BACKGROUND
Modern gas turbines, especially aircraft engines, must satisfy the
highest demands with respect to reliability, weight, power, economy, and operating
service life. In the development of aircraft engines, the material selection, the search
for new suitable materials, as well as the search for new production methods, among
other things, play an important role in meeting standards and satisfying the demand.
The materials used for aircraft engines or other gas turbines include
titanium alloys, nickel alloys (also called super alloys) and high strength steels.
Titanium alloys are generally used for compressor parts, nickel alloys are suitable for
the hot parts of the aircraft engine, and the high strength steels are used, for example,
for compressor housings and turbine housings. The highly loaded or stressed gas
turbine components, such as components for a compressor for example, are typically
forged parts. Components for a turbine, on the other hand, are typically embodied as
investment cast parts.
It is generally difficult to investment cast titanium and titanium alloys
and similar reactive metals in conventional investment molds and achieve good
results because of the metal's high affinity for elements such oxygen, nitrogen, and
carbon. At elevated temperatures, titanium and its alloys can react with the mold
facecoat. Any reaction between the molten alloy and the mold will result in a poor
surface finish of the final casting which is caused by gas bubbles. In certain situations
2
the gas bubbles effect the chemistry, microstructure, and properties of the final
casting.
Once the final component is produced by casting, machining, or
forging, further improvements in surface finish are typically necessary before it can
be used in the final application. Asperities and pits on the surfaces of components can
reduce aerodynamic performance in turbine blade applications, and increase
wearlfriction in rotating or reciprocating part applications.
In the case of titanium aluminide turbine blades, the cast airfoils may
have regions in the dovetail, airfoil, or shroud that are castlforged oversize. To
machine these thin stock regions to the final dimensions, either mechanical machining
(such as milling or grinding) or non-mechanical machining (such as electrochemical
machining) are typically used. However, in either case, the costs of tooling and labor
are high and result in manufacturing delays.
Moreover, the limited ductility and sensitivity to cracking of alloys,
including titanium aluminide cast articles, may prevent the improvement of the
surface finish of cast articles using conventional grinding and polishing techniques.
Accordingly, there is a need for an intermetallic-based article for use in aerospace
applications that has an improved surface finish and associated methods for
manufacturing such an article.
SUMMARY
3
One aspect of the present disclosure is a method for removing material
from a titanium aluminide alloy-containing article. The method comprises providing
a titanium aluminide alloy-containing article; passing a fluid at high pressure across a
surface of said titanium aluminide alloy-containing article; deforming the surface of
the titanium aluminide alloy-containing article; and removing material from the
titanium aluminide alloy-containing article. In one aspect, the method provides for
asperities and pits from the surface of the titanium aluminide alloy-containing article
be removed without cracking or damaging the surface of the article. In one aspect,
the present disclosure is a titanium aluminide alloy-containing article made according
to the process as recited above.
In another aspect, the present disclosure is a method for removing
overstock material from the convex surface of an titanium aluminide containing
turbine blade, said method comprising: providing a titanium aluminide alloycontaining
turbine blade; passing a fluid at high pressure across the convex surface of
said titanium aluminide containing turbine blade; and removing about 0.025 mm to
about 5.0 mm of overstock material from the convex surface of the titanium aluminide
containing turbine blade.
In one embodiment, the fluid at high pressure makes contact with the
titanium aluminide microstructure. In another embodiment, the motion of the nozzle
from which the fluid at high pressure exits is selected from a group consisting of
rotational, translational, oscillatory, or a combination thereof. In one example, the
fluid at high pressure is passed at about 5 inches per minute to about 100 inches per
minute over the surface of the titanium aluminide alloy-containing article. The fluid,
in one example, comprises water, oil, glycol, alcohol, or a combination thereof. In
one example, particles ranging from about 50 microns to about 400 microns are
suspended in the fluid before the fluid is passed across the surface of the article, and
the solids loading of the fluid is about 10% to 40% by mass flow. In one
embodiment, the fluid is passed along with or concurrent to passing a medium of
particles ranging from about 50 microns to about 400 microns across the surface of
the article. In another example, the fluid is passed along with or concurrent to passing
a medium of particles across the surface of the article, wherein the fluid further
comprises particles ranging from about 50 microns to about 400 microns. The fluid,
in one embodiment, may be heated above room temperature prior to passing the fluid
across the surface of the article.
The deforming step, can for example, comprise plastically deforming
the titanium aluminide alloy. In one embodiment, after the fluid at high pressure is
passed across the surface of the titanium aluminide alloy-containing article, the
surface of the article is deformed over a depth of less than about 100 microns from the
surface of the article and perpendicularly into the article. In a related embodiment,
this depth is less than about 10 microns.
The titanium aluminide alloy, in one example, comprises a gamma
TiAl based phase and an a2 (Ti3Al) phase. By practicing the presently taught
method, the roughness of the surface of the article can be reduced by at least about
50%. In another embodiment, by practicing the presently taught method, the
roughness of the surface of the article is reduced by at least about 25%.
In one embodiment, the surface of the titanium aluminide alloycontaining
article has an initial roughness of greater than about 100 Ra, and wherein
the roughness of the surface of the article is reduced to at least about 50 Ra. In
another embodiment, 'the roughness of the surface of the article is reduced to at least
20 Ra. In one embodiment, fluid at high pressure includes high linear speeds of the
fluid of at least 5 inches per minute. In one embodiment, high linear speed comprises
at least 50 inches per minute. In another embodiment, high linear speed comprises at
least 100 inches per minute. In yet another embodiment, high linear speed comprises
at least 1000 inches per minute. In a particular embodiment, the fluid at high pressure
is passed at speeds of about 50 inches per minute to about 1000 inches per minute
across the surface of the titanium aluminide-containing alloy.
In one embodiment, the titanium alwninide alloy-containing article
comprises a titanium aluminide alloy-containing engine. In another embodiment, the
titanium aluminide alloy-containing article comprises a titanium aluminide alloycontaining
turbine. In one embodiment, the titanium aluminide alloy-containing
article comprises a titanium aluminide alloy-containing turbine blade. In one
embodiment, the article is a turbine engine blade having an average roughness (Ra) of
less than about 20 microinches across at least a portion of the working surface of the
blade.
The fluid at high pressure in one example further comprises particles
of alumina, garnet, silica, silicon carbide, boron carbide, diamond, tungsten carbide,
6
and compositions thereof. In one example, the fluid at high pressure is passed along
with or concurrent to passing a medium of particles ranging from about 50 microns to
about 400 microns across the surface of the article. In another example, the fluid at
high pressure is passed along with or concurrent to passing a medium of particles
ranging from about 20 microns to about 200 microns across the surface of the article.
In another embodiment, these particles are from about 50 microns to about 150
microns.
In one embodiment, the roughness of the surface of the article is
reduced at least about 25%. In another embodiment, the roughness of the surface of
the article is reduced at least about 50%. In one embodiment, the surface has an
initial roughness of greater than about 100 Ra, and wherein the roughness of the
surface of the article is reduced to about 50 Ra or less after treatment. In one
embodiment, the roughness of the surface of the article is reduced to 20 Ra or less
after treatment. That is, the improvement comprises reducing the roughness of the
surface of the article to about 20 Ra or less. In another embodiment, the improvement
comprises reducing the roughness of the surface of the article by more than about 50
Ra. In one embodiment, after treatment, the Ra value is reduced by a factor of about
three to a factor of about six. In a particular example, the roughness of the surface of
the article after treatment is less than about two microns. In another embodiment, the
roughness of the surface of the article after treatment is less than about one micron.
The stabilizing step in one example comprises one or more of fixing,
attaching, and binding said titanium aluminide alloy-containing article to the
structure. Passing of the fluid at high pressure and/or small particle containing
medium, such as garnet, across the surface of the article may comprise interacting the
fluid and/or medium at high pressure with phases of the titanium aluminide
microstructure.
Another aspect of the present disclosure is a method for changing a
surface of a titanium aluminide alloy-containing article, comprising: stabilizing the
titanium aluminide alloy-containing article on a structure; passing a fluid across a
surface of said stabilized titanium aluminide alloy-article at high linear speed; and
deforming both a gamma titanium aluminide based phase and an a2 (Ti3Al) phase of
the titanium aluminide alloy, wherein material is removed from the surface of the
titanium aluminide alloy-containing article and thereby the surface of the article is
changed. In one aspect, the present disclosure is a titanium aluminide alloycontaining
article made according to the process as recited above.
In another aspect, the present disclosure is a method for machining the
surface of a titanium aluminide alloy-containing article, said method comprising:
providing a titanium aluminide alloy-containing article; passing a fluid at high
pressure across a surface of said titanium aluminide alloy-containing article;
deforming the surface of the titanium aluminide alloy-containing article; and
removing material from the surface of the titanium aluminide alloy-containing article.
In another aspect, the present disclosure is a method for removing
overstock material from a titanium aluminide alloy-containing article, comprising:
providing a titanium aluminide alloy-containing article; passing a fluid at high
8
pressure across a surface of said titanium alurninide alloy-containing article;
deforming the surface of the titanium aluminide alloy-containing article; and
removing overstock from the article, wherein asperities and pits from the surface of
the titanium aluminide alloy-containing article are removed without cracking or
damaging the surface of the article.
BRIEF DESCRIPTION OF THE FIGURES
These and other features, aspects, and advantages of the present
articles and methods will become better understood when the following detailed
description is read with reference to the accompanying drawings in which like
characters represent like parts throughout the drawings, and wherein:
Figure 1 shows a schematic perspective of the fluid jet nozzle
positioned with respect to the airfoil according to one embodiment. In this example,
the nozzle is positioned such that the fluid jet interacts with the convex side of the
article, such as an airfoil, removing overstock material from the convex side of the
article.
Figure 2 shows a schematic perspective of the contour of the article
from Figure 1 before and after the high pressure fluid jet treatment according to one
embodiment.
Figure 3 shows a diagram showing one erample of a configuration of
the abrasive water jet nozzle in relation to the blade surface that is machined. Figures
1-3 show a setup that was used to remove 0.004" from the trailing edge of a cast
titanium aluminide blade.
Figure 4 is a schematic depicting the space-time integral of the cloud
patterns that are used to perform abrasive water jet machining.
Figure 5 shows an image of the abrasive water jet machined blade,
showing regions 1 (as-received), region 2 (as produced using example I), and region
3 (as produced using example 3).
Figure 6 shows an image of the abrasive water jet machined blade,
showing the blade surface and trailing of regions 1 (as-received), region 2 (as
produced using example l), and region 3 (as produced using example 3).
Figure 7 is an image of the abrasive water jet machined blade, showing
the blade trailing region 1 (as-received), region 2 (as produced using example l), and
region 3 (as produced using example 3). The unacceptable control of material
removal can be seen in region 3.
Figures 8a and 8b show flow charts, in accordance with certain aspects
of the disclosure for removing material from and improving the surface of a titanium
aluminide alloy-containing article.
DETAILED DESCRIPTION
10
The present disclosure relates generally to titanium and titanium
alloys containing articles having improved surface finishes, and methods for
improving surface finishes on such articles. In one example, the present
disclosure relates to turbine blades having improved surface finishes that exhibit
superior properties, and methods for producing the same.
Conventional gas and steam turbine blade designs typically have airfoil
portions that are made entirely of metal or a composite. The all-metal blades,
including costly wide-chord hollow blades, are heavier in weight, resulting in lower
fuel performance and requiring sturdier blade attachments. In a gas turbine aircraft
application, the gas turbine blades that operate in the hot gas path are exposed to some
of the highest temperatures in the gas turbine. Various design schemes have been
pursued to increase the longevity and performance of the blades in the hot gas path.
As used herein, the term "turbine blade" refers to both steam turbine blades and gas
turbine blades.
The instant application discloses that high shear rate local deformation
of the surface of a titanium aluminide component, such as a turbine blade, can provide
a substantial improvement of the surface finish and improve performance. One aspect
is to provide an intermetallic-based article, such as a titanium aluminide based article,
with an improved surface finish. In one embodiment, a cast titanium aluminide based
article is subjected to a high shear rate surface treatment to improve the surface finish
to a roughness of less than 20 microinches (Ra). This new surface treatment improves
surface finish and does not introduce any additional damage or cracks in the surface
of the component.
In one example, the high rate local shear deformation acts over a depth
of less than about 100 microns from the surface into the component. In one
embodiment, the high rate local shear deformation acts over a depth of less than about
10 microns from the surface into the component. This method of removing of
overstock from the article is new and useful, and is different to steps taken to polish a
surface. In one example, to remove material from the surface of the article, a fluid at
high pressure is used, wherein the fluid is passed across the surface of the article. In
another example, a fluid at high pressure is used with a medium comprising particles
that range in size from about 50 microns to 400 microns, wherein the fluid and
particle mixture is passed across the surface of the article. One advantage to this
approach is that it does not require high-stiffness or heavy tooling to support the part,
as is the case for milling.
Surface roughness, often shortened to roughness, is a measure of the
texture of a surface. It is quantified by the vertical deviations of a real surface from
their calculated mean. If these deviations are large, the surface is rough; if they are
small the surface is smooth. Roughness is typically considered to be the high
frequency, short wavelength component of a measured surface. Roughness plays an
important role in determining how a real object will interact with its environment.
For example, rough surfaces usually wear more quickly and have higher friction
coefficients than smooth surfaces.
Flaws, waviness, roughness and lay, taken collectively, are the
12
properties which constitute surface texture. Flaws are unintentional, unexpected and
unwanted interruptions of topography of the work piece surface. Flaws are typically
isolated features, such as burrs, gouges and scratches, and similar features.
Roughness refers to the topographical irregularities in the surface texture of high
frequency (or short wavelength), at the finest resolution to which the evaluation of the
surface of the work piece is evaluated. Waviness refers to the topographical
irregularities in the surface texture longer wave lengths, or lower frequency than
roughness of the surface of a work piece. Waviness may arise, for example, from
machine or work piece vibration or deflection during fabrication, tool chatter and the
like.
The term polishing results in a reduction in roughness of work piece
surfaces. Lay is the predominant direction of a pattern of a surface texture or a
component of surface texture. Roughness and waviness may have different patterns
and differing lay on a particular work piece surface.
The inventors of the instant application provide an intermetallicbased
article, such as a titanium aluminide based article, with a surface that
possesses improved properties, such as reduced roughness and enhanced
mechanical integrity. In one aspect, the present technique includes removing
material from a titanium aluminide alloy-containing article. The method comprises
providing a titanium aluminide alloy-containing article; passing a fluid at high
pressure across a surface of said titanium alurninide alloy-containing article;
deforming the surface of the titanium aluminide alloy-containing article; and
removing material from the titanium aluminide alloy-containing article. By practicing
this method, asperities and pits from the surface of the titanium alurninide alloycontaining
article were removed without cracking or damaging the surface of the
article. In one embodiment, the removing includes removing surface roughness and
removing overstock material from the article. In one aspect, the present disclosure is
a titanium aluminide alloy-containing article made according to the process as recited
above.
Titanium alloys have high relative strength and excellent corrosion
resistance, and have mainly been used in the fields of aerospace, deep sea exploration,
chemical plants, and the like. One example of a titanium alloy is titanium aluminide.
The titanium aluminide alloy typically comprises a gamma titanium aluminide based
phase and an a2 (Ti3A1) phase of the titanium aluminide alloy.
The deforming step according to one technique comprises plastically
deforming the titanium aluminide alloy; as a result of plastic deformation of the
titanium aluminide alloy, at least one of the phases in the alloy is deformed
permanently or irreversibly. This deformation of the titanium aluminide alloy is
achieved by passing a fluid at high pressure across the surface of the article, causing
an interaction of the fluid with the titanium aluminide microstructure. The fluid is
passed across the surface of the component at high linear speeds and the resultant high
shear rate generates the local surface deformation. In one embodiment, an abrasive
medium comprising particles, such as alumina or garnet, are suspended in the fluid
prior to the passing of the fluid across the surface of the article. The impact of the
mixture, with or without particles, provides the shear necessary to remove asperities
without cracking or damaging the surface.
The abrasive medium according to one example is selected from at
least one of alumina, garnet, silica, silicon carbide, boron carbide, diamond, tungsten
carbide, and compositions thereof. The abrasive medium can also be an abrasive jet
of fluid. In certain embodiments, the fluid is an abrasive high pressure jet of fluid and
further comprises at least one of alumina, garnet, silica, silicon carbide, boron carbide,
diamond, tungsten carbide, and compositions thereof. In one example, the fluid
comprises water. In certain embodiments, the harder the abrasive, the faster and more
efficient the polishing operation. The reuse of the abrasive medium permits economic
use of harder, but more expensive abrasives, with resulting enhancements in the
efficiency of polishing and machining operations to increase the polishing rate when
required. For example, alumina or silicon carbide may be substituted in polishing
operations where garnet is used.
Abrasive water jet polishing in conjunction with 4 or 5 axis
manipulation capability provides rapid, efficient, and low-cost means to modify the
cast component geometry to comply with the precise requirements for the final part
dimensions and the necessary surface finish. The high shear rate local surface
deformation is generated by passing the fluid that exits the nozzle at high pressure
with or without the abrasive medium across the surface of the article. The motion of
the nozzle from which the high pressure fluid exits can be rotational, translational, or
oscillatory. For example, using this nozzle, linear speeds in excess of 50 inches per
minute may be achieved, and this level of speed in conjunction with abrasive particles
of a size range from 50 microns to 400 microns, can lead to substantial removal of
material, including overstock, from the surface of the intermetallic alloy article. In
one example, the speed of the nozzle ranges between 1 x 10" and 10 x inches per
minute.
In one aspect, the present disclosure is a method for removing
overstock material from the convex surface of an titanium aluminide containing
turbine blade, the method comprising: providing a titanium aluminide alloycontaining
turbine blade; passing a fluid at high pressure across the convex surface of
the titanium aluminide containing turbine blade; and removing overstock material
from the convex surface of the titanium alurninide containing turbine blade.
According to one example, 0.025 mm to 5 mm of material is removed by the kerf at a
prescribed distance from the nozzle exit. According to one example, 0.5 rnrn to 3 mm
of material is removed by the kerf at a prescribed distance from the nozzle exit. In
one example, about 1 mm to 2 rnrn of material is removed.
In one example, the gap between the nozzle from which the fluid exits
at high pressure and the surface of a work piece, such as for example a turbine blade,
is about 0.1 cm to about 5.0 cm. In a related embodiment, the distance between the
nozzle and the surface of the work piece is about 0.1 cm, 1.0 cm, 1.5 cm, 2 cm, or 2.5
cm. This distance can be adjusted to suit the requirements for any given piece. For
example, if all other variables are kept constant, the closer the nozzle opening is to the
surface of the work piece, the higher the impact of the fluid exiting the nozzle and
interacting and coming in contact with the surface of the work piece. The closer the
nozzle, the narrower the kerf - the more well-defined the jet, so higher accuracy is
possible but is counteracted by exponentially higher material removal rate.
Conversely, if the nozzle is further away from the work piece, the rate and/or amount
of material that can be removed is less than if the nozzle is kept in much closer
proximity with the surface of the portion of the work piece that is to be removed.
Similarly, the angle at which the fluid that exits the nozzle opening contacts the
surface of the work piece is a factor at determining the rate and/or amount of material
that is removed from the surface of the work piece. The work piece, such as a turbine
blade or another titanium aluminide alloy-containing article, in one example, is fixed
and the nozzle moves relative to the surface of the work piece (see Figure 1-3).
In accordance with the teachings herein, the fluid is discharged at high
pressure from the nozzle, with or without the abrasive medium, and passes across the
surface of the titanium aluminide alloy-containing article. The pressure typically is at
about 5000 to about 10,000 pounds per square inch on the surface. In one
embodiment, the pressure on the surface is at about 40,000 to about 80,000 pounds
per square inch. In another embodiment, the pressure of the fluid at the nozzle
opening is at about 80,000 pounds per square inch to about 150,000 pounds per square
inch. The shear forces generated by the interaction between the article surface and the
high pressure fluid generates local flow of the intermetallic material without cracking
or damaging the surface. This process removes asperities and removes pits in the
surface. The titanium aluminide alloy-containing article or work piece comprises a
titanium aluminide alloy-containing engine, a turbine, or a turbine blade.
17
The passing step can include, in one example, a two step process or up
to a five step process. For example, the passing step includes passing different sizes
of the abrasive medium suspended in a fluid and this fluid is then passed at high speed
across the surface of the titanium aluminide alloy-containing article. The size of the
particles that make up the abrasive medium is an aspect of the disclosure. For
example, the passing step comprises suspending different sized particles in the fluid
and then passing a first abrasive medium of particles that are suspended in the fluid
and range from about 140 microns to about 195 microns across the surface, then
passing a second abrasive medium of particles that are suspended in the fluid and
range from about 115 microns to about 145 microns across the surface, and then
passing a third abrasive medium of particles that are suspended in the fluid and range
from about 40 microns to about 60 microns across the surface.
The abrasive medium of different sizes, in one example, are suspended
in the fluid sequentially and the fluid is passed at high speed across the surface of the
article such that decreasing size of particles come in contact with the surface of the
article over the period of time that the fluid is passed over the article's surface. For
example, the passing step comprises first passing an abrasive medium of particles
suspended in a fluid and ranging from about 70 microns to about 300 microns across
the surface, followed by passing an abrasive medium of particles suspended in a fluid
and ranging from about 20 microns to about 60 microns across the surface. In another
example, the passing step comprises first passing an abrasive medium of particles
suspended in a fluid and ranging from about 140 microns to about 340 microns across
the surface, followed by passing an abrasive medium of particles suspended in a fluid
18
and ranging from about 80 microns to about 140 microns across the surface, and
further followed by passing an abrasive medium of particles suspended in a fluid and
ranging from about 20 microns to about 80 microns across the surface.
In a particular embodiment, the third or final pass of the abrasive
medium involves passing particles suspended in a fluid and ranging from about 5
microns to about 20 microns across the surface. In a particular embodiment, the final
pass of the abrasive medium involves passing particles suspended in a fluid and
ranging from about 10 microns to about 40 microns across the surface. In a related
embodiment, the final pass of the abrasive medium may be the second, third, fourth,
or fifth pass of the suspended abrasive medium across the surface. In one
embodiment, the units for the particles reflect the size of the particle. In another
embodiment, the units for the particles reflect the outside dimension of the particle,
such as width or diameter. In certain embodiments, the abrasive medium can be the
same composition of matter with different sizes across the surface, or it can be one or
more different compositions of matter. For example, the abrasive medium is alumina
particles of varying size, or a mixture of alumina particles and garnet of varying size.
The particle size of the abrasive according to an exemplary
embodiment should be the smallest size consistent with the required rate of working,
in light of the hardness and roughness of the surface to be worked and the surface
finish to be attained. In general terms, the smaller the particle or "grit" size of the
abrasive, smaller pieces of particles can be removed and a smoother surface is
obtained attained. The abrasive will most often have a particle size of from as low as
about 50 microns up to about 600 microns. More commonly, the abrasive grain size
will be in the range of from about 100 to about 300 microns.
The fluid, in one example, is selected from a group consisting of water,
oil, glycol, alcohol, or a combination thereof. In one example, particles ranging from
about 50 microns to about 400 microns are entrained in the fluid before the fluid is
passed across the surface of the article, and the solids loading of the fluid is about
10% to about 40% by mass flow. In one embodiment, the solids loading of the fluid
is about 5% to about 50%. In another embodiment, the solids loading of the fluid is
about 15% to about 30%.
As well as the size of the particles constituting the abrasive medium,
the speed of the particles across the surface of the article and the duration of time for
each passing step are controlled. In one embodiment, the passing speed is such that it
takes less than one minute for the particles to pass across one foot of the article. In
another embodiment, it takes between 10 seconds to 40 seconds for the particles to
pass across one foot of the article. In another embodiment, it takes between 1 second
to 20 seconds for the particles to pass one foot of the article.
In one aspect, the fluid at high pressure has a high linear speed. This
high linear speed comprises at least 50 inches per minute, in another example is at
least 100 inches per minute, and in another example is at least 1000 inches per
minute. This refers to the linear speed of the jet in the direction of the travel of the
cutting head as the cutting head moves. In certain embodiments, the fluid with the
abrasive medium is passed across the surface of the titanium aluminide alloy-
20
containing article at high linear speeds of about 50 inches per minute to about 1000
inches per minute. Where the linear speed describes the velocity of the jet itself, in
one example, the velocity is from about 200 m/s to about 1000 m/s, and in another
example is from about 300 m/s to about 700 m/s. The fluid with the abrasive
medium, in one example, is passed across the surface of the article and interacts with
the titanium aluminide microstructure.
The presently taught method for the high shear rate removal of
material from the titanium aluminide containing article's surface allows smoothing of
the surface and elimination of asperities and pits on the surface of the article. That is,
the presently taught methods allow material to be removed from the article without
generating surface cracks or other damage on the surface of the article. Only local
plastic deformation of the titanium aluminide containing-alloy occurs, typically over a
depth of 10-150 microns, according to the teachings of the present
disclosure.However, this is in contrast to techniques where at least one phase of the
titanium aluminide containing-alloy is plastically deformed. In one embodiment, the
fluid is heated above room temperature prior to passing the fluid across the surface of
the article. A feature of the present technique is the manner in which the surface
deformation process interacts with the phases in the alloy microstructure beneath the
surface.
The passing and deforming steps of the presently taught method may
be sequentially repeated, until the desired removal of material from the surface of the
article or the desired roughness value is achieved. In one example, it is desired that
the surface of high performance articles, such as turbine blades, turbine vanes/nozzles,
turbochargers, reciprocating engine valves, pistons, and the like, have a roughness
(Ra) of about 20 microinches or less. In some instances, the passing and deforming
steps are sequentially repeated at least two times. In some instances, the passing and
deforming steps are sequentially repeated multiple times with a fluid suspension
comprising abrasive medium of varying size or of sequentially decreasing size. This
is performed until the desired surface finish is obtained. For example, the passing
step comprises passing a first abrasive medium of particles suspended in a fluid and
ranging from about 140 microns to about 195 microns across the surface, then passing
a second abrasive medium of particles suspended in a fluid and ranging from about
115 microns to about 145 microns across the surface, and then passing a third
abrasive medium of particles suspended in a fluid and ranging from about 40 microns
to about 60 microns across the surface.
In contrast to the presently taught method, typically, surface finishing
of titanium aluminide components is performed by multi-axis milling, grinding,
abrasive polishing, tumbling processes, or chemical polishing. In contrast to the
presently taught method, the mechanical methods present a risk of surface damage,
while the chemical methods are time-consuming. There are limitations to this
conventional processing on the surface finish that can be generated consistently. The
forces introduced by these bulk machining techniques can introduce undesirable
stresses that can lead to surface cracking of the components. The limited ductility and
sensitivity to cracking of typical titanium aluminide cast articles limit the
improvement of the surface finish of cast articles using conventional grinding and
polishing techniques. The present techniques provide for improved surface finish
with greatly reduced risk of the aforementioned disadvantages.
Another aspect of the present disclosure is a method for changing a
surface of a titanium aluminide alloy-containing article. In one embodiment, this
comprises stabilizing the titanium aluminide alloy-containing article on a structure;
passing a fluid across a surface of the stabilized titanium aluminide alloy-article at
high linear speed; and deforming both a gamma titanium aluminide based phase and
an a2 (Ti3Al) phase of the titanium aluminide alloy, wherein material is removed
from the surface of the titanium aluminide alloy-containing article and thereby the
surface of the article is changed. The stabilizing step in one example comprises one
or more of fixing, attaching, and binding said titanium aluminide alloy-containing
article to the structure. Passing the fluid comprising the abrasive medium across the
surface of the article, wherein there is an interaction between the fluid comprising the
abrasive medium and the phases of the titanium aluminide microstructure. In one
aspect, the present disclosure is a titanium aluminide alloy-containing article made
according to the process as recited above. In one embodiment, the titanium aluminide
alloy-containing article comprises a titanium alurninide alloy-containing engine,
titanium aluminide alloy-containing turbine, or a titanium aluminide alloy-containing
turbine blade.
In another aspect, the present disclosure is a method for machining the
surface of a titanium aluminide alloy-containing article, the method comprising:
providing a titanium aluminide alloy-containing article; passing a fluid at high
pressure across a surface of the titanium alurninide alloy-containing article; deforming
the surface of the titanium aluminide alloy-containing article; and removing material
from the surface of the titanium aluminide alloy-containing article.
In another aspect, the present disclosure is a method for removing
overstock material from a titanium aluminide alloy-containing article, comprising:
providing a titanium aluminide alloy-containing article; passing a fluid at high
pressure across a surface of the titanium aluminide alloy-containing article;
deforming the surface of the titanium alurninide alloy-containing article; and
removing overstock from the article, wherein asperities and pits from the surface of
the titanium aluminide alloy-containing article are also removed without cracking or
damaging the surface of the article.
Another aspect of the present technique is a method for reducing the
Ra value of the surface of a titanium aluminide alloy-containing article, comprising:
stabilizing the titanium aluminide alloy on a structure; passing at high pressure
sequentially decreasing grit sizes suspended in a fluid across the surface of the
stabilized titanium alurninide alloy at high speeds; and deforming both the TiAl based
phase and the a2 (Ti3A1) phase of the titanium aluminide alloy plastically, and
thereby reducing the Ra value of the surface of the titanium aluminide alloy.
An example of the present technique involves removing material, for
example excess overstock material (see for e.g. Figures 1-3) from the surface of
titanium aluminide containing articles that have been produced by casting.
Depending on the type of particle used and their size and conditions including how
24
long the fluid that contains the particles is passed over the article, one can obtain
titanium aluminide containing articles that have reduced Ra values compared to
before treatment. An Ra value of 70 microinches corresponds to approximately 2
microns; and an Ra value of 35 microinches corresponds to approximately 1 micron.
It is typically required that the surface of high performance articles, such as turbine
blades, turbine vanes/nozzles, turbochargers, reciprocating engine valves, pistons, and
the like, have an Ra of about 20 microinches or less. By practicing the presently
taught method, the roughness of the surface of the article is reduced at least about
50%. For example, the surface of the titanium aluminide alloy-containing article has
an initial Ra of greater than about 100 microinches, and wherein the Ra of the surface
of the article is reduced to about 50 microinches or less after treatment. In one aspect,
the present disclosure is a titanium aluminide alloy-containing article, for example a
turbine blade, and it has a roughness of less than about one micron across at least a
portion of its surface.
In one example, the roughness of the surface of the article after
treatment is about 20 microinches Ra or less. In another example, the roughness of
the surface of the article after treatment is about 15 microinches Ra or less. In another
embodiment, after treatment, the Ra value is reduced to 10 rnicroinches or less. In
certain embodiments, after treatment, the Ra value is reduced by a factor of about
three to about six. For example, after treatment, the Ra value is reduced by a factor of
about five. In one embodiment, the Ra value is improved from a level of 70-100
microinches on a casting before treatment to a level of less than 20 microinches after
treatment.
25
In accordance with the teachings of the present techniques, the
roughness of the surface of the article can be reduced at least about 25%. In some
instances, the roughness of the surface of the article is reduced at least about 50%. In
one embodiment, the roughness of the surface of the article can be reduced by 20 % to
80%, when compared to pre-treatment levels. In one embodiment, the roughness of
the surface of the article can be reduced by about 2 times, when compared to pretreatment
levels. In one embodiment, the roughness of the surface of the article can
be reduced by about 4 times, when compared to pre-treatment levels. In one
embodiment, the roughness of the surface of the article can be reduced by about 6
times, when compared to pre-treatment levels. In one embodiment, the roughness of
the surface of the article can be reduced by about 8 times, when compared to pretreatment
levels. In one embodiment, the roughness of the surface of the article can
be reduced by about 10 times, when compared to pre-treatment levels. In another
embodiment, the roughness of the surface of the article can be reduced by about 2
times to about 10 times, when compared to pre-treatment levels.
The surface of the titanium aluminide alloy-containing article may
have an initial roughness of greater than about 100 microinches Ra, and after
treatment, the roughness of the surface of the article is reduced to about 50
microinches Ra or less. In another embodiment, the roughness of the surface of the
article is reduced to about 20 microinches Ra or less. In one embodiment, the surface
of the titanium aluminide alloy-containing article has an initial roughness of about
120 microinches Ra, and this roughness is reduced to about 20 microinches Ra after
treatment. In one embodiment, the surface of the titanium aluminide alloy-containing
26
article has an initial roughness of about 115 microinches Ra, and this roughness is
reduced to about 10 microinches Ra after treatment. In one embodiment, the surface
of the titanium aluminide alloy-containing article has an initial roughness of 110
microinches Ra or more, and this roughness is reduced to 30 microinches Ra or less
after treatment.
The present embodiment provides a finished article with a substantially
defect-free surface. In addition, by practicing the teachings of the present technique,
the finished article that is obtained (for example, a turbine blade) has a roughness of
less than 50 microinches, and in the alternative less than 10 microinches, across at
least a portion of the article's surface.
One aspect is a titanium aluminide alloy-containing article having a
roughness of less than about one micron across at least a portion of a surface
containing titanium aluminide alloy. In one embodiment, this article is cast article. In
one example, the article is an investment cast article. In another example, the article
is heat treated or processed by hot isostatic pressing. Hot isostatic pressing (HIP) is a
manufacturing process used to reduce the porosity of metals and increase the density
of many ceramic materials. This improves the material's mechanical properties and
workability. The HIP process subjects a component to both elevated temperature and
isostatic gas pressure in a high pressure environment, for example, a containment
vessel. Argon is typically used as the pressurizing gas. An inert gas such as Argon is
used, so that the article does not chemically react. The chamber is heated, causing the
pressure inside the vessel to increase, applying pressure to the article from all
directions (hence the term "isostatic"). In one example, the inert gas is applied
between 7,350 psi (50.7 MPa) and 45,000 psi (3 10 MPa), with 15,000 psi (100 MPa)
being one example.
The article can be an engine or a turbine. In a specific embodiment,
the article is a turbine blade. In another embodiment, the titanium aluminide alloycontaining
article comprises a titanium aluminide alloy-containing turbine blade. In
one example, the titanium aluminide alloy-containing article is a turbine blade and at
least a portion of a working surface of the turbine blade has an Ra roughness of less
than about 40 microinches. In another embodiment, the majority of the surface area
of the titanium aluminide alloy article is substantially planar and has a roughness of
less than about 20 microinches Ra. In a specific embodiment, the article is a turbine
engine blade having an average roughness of less than about 15 microinches Ra
across at least a portion of the working surface of the blade.
Conventional Abrasive Waterjet (AWJ) is used for cutting metal with
the jet completely cutting through the workpiece material. The present disclosure
applies a modified version of AWJ to generate a skim cut, or surface polish. The
abrasive water jet is set up to skim over the workpiece surface for light cut or polish
of the surface of the component. The AWJ process is set up for the purpose of
correcting casting overstock errors and finishing machining the part to meet tolerance
and surface finishing requirements. The jet is moved relative to the workpiece with a
complex tool path to follow the workpiece contour. The relative motion is provided
by a multi-axis CNC driver. The jet spatial contour matches the workpiece contour in
the machining areas.
Waterjet is an abrasive process and has low cutting forces. Another
advantage is that the tooling cost is low. Another advantage of the presently taught
method is that the high pressure jet cuts and polishes the material with a high removal
rate, leading to low cycle time. Abrasive water jet polishing can also be performed
with a jet with a controlled tool path. This is an alternative process to conventional
machining and surface polishing approaches.
In general, the abrasive will desirably be employed at concentrations in
the formulation at levels of from about 10 to about 30 percent by mass flow. The rate
at which work is performed on the article is related to the spatial concentration of the
abrasive, and it is appropriate to assure that the concentration is sufficient to attain the
process cycle times and productivity for best efficiency in the working of the
titanium-containing article. There is no literal lower limit to the abrasive
concentration, although it should be kept in mind that the abrasive content is a major
determinant of the cutting power of the medium, and when this is too low, the
required deformation may not occur. When low concentrations of abrasive are
employed, other techniques for attaining the required cutting power may be
employed, such as increasing jet pressure and velocity. The surface deformation
polishing approach using a fluid at high pressure generates components with
improved surface finish and has several advantages in comparison with conventional
milling and grinding methods. For example, the present technique provides a fast and
simple method for providing an improved surface finish while generating minimal
surface defects. The approach has low cost, and is also amenable to high-rate
automation.
Typical literature information regarding abrasive water jet cutting, and
general knowledge of those skilled in the art, indicates that the random nature of the
abrasive particle distribution in a jet prevents the user from having a rough-cutting
accuracy better than *0.010". Thus, Applicants believe the prior art/knowledge of
those skilled in the art restricts the AWJ process to rough-cutting of bulk material.
Typically, abrasive water jet cutting is used for cutting completely through objects,
rather than for surface machining. The present invention describes a new mode of
abrasive water jet milling, or machining, that allows removal of small amounts of
material (0.001" to 0.020") in a controlled manner. Typical configurations for surface
abrasive water jet milling, as described in the present disclosure, are shown for
example in Figures 1-3.
Contrary to prior practice of those skilled in the art of abrasive water
jet cutting, the present disclosure makes direct use of the random nature of the particle
distribution in the water jet in conjunction with the high mass flow rate to achieve
material removal from the surface of overstock parts, rather than through-thickness
cutting. The present invention controls and employs the abrasive water jet kerf.
Typically in cutting processes, the 'kerf is considered to be a feature that results in
lost material (the kerf is defined as the width of a groove made by a cutting tool in
conventional machining), and is therefore detrimental.
However, in the present disclosure, the kerf is re-defined as a time-
3 0
series integral of the spatial distribution of the abrasive in the jet that impinges upon
the surface to be machined over a series of different times, as described in Figure 4.
This integrated result is a probability density function (PDF) that is used to describe
the cutting geometry. The kerf is controlled so that it can be used constructively to
remove excess material from a part in a controlled manner. The cutting geometry is
represented much like the side of a conventional milling cutter, except that residence
time (which is controlled by the feedrate, or the rate of translation of the jet) directly
controls the material removal rate. The control of the jet characteristics and the
motion of the jet play a part in controlling the rate of material removal.
EXAMPLES
The techniques, having been generally described, may be more readily
understood by reference to the following examples, which are included merely for
purposes of illustration of certain aspects and embodiments, and are not intended to
limit the system and methods in any way.
A roughness value can either be calculated on a profile or on a surface.
The profile roughness parameter (Ra, Rq, ...) are more common. Each of the
roughness parameters is calculated using a formula for describing the surface. There
are many different roughness parameters in use, but R, is by far the most common.
Other common parameters include Rz, Rq, and Rsk.
The average roughness, Ra, is expressed in units of height. In the
Imperial (English) system, 1 Ra is typically expressed in "millionths" of an inch. This
3 1
is also referred to as "microinches". The Ra values indicated herein refer to
microinches. Amplitude parameters characterize the surface based on the vertical
deviations of the roughness profile from the mean line. A profilometer is a device
that uses a stylus to trace along the surface of a part and determine its average
roughness.
The surface roughness is described by a single number, such as the Ra.
There are many different roughness parameters in use, but Ra is the most common.
All of these parameters reduce all of the information in a surface profile to a single
number. Ra is the arithmetic average of the absolute values and R, is the range of the
collected roughness data points. Ra is one of the most common gauges for surface
finish.
The following table provides a comparison of surface roughness, as
described using typical measurements of surface roughness.
Roughness values Ra
micrometers
50
Roughness values Ra
microinches
2000
Roughness
Grade Numbers
N12
In one example, the nozzle is set up so that it is almost in contact with
the work piece, such as for example a turbine blade, as shown in Figure 1. Here, the
longitudinal axis of the jet that emanates from the nozzle is aligned as shown in
Figure 1 and it is moved with respect to the overstock part in accordance with
thecontour of the surface that is to be produced after the removal of the material from
the cast airfoil with overstock on the convex side. The water jet was set up to provide
a jet of fluid, such as for example water, that contains, for example, garnet or yttrium
aluminate particles with a size of about 50 to about 600 microns. The high pressure
fluid jet used has a circular nozzle orifice diameter of 0.030 inches. The jet is moved
relative to work piece with a complex tool path, and the relative motion was provided
by a multi-axis CNC driver. The overstock cast part possesses, for example, lmm of
overstock material only on the convex side of the airfoil.
The overstock is employed to allow for solidification shrinkage during
casting, for reaction with the mold, for reaction with the environment during heat
treatment, and to accommodate dimensional variation in the casting that can be
accommodated during final machining of the part. The spatial profile of the abrasive
fluid jet nozzle is set up to follow the work piece contour in the areas of the blade on
the convex surface where the overstock material has to be removed (see Figure 2,
showing an example of the before and after contour). The range of material
thicknesses that can be removed with the skim cut is from about 0.05mm to about 5.0
3 3
mm. In a specific example, about 0. lmm to about 2.5mm of material can be removed
with the skim cut. In one embodiment, nozzles of alternate geometries can be
employed, such as a slot rather than a circle; other nozzle geometries that may be
more suitable for the contour of the airfoil can also be employed.
In one embodiment, bulk pieces of overstock material were trimmed
off the blade with a linear speed of 10 inches/min using 150-300 micron size grit.
During this operation, the kerf acts as a saw to remove large blocks of material. In
another embodiment, the kerf further from the nozzle jet acts as a diffuse contact
mechanism which allows time-controlled cut depth. This experiment was performed
by orienting the blade such that is was 10" from the vertical axis. Cuts were made at a
slow speed, e.g. 2 idmin, and at oscillating high speed, e.g. 100 idmin back and
forth. Evaluative cuts were also performed to determine the influence of the
exposure-time variable and its effect on cut depth. The surface roughness of the part
was less than 80 microinches Ra, and the amount of material removed was 4
thousandths of an inch.
Three additional examples are described below of abrasive water jet
machining of the trailing edge of a turbine blade to finish machine the part to the final
dimensions. Figure 3 shows an experimental setup that was used to remove 0.004"
from the convex face surface of the turbine blade/airfoil in a region within
approximately 1" of the trailing edge. The titanium aluminide containing article, in
this case a turbine blade, was placed in a fixture to stabilize it. The fixture was set up
on a rotary axis such that the blade could be rotated about an axis parallel to the
longitudinal axis of the blade. The blade was oriented on the fixture such that the face
of the blade platform lay directly on the horizontal reference of the fixture. The
fixture was then rotated such that the tangent of the trailing edge surface within 1" of
the trailing edge surface was presented 10' off the vertical axis that was coincident
with the wate jet nozzle.
Photographic images of the trailing edge of the blade that were
machined are shown in Figures 5-7. The specific regions of interest are labeled
regions 1, 2, and 3 in the images. Region 1 is the original material, and region 2
shows the abrasive water jet machined surface in example 1, as described infra.
Region 3 shows the abrasive water jet machined surface in example 3, as described
infra. The surfaces finish obtained in example 1 and example 2 are acceptable, and
the surface finish obtained in example 3 is not acceptable.
In a first example, the part was brought into glancing contact with the
jet, and the jet was moved along the longitudinal axis of the blade in the following
mode to successfully remove material from the convex surface of the blade. The jet
was oscillated over a region 2" in length parallel with the longitudinal axis of the
blade at a maximum feedrate of about 100 inches per minute. Four complete cycles
(+2", -2") were performed and the resulting surface is shown in Region 2 in the
photographs in Figure 5-7; these figures show different perspectives of the machined
surface. Approximately 0.004" of titanium aluminide was successfully removed in a
controlled manner. The original surface before machining can be seen in region 1 in
the photographs in Figures 5-7. A good surface finish of less than an Ra of 80
microinches was obtained on the abrasive water jet milled surface (e.g. see Figure 8).
In a second example, the titanium aluminide turbine airfoil was
brought into glancing contact with the abrasive water jet, and the jet was moved along
the longitudinal axis of the blade in the following mode: the jet was moved
continuously at a slow rate of about 1 inch per minute across a traverse length of
about 1" parallel with the longitudinal axis of the blade in a separate region of the
trailing edge of blade from the first example. Approximately 0.004" of material were
successfully removed. A surface finish of less than an Ra of 80 microinches was
obtained.
In a third example, the part was brought into glancing contact with the
abrasive water jet in a new region of the as-received blade, and the jet was translated
along the longitudinal axis of the blade. The motion of the jet across the blade surface
was interrupted, and the speed approached zero. When the speed became low and
approached zero, the rate of material removal increased substantially, and the ability
to control the amount of material removed was reduced. For example, in region 3 as
the jet speed approached zero and remained in place for 5 seconds, a maximum of
0.025" of material thickness was removed in an uncontrolled manner; undesirable
grooves were generated in the surface of the turbine blade. Unlike the conditions for
examples 1 and 2, in example 3, it is not possible to control the rate of material
adeqautely. This machining response can seen on the face of the blade in Figure 5
and on the trailing edge of the blade in Figures 6 and 7.
The abrasive water jet machining operation was performed using a 4
3 6
axis computer numerically controlled machine with a conventional high pressure
water jet system. In each of the three examples that were described, standard garnet
(150-300 micron particle distribution) was employed at 1 pound per minute of mass
flow rate and a water pressure of 85,000 pounds per square inch was employed.
This 10' presentation angle of the abrasive water jet to the surface to
be milledmachined, represents just one of several presentation angles that are
possible depending on the amount of material removal that is desired. In general, the
steeper the angle, the smaller the region machined or polished and the faster the
operation. A shallower angle will affect a larger linear range of material removal, and
remove material slower, allowing finer control. The preferred range of presentation
angles is 5 to 20 degrees. In another embodiment, the range of presentation angles is
7 to 12 degrees. In one embodiment, the angle is about 10 degrees.
It is to be understood that the above description is intended to be
illustrative, and not restrictive. For example, the above-described embodiments
(andor aspects thereof) may be used in combination with each other. In addition,
many modifications may be made to adapt a particular situation or material to the
teachings of the various embodiments without departing from their scope. While the
dimensions and types of materials described herein are intended to define the
parameters of the various embodiments, they are by no means limiting and are merely
exemplary. Many other embodiments will be apparent to those of skill in the art upon
reviewing the above description. The scope of the various embodiments should,
therefore, be determined with reference to the appended claims, along with the full
scope of equivalents to which such claims are entitled. In the appended claims, the
terms "including" and "in which" are used as the plain-English equivalents of the
respective terms "comprising" and "wherein." Moreover, in the following claims, the
terms "first," "second," and "third," etc. are used merely as labels, and are not
intended to impose numerical requirements on their objects. Further, the limitations
of the following claims are not written in means-plus-function format and are not
intended to be interpreted based on 35 U.S.C. 5 112, sixth paragraph, unless and until
such claim limitations expressly use the phrase "means for" followed by a statement
of function void of further structure. It is to be understood that not necessarily all
such objects or advantages described above may be achieved in accordance with any
particular embodiment. Thus, for example, those skilled in the art will recognize that
the systems and techniques described herein may be embodied or carried out in a
manner that achieves or optimizes one advantage or group of advantages as taught
herein without necessarily achieving other objects or advantages as may be taught or
suggested herein.
While the invention has been described in detail in connection with
only a limited number of embodiments, it should be readily understood that the
invention is not limited to such disclosed embodiments. Rather, the invention can be
modified to incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are commensurate with
the spirit and scope of the invention. Additionally, while various embodiments of the
invention have been described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the invention is not to
38
be seen as limited by the foregoing description, but is only limited by the scope of the
appended claims. All publications, patents, and patent applications mentioned herein
are hereby incorporated by reference in their entirety as if each individual publication
or patent was specifically and individually indicated to be incorporated by reference.
In case of conflict, the present application, including any definitions herein, will
control.
This written description uses examples to disclose the invention,
including the best mode, and also to enable any person skilled in the art to practice the
invention, including making and using any devices or systems and performing any
incorporated methods. The patentable scope of the invention is defined by the claims,
and may include other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims if they have structural
elements that do not differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from the literal language
of the claims.

WE CLAIM :
1. A method for removing material from a titanium aluminide alloy-containing
article, comprising:
providing a titanium aluminide alloy-containing article;
passing a fluid at high pressure across a surface of said titanium aluminide
alloy-containing article;
deforming the surface of the titanium aluminide alloy-containing article; and
removing material from the titanium aluminide alloy-containing article,
^ ^ wherein asperities and pits from the surface of the titanium aluminide alloycontaining
article are removed without cracking or damaging the surface of the
article.
2. The method as recited in claim 1, wherein the fluid is passed along with or
concurrent to passing a medium of particles across the surface of the article, and
wherein the fluid further comprises particles ranging from about 50 microns to about
400 microns.
3. The method as recited in claim 1, wherein the motion of the nozzle from
which fluid at high pressure exits is selected from a group consisting of rotational,
translational, oscillatory, or a combination thereof
4. The method as recited in claim 1, wherein the fluid is selected from a group
consisting of water, oil, glycol, alcohol, or a combination thereof
40
5. The method as recited in claim 1, wherein particles ranging from about 50
microns to about 400 microns are suspended in the fluid before the fluid is passed
across the surface of the article, and wherein the solids loading of the fluid is about
10% to 40% by mass flow.
6. The method as recited in claim 1, wherein the fluid is passed at about 2 inches
per minute to about 100 inches per minute over the surface of the titanium aluminide
alloy-containing article.
#
7. The method as recited in claim 1, wherein after the fluid is passed across the
surface of the titanium aluminide alloy-containing article, the surface of the article is
deformed over a depth of less than about 100 microns from the surface of the article
and perpendicularly into the article.
8. The method as recited in claim 1, wherein the titanium aluminide alloy
comprises a gamma titanium aluminide-based phase and an a2 (TisAl) phase.
^ B 9. The method as recited in claim 1, wherein the titanium aluminide alloycontaining
article comprises a titanium aluminide alloy-containing turbine blade.
10. The method as recited in claim 1, wherein the roughness of the surface of the
article is reduced by at least about 50%.
41
11. The method as recited in claim 1, wherein the fluid further comprises particles
of alumina, garnet, silica, silicon carbide, boron carbide, diamond, tungsten carbide,
and compositions thereof.
12. The method as recited in claim 1, wherein the removing step comprises
reducing the roughness of the surface of the article by more than about 50
microinches Ra.
^ ^ 13. The method as recited in claim 1, wherein the roughness of the surface of the
article after treatment is less than about two microns.
14. A method for changing a surface of a titanium aluminide alloy-containing
article, comprising:
stabilizing the titanium aluminide alloy-containing article on a structure;
passing a fluid across a surface of said stabilized titanium aluminide alloyarticle
at high linear speed; and
deforming both a gamma titanium aluminide based phase and an a2 (TisAl)
^ B phase of the titanium aluminide alloy, wherein material is removed from the surface
of the titanium aluminide alloy-containing article and thereby changing the surface of
the article.
15. The method as recited in claim 14, wherein the fluid at high pressure is passed
along with or concurrent to passing a medium of particles ranging from about 50
42
microns to about 400 microns across the surface of the article.
16. The method as recited in claim 14, wherein the fluid is passed at about 5
inches per minute to about 1000 inches per minute over the siuface of the titanium
aluminide alloy-containing article.
17. The method as recited in claim 14, wherein after the fluid at high pressure is
passed across the surface of the titanium aluminide alloy-containing article, the
surface of the article is deformed over a depth of less than about 100 microns from the
^m surface of the article and perpendicularly into the article.
18. The method as recited in claim 14, wherein the titanium aluminide alloycontaining
article comprises a titanium aluminide alloy-containing turbine blade.
19. The method as recited in claim 14, wherein the roughness of the surface of the
article is reduced by at least about 50%.
20. The method as recited in claim 14, wherein the fluid at high pressure further
mm comprises particles of alumina, garnet, silica, silicon carbide, boron carbide, diamond,
tungsten carbide, and compositions thereof
21. The method as recited in claim 14, wherein the fluid is selected from a group
consisting of water, oil, glycol, alcohol, or a combination thereof
43
22. The method as recited in claim 14, wherein particles ranging from about 50
microns to about 400 microns are suspended in the fluid before the fluid is passed
across the surface of the article, and wherein the solids loading of the fluid is about
10% by 40% by mass flow.
23. The method as recited in claim 14, wherein after treatment the Ra value is
reduced by a factor of about three to a factor of about six.
24. The method as recited in claim 14, wherein the roughness of the surface of the
^ ^ article after treatment is less than about two microns.
25. A titanium aluminide alloy-containing article made according to the process as
recited in claim 1.
26. A method for machining the surface of a titanium aluminide alloy-containing
article, said method comprising:
providing a titanium aluminide alloy-containing article;
passing a fluid at high pressure across a surface of said titanium aluminide
^ | p alloy-containing article;
deforming the surface of the titanium aluminide alloy-containing article; and
removing material from the sxxrface of the titanium aluminide alloy-containing
article.
27. The method as recited in claim 26, wherein the fluid at high pressure is passed
44
along with or concurrent to passing a medium of particles ranging from about 50
microns to about 400 microns across the surface of the article.
28. The method as recited in claim 26, wherein the fluid is passed at about 50
inches per minute to about 1000 inches per minute over the surface of the titanium
aluminide alloy-containing article.
29. The method as recited in claim 26, wherein after the fluid at high pressure is
passed across the surface of the titanium aluminide alloy-containing article, the
^ ^ surface of the article is deformed over a depth of less than about 100 microns from the
surface of the article and perpendicularly into the article.
30. The method as recited in claim 26, wherein the titanium aluminide alloycontaining
article comprises a titanium aluminide alloy-containing turbine blade.
31. The method as recited in claim 26, wherein the fluid at high pressure fixrther
comprises particles of alumina, garnet, silica, silicon carbide, boron carbide, diamond,
tungsten carbide, and compositions thereof
32. The method as recited in claim 26, wherein particles ranging from about 50
microns to about 400 microns are suspended in the fluid before the fluid is passed
across the surface of the article, and wherein the solids loading of the fluid is about
2000 grams per liter to about 5000 grams per liter.
45
33. A method for removing overstock material from the convex surface of an
titanium aluminide containing turbine blade, said method comprising: providing a
titanium aluminide alloy-containing turbine blade; passing a fluid at high pressure
across the convex surface of said titanium aluminide containing turbine blade; and
removing about 0.025 mm to about 5.0 mm of overstock material from the convex
surface of the titanium aluminide containing turbine blade.