U.S. patent application number 11/805043 was filed with the patent office on 2010-01-21 for titanium aluminide based alloy.
This patent application is currently assigned to GKSS-Forschungszentrum Geesthacht GmbH. Invention is credited to Fritz Appel, Uwe Lorenz, Michael Oehring, Jonathan Paul.
Application Number | 20100015005 11/805043 |
Document ID | / |
Family ID | 35134314 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100015005 |
Kind Code |
A1 |
Oehring; Michael ; et
al. |
January 21, 2010 |
Titanium aluminide based alloy
Abstract
The invention concerns alloys made through the use of melting
and powdered metallurgical techniques on the basis of titanium
aluminides with an alloy composition of Ti-z Al-y Nb where 44.5
Atom %.ltoreq.z.ltoreq.47 Atom %, 44.5 Atom %.ltoreq.z.ltoreq.45.5
Atom %, and 5 Atom %.ltoreq.y.ltoreq.10 Atom % with possibly the
addition of B and/or C at a content between 0.05 Atom % and 0.8
Atom %. Said alloy is characterized in that it contains a
molybdenum (Mo) content ranging between 0.1 Atom % to 3.0 Atom
%.
Inventors: |
Oehring; Michael;
(Geesthacht, DE) ; Paul; Jonathan; (Hamburg,
DE) ; Lorenz; Uwe; (Bardowick, DE) ; Appel;
Fritz; (Geesthacht, DE) |
Correspondence
Address: |
MICHAUD-DUFFY GROUP LLP
306 INDUSTRIAL PARK ROAD, SUITE 206
MIDDLETOWN
CT
06457
US
|
Assignee: |
GKSS-Forschungszentrum Geesthacht
GmbH
Geesthacht
DE
|
Family ID: |
35134314 |
Appl. No.: |
11/805043 |
Filed: |
May 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP05/09402 |
Sep 1, 2005 |
|
|
|
11805043 |
|
|
|
|
Current U.S.
Class: |
420/580 |
Current CPC
Class: |
C22C 14/00 20130101;
B22D 21/005 20130101 |
Class at
Publication: |
420/580 |
International
Class: |
C22C 30/00 20060101
C22C030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 23, 2004 |
DE |
10 2004 056 582.1 |
Claims
1. An alloy made on the basis of titanium aluminide through the use
of melting and powdered metallurgical techniques the alloy
comprising Ti-z Al-y Nb where 44.5 Atom % is .ltoreq.z.ltoreq.47
Atom %, and where 5 Atom % is .ltoreq.y.ltoreq.10 Atom %, and the
alloy containing molybdenum (Mo) in between 0.1 Atom % to 3 Atom
%.
2. An alloy as defined by claim 1 wherein 44.5 Atom % is
.ltoreq.z.ltoreq.45.5 Atom %.
3. An alloy on the basis of titanium aluminide made with the use of
melting and powdered metallurgical techniques the alloy comprising
Ti-z Al-y Nb-x B where 44.5 Atom % is .ltoreq.z.ltoreq.47 Atom %
and where 5 Atom % is .ltoreq.y.ltoreq.10 Atom % and 0.05 Atom % is
.ltoreq.x.ltoreq.0.8 Atom % and wherein the alloy contains
molybdenum (Mo) in the region of between 0.1 Atom % to 3 Atom
%.
4. An alloy as defined by claim 3 wherein 44.5 Atom % is
.ltoreq.z.ltoreq.45.5 Atom %.
5. An alloy on the basis of titanium aluminide made with the use of
melting and powdered metallurgical techniques the alloy comprising
Ti-z Al-y Nb-w C where 44.5 Atom % is .ltoreq.z.ltoreq.47 Atom %,
and where 5 Atom % is .ltoreq.y.ltoreq.10 Atom % and 0.05 Atom % is
.ltoreq.w.ltoreq.0.8 Atom %, and wherein the alloy contains
molybdenum (Mo) in the region of between 0.1 Atom % to 3 Atom
%.
6. An alloy as defined by claim 5 wherein 44.5 Atom % is
.ltoreq.z.ltoreq.45.5 Atom %.
7. An alloy as defined by claim 5 wherein the alloy contains
molybdenum in the region of between 0.5 Atom % to 3 Atom %.
8. An alloy on the basis of titanium aluminide made with the use of
melting and powdered metallurgical techniques the alloy comprising
Ti-z Al-y Nb-x B-w C where 44.5 Atom % is .ltoreq.z.ltoreq.47 Atom
%, and where 5 Atom % is .ltoreq.y.ltoreq.10 Atom % and 0.05 Atom %
is .ltoreq.x.ltoreq.0.8 Atom % and 0.05 Atom % is
.ltoreq.w.ltoreq.0.8 Atom %, and wherein the alloy contains
molybdenum (Mo) in the region of between 0.1 Atom % to 3 Atom
%.
9. An alloy as defined by claim 8 wherein 44.5 Atom
%.ltoreq.z.ltoreq.45.5 Atom %.
10. A construction component made from an alloy according to claim
1.
11. A construction component made from an alloy according to claim
3.
12. A construction component made from an alloy according to claim
5.
13. A construction component made from an alloy according to claim
8.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
International Patent Application No. PCT/EP2005/009402 filed on
Sep. 1, 2005, which claims priority to German Patent Application
No. 10-2004-056582.1 filed on Nov. 23, 2004, subject matter of
these patent documents is incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] The invention concerns alloys made through the use of
melting and powdered metallurgical techniques on the basis of
titanium aluminides with an alloy composition of Ti-z Al-y Nb where
44.5 Atom %.ltoreq.z.ltoreq.47 Atom %, especially where 44.5 Atom
%.ltoreq.z.ltoreq.45.5 Atom %, and 5 Atom %.ltoreq.y.ltoreq.10 Atom
% with possibly the addition of B and/or C at a content between
0.05 Atom % and 0.8 Atom %.
BACKGROUND OF THE INVENTION
[0003] Titanium aluminide alloys have properties which make those
alloys highly suitable for use as light weight work materials,
especially for high temperature applications. For industrial
practice those alloys are of special interest which are based on an
intermetalic phase .gamma.-(TiAl) with tetragonal structure and
along with the majority phase .gamma.-(TiAl) also contain minority
portions of the intermetalic phase .alpha..sub.2(Ti.sub.3Al) with
hexagonal structure. These .gamma.-titanium aluminide alloys
distinguish themselves by properties such lightweight (3.85-4.2
g/cm.sup.3), high elastic modulus, high strength and creep
resistance up to 700.degree. C., which makes them attractive as
work materials for moving parts at high operating temperatures.
Examples of such uses are for turbine blades in aircraft engines
and in stationary gas turbines, engine valves and hot gas
ventilators.
[0004] In the technically important area of alloys with aluminum
content between 45 Atom % and 49 Atom % there appears during the
solidification of the melt and during the subsequent cooling a
series of phase changes. The solidification can take place either
entirely by way of .beta.-mixed crystal cubic space centered
structure (high temperature phase) or in two peritectic reactions
in which .alpha.-mixed crystals with hexagonal structure and the
.gamma.-phase participate.
[0005] It is further known that the element niobium (Nb) leads to
an increase in strength, creep resistance, oxidation resistance and
also ductility. With the element boron which is practically
insoluble in the .gamma.-phase a fine graining can be achieved both
in the cast condition and also after reshaping with subsequent heat
treatment in the .alpha.-region. An increased portion of the
.beta.-phase in the structure as a result of low aluminum content
and high concentration of .beta.-stabilizing elements can lead to a
coarse dispersion of this phase and to an impairment of the
mechanical properties.
[0006] The mechanical properties of .gamma.-titanium aluminide
alloys are, as to their deformation and break behaviors, but also
because of the structural anisotropy of the preferred use of
laminated structures or duplex-structures, strongly anisotropic.
For a desired use of structure and texture in the making of
components from titanium aluminides, casting methods, different
powdered metal metallurgies and reshaping processes as well as
combinations of these manufacturing methods are useable.
[0007] From the publication of Y-W. Kim and D. M. Dimiduk in
"Structural Intermetallics 1997", editors M. V. Nathanal, R.
Darolia, C. T. Liu, P. L. Martin, D. B. Miracle, R. Wagner, M.
Yamaguchi, TMS, Warrendale Pa., 1996, page 531 it is known that in
the course of different development programs the effect of a large
number of alloying elements with respect to constitution,
structural tuning in different manufacturing processes and
individual properties have been investigated. The discovered
relationships are thereby similarly complex as for the case with
the other structured metals, for example, steels and can only be
summarized by rules which are limited and of very general form.
Therefore certain mixtures can have exceptional combinations of
properties.
[0008] A titanium aluminide alloy is known from EP 1015 605 B1
which has a structural and chemically homogenous structure. In this
case the majority phases .gamma.(TiAl) and .alpha..sub.2
(Ti.sub.3Al) are separated into a fine dispersion. The disclosed
titanium aluminide alloy with an aluminum content of 45 Atom %
distinguishes itself by exceptionally good mechanical properties
and high temperature properties.
[0009] A general problem of all titanium aluminide alloys is their
low ductility. For a long time one has not succeeded in improving
the pregiven high brittleness and low damage tolerance of titanium
aluminide alloys arising from the nature of the intermetallic
phases (compare "Structural Intermetallics 1997", page 531, see
above). For many of the above mentioned uses indeed plastic
fracture elongations of .gtoreq.1% are sufficient. For the making
of turbines and motors however it is necessary that this minimum
amount of ductility be guaranteed in industrial manufacturing
throughout large batch numbers. Since the ductility is sensitively
dependent on structure in industrial manufacturing processes it is
extremely difficult to assuredly obtain a highly homogenous
structural configuration. For high tensile strength alloys a
maximum tolerable defect size, for example the maximum grain or
lamina colony size, is very small so that for such alloys a very
high structural homogeneity is desirable. This homogeneity can
however, because of the unavoidable fluctuation of the alloying
mixture from, for example .+-.0.5 Atom % in aluminum content, only
be reached with difficulty.
[0010] At the present time of the many possible structural types of
.gamma.-titanium aluminide alloys only lamellar and so called
duplex structures are taken into consideration for high temperature
uses. Upon the cooling from the single phase region the
.alpha.-mixed crystals first appear while plates of the
.gamma.-phase crystallographically become oriented and separate
from the .alpha.-mixed crystals.
[0011] Compared to this, duplex structures consisting of lamina
colonies and .gamma.-grains arise when the material has been heated
into the second phase area .alpha.+.gamma.. Then upon cooling the
.alpha.-grains lying in the second phase area again change into two
phased lamina colonies. Above all, coarse structural components
exist in .gamma.-titanium aluminide alloys since during the running
through of the .alpha.-area large .alpha.-grains are formed. This
can indeed happen during the solidification when large stalk
crystals of the .alpha.-phase are formed from the melt. Accordingly
as much as possible the single phase area of the .alpha.-mixed
crystals must be avoided during processing. Since in practice
however fluctuations in the composition and processing temperatures
appear and thereby locally vary the constitution in work pieces,
the formation of large lamina colonies is not to be prevented.
[0012] Proceeding from this state of the art the present invention
has as its object the making available of a titanium aluminide
alloy with a fine and homogeneous structural morphology, as to
which alloy the variations of the alloy composition as well as
unavoidable temperature fluctuations which appear during
manufacturing processes of industrial practice have hardly any or
no significant effect on the homogeneity of the alloy, and
especially without having to make any basic changes in the
manufacturing processes. Therefore a further object of the
invention is to make available a structural component consisting of
a homogenous alloy.
SUMMARY OF THE INVENTION
[0013] This object is solved by means of an alloy based on titanium
aluminide made through the use of melting and powdered
metallurgical technologies with an alloy composition of Ti-z Al-y
Nb where 44.5 Atom %.ltoreq.z.ltoreq.47 Atom %, especially where
44.5 Atom %.ltoreq.z.ltoreq.45.5 Atom %, and 5 Atom
%.ltoreq.y.ltoreq.10 Atom %, which is further formed in that this
alloy contains molybdenum (Mo) in the range of between 0.1 Atom %
to 3.0 Atom %. The remainder of the alloy is made up of Ti
(titanium).
[0014] Investigations have shown that the alloying of molybdenum
with titanium aluminide having a niobium portion usually results in
an alloy for which the .beta.-phase is not stable over the entire
temperature region, and therefore in a customary process procedure
such as extrusion the remainder of the high temperature
.beta.-phase dissolves, and a better structural homogeneity of the
alloy is obtained. In this way over the entire temperature range
relevant to the before mentioned manufacturing process a portion of
the volume of the .beta.-phase without grain coarseness is
realized. This type of alloy according to the invention therefore,
because of the fine and very uniform dispersion of the
.beta.-phase, has a homogenous structure with high strength
values.
[0015] Therefore an alloy is presented by the invention which is
suitable as a lightweight work material for high temperature
applications, such as for turbines blades or engine and turbine
components. The alloy of the invention is made through the use of
casting metallurgy, melting metallurgy or powdered metal metallurgy
methods or by the use of these methods in combination with
reshaping techniques.
[0016] Above all in the case of Ti-(44.5 Atom % to 45.5 Atom %)
Al-(5 Atom % to 10 Atom %) Nb the addition of molybdenum at a
content of about 1.0 Atom % to 3.0 Atom % leads to good
microstructures with a high structural homogeneity.
[0017] Moreover an alloy according to the invention has a
composition of Ti-z Al-y Nb-x B where 44.5 Atom
%.ltoreq.z.ltoreq.47 Atom %, especially where 44.5 Atom
%.ltoreq.z.ltoreq.45.5 Atom %, 5 Atom %.ltoreq.y.ltoreq.10 Atom %
and 0.05 Atom %.ltoreq.x.ltoreq.0.8 Atom %, or a composition of
Ti-z Al-y Nb-w C where 44.5 Atom %.ltoreq.z.ltoreq.47 Atom %,
especially where 44.5 Atom %.ltoreq.z.ltoreq.45.5 Atom %, 5 Atom %
is .ltoreq.y.ltoreq.10 Atom % and 0.05 Atom %.ltoreq.w.ltoreq.0.8
Atom %, each of which alloys contains molybdenum (Mo) in the region
of between 0.1 Atom % to 3 Atom %, especially in the region of
between 0.5 Atom % to 3 Atom %.
[0018] Alternatively the alloy is made up of Ti-z Al-y Nb-x B-w C
where 44.5 Atom %.ltoreq.z.ltoreq.47 Atom %, especially where 44.5
Atom %.ltoreq.z.ltoreq.45.5 Atom %, 5 Atom %.ltoreq.y.ltoreq.10
Atom %, 0.05 Atom %.ltoreq.x.ltoreq.0.8 Atom % and 0.05 Atom
%.ltoreq.w.ltoreq.0.8 Atom % and additionally of molybdenum in the
region of between 0.1 Atom % to 3 Atom %.
[0019] By means of the given alloying and the corresponding
alloying proportions high strength .gamma.-titanium aluminide
alloys with a fine dispersion of the .beta.-phase are created for a
wide range of processing temperature.
[0020] In the case of the present invention the strived for
structural stability and process security are thereby achieved in
that the appearance of single phase regions are avoided over the
entire temperature region traversed in the manufacturing processes
and upon use, by the aimed for inclusion of the cubic space
centered .beta.-phase. Principally the .beta.-phase appears as the
high temperature phase for all technical titanium aluminide alloys
at temperatures .gtoreq.1350.degree. C.
[0021] From the literature it is known that this phase can be
stabilized at low temperatures by different elements such as Mo, W,
Nb, Cr, Mn, and V. The special problem with the alloying of these
elements exists however in that the .beta.-stabilizing elements
have to be very accurately tuned to the Al content. Moreover in the
case of the addition of these elements undesirable exchange effects
appear which lead to higher portions of the .beta.-phase and to a
coarse dispersion of this phase. Such a constitution is most
disadvantageous for the mechanical properties. Further, the
properties of the .beta.-phase are dependent on the alloying
elements and their composition. Especially the constitution must be
so chosen so that a precipitation of the brittle .omega.-phase from
the .beta.-phase must be substantially avoided. Because of this
relationship an alloying composition is presented whereby for the
mechanical properties an optimum composition and dispersion of the
.beta.-phase can be realized for a wide region of processing
temperatures. At the same time the best possible strength
properties are achieved.
[0022] According to a preferred form of the invention the alloy
likewise contains boron, preferably with a boron content in the
alloy in the area of from 0.05 Atom % to 0.8 Atom %. The addition
of boron leads advantageously to the formation of stable
precipitates which likewise contribute to the mechanical hardening
of the alloy and to the stabilization of the structure.
[0023] The object of the invention is further solved by a
construction component made from an alloy of the invention. To
avoid repetition reference is made to the previous exposition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In the following the invention, without limitation to the
general thought of the invention, is described by way of exemplary
embodiments with reference to the accompanying schematic drawings,
to which in regard to publication reference is made for all details
of the invention not more closely explained in the text. The
drawings are:
[0025] FIG. 1 shows a raster electron microscope picture of a cast
block having an alloying of Ti-45Al-8Nb-0.2C (Atom %);
[0026] FIG. 2a to 2c each shows a picture of the structure in an
alloy of Ti-45Al-8Nb-0.2C (Atom %) taken by a raster electron
microscope after different processing steps;
[0027] FIGS. 3a and 3b each shows a picture of the structure in an
alloy of the invention of Ti-45Al--Nb-2 Mo (Atom %) after different
processing steps, and
[0028] FIG. 4 is a diagram with tension-elongation curves resulting
from tests of the alloy Ti-45Al-5Nb-2 Mo (Atom %).
DETAILED DESCRIPTION
[0029] FIG. 1 shows two pictures of a structure in a cast block
made of the alloy Ti-45Al-8Nb-0.2C (Atom %). The pictures as well
as the further pictures in the following figures were taken by
means of back scattered electrons in a raster electron
microscope.
[0030] The structure (FIG. 1) shows lamina colonies of the
.alpha..sub.2-phase and the .gamma.-phase, which originate from
former .gamma.-lamina. The former .gamma.-lamina are separated by
stripes of bright pictured grains of .beta.-phase or B2-phase. The
.alpha.-lamina next formed in the .beta.- .alpha.-conversion decay
upon further cooling into .alpha..sub.2-lamina and
.gamma.-lamina.
[0031] In FIGS. 2a to 2c two further pictures of the structure of
the alloy Ti-45Al-8Nb-0.2C taken in the raster electron microscope
and after different processing steps are shown. FIG. 2a shows the
structure after extrusion at 1230.degree. C. The extrusion
direction runs horizontally. The structure shows grains of the
.alpha..sub.2- and .beta.-phase, with the cubic space centered
.beta.-phase having vanished.
[0032] FIG. 2b shows the structure of the alloy after the extrusion
at 1230.degree. C. and a further forging step at 1100.degree. C.
This structure shows grains of the .alpha..sub.2- and .gamma.-phase
and a few .alpha..sub.2/.gamma. lamina colonies.
[0033] In FIG. 2c is shown the structure of the alloy after
extrusion at 1230.degree. C. and a subsequent heat processing at
1330.degree. C. This structure exhibits likewise grains of the
.alpha..sub.2- and .gamma.-phase. The picture shows a fully laminar
structure with lamina of the .alpha..sub.2- and .gamma.-phase. The
lamina colony size has a value of about 200 .mu.m, with colonies
also appearing which are clearly larger than 200 .mu.m.
[0034] As in the structure illustrated in FIG. 2a, also in the
structures illustrated in FIGS. 2b and 2c the cubic space centered
phase does not appear. So the .beta.-phase in this temperature
range with a heat processing after the extrusion is
thermodynamically not stable.
[0035] In FIGS. 3a and 3b are illustrated raster electron
microscope pictures of the structure of an alloy in accordance with
the invention. Proceeding from an alloy of Ti-45Al-5Nb the alloying
agent molybdenum was added at 2 Atom %. This starting alloy
Ti-45Al-5Nb-2Mo is based on a composition as described in European
Patent EP 1 015 650 B1.
[0036] FIGS. 3a and 3b show the structure of this alloy of the
invention after an extrusion at 1250.degree. C. and a subsequent
heat treatment at 1030.degree. C. (FIG. 3a) as well as observed at
1270.degree. C. (FIG. 3b).
[0037] The structure of FIG. 3a exhibits grains of the
.alpha..sub.2-phase, the .gamma.-phase and the brightly pictured
.beta.-phase, with the latter being arranged in strips. The
structure in FIG. 3b shows lamina colonies of .alpha..sub.2- and
.gamma.-phases as well as grains of the brightly pictured
.beta.-phase, which again have precipitated from the
.gamma.-phase.
[0038] The structures of FIGS. 3a and 3b are fine, very homogenous
and show uniform distribution of the .beta.-phase. After the heat
treatment of 1030.degree. C. a globular structure is presented,
with it having grains of .beta.-phase in strips parallel to the
extrusion direction, while the material heat treated at
1270.degree. C. exhibits a very homogenous, fully lamellar
structure with uniformly distributed .beta.-grains (FIG. 3b).
[0039] The colony size of the alloy Ti-45Al-5Nb-2Mo has a value of
between 20 to 30 .mu.m and is therefore at least about 5 times
smaller than in the fully laminar structure of .gamma.-titanium
aluminide alloy. Moreover, in the .beta.-phase the .gamma.-phase
has been eliminated so that the .beta.-grains are very finely
subdivided. Therefore, in summary, a very fine and homogenous
structure has been achieved.
[0040] Tests have shown that this fine and homogenous structure
morphology after heat treatment is present for the entire high
temperature range up to 1320.degree. C. The structures show clearly
that over the entire temperature range relevant for the
manufacturing processes a sufficient volume of the .beta.-phase is
provided and the grain growth is effectively suppressed.
[0041] In tension tests carried out on the material which was heat
treated at 1030.degree. C., at room temperature a stretch limit of
867 MPa, a tensile strength of 816 MPa and a plastic elongation at
rupture at 1.8% were measured.
[0042] FIG. 4 shows measured tension-elongation curves from test of
the alloy Ti-45Al-5Nb-2Mo in tension tests. The test material was
extruded at 1250.degree. C. and subsequently subjected to a heat
treatment for two hours at 1030.degree. C. and was then subjected
to an oven cooling. The curves taken at 700.degree. C. and
900.degree. C. show that the alloy is suitable for many high
temperature applications. By the alloying of a small amount of
molybdenum a very uniform microstructure in the alloy is achieved
so that this alloy can be well used as a high temperature work
material.
[0043] Moreover in FIG. 4 the results of a tension test at room
temperature (25.degree. C.) on the material of the invention is
illustrated, with the tension .sigma. in MPa being shown against
the elongation .epsilon. in %. Thereby an elongation limit increase
was found which otherwise up to now has not been observed for
.gamma.-titanium aluminide alloys. This represents an indication of
an especially fine and homogenous structure. The elongation limit
increase indicates that the material can react to local tensions by
plastic flow, which is very beneficial for ductility and damage
resistance.
[0044] The homogeneity of the alloy of the invention in the region
of relevant processing temperatures is not dependent on technically
unavoidable fluctuations of the temperature or of the
composition.
[0045] The titanium aluminide alloys of the invention are made
through the use of metallurgical casting or powdered metal
techniques. For example, the alloys of the invention can be
processed by hot forging, hot pressing and hot extrusion and hot
rolling.
[0046] The invention offers the advantage that despite the
fluctuations of the alloying composition appearing with the
industrial finishing and unavoidable processing requirements as
previously, a titanium aluminide alloy with very uniform
microstructure and high strength has been made available.
[0047] The titanium aluminide alloy of the invention achieve high
strength up to a temperature in the region of 700.degree. C. to
800.degree. C. as well as good room temperature ductility.
Therefore the alloys are suitable for numerous areas of application
and can for example be used for highly loaded components or as
titanium aluminide alloys for exceptionally high temperatures.
* * * * *