formed from a niobium silicide refractory
intermetallic composite, said niobium silicide refractory
intermetallic composite comprising: between about 19 atomic percent
and about 24 atomic percent titanium; between about 1 atomic
percent and about 5 atomic percent hafnium; between about 16 atomic
percent and about 22 atomic percent silicon; between about 7 atomic
percent and about 14 atomic percent chromium; and a balance of
niobium.
2. The turbine component of claim 1, further comprising tantalum,
germanium, boron, iron, aluminum, tin, tungsten, and
molybdenum.
3. The turbine component of claim 2, wherein a ratio of a sum of
atomic percentages of niobium and tantalum present in said niobium
silicide refractory intermetallic composite to a sum of atomic
percentages of titanium and hafnium present in said niobium
silicide refractory intermetallic composite has a value of between
about 1.4 and about 2.2, wherein chromium and iron together
comprise between about 7 atomic percent and about 15 atomic percent
of said niobium silicide refractory intermetallic composite; and
wherein silicon, germanium, and boron together comprise between
about 16 atomic percent and about 22 atomic percent of said niobium
silicide refractory intermetallic composite.
4. The turbine component of claim 3, wherein said turbine component
is a component selected from the group consisting of a bucket, a
blade, a rotor, and a nozzle.
5. The turbine component of claim 3, wherein said turbine component
is a component is a turbine selected from the group consisting of
land-based turbines, marine turbines, aeronautical turbines, and
power generation turbines.
6. A niobium silicide refractory intermetallic composite adapted
for use in a turbine component, said niobium silicide refractory
intermetallic composite comprising: between about 19 atomic percent
and about 24 atomic percent titanium; between about 1 atomic
percent and about 5 atomic percent hafnium; up to about 7 atomic
percent tantalum; between about 16 atomic percent and about 22
atomic percent silicon; up to about 6 atomic percent germanium; up
to about 5 atomic percent boron; between about 7 atomic percent and
about 14 atomic percent chromium; up to about 4 atomic percent
iron; up to about 4 atomic percent aluminum; up to about 3 atomic
percent tin; up to about 3 atomic percent tungsten; up to about 3
atomic percent molybdenum; and a balance of niobium, wherein a
ratio of a sum of atomic percentages of niobium and tantalum
present in said niobium silicide refractory intermetallic composite
to a sum of atomic percentages of titanium and hafnium present in
said niobium silicide refractory intermetallic composite has a
value between about 1.4 and about 2.2, wherein chromium and iron
together comprise between about 7 atomic percent and about 15
atomic percent of said niobium silicide refractory intermetallic
composite; and wherein silicon, germanium, and boron together
comprise between about 16 atomic percent and about 22 atomic
percent of said niobium silicide refractory intermetallic
composite.
7. The niobium silicide refractory intermetallic composite of claim
6, wherein said niobium silicide refractory intermetallic composite
includes at least one metallic phase, said metallic phase
comprising at least 30 volume percent of said niobium silicide
refractory intermetallic composite.
8. The niobium silicide refractory intermetallic composite of claim
6, wherein said niobium silicide refractory intermetallic composite
includes at least one Laves phase, said Laves phase comprising up
to about 20 volume percent of said niobium silicide refractory
intermetallic composite.
9. The niobium silicide refractory intermetallic composite of claim
6, wherein said niobium silicide refractory intermetallic composite
is resistant to oxidation at temperatures in the range from between
about 1800.degree. F. to about 2200.degree. F.
10. The niobium silicide refractory intermetallic composite of
claim 9, wherein a radius of a cylindrical sample formed from said
niobium silicide refractory intermetallic composite changes less
than about 6 mils when heated to about 2200.degree. F. for 100
hours.
11. A turbine component formed from a niobium silicide refractory
intermetallic composite, said niobium silicide refractory
intermetallic composite comprising: between about 19 atomic percent
and about 24 atomic percent titanium; between about 1 atomic
percent and about 5 atomic percent hafnium; up to about 7 atomic
percent tantalum; between about 16 atomic percent and about 22
atomic percent silicon; up to about 6 atomic percent germanium; up
to about 5 atomic percent boron; between about 7 atomic percent and
about 14 atomic percent chromium; up to about 4 atomic percent
iron; up to about 4 atomic percent aluminum; up to about 3 atomic
percent tin; up to about 3 atomic percent tungsten; up to about 3
atomic percent molybdenum; and a balance of niobium.
12. The turbine component of claim 11, wherein a ratio of a sum of
atomic percentages of niobium and tantalum present in said niobium
silicide refractory intermetallic composite to a sum of atomic
percentages of titanium and hafnium present in said niobium
silicide refractory intermetallic composite has a value between
about 1.4 and about 2.2; chromium and iron together comprise
between about 7 atomic percent and about 15 atomic percent of said
niobium silicide refractory intermetallic composite; and silicon,
germanium, and boron together comprise between about 16 atomic
percent and about 22 atomic percent of said niobium silicide
refractory intermetallic composite.
13. The turbine component of claim 12, wherein said turbine
component is a component selected from the group consisting of a
bucket, a blade, a rotor, and a nozzle.
14. The turbine component of claim 12, wherein said turbine
component is a turbine component in a turbine selected from the
group consisting of land-based turbines, marine turbines,
aeronautical turbines, and power generation turbines.
15. The turbine component of claim 12, wherein said niobium
silicide refractory intermetallic composite includes at least one
metallic phase, said metallic phase comprising at least 30 volume
percent of said niobium silicide refractory intermetallic
composite.
16. The turbine component of claim 12, wherein said niobium
silicide refractory intermetallic composite includes at least one
Laves phase, said Laves phase comprising up to about 20 volume
percent of said niobium silicide refractory intermetallic
composite.
17. The turbine component of claim 12, wherein said niobium
silicide refractory intermetallic composite is resistant to
oxidation at temperatures in the range from between about
1800.degree. F. to about 2200.degree. F.
18. The turbine component of claim 17, wherein a radius of a
cylindrical sample formed from said niobium silicide refractory
intermetallic composite changes less than about 6 mils due to
oxidation of said sample when said sample is heated to about
2200.degree. F. for 100 hours.
Description
BACKGROUND OF THE INVENTION
[0002] The invention relates to Niobium (Nb)-silicide based
composite compositions. In particular, the invention relates to
Nb-silicide based composite compositions having properties that
permit the Nb-silicide based composite compositions to find
applications in turbine components.
[0003] Turbines and their components (hereinafter "turbine
components"), such as, but not limited to, aeronautical turbines,
land-based, turbines, marine-based turbines, and the like, have
typically been formed from nickel (Ni)-based materials, which are
often referred to as Ni-based superalloys. Turbine components
formed from these Ni-based superalloys exhibit desirable chemical
and physical properties under the high temperature, high stress,
and high-pressure conditions generally encountered during turbine
operation. For example, turbine components, such as an airfoil, in
modem jet engines can reach temperatures as high as about
1,150.degree. C., which is about 85% of the melting temperatures
(T.sub.m) of most Ni-based superalloys.
[0004] Because Ni-based superalloys have provided the level of
performance desired in such applications, the development of such
Ni-based superalloys has been widely explored. Consequently, the
field has matured and few significant improvements have been
realized in this area in recent years. In the meantime, efforts
have been made to develop alternative turbine component materials.
These alternate materials include niobium (Nb)-based refractory
metal intermetallic composites (hereinafter "RMIC"s). Most RMICs
have melting temperatures of about 1700.degree. C. If RMICs can be
used at about 80% of their melting temperatures, they will have
potential use in applications in which the temperature exceeds the
current service limit of Ni-based superalloys.
[0005] RMICs comprising at least niobium (Nb), silicon (Si),
titanium (Ti), hafnium (Hf), chromium (Cr), and aluminum (Al) have
been proposed for turbine component applications. These
silicide-based RMICs exhibit a high temperature capability that
exceeds that of current Ni-based superalloys. Exemplary
silicide-based RMICs are set forth in U.S. Pat. No. 5,932,033, to
M. R. Jackson and B. P. Bewlay, entitled "Silicide Composite with
Nb-Based Metallic Phase and Si-Modified Laves-Type Phase" and U.S.
Pat. No. 5,942,055, to Jackson and Bewlay, entitled "Silicide
Composite with Nb-Based Metallic Phase and Si-Modified Laves-Type
Phase".
[0006] Some known Nb-silicide based composites--including
silicide-based RMIC materials--have adequate oxidation resistance
characteristics for turbine component applications. These materials
have compositions within the following approximate ranges: 20-25
atomic percent titanium (Ti), 1-5 atomic percent hafnium (Hf), and
0-2 atomic percent tantalum (Ta), where the concentration ratio
(Nb+Ta):(Ti+Hf) has a value of about 1.4; 12-21 atomic percent
silicon (Si), 2-6 atomic percent germanium (Ge), and 2-5 atomic
percent boron (B), where the sum of the Si, B, and Ge
concentrations is in the range between 22 atomic percent and 25
atomic percent; 12-14 atomic percent chromium (Cr) and 0-4 atomic
percent iron (Fe), where the sum of the Fe and Cr concentrations is
between 12 atomic percent and 18 atomic percent; 0-4 atomic percent
aluminum (Al); 0-3 atomic percent tin (Sn); and 0-3 atomic percent
tungsten (W). Other known Nb-based silicide composites--including
silicide-based RMIC materials--possess adequate creep-rupture
resistance for turbine component applications. These materials have
compositions within the following approximate ranges: 16-20 atomic
percent Ti, 1-5 atomic percent Hf, and 0-7 atomic percent Ta, where
the concentration ratio (Nb+Ta):(Ti+Hf) has a value of about 2.25;
17-19 atomic percent Si, 0-6 atomic percent Ge, and 0-5 atomic
percent B, where the sum of the Si, B, and Ge concentrations is in
the range between 17 atomic percent and 21 atomic percent; 6-10
atomic percent Cr and 0-4 atomic percent Fe, where the sum of the
Fe and Cr concentrations is in the range between 6 atomic percent
and 12 atomic percent; 0-4 atomic percent Al; 0-3 atomic percent
Sn; 0-3 atomic percent W; and 0-3 atomic percent Mo. In addition,
some known Nb-silicide based composites--including silicide-based
RMIC materials--have adequate fracture toughness for turbine
component applications. Such materials contain greater than or
equal to about 30 volume percent of metallic phases present in such
components.
[0007] Although the above Nb-silicide based composites and
silicide-based RMIC materials possess beneficial mechanical and
chemical properties, they do not adequately balance oxidation
resistance properties with toughness and creep resistance
properties. Thus, a single silicide-based RMIC alloy material
composition that can provide adequate creep, oxidation resistance,
and toughness for turbine component applications is currently not
available.
[0008] While the oxidation performance and creep-rupture resistance
for turbine component applications of known RMICs are desirable,
these materials and their properties may still be further improved
for turbine component applications. For example, the chemistries
and compositions of the RMIC material may be modified to enhance
oxidation resistance for applications that subject the turbine
component to high stresses at temperatures ranging from about
1300.degree. F. to about 1700.degree. F. (about 700.degree. C. to
about 925.degree. C.) over extended periods of time.
[0009] Therefore, what is needed is a material having a
composition, chemistry, and properties that are suitable for
various applications such as, but not limited to, turbine
components, in which high stresses at elevated temperatures are
encountered over long periods of time. More particularly, what is
needed is a Nb-silicide based RMIC having improved oxidation
resistance and creep resistance for use in turbine component
applications in which high stresses at elevated temperatures are
encountered over long periods of time.
SUMMARY OF THE INVENTION
[0010] Accordingly, one aspect of the present invention is to
provide a turbine component formed from a niobium silicide
refractory intermetallic composite, the niobium silicide refractory
intermetallic composite comprising: between about 19 atomic percent
and about 24 atomic percent titanium; between about 1 atomic
percent and about 5 atomic percent hafnium; between about 16 atomic
percent and about 22 atomic percent silicon; between about 7 atomic
percent and about 14 atomic percent chromium; and a balance of
niobium.
[0011] A second aspect of the invention is to provide a niobium
silicide refractory intermetallic composite adapted for use in a
turbine component. The niobium silicide refractory intermetallic
composite comprises: between about 19 atomic percent and about 24
atomic percent titanium; between about 1 atomic percent and about 5
atomic percent hafnium; up to about 7 atomic percent tantalum;
between about 16 atomic percent and about 22 atomic percent
silicon; up to about 6 atomic percent germanium; up to about 5
atomic percent boron; between about 7 atomic percent and about 14
atomic percent chromium; up to about 4 atomic percent iron; up to
about 4 atomic percent aluminum; up to about 3 atomic percent tin;
up to about 3 atomic percent tungsten; up to about 3 atomic percent
molybdenum; and a balance of niobium. A ratio of a sum of atomic
percentages of niobium and tantalum present in the niobium silicide
refractory intermetallic composite to a sum of atomic percentages
of titanium and hafnium present in the niobium silicide refractory
intermetallic composite has a value of between about 1.4 and about
2.2 (i.e., 1.4<(Nb+Ta):(Ti+Hf)<2.2). Chromium and iron
together comprise between about 7 atomic percent and about 15
atomic percent of the niobium silicide refractory intermetallic
composite, and silicon, germanium, and boron together comprise
between about 16 atomic percent and about 22 atomic percent of the
niobium silicide refractory intermetallic composite.
[0012] A third aspect of the invention is to provide a turbine
component formed from a niobium silicide refractory intermetallic
composite, the niobium silicide refractory intermetallic composite
comprising: between about 19 atomic percent and about 24 atomic
percent titanium; between about 1 atomic percent and about 5 atomic
percent hafnium; up to about 7 atomic percent tantalum; between
about 16 atomic percent and about 22 atomic percent silicon; up to
about 6 atomic percent germanium; up to about 5 atomic percent
boron; between about 7 atomic percent and about 14 atomic percent
chromium; up to about 4 atomic percent iron; up to about 4 atomic
percent aluminum; up to about 3 atomic percent tin; up to about 3
atomic percent tungsten; up to about 3 atomic percent molybdenum;
and a balance of niobium.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The niobium (Nb)-silicide based alloy composite of the
present invention comprises Nb-silicide refractory metal
intermetallic composites (hereinafter "RMICs") having compositions
and chemical properties that provide the necessary balance among
oxidation characteristics, creep resistance, and toughness. The
Nb-silicide RMICs comprise between about 19 atomic percent and
about 24 atomic percent titanium; between about 1 atomic percent
and about 5 atomic percent hafnium; up to about 7 atomic percent
tantalum; between about 16 atomic percent and about 22 atomic
percent silicon; up to about 6 atomic percent germanium; up to
about 5 atomic percent boron; between about 7 atomic percent and
about 14 atomic percent chromium; up to about 4 atomic percent
iron; up to about 4 atomic percent aluminum; up to about 3 atomic
percent tin; up to about 3 atomic percent tungsten; up to about 3
atomic percent molybdenum; and a balance of niobium, wherein a
ratio of a sum atomic percentages of niobium and tantalum present
in the niobium silicide refractory intermetallic composite to a sum
of atomic percentages of titanium hafnium present in the niobium
silicide refractory intermetallic composite has a value of between
about 1.4 and about 2.2 (i.e., 1.4<(Nb+Ta):(Ti+Hf)<2.2),
wherein chromium and iron together comprise between about 7 atomic
percent and about 15 atomic percent of the niobium silicide
refractory intermetallic composite; and wherein silicon, germanium,
and boron together comprise between about 16 atomic percent and
about 22 atomic percent of the niobium silicide refractory
intermetallic composite. The atomic percent given for each element
are approximate unless otherwise specified.
[0014] The Nb-silicide based RMICs of the present invention exhibit
oxidation and rupture resistance characteristics which are provided
by the addition of Si, Cr and Al, and lesser amounts of Ti, Hf, and
B. The Nb-silicide RMICs disclosed in the present invention can be
used to form turbine components such as, but not limited to,
buckets, blades, rotors, nozzles, and the like for applications in
land-based turbines, marine turbines, aeronautical turbines, power
generation turbines, and the like.
[0015] Formation of a hexagonal M.sub.5Si.sub.3 silicide (where M
is titanium, hafnium, or combinations thereof), which has been
found to be detrimental to creep resistance, is aided when the
(Nb+Ta):(Ti+Hf) ratio of the Nb-silicide RMIC has a value of less
than 1.5. Values for the ratio (Nb+Ta):(Ti+Hf) are reported in
Table 1. Samples A2, A4, A21, A22, A24, A25, and A26, which
represent the preferred Nb-silicide RMIC compositions of the
present invention, exhibited radius changes due to oxidation of
less than or equal to about 5.5 mils (about 140 microns) and less
than or equal about 32 mils (about 810 microns) after 100 hours at
temperatures in the range from about 1800.degree. F. to about
2200.degree. F., and after about 73 hours at a temperature of about
2400.degree. F., respectively. A weight change occurring with
little change in radius in a refractory material alloy is
indicative of oxidation attack at the ends of the sample. This type
of oxidation leads to rounding of the sample edges, even though the
degree of radial attack on the pin is small.
[0016] The Nb-silicide RMICs of the present invention include
constituents that reduce the oxide growth rate in Nb-silicide RMICs
containing additional metallic and Laves-type phases. In the
present invention, Laves-type phases preferably comprise up to
about 20 volume percent of the Nb-silicide RMICs. Metallic phases
preferably comprise at least 25 volume percent of the Nb-silicide
RMICs. Maintaining a relatively high level of titanium in the
Nb-silicide RMIC improves material performance. Increasing the
titanium concentration, however, tends to increase creep rate.
Thus, the composition of the Nb-based RMICs must be adjusted to
balance desired creep rupture requirements with the reduced
oxidation rate.
EXAMPLE 1
[0017] A series of Nb-silicide RMIC samples, as embodied by the
present invention, were prepared by arc casting tapered disks about
0.8" thick and with a diameter tapering from about 2.5" to about
3". Pins having a diameter of about a 0.12" and a length of about a
1.25" were prepared by conventional machining processes, such as
EDM and centerless grinding. The pins were then subjected to 100
hours exposure (hot time) with a total test exposure of about 117
hours in one-hour cycles. The heating cycles were followed with
cooling to room temperature after each hour of hot time at either
1800.degree. F. (982.degree. C.), 2000.degree. F. (1095.degree.
C.), 2200.degree. F. (1205.degree. C.), or 2400.degree. F.
(1315.degree. C.).
[0018] Each Nb-silicide RMIC sample was weighed before testing,
periodically during the tests, and after testing to determine an
average weight change per unit area as a function of exposure time.
Each sample was then cut at its approximate mid-section and
prepared for metallographic evaluation of changes in diameter and
in microstructure. Evaluation of the samples was not necessarily
limited to a metallographic examination.
[0019] Results of the weight change (listed in columns labeled
`wt`) and metallographic measurements of diameter changes (listed
in columns labeled `mil`) obtained at completion of the test are
listed as a function of alloy composition for a series of
Nb-silicide RMICs in Table 1. The atomic percentages listed in
Table 1 are approximate. Values for the (Nb+Ta):(Ti+Hf) ratio are
also provided.
1TABLE 1 CYCLIC OXIDATION RESULTS FOR ARC CAST COMPOSITE ALLOYS
Sam- 1800 1800 2000 2000 2200 2400 2400 2400 2400 ple ratio Nb Ti
Hf Si Al Cr B Ta Ge Mo W Sn Fe wt mil wt mil wt mil wt hours mil A1
1.5 41.0 23 0 4 17 2 13 -193 -12 -255 -4 -216 -3 -455 73 -39 A2 1.5
38.5 21.5 4 17 2 13 4 -55 -5 -25 -2.5 -48 -3.5 -284 100 -16 A3 1.5
35.0 23 0 4 17 2 13 6 -361 -21 -147 0 -143 -3 -360 31 -22 A4 1.5
41.0 23 0 4 12 2 13 5 -28 -3 7 0 -38 -4 -321 100 -28 A5 1.5 40.5
22.5 4 17 2 13 1 -61 -4 -132 -7 -222 -13 5 -405 52 xx A6 1.5 40.5
22.5 4 17 2 13 1 -201 -3 -207 -9 -105 -3 -423 3 -35 A7 1.5 40.0
22.5 4 17 2 13 1.5 -151 -7 -439 -32 -88 -2.5 -350 73 -22 A8 1.5
40.0 22.5 4 17 2 13 2 No No -37 -2 -441 73 -31 test test A9 1.5
42.5 23.5 4 17 13 -95 -6 -153 -6.5 -129 -6 -495 73 -38 A10 1.5 42.5
25.5 2 17 13 -260 -17 -161 -5 -111 -6 -489 73 -52 A11 2.5 48.5 15.5
4 17 2 13 dust -60 dust -60 -420 -28 -470 31 -37 A12 2.5 46.0 14.0
4 17 2 13 4 -372 -60 -210 -13 -302 -23.5 -322 31 -26 A13 2.5 42.5
15.5 4 17 2 13 6 xx xx xx xx No No xx xx xx test test A14 2.5 48.5
15.5 4 12 2 13 5 -39 -3 -22 -2 -148 -13 5 -460 73 -30 A15 2.5 48.0
15.0 4 17 2 13 1 -475 -40 No (-492) -60 -393 31 -31 test A16 2.5
48.0 15.0 4 17 2 13 1 dust -60 dust -60 -482 -37 -387 31 -25 A17
2.5 47.5 15.0 4 17 2 13 1.5 -381 -27 dust -60 (-484) -60 -482 73
-40 A18 2.5 47.5 15.0 4 17 2 13 2 dust -60 -372 -22 -275 -16 -397
31 -32 A19 2.5 50.0 16.0 4 17 13 dust -60 dust -60 (-433) -60 -518
31 -36 A20 2.5 50.0 18.0 2 17 13 dust -60 dust -60 -347 -14.5 -445
31 -33 A21 1.5 32.5 23.0 2 17 13 4 6 1 2 -35 -3 -20 -3 -102 -5.5
-222 100 -14 A22 1.5 29.5 21.0 2 17 13 4 6 5 1 1.5 7 -5 10 0 -17 -1
-175 100 xx A23 1.5 40.5 22.5 4 20 13 -189 -11 -195 -20 -114 -7
-498 73 -50 A24 1.5 40.5 22.5 4 15 13 5 -17 -5 10 0 17 -0.5 -334 73
-12 A25 1.5 39 24 2 15 2 10 5 3 9 -1 14 -1 A26 2.0 43.3 19.7 2 15 2
10 5 3 -12 -1 18 -4
[0020] As can be seen from Table 1, the addition of boron and iron
to the Nb-silicide RMICs of the present invention provide improves
oxidation resistance over the temperature range of the tests. In
addition, partial substitution of germanium for silicon in the
Nb-silicide RMICs also improves oxidation resistance over the
temperature range tested. Oxidation resistance of the Nb-silicide
RMICs of the present invention over the temperature range tested is
not degraded by the addition of either about 6 atomic percent
tantalum or about 1 atomic percent tungsten. The presence of about
1 atomic percent molybdenum had a negative effect on the oxidation
resistance of the Nb-silicide RMICs, and additions of about 1.5
atomic percent tin had a neutral effect on the high temperature
oxidation resistance of the Nb-silicide RMICs.
[0021] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations or improvements therein may be made by those
skilled in the art, and are within the scope of the invention.
* * * * *