U.S. patent application number 10/913528 was filed with the patent office on 2005-04-21 for method of heat treating titanium aluminide.
Invention is credited to Hu, Dawei, Loretto, Michael, Wu, Xinhua.
Application Number | 20050081967 10/913528 |
Document ID | / |
Family ID | 28052473 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050081967 |
Kind Code |
A1 |
Hu, Dawei ; et al. |
April 21, 2005 |
Method of heat treating titanium aluminide
Abstract
A gamma titanium aluminide alloy consisting of 46 at %
aluminium, 8 at % niobium, up to 0.07 at % carbon and the balance
titanium plus incidental impurities has an alpha transus
temperature T.sub..alpha.=1335.degree. C. The gamma titanium
aluminide alloy was heated to a temperature T.sub.1=1360.degree. C.
and was held at T.sub.1=1360.degree. C. for 1 hour or longer. The
gamma titanium aluminide alloy was fluidised bed, or salt bath,
quenched to a temperature T.sub.2, where 900.degree.
C.<T.sub.2<1200.degree. C., and was held at temperature
T.sub.2 for a sufficient time to allow the massive transformation
to go to completion. The gamma titanium aluminide alloy was heated
to a temperature T.sub.3=1300.degree. C. or 1320.degree. C. and was
held at T.sub.2 for 4 hours. The gamma titanium aluminide alloy was
air cooled to ambient temperature. The gamma titanium aluminide
alloy has a fine duplex microstructure comprising differently
orientated alpha plates in a massively transformed gamma matrix.
The heat treatment reduces quenching stresses, allows larger
castings and a broader range of titanium aluminide alloys to be
grain refined.
Inventors: |
Hu, Dawei; (Birmingham,
GB) ; Wu, Xinhua; (Birmingham, GB) ; Loretto,
Michael; (Birmingham, GB) |
Correspondence
Address: |
MANELLI DENISON & SELTER
2000 M STREET NW SUITE 700
WASHINGTON
DC
20036-3307
US
|
Family ID: |
28052473 |
Appl. No.: |
10/913528 |
Filed: |
August 9, 2004 |
Current U.S.
Class: |
148/669 |
Current CPC
Class: |
C22F 1/183 20130101 |
Class at
Publication: |
148/669 |
International
Class: |
C22F 001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2003 |
GB |
0319061.8 |
Claims
1. A method of heat-treating titanium aluminide alloy, the titanium
aluminide alloy having a single alpha phase field and being capable
of producing a massively transformed gamma microstructure, the
method comprising the steps of (a) heating a titanium aluminide
alloy to a temperature above the alpha transus temperature, (b)
maintaining the titanium aluminide alloy at a temperature above the
alpha transus temperature in the single alpha phase field for a
predetermined time period, (c) cooling the titanium aluminide alloy
from the single alpha phase field to a temperature in the range of
900.degree. C. to 1200.degree. C., (d) maintaining the titanium
aluminide alloy at the temperature in the range of 900.degree. C.
to 1200.degree. C. for a predetermined time period to produce a
massively transformed gamma microstructure, (e) heating the
titanium aluminide alloy to a temperature below the alpha transus
temperature in the alpha and gamma phase field, (f) maintaining the
titanium aluminide alloy at the temperature below the alpha transus
temperature for a predetermined time period to precipitate alpha
plates in the massively transformed gamma microstructure such that
a refined microstructure is produced in the titanium aluminide
alloy, (g) cooling the titanium aluminide alloy to ambient
temperature.
2. A method as claimed in claim 1 wherein in step (b) the
predetermined time period is up to 2 hours.
3. A method as claimed in claim 1 wherein in step (f) the
predetermined time period is up to 4 hours.
4. A method as claimed in claim 1 wherein step (e) comprises
heating the titanium aluminide alloy to a temperature about
30.degree. C. to 60.degree. C. below the alpha transus
temperature.
5. A method as claimed in claim 1 wherein step (a) comprises
heating the titanium aluminide alloy to a temperature of about
20.degree. C. to 30.degree. C. above the alpha transus
temperature.
6. A method as claimed in claim 1 wherein step (g) comprises
air-cooling or furnace cooling.
7. A method as claimed in claim 1 wherein step (c) comprises
fluidised bed cooling or salt bath cooling.
8. A method as claimed in claim 1 comprising cooling the titanium
aluminide to ambient temperature after step (d) and before step
(e).
9. A method as claimed in claim 8 wherein the titanium aluminide is
cooled to ambient temperature by air-cooling or oil cooling.
10. A method as claimed in claim 1 wherein the titanium aluminide
alloy comprises 48 at % aluminium, 2 at % chromium, 2 at% niobium
and the balance titanium and incidental impurities.
11. A method as claimed in claim 10 wherein the alpha transus
temperature is about 1360.degree. C., step (a) comprises heating to
a temperature of 1380.degree. C., step (b) comprises maintaining
the titanium aluminide alloy at a temperature of about 1380.degree.
C. for about 1 hour, step (c) and (d) comprise salt bath, or
fluidised bed, cooling the titanium aluminide alloy from a
temperature of 1380.degree. C. to a temperature between 900.degree.
C. and 1200.degree. C. and maintaining the titanium aluminide alloy
at the temperature in the range of 900.degree. C. to 1200.degree.
C. for a predetermined time period to produce a massively
transformed gamma microstructure, steps (e) and (f) comprise
heating the titanium aluminide alloy to a temperature of about
1320.degree. C. for about 2 hours to precipitate alpha plates in
the massively transformed gamma microstructure such that a refined
microstructure is produced in the titanium aluminide alloy, and
step (g) comprises air cooling the titanium aluminide alloy to
ambient temperature.
12. A method as claimed in claim 1 wherein the titanium aluminide
alloy comprises 46 at % aluminium, 8 at % niobium, up to 0.07 at %
carbon and the balance titanium and incidental impurities.
13. A method as claimed in claim 12 wherein the alpha transus
temperature is about 1335.degree. C., step (a) comprises heating to
a temperature of 1360.degree. C., step (b) comprises maintaining
the titanium aluminide alloy at a temperature of about 1360.degree.
C. for about 1 hour, steps (c) and (d) comprise salt bath cooling,
or fluidised bed cooling, the titanium aluminide alloy from a
temperature of 1360.degree. C. to a temperature between 900.degree.
C. and 1200.degree. C. and maintaining the titanium aluminide alloy
at the temperature in the range of 900.degree. C. to 1200.degree.
C. for a predetermined time period to produce a massively
transformed gamma microstructure, steps (e) and (f) comprise
heating the titanium aluminide alloy to a temperature of about
1300.degree. C. to about 1320.degree. C. for about 4 hours to
precipitate alpha plates in the massively transformed gamma
microstructure such that a refined microstructure is produced in
the titanium aluminide alloy, and step (f) comprises air cooling
the titanium aluminide alloy to ambient temperature.
14. A method as claimed in claim 1 wherein the titanium aluminide
alloy consists of 45-46 at % aluminium, 8 at % niobium, up to 0.07
at % carbon and the balance is titanium and incidental
impurities.
15. A method as claimed in claim 1 wherein the titanium aluminide
alloy consists of 45-46 at % aluminium, 2-6 at % niobium, 2-6 at %
hafnium and the balance is titanium plus incidental impurities.
16. A method as claimed in claim 1 wherein the titanium aluminide
alloy is a cast titanium aluminide component.
17. A method as claimed in claim 1 wherein comprising hot isostatic
pressing of the cast titanium aluminide alloy component.
18. A method as claimed in claim 17 wherein the hot isostatic
pressing of the cast titanium aluminide alloy component is
concurrent with step (f).
19. A method as claimed in claim 17 wherein the hot isostatic
pressing comprises applying a pressure of about 150 MPa for about 4
hours.
20. A method as claimed in claim 1 wherein the titanium aluminide
alloy is a compressor blade or a compressor vane.
Description
[0001] The present invention relates to a method of heat-treating
titanium aluminide and in particular to a method of heat-treating
gamma titanium aluminide.
[0002] There is a requirement to refine the microstructure of a
titanium aluminide alloy, in particular cast titanium aluminide
alloy, which does not involve hot working of the titanium aluminide
alloy.
[0003] Our European patent application no. 03253539.5 filed 4 Jun.
2003 discloses a method of heat-treating a titanium aluminide alloy
having a single alpha phase field and being capable of producing a
massively transformed gamma microstructure. In that method of
heat-treating the titanium aluminide alloy is heated to a
temperature above the alpha transus temperature, is maintained
above the alpha transus temperature in the single alpha phase field
for a predetermined time period, is cooled from the single alpha
phase field to ambient temperature to produce a massively
transformed gamma microstructure, is heated to a temperature below
the alpha transus temperature in the alpha and gamma phase field,
is maintained at the temperature below the alpha transus
temperature for a predetermined time period to precipitate alpha
plates in the massively transformed gamma microstructure such that
a refined microstructure is produced and is then cooled to ambient
temperature.
[0004] A problem with this heat-treatment is that the cooling,
quenching, of the titanium aluminide from above the alpha transus
to ambient temperature induces quenching stresses in the titanium
aluminide. A further problem is that the heat-treatment is only
suitable for relatively thin castings. Another problem is that the
heat-treatment is only applicable to compositions of titanium
aluminide with a particular range of aluminium.
[0005] Accordingly the present invention seeks to provide a novel
method of heat-treating titanium aluminide alloy which reduces,
preferably overcomes, the above-mentioned problems.
[0006] Accordingly the present invention provides a method of
heat-treating titanium aluminide alloy, the titanium aluminide
alloy having a single alpha phase field and being capable of
producing a massively transformed gamma microstructure, the method
comprising the steps of:-
[0007] (a) heating a titanium aluminide alloy to a temperature
above the alpha transus temperature,
[0008] (b) maintaining the titanium aluminide alloy at a
temperature above the alpha transus temperature in the single alpha
phase field for a predetermined time period,
[0009] (c) cooling the titanium aluminide alloy from the single
alpha phase field to a temperature in the range of 900.degree. C.
to 1200.degree. C.,
[0010] (d) maintaining the titanium aluminide alloy at the
temperature in the range of 900.degree. C. to 1200.degree. C. for a
predetermined time period to produce a massively transformed gamma
microstructure,
[0011] (e) heating the titanium aluminide alloy to a temperature
below the alpha transus temperature in the alpha and gamma phase
field,
[0012] (f) maintaining the titanium aluminide alloy at the
temperature below the alpha transus temperature for a predetermined
time period to precipitate alpha plates in the massively
transformed gamma microstructure such that a refined microstructure
is produced in the titanium aluminide alloy,
[0013] (g) cooling the titanium aluminide alloy to ambient
temperature.
[0014] Preferably in step (b) the predetermined time period is up
to 2 hours.
[0015] Preferably in step (f) the predetermined time period is up
to 4 hours.
[0016] Preferably step (e) comprises heating the titanium aluminide
alloy to a temperature about 30.degree. C. to 60.degree. C. below
the alpha transus temperature.
[0017] Preferably step (a) comprises heating the titanium aluminide
alloy to a temperature of about 20.degree. C. to 30.degree. C.
above the alpha transus temperature.
[0018] Preferably step (g) comprises air-cooling or furnace
cooling.
[0019] Preferably step (c) comprises fluidised bed cooling or salt
bath cooling.
[0020] It may be possible to cool the titanium aluminide to ambient
temperature after step (d) and before step (e) The titanium
aluminide may be cooled to ambient temperature by air-cooling or
oil cooling
[0021] The titanium aluminide alloy may comprise 48 at % aluminium,
2 at % chromium, 2 at % niobium and the balance titanium and
incidental impurities.
[0022] The alpha transus temperature is about 1360.degree. C., step
(a) comprises heating to a temperature of 1380.degree. C., step (b)
comprises maintaining the titanium aluminide alloy at a temperature
of about 1380.degree. C. for about 1 hour, step (c) and (d)
comprise salt bath, or fluidised bed, cooling the titanium
aluminide alloy from a temperature of 1380.degree. C. to a
temperature between 900.degree. C. and 1200.degree. C. and
maintaining the titanium aluminide alloy at the temperature in the
range of 900.degree. C. to 1200.degree. C. for a predetermined time
period to produce a massively transformed gamma microstructure,
steps (e) and (f) comprise heating the titanium aluminide alloy to
a temperature of about 1320.degree. C. for about 2 hours to
precipitate alpha plates in the massively transformed gamma
microstructure such that a refined microstructure is produced in
the titanium aluminide alloy, and step (g) comprises air cooling
the titanium aluminide alloy to ambient temperature.
[0023] The titanium aluminide alloy may comprise 46 at % aluminium,
8 at % niobium, up to 0.07 at % carbon and the balance titanium and
incidental impurities.
[0024] The alpha transus temperature is about 1335.degree. C., step
(a) comprises heating to a temperature of 1360.degree. C., step (b)
comprises maintaining the titanium aluminide alloy at a temperature
of about 1360.degree. C. for about 1 hour, steps (c) and (d)
comprise salt bath cooling, or fluidised bed cooling, the titanium
aluminide alloy from a temperature of 1360.degree. C. to a
temperature between 900.degree. C. and 1200.degree. C. and
maintaining the titanium aluminide alloy at the temperature in the
range of 900.degree. C. to 1200.degree. C. for a predetermined time
period to produce a massively transformed gamma microstructure,
steps (e) and (f) comprise heating the titanium aluminide alloy to
a temperature of about 1300.degree. C. to about 1320.degree. C. for
about 4 hours to precipitate alpha plates in the massively
transformed gamma microstructure such that a refined microstructure
is produced in the titanium aluminide alloy, and step (g) comprises
air cooling the titanium aluminide alloy to ambient
temperature.
[0025] The titanium aluminide alloy may consist of 45-46 at %
aluminium, 8 at % niobium, up to 0.07 at % carbon and the balance
is titanium and incidental impurities.
[0026] The titanium aluminide alloy may consist of 45-46 at %
aluminium, 2-6 at % niobium, 2-6 at % hafnium and the balance is
titanium plus incidental impurities.
[0027] The titanium aluminide alloy may be a cast titanium
aluminide component.
[0028] The method may comprise hot isostatic pressing of the cast
titanium aluminide alloy component.
[0029] Preferably the hot isostatic pressing of the cast titanium
aluminide alloy component is concurrent with step (f).
[0030] Preferably the hot isostatic pressing comprises applying a
pressure of about 150 MPa for about 4 hours.
[0031] The titanium aluminide alloy may be a compressor blade or a
compressor vane.
[0032] The present invention will be more fully described by way of
example with reference to the accompanying drawings in which:
[0033] FIG. 1 is graph of temperature versus time illustrating the
method of heat-treating a titanium aluminide alloy according to the
present invention.
[0034] FIG. 2 is a gamma titanium aluminide alloy gas turbine
engine compressor blade heat treated according to the present
invention.
[0035] A method of heat-treating a titanium aluminide alloy
according to the present invention is described with reference to
FIG. 1. The present invention is concerned with heat-treating gamma
titanium aluminide alloys with at least 46 at % aluminium and a
single alpha phase field.
[0036] The heat treatment process comprises heating the gamma
titanium aluminide to a temperature T.sub.1 above the alpha transus
temperature T.sub..alpha.. The gamma titanium aluminide alloy is
then maintained at a temperature T.sub.1 above the alpha transus
temperature T.sub..alpha. in the single alpha phase field for a
predetermined time period t.sub.1. The gamma titanium aluminide is
quenched, for example fluidised bed cooled, or slat bath cooled,
from the single alpha phase field at temperature T.sub.1 to a
temperature T.sub.2. The gamma titanium aluminide alloy is
maintained at temperature T.sub.2 for a predetermined time period
t.sub.2 to produce a massively transformed gamma microstructure.
The gamma titanium aluminide alloy is then heated to a temperature
T.sub.3 below the alpha transus temperature T.sub..alpha.. The
gamma titanium aluminide alloy is maintained at the temperature
T.sub.3 in the alpha and gamma phase field for a predetermined time
period t.sub.3 to precipitate alpha plates in the massively
transformed gamma microstructure such that a refined microstructure
is produced in the titanium aluminide alloy. The gamma titanium
aluminide is cooled, for example air cooled, or furnace cooled, to
ambient temperature.
[0037] In particular, the gamma titanium aluminide is heated to a
temperature T.sub.1 about 20.degree. C. to 30.degree. C. above the
alpha transus temperature T.sub..alpha.. The gamma titanium
aluminide alloy is maintained at the temperature T.sub.1 for up to
2 hours. The gamma titanium aluminide alloy is then quenched, for
example fluidised bed cooled, or salt bath cooled, to a temperature
T.sub.2 about 900.degree. C. to 1200.degree. C. and maintained for
a predetermined time period to induce a massively transformed gamma
microstructure. The gamma titanium alloy is heated to a temperature
T.sub.3 about 30.degree. C. to 60.degree. C. below the alpha
transus temperature T.sub..alpha.. The gamma titanium aluminide
alloy is maintained at the temperature T.sub.3 for up to 4 hours to
precipitate fine alpha plates with different orientations in the
massively transformed gamma microstructure due to the massive gamma
to alpha+gamma phase transformation. This gives rise to a very fine
duplex microstructure. The differently orientated alpha plates
precipitated in the massive gamma phase matrix effectively reduce
the grain size of the gamma titanium aluminide. The gamma titanium
aluminide alloy is then cooled, for example air cooled, or furnace
cooled, to ambient temperature.
[0038] The holding at temperature T.sub.1 for a time period t.sub.1
also acts a homogenisation process for cast titanium aluminide
alloys.
EXAMPLE
[0039] A gamma titanium aluminide alloy consisting of 46 at %
aluminium, 8 at % niobium, up to 0.07 at % carbon and the balance
titanium plus incidental impurities was heat treated according to
the present invention. This gamma titanium aluminide alloy has an
alpha transus temperature T.sub..alpha.=1335.degree. C. The gamma
titanium aluminide alloy was heated to a temperature
T.sub.1=1360.degree. C. and was held at T.sub.1=1360.degree. C. for
1 hour for small components and longer for larger components. The
gamma titanium aluminide alloy was fluidised bed, or salt bath,
quenched to a temperature 900.degree. C.<T.sub.2<1200.degree.
C. and was held at temperature T.sub.2, where 900.degree.
C.<T.sub.2<1200.degree. C., for a sufficient time to allow
the massive transformation to go to completion. The gamma titanium
aluminide alloy was heated to a temperature T.sub.3=1300.degree. C.
or 1320.degree. C. and was held at T.sub.2=1300.degree. C. or
1320.degree. C. for 4 hours. The gamma titanium aluminide alloy was
air cooled to ambient temperature.
[0040] As an alternative the gamma titanium aluminide alloy is
air-cooled or oil cooled from temperature T.sub.2 to ambient
temperature before the gamma titanium aluminide alloy is heated to
the temperature T.sub.3.
[0041] The present invention is applicable to a gamma titanium
aluminide alloy consisting of 46 at % aluminium, 5 at % niobium,
0.3 at % boron, 0.2 at % carbon and the balance titanium plus
incidental impurities. The present invention is applicable to a
gamma titanium aluminide alloy consisting of 47 at % aluminium, 2
at % niobium, 1 at % tungsten, 1 at % chromium, 1 at % boron, 0.2
at % silicon and the balance titanium plus incidental impurities.
The present invention is applicable to gamma titanium aluminide
alloy consisting of 47 at % aluminium, 2 at % tantalum, 1 at %
chromium, 1 at % manganese, 1 at % boron, 0.2 at % silicon and the
balance titanium plus incidental impurities. The present invention
is also applicable to gamma titanium aluminide alloy consisting of
46 at % aluminium, 5 at % niobium, 1 at % tungsten and the balance
titanium plus incidental impurities. The present invention is
applicable to a gamma titanium aluminide alloy consisting of 45-46
at % aluminium, 8 at % niobium, up to 0.07 at % carbon and the
balance is titanium and incidental impurities. The present
invention is also applicable to a gamma titanium aluminide alloy
consisting of 45-46 at % aluminium, 2-6 at % niobium, 2-6 at %
hafnium and the balance is titanium plus incidental impurities. The
present invention is also applicable to a gamma titanium aluminide
alloy consisting of 48 at % aluminium, 2 at % chromium, 2 at %
niobium and the balance titanium and incidental impurities.
[0042] The advantages of the present invention are that the
cooling, quenching, of the titanium aluminide from above the alpha
transus to an intermediate temperature induces reduced levels of
quenching stresses compared to cooling, quenching, to ambient
temperature as described in our European patent application no.
03253539.5. A further advantage is that at temperatures above about
1000.degree. C. the titanium aluminide is relatively ductile and
the quenching stresses do not cause fracture. Another advantage is
that the heat-treatment is suitable for relatively thin castings
and for larger castings so that they all have improved ductility
and high strength. Also the heat-treatment is applicable to
compositions of titanium aluminide with a broader range, a lower
level, of aluminium and hence it is applicable to stronger titanium
aluminide alloys. It is believed that the lower level of aluminium
may be 45 at % and possibly 44 at %. Thus, the present invention
provides a heat treatment for gamma titanium aluminide alloy
components, which provides grain refinement. It is particularly
suitable for relatively large and complex shaped cast components
where the previous heat treatment would induce high residual
stresses and possibly cracking of the gamma titanium aluminide
alloy components. The heat treatment also permits grain refinement
throughout relatively large and complex shaped components rather
than just the surface regions of the component.
[0043] It may be possible to heat the titanium aluminide alloy
component to a temperature of about 1300.degree. C. and to maintain
the titanium aluminide alloy component at about 1300.degree. C. to
allow the temperature to equilibrate in the titanium aluminide
alloy component so that the titanium aluminide alloy component
needs to be maintained at temperature T.sub.1 for a shorter time
period.
[0044] In the case of cast gamma titanium aluminide alloy
components it may be necessary to remove porosity from the cast
gamma titanium aluminide alloy component. In this case the cast
gamma titanium aluminide alloy component may be hot isostatically
pressed (HIP) to remove the porosity. The hot isostatic pressing
preferably occurs at the same time as the heat treatment
temperature T.sub.2 and for the time period of about 4 hours at a
pressure of about 150 MPa and this is beneficial because this
dispenses with the requirement for a separate hot isostatic
pressing step.
[0045] The present invention is particularly suitable for gamma
titanium aluminide gas turbine engine compressor blades as
illustrated in FIG. 2. The compressor blade 10 comprises a root 12,
a shank 14, a platform 16 and an aerofoil 18. The present invention
is also suitable for gamma titanium aluminide gas turbine engine
compressor vanes or other gamma titanium aluminide gas turbine
engine components. The present invention may also be suitable for
gamma titanium aluminide components for other engine, machines or
applications.
* * * * *