U.S. patent application number 10/283066 was filed with the patent office on 2003-03-20 for method of adding boron to a heavy metal containing titanium aluminide alloy and a heavy metal containing titanium aluminide alloy.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Blenkinsop, Paul A., Godfrey, Alastair B..
Application Number | 20030051780 10/283066 |
Document ID | / |
Family ID | 10856426 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030051780 |
Kind Code |
A1 |
Blenkinsop, Paul A. ; et
al. |
March 20, 2003 |
Method of adding boron to a heavy metal containing titanium
aluminide alloy and a heavy metal containing titanium aluminide
alloy
Abstract
A method of adding boron to a tungsten, or tantalum, containing
titanium aluminide alloy to form a boride dispersion in the
tungsten, or tantalum, containing titanium aluminide. A molten
tungsten, or tantalum, containing titanium aluminide alloy is
formed and tungsten, or tantalum, boride is added to the molten
tungsten, or tantalum, containing titanium aluminide alloy to form
a molten mixture. The molten mixture is cooled and solidified to
form a tungsten, or tantalum, containing titanium aluminide alloy
having a uniform dispersion of tungsten, or tantalum, boride
particles substantially without the formation of clusters of
tungsten, or tantalum, boride. The titanium aluminide alloy
comprises between 0.5 at % and 2.0 at % boron.
Inventors: |
Blenkinsop, Paul A.; (Sutton
Coldfield, GB) ; Godfrey, Alastair B.; (Birmingham,
GB) |
Correspondence
Address: |
MANELLI DENISON & SELTER
2000 M STREET NW SUITE 700
WASHINGTON
DC
20036-3307
US
|
Assignee: |
ROLLS-ROYCE PLC
|
Family ID: |
10856426 |
Appl. No.: |
10/283066 |
Filed: |
October 30, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10283066 |
Oct 30, 2002 |
|
|
|
09608228 |
Jun 30, 2000 |
|
|
|
6488073 |
|
|
|
|
Current U.S.
Class: |
148/538 ;
148/421 |
Current CPC
Class: |
B22F 2998/00 20130101;
C22C 1/1036 20130101; C22C 32/0073 20130101; B22F 3/1003 20130101;
C22C 14/00 20130101; B22F 2998/00 20130101 |
Class at
Publication: |
148/538 ;
148/421 |
International
Class: |
C22C 014/00; C22F
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 1999 |
GB |
9915394.2 |
Nov 2, 2001 |
GB |
0126371.4 |
Claims
We claim:
1. A method of adding boron to a heavy metal containing titanium
aluminide alloy to form a boride dispersion in the heavy metal
containing titanium aluminide, comprising: (a) forming molten heavy
metal containing titanium aluminide alloy, (b) adding heavy metal
boride particles to the molten heavy metal containing titanium
aluminide alloy to form a molten mixture, the heavy metal boride
particles having the same form as undesirable heavy metal boride
precipitate clusters, (c) cooling and solidifying the molten
mixture to form a heavy metal containing titanium aluminide alloy
having a uniform dispersion of heavy metal boride particles
substantially without the formation of heavy metal boride
precipitate clusters.
2. A method as claimed in claim 1 wherein step (a) comprises
forming molten tungsten containing titanium aluminide alloy, (b)
adding tungsten boride to the molten tungsten containing titanium
aluminide alloy to form a molten mixture, the tungsten boride
particles having the same form as undesirable tungsten boride
precipitate clusters, (c) cooling and solidifying the molten
mixture to form a tungsten containing titanium aluminide alloy
having a dispersion of tungsten boride particles substantially
without the formation of tungsten boride precipitate clusters.
3. A method as claimed in claim 1 wherein step (a) comprises
forming molten tantalum containing titanium aluminide alloy, (b)
adding tantalum boride to the molten tantalum containing titanium
aluminide alloy to form a molten mixture, the tantalum boride
particles having the same form as undesirable tantalum boride
precipitate clusters, (c) cooling and solidifying the molten
mixture to form a tantalum containing titanium aluminide alloy
having a dispersion of tantalum boride particles substantially
without the formation of tantalum boride precipitate clusters.
4. A method as claimed in claim 1, wherein the titanium aluminide
alloy comprises up to 2.0 at % boron.
5. A method as claimed in claim 4 wherein the titanium aluminide
alloy comprises up to 1.0 at % boron.
6. A method as claimed in claim 1 wherein the titanium aluminide
alloy comprises more than 0.5 at % boron.
7. A method as claimed in claim 1 wherein the heavy metal boride
particles added have a size of 1 to 5 .mu.m.
8. A method as claimed in claim 1 wherein the density of heavy
metal boride precipitate clusters is up to 3 cm.sup.-2.
9. A method as claimed in claim 8 wherein the density of heavy
metal boride precipitate clusters is less than 2 cm.sup.-2.
10. A method as claimed in claim 1 wherein the heavy metal boride
precipitate clusters have a maximum size of 150 .mu.m.
11. A method as claimed in claim 1 wherein the heavy metal boride
precipitate clusters have a maximum size of 100 .mu.m.
12. A method as claimed in claim 1 wherein the titanium aluminide
alloy comprises a gamma titanium aluminide.
13. A method as claimed in claim 12 wherein the gamma titanium
aluminide alloy preferably comprises 44 to 52 at % aluminum, one or
more of tungsten and tantalum each in an amount of 0.05 to 8.0 at
%, up to 2.0 at % boron and balance titanium plus incidental
impurities.
14. A method as claimed in claim 13 wherein the gamma titanium
aluminide additionally comprises up to 3 at % chromium, up to 6 at
% niobium, up to 2 at % manganese.
15. A method as claimed in claim 13 wherein the gamma titanium
aluminide alloy comprises 45 to 47 at % aluminum, 2 to 6 at %
niobium, 0.25 to 2 at % tungsten and the balance titanium plus
incidental impurities.
16. A method as claimed in claim 15 wherein the gamma titanium
aluminide comprises 45 at % aluminum, 5 at % niobium and 1 at %
tungsten.
17. A method as claimed in claim 16 wherein the gamma titanium
aluminide alloy comprises 1 to 2 at % chromium and/or 1 to 2 at %
manganese.
18. A method as claimed in claim 1 wherein the method comprises
forming the titanium aluminide alloy into a turbine blade, a
turbine vane, a compressor blade, or a compressor vane.
19. A method as claimed in claim 18 wherein the titanium aluminide
alloy is cast or forged.
20. A heavy metal containing titanium aluminide alloy, the titanium
aluminide containing heavy metal boride particles substantially
without heavy metal boride precipitate clusters, the heavy metal
boride particles having the same form as the undesirable heavy
metal boride precipitate clusters, and the titanium aluminide alloy
comprises up to 2.0 at % boron.
21. A heavy metal containing titanium aluminide alloy as claimed in
claim 20 wherein the density of the heavy metal boride precipitate
clusters is less than 2 cm.sup.-2.
22. A heavy metal containing titanium aluminide alloy as claimed in
claim 20 wherein the heavy metal boride precipitate clusters have
maximum size of 100 .mu.m.
23. A heavy metal containing titanium aluminide alloy as claimed in
claim 20 wherein the heavy metal is tungsten and the heavy metal
boride is tungsten boride.
24. A heavy metal containing titanium aluminide alloy as claimed in
claim 20 wherein the heavy metal is tantalum and the heavy metal
boride is tantalum boride.
25. A heavy metal containing titanium aluminide alloy as claimed in
claim 20 wherein the titanium aluminide alloy comprises a gamma
titanium aluminide.
26. A heavy metal containing titanium aluminide as claimed in claim
25 wherein the gamma titanium aluminide alloy preferably comprises
44 to 52 at % aluminum, one or more of tungsten and tantalum each
in an amount of 0.05 to 8.0 at %, up to 2.0 at % boron and balance
titanium plus incidental impurities.
27. A heavy metal containing titanium aluminide as claimed in claim
26 wherein the gamma titanium aluminide additionally comprises up
to 3 at % chromium, up to 6 at % niobium, up to 2 at %
manganese.
28. A heavy metal containing titanium aluminide as claimed in claim
27 wherein the gamma titanium aluminide alloy comprises 45 to 47 at
% aluminum, 2 to 6 at % niobium, 0.25 to 2 at % tungsten and the
balance titanium plus incidental impurities.
29. A heavy metal containing titanium aluminide as claimed in claim
28 wherein the gamma titanium aluminide comprises 45 at % aluminum,
5 at % niobium and 1 at % tungsten.
30. A heavy metal containing titanium aluminide as claimed in claim
27 wherein the gamma titanium aluminide alloy comprises 1 to 2 at %
chromium and/or 1 to 2 at % manganese.
31. A heavy metal containing titanium aluminide alloy as claimed in
claims 20 wherein the titanium aluminide alloy is in the shape of a
turbine blade, a turbine vane, a compressor blade, or a compressor
vane.
Description
[0001] The present invention relates to a titanium aluminide alloy,
particularly to titanium aluminide alloys comprising heavy metals,
for example tungsten, or tantalum, and which have a dispersion of
boride particles.
[0002] Titanium aluminide alloys have potential for use in gas
turbine engines, particularly for turbine blades and turbine vanes
in the low pressure turbine and compressor blades and vanes in the
high pressure compressor. The gamma titanium aluminides provide a
weight reduction compared to the alloys currently used for these
purposes.
[0003] It is known to provide some titanium aluminide alloys with
tungsten, such as for example see U.S. Pat. No. 5,296,056, and it
is known to provide some titanium aluminide alloys with tantalum,
for example see UK patent application GB2245593A and UK patent
application GB2250999A.
[0004] It is also known that titanium aluminide alloys may be
modified to improve the mechanical properties of the titanium
aluminide alloy articles by the addition of boron which forms
titanium diboride when the titanium aluminide alloy has solidified.
The titanium diboride is an effective grain refiner for the
titanium aluminide alloy which improves the castability, mechanical
formability and mechanical properties, in particular increased
ductility and creep resistance, of the titanium aluminide alloy.
See for example U.S. Pat. No. 5,284,620, U.S. Pat. No. 5,429,796,
UK patent application GB2245593A and UK patent application
GB2250999A. In order to provide grain refinement the addition of
boron in quantities of about 0.5 to about 2 at % is required.
[0005] However, it has been found that the addition of boron, or
borides, into a tantalum, or tungsten, containing titanium
aluminide alloy may result in the formation of precipitate clusters
and/or stringers of tantalum boride, or tungsten boride, in the
titanium aluminide alloy. This is because the tungsten, or
tantalum, in the titanium aluminide alloy reacts with the boron to
form the tungsten boride or tantalum boride. The precipitate
clusters have a maximum dimension of about 500 .mu.m and are
predominantly tungsten boride in tungsten containing titanium
aluminides or tantalum boride in tantalum containing titanium
aluminides.
[0006] U.S. Pat. No. 5,284,620 and U.S. Pat. No. 5,429,796 add the
borides into the titanium aluminide alloy in the form of titanium
diboride particles and it has been found that the addition of
titanium diboride particles to the tungsten, or tantalum,
containing titanium aluminide alloys results in the formation of
the tungsten boride, or tantalum boride, precipitate clusters.
[0007] GB2245593A and GB2250999A add the boride into the titanium
aluminide alloy in the form of elemental boron and it believed that
the addition of elemental boron to the tungsten, or tantalum,
containing titanium aluminide alloys may result in the formation of
the tungsten boride, or tantalum boride, precipitate clusters.
[0008] Accordingly the present invention seeks to provide a novel
way of adding boron to a heavy metal containing titanium aluminide
alloy which at least reduces the above mentioned problems.
[0009] Accordingly the present invention provides a method of
adding boron to a heavy metal containing titanium aluminide alloy
to form a boride dispersion in the heavy metal containing titanium
aluminide, comprising:
[0010] (a) forming molten heavy metal containing titanium aluminide
alloy,
[0011] (b) adding heavy metal boride particles to the molten heavy
metal containing titanium aluminide alloy to form a molten mixture,
the heavy metal boride particles having the same form as
undesirable heavy metal boride precipitate clusters,
[0012] (c) cooling and solidifying the molten mixture to form a
heavy metal containing titanium aluminide alloy having a uniform
dispersion of heavy metal boride particles substantially without
the formation of heavy metal boride precipitate clusters.
[0013] Preferably step (a) comprises forming molten tungsten
containing titanium aluminide alloy,
[0014] (b) adding tungsten boride to the molten tungsten containing
titanium aluminide alloy to form a molten mixture, the tungsten
boride particles having the same form as undesirable tungsten
boride precipitate clusters,
[0015] (c) cooling and solidifying the molten mixture to form a
tungsten containing titanium aluminide alloy having a dispersion of
tungsten boride particles substantially without the formation of
tungsten boride precipitate clusters.
[0016] Alternatively step (a) comprises forming molten tantalum
containing titanium aluminide alloy,
[0017] (b) adding tantalum boride to the molten tantalum containing
titanium aluminide alloy to form a molten mixture, the tantalum
boride particles having the same form as undesirable tantalum
boride precipitate clusters,
[0018] (c) cooling and solidifying the molten mixture to form a
tantalum containing titanium aluminide alloy having a dispersion of
tantalum boride particles substantially without the formation of
tantalum boride precipitate clusters.
[0019] Preferably the titanium aluminide alloy comprises up to 2.0
at % boron, more preferably the titanium aluminide alloy comprises
up to 1.0 at % boron and preferably the titanium aluminide alloy
comprises more than 0.5 at % boron.
[0020] Preferably the heavy metal boride particles added have a
size of 1 to 5 .mu.m.
[0021] Preferably the density of heavy metal boride precipitate
clusters is up to 3 cm.sup.-2, more preferably the density of heavy
metal boride precipitate clusters is less than 2 cm.sup.-2, more
preferably there are substantially no heavy metal boride
precipitate clusters.
[0022] Preferably the heavy metal boride precipitate clusters have
a maximum size of 150 .mu.m, more preferably the heavy metal boride
precipitate clusters have a maximum size of 100 .mu.m.
[0023] Preferably the titanium aluminide alloy comprises a gamma
titanium aluminide.
[0024] Preferably the method comprises forming the titanium
aluminide alloy into a turbine blade, a turbine vane, a compressor
blade, or a compressor vane.
[0025] Preferably the titanium aluminide alloy is cast or
forged.
[0026] The present invention also seeks to provide a heavy metal
containing titanium aluminide alloy, the titanium aluminide
containing heavy metal boride particles substantially without heavy
metal boride precipitate clusters, the heavy metal boride particles
having the same form as the undesirable heavy metal boride
precipitate clusters, and the titanium aluminide alloy comprises up
to 2.0 at % boron.
[0027] Preferably the density of the heavy metal boride precipitate
clusters is less than 2 cm.sup.-2.
[0028] Preferably the heavy metal boride precipitate clusters have
maximum size of 100 .mu.m.
[0029] Preferably the heavy metal is tungsten and the heavy metal
boride is tungsten boride.
[0030] Alternatively the heavy metal is tantalum and the heavy
metal boride is tantalum boride.
[0031] Preferably the titanium aluminide alloy comprises a gamma
titanium aluminide.
[0032] Preferably the titanium aluminide alloy is in the shape of a
turbine blade, a turbine vane, a compressor blade, or a compressor
vane.
[0033] The present invention will be more fully described by way of
example with reference to the accompanying drawings in which:
[0034] FIG. 1 shows a titanium aluminide turbine blade having a
protective coating according to the present invention.
[0035] A gas turbine engine compressor turbine 10, as shown in FIG.
1, comprises an aerofoil 12, a platform 14 and a root 16. The
turbine blade 10 comprises a titanium aluminide alloy, preferably
gamma titanium aluminide alloy.
[0036] The titanium aluminide alloy comprises one or more of
tungsten, tantalum or other heavy metals and particles of tungsten
boride, tantalum boride or other heavy metal boride respectively.
The density of the tungsten, tantalum or other heavy metal boride
particles is up to 3 cm.sup.-2 and the tungsten, tantalum or other
heavy metal boride particles have a maximum size of 150 .mu.m.
Preferably the tungsten, tantalum or other heavy metal boride
particles have maximum size of 100 .mu.m. Preferably the density of
the tungsten, tantalum or other heavy metal boride particles is
less than 2 cm.sup.-2, most preferably the density of the tungsten,
tantalum or other heavy metal boride particles is zero. If the
titanium aluminide alloy comprises for example tungsten and
tantalum then there may be tungsten boride particles and tantalum
boride particles.
[0037] The boride particles refine the grain size of the gamma
titanium aluminide alloy making the gamma titanium aluminide alloy
more ductile.
[0038] The boron is added into the heavy metal containing gamma
titanium aluminide alloy by forming the molten heavy metal
containing titanium aluminide alloy. Then heavy metal boride is
added to the molten heavy metal containing titanium aluminide alloy
to form a molten mixture. The heavy metal boride is added in the
same form as the heavy metal boride precipitate clusters which
normally form in the heavy metal containing titanium aluminide
alloy. The molten mixture is then cooled and solidified to form a
heavy metal containing titanium aluminide alloy having a dispersion
of heavy metal boride particles. The titanium aluminide alloy
comprises up to 2.0 at % boron and more than 0.5 at % boron.
EXAMPLES
Example 1
[0039] A titanium aluminide alloy comprising 47 at % aluminum, 2 at
% tantalum, 1 at % chromium, 1 at % manganese, 1 at % boron, 0.2 at
% silicon and the balance titanium and incidental impurities was
prepared. The titanium aluminide alloy was for example prepared by
mixing aluminum shot, granular titanium, flakes of chromium, flakes
of manganese, chips of silicon, chopped niobium plate, chopped
tantalum plate and boron was added in the form of aluminum boride.
The aluminum boride comprises AlB.sub.12 and an Al matrix.
[0040] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy was
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0041] The microstructure of the resulting titanium aluminide alloy
was examined and was fine grained and fully lamellar. The average
grain size was about 170 .mu.m. Additionally there were quantities
of precipitate clusters in the structures in the titanium aluminide
alloy.
Example 2
[0042] A titanium aluminide alloy comprising 47 at % aluminum, 2 at
% tantalum, 1 at % chromium, 1 at % manganese, 0.2 at % silicon and
the balance titanium and incidental impurities was prepared. This
is the same alloy as in Example 1 except without the boron.
[0043] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0044] It was found that there were no precipitate clusters in the
structures in the titanium aluminide alloy.
Example 3
[0045] A titanium aluminide alloy comprising 47 at % aluminum, 2 at
% tantalum, 1 at % manganese, 1 at % chromium, 1 at % boron, 0.2 at
% silicon and the balance titanium and incidental impurities was
prepared. The titanium aluminide alloy was for example prepared by
mixing master alloys and boron was added in the form of aluminum
boride. The aluminum boride comprises AlB.sub.12.
[0046] The tantalum was added in the form of a tantalum and
aluminum master alloy (70 wt % Ta).
[0047] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy was
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0048] The microstructure of the resulting titanium aluminide alloy
was examined and was fine grained and equiaxed. The average grain
size was about 170 .mu.m. Additionally there were abundant
quantities of precipitate clusters in the structures similar to
those in Example 1. These precipitate clusters had a maximum size
of 500 .mu.m and the density of the precipitate clusters was 90
cm.sup.-2.
Example 4
[0049] A titanium aluminide alloy comprising 47 at % aluminum, 1 at
% tungsten, 2 at % niobium, 1 at % chromium, 1 at % boron, 0.2 at %
silicon and the balance titanium and incidental impurities was
prepared. The titanium aluminide alloy was for example prepared by
mixing master alloys and boron was added in the form of aluminum
boride. The aluminum boride comprises AlB.sub.12.
[0050] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy was
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0051] The microstructure of the resulting titanium aluminide alloy
was examined and was fine grained and equiaxed. The average grain
size was about 250 .mu.m. Additionally there were abundant
quantities of precipitate clusters in the structures similar to
those in Example 3.
[0052] The precipitate clusters formed in Examples 1, 3 and 4 were
examined and it was determined that they were tantalum boride (TaB)
in Examples 1 and 3 and tungsten boride (WB) in Example 4. It is
believed that the tantalum reacts with the aluminum boride to form
the tantalum boride precipitate clusters or that the tungsten
reacts with the aluminum boride to form the tungsten boride
precipitate clusters.
Example 5
[0053] A titanium aluminide alloy comprising 47 at % aluminum, 2 at
% tantalum, 1 at % manganese, 1 at % chromium, 1 at % boron, 0.2 at
% silicon and the balance titanium and incidental impurities was
prepared. The titanium aluminide alloy was for example prepared by
mixing master alloys and boron was added in the form of aluminum
boride. The aluminum boride comprises AlB.sub.12.
[0054] The tantalum was added in the form of fine tantalum powder
with a powder size of 9 .mu.m.
[0055] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy was
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0056] The microstructure of the resulting titanium aluminide alloy
was examined and was fine grained and equiaxed. The average grain
size was about 170 .mu.m. Additionally there were abundant
quantities of precipitate clusters in the structure similar to
those in Example 3. These precipitate clusters had a maximum size
of 400 .mu.m and the density of the precipitate clusters was 30
cm.sup.-2.
[0057] This showed that the form of addition of the tantalum to the
titanium aluminide alloy did not control the formation of the
tantalum boride precipitate clusters.
Example 6
[0058] A titanium aluminide alloy comprising 47 at % aluminum, 2 at
% tantalum, 1 at % manganese, 1 at % chromium, 1 at % boron, 0.2 at
% silicon and the balance titanium and incidental impurities was
prepared. The titanium aluminide alloy was for example prepared by
mixing master alloys and tantalum and boron were added in the form
of tantalum boride. The remaining tantalum was added in the form of
a tantalum and aluminum master alloy. The tantalum boride comprises
a mixture of TaB.sub.2 and TaB. The tantalum boride was added in
the form of fine tantalum boride powder with a powder size of 1-5
.mu.m.
[0059] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy was
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0060] The microstructure of the resulting titanium aluminide alloy
was examined and was fine grained and equiaxed. The average grain
size was about 170 .mu.m. Additionally there were much reduced
quantities of precipitate clusters in the structures similar to
those in Example 3. These precipitate clusters had a maximum size
of about 100 .mu.m and the density of the precipitate clusters was
about 3 cm.sup.-2.
Example 6
[0061] A titanium aluminide alloy comprising 47 at % aluminum, 2 at
% tantalum, 1 at % manganese, 1 at % chromium, 1 at % boron, 0.2 at
% silicon and the balance titanium and incidental impurities was
prepared. The titanium aluminide alloy was for example prepared by
mixing master alloys and tantalum and boron was added in the form
of tantalum boride. The remaining tantalum was added in the form of
a tantalum and aluminum master alloy. The tantalum boride comprises
TaB. The tantalum boride was added in the form of fine tantalum
boride powder with a powder size of 1-5 .mu.m.
[0062] The above mixture was heated in a vacuum chamber back filled
with argon to 1 bar pressure and the titanium aluminide alloy was
melted using a plasma torch and was cast into a water cooled copper
crucible.
[0063] The microstructure of the resulting titanium aluminide alloy
was examined and was fine grained and equiaxed. The average grain
size was about 170 .mu.m. Additionally substantially no precipitate
clusters in the structures similar to those in Example 3 were seen
by microstructural analysis.
[0064] It is believed, in the tantalum containing titanium
aluminide, that tantalum boride (TaB) precipitate clusters are
formed as soon as the tantalum comes into contact with the aluminum
boride during the melting procedure. It is believed that once the
tantalum boride precipitate clusters have formed it is difficult to
remove the tantalum boride precipitate clusters from the titanium
aluminide alloy because the melting point of tantalum boride (TaB)
is about 2460.degree. C.
[0065] Similarly it is believed, in the tungsten containing
titanium aluminide, that tungsten boride (WB) precipitate clusters
are formed as soon as the tungsten comes into contact with the
aluminum boride during the melting procedure. It is believed that
once the tungsten boride precipitate clusters have formed it is
difficult to remove the tungsten boride precipitate clusters from
the titanium aluminide alloy because the melting point of tungsten
boride (WB) is about 2655.degree. C.
[0066] It is believed that the large precipitate clusters of
tantalum boride (TaB), in the tantalum containing titanium
aluminide alloy, are prevented because the addition of the tantalum
boride (TaB) particles changes the reaction kinetics and prevents
the large scale segregation of tantalum and boron to form the
tantalum boride precipitate clusters. The tantalum boride (TaB)
added is distributed, or dispersed, uniformly throughout the
tantalum containing titanium aluminide alloy.
[0067] Similarly it is believed that the large precipitate clusters
of tungsten boride (WB), in the tungsten containing titanium
aluminide alloy, are prevented because the addition of the tungsten
boride (WB) particles changes the reaction kinetics and prevents
the large scale segregation of tungsten and boron to form the
tungsten boride precipitate clusters. The tungsten boride (WB)
added is distributed, or dispersed, uniformly throughout the
tungsten containing titanium aluminide alloy.
[0068] Thus it is clear that the boron must be added to the heavy
metal containing titanium aluminide alloy in the same form in which
boride occurs in the precipitate clusters, to change the reaction
kinetics which result in the formation of the precipitate
clustering of the heavy metal and boron. Thus TaB is added to a
tantalum containing titanium aluminide alloy, WB is added to a
tungsten containing titanium aluminide since TaB and WB are the
boride precipitate clusters formed. The addition of TaB.sub.2 to a
tantalum containing titanium aluminide alloy does not prevent the
formation of the TaB precipitate clusters and an addition of
WB.sub.2 to a tungsten containing titanium aluminide does not
prevent the formation of the WB precipitate clusters.
[0069] The size of the heavy metal boride particles in the titanium
aluminide alloy is generally limited to that of the size of the
heavy metal boride particles added to the titanium aluminide
alloy.
[0070] Although the titanium aluminide alloy has been described as
being used for turbine blades it may also be used for turbine
vanes, compressor blades, compressor vanes. It may also be used for
internal combustion engine components.
[0071] The gamma titanium aluminide alloy preferably comprises 44
to 52 at % aluminum, one or more of tungsten and tantalum each in
an amount of 0.05 to 8.0 at %, up to 2.0 at % boron and balance
titanium plus incidental impurities. The gamma titanium aluminide
may additionally comprise up to 3 at % chromium, up to 6 at %
niobium, up to 2 at % manganese.
[0072] The gamma titanium aluminide alloy preferably comprises 45
to 47 at % aluminum, 2 to 6 at % niobium, 0.25 to 2 at % tungsten
and the balance titanium plus incidental impurities. Preferably the
gamma titanium aluminide comprises 45 at % aluminum, 5 at %
niobium, 1 at % tungsten. The gamma titanium aluminide alloy may
comprise 1 to 2 at % chromium and/or 1 to 2 at % manganese. The
boron is added to a level between 0.5 and 2.0 at %.
* * * * *