PWA Ver Snyder Gas turbine element –DS-Casting 1966
US3260505A
Publication
Number: US3260505A
Publication
Date: 1966-07-12
Priority
Number: US1963317535A |
US1964361323A
Application
Date: 1964-04-17
Title:
Gas turbine element
Inventor
- w/address: VER SNYDER FRANCIS L
Assignee/Applicant:
UNITED AIRCRAFT CORP
Front Page Drawing:
Description
The present
invention relates to a novel and improved cast gas contacting blade for gas
turbine power plants.
The gas
contacting blades for gas turbine power plants can either be of the moving
type, the so-called turbine rotor blades, or of the stationary type, sometimes
called turbine stator vanes. The object of this invention is to provide such
blades, whether movable or stationary, which, for a given stress and
temperature, exhibit longer life before rupture, and have a greater uniformity
of stress rupture life than prior conventionally cast gas contacting blades of
the same alloy. A further object is the provision of cast gas contacting blades
for gas turbines which exhibit "third stage creep" so that
predictable changes in creep rate may be utilized in the estimation or
determination of time between engine overhauls. Still another object is the
provision of a novel and improved cast gas contacting blade for gas turbine
power plants which has exceptionally good tensile elongation properties, and
can be operated at substantially higher temperatures than prior, conventionally
cast blades made from the same alloy. The invention further provides gas
turbine blades having good ductility and elongation, extended life, unusually
uniform strength properties, and relatively high tensile strength, although
formed of alloys which normally and conventionally have good high temperature
strength, but are deficient in that they exhibit low ductility and elongation
which is an indication of their relative brittleness ' Heretofore, gas turbine
blades made from cast high temperature resistant alloys have been widely used
but have been subject to limitation as to their useful life between engine
overhauls and it is standard practice to limit the useful life of a gas turbine
before rebuilding to a total number of hours which is much less than the
expected life of the blades, based upon the statistically expected life of the
blades for the reason that the-useful life must be less than the minimum life
of any blade, although most blades would far exceed that minimum life in actual
use.
As contrasted
with the relatively erratic behavior of conventionally cast blades, the gas
turbine blades of the present invention, although made from alloys of the same
constituents as the alloys of prior conventionally cast blades, having a face
centered, cubic, crystal structure, uniformly exhibit a longer life under
similar conditions of stress and temperature and do not fail without warning,
but rather, after they have been used for this longer life period, the
blades-generally elongate during a period of many hours, thereby allowing
longer operating life between engine overhauls and contributing to greater
economy in actual operation.
The blades of the
present invention have an elongated, columnar macro-grain structure with
substantially unidirectional crystals aligned substantially parallel to the
axis of the cast blade; that is, with a columnar structure in the alloy of the
blade. The grain boundaries of the alloy of the cast blade are oriented so as
to be substantially parallel to the principal stress axis of the blade, and
there is an almost complete elimination of grain boundaries normal to this
stress axis.
Alloys which are
suitable for use in making the novel cast gas turbine blades of the present
invention are preferably nickel base (containing at least 35% nickel and
preferably and more usually more than 50% nickel) high temperature alloys,
falling within the following weight percentage ranges for the various
constituents of the alloy, although, as set forth below, certain cobalt base
alloys are also suitable for use in accordance with the present invention.
Certain cobalt
alloys are also useful in the present invention and these include the alloys
comprised within the following analyses: (See PDF)
As with the
nickel alloys, the cobalt alloys may include trivial amounts of impurities such
as sulfur, phosphorus, copper, and the like in amounts which do not
deleteriously affect the novel advantageous characteristics of the cast blades
in their novel crystalline form.
Among the alloys
which are suitable for making the cast gas turbine blades of the present
invention are many of the alloys falling within the ranges specified above and
disclosed in the prior United States patents to: Thielemann, 7o 3,026,198 of
1962; Thielemann, 2,948, 606 of 1960; Bieber, 3,,061,426 of 19,62; Johnson,
2,747,993 of 1956; and the alloys which are commercially known as IN 100, SM
200, 3 SM 302, X-40, WI-52 and Inconel 713C, which are selected from the group
consisting of the nickel-rich and cobalt-rich alloys, such as are
conventionally used in making gas-turbine blades for use under high
temperatures and-are characterized by their good strength, corrosion
resistance, erosion-resistance, good stress-rupture properties, and their face
centered, cubic, crystal structures.
More
specifically, the following alloys are preferred:
Inconel 713C which
has a nominal chemical composition as follows: (See PDF)
Other cobalt alloys which are useful in carrying out the
present invention are those generally known as "WI-52" and
"X-40", the compositions of which are as follows: (See PDF)
According to the process of the present invention, the alloy
to be cast into the form of a gas turbine, gas contacting blade is melted in a
vacuum furnace with a vacuum of 50A or better, and after having been held at a
temperature of from 100 to 250 above its melting point for a short period of
time, is cast in a mold. The mold is preferably formed of ceramic or silicious
material, such as a "shell mold" formed of alternate layers of finely
divided silicious material, such as silicates, zirconia, or other argillaceous
or refractory material and finely divided sand or like material, there usually
being several layers of each of the two materials. Such shell molds are usually
formed on a wax pattern, and after drying, the mold is fired to remove the wax
as is customary in the "lost wax” molding method.
In the vacuum
molding (and furnace) apparatus, the mold is provided with the electrical
heating means so that its upper portion can be heated to a temperature,
preferably at least 100' F. above the melting point of the alloy, prior to the
pouring of the metal into the mold.
When in casting
position, the mold is supported with its bottom open end on a support member
which can be chilled and will remain substantially colder than the body of the
mold during the casting operation, thereby chilling the cast metal in the mold
at its lower end.
The chilling of
the cast metal at one end causes the blade to crystallize in a columnar
structure having uni, directionally oriented crystals aligned substantially
parallel to the axis of the cast blade and with almost complete avoidance of
grain boundaries normal to the stress axis of the cast blade.
When the casting
has cooled to room temperature, or sufficiently so that it does not react with
the atmosphere, the vacuum may be-destroyed and the cast blade and its mold are
removed from the apparatus, after which the mold is removed, usually
destructively, from the casting, and the casting is then ready to be
finish-machined to complete its manufacture.
The foregoing
general description of the gas turbine blades of the present invention and the
process of making them is explanatory of the present invention and the
principles thereof, and the following detailed description sets forth the
preferred forms of the invention,-as well as a variety of illustrative working
examples of the present invention.
The process of
making gas turbine blades according to the present invention is carried out in
a vacuum chamber.
Consequently, the
process is particularly suited to the casting of high temperature
creep-resistant alloys which 8,260,505 require melting and casting in a vacuum,
preferably 501L or better. The process involves unidirectional solidification
so as to establish all-rain boundaries oriented parallel to the anticipated
principal stress axis. The turbine blades are preferably formed by casting a
molten alloy into a refractory mold heated by electrical means to provide a
temperature gradient. The temperature gradient-so established should consist of
a temperature below the melting point of the alloy at the base of the mold, to
a temperature above the melting point of the alloy maintained in the direction
of the axis of the mold. The internal surfaces of the walls of the mold should
be sufficiently smooth so as to prevent nucleation of solid in the liquid at
the mold walls. A practical rate of growth of the grain oriented structure is
obtained by making the bottom of the mold of high thermally conductive
material, e.g., a water cooled copper plate. This results in a more rapid rate
of beat removal from the bottom of the solidifying casting. The process, as
described, results in unidirectional solidification of the molten metal along
the temperature gradient. In particular, the macro-grain structure of the
casting is aligned parallel to the axis of the casting, that is, the g-rain
structure is "columnar." The desired columnar structures can be
produced since the following two conditions are met in the procedure outlined
above. (1) The heat flow must be unidirectional, causing the liquid solid interface
at the growing grains to move in on-, direction. (2) There must be no
nucleation in the melt ahead of the advancing interface.
The results of
producing such a columnar structure in a casting are: (a) a grain boundary
structure oriented with respect to the cast shape; and (b) a preferred
orientation of the crystal structure of the grains.
Careful
establishment of these conditions by the procedures outlined above results in
cast gas turbine, gas contacting blades of the desired shape and dimensions.
A ceramic blade
mold is prepared for directional solidification by first preparing the base of
the mold so that the basal wall surfaces will fit smoothly on the water cooled
copper plate, and second, double winding the mold with molybdenum heater wire.
The heater wires are connected to a power source and used to control the
temperature of the melt in the blade mold during solidification. A gas turbine
rotor blade obtained by employing this process is shown in FIGURE 1. A gas
turbine stator vane obtained by employing this process is shown in FIGURE 11.
The difference between the grain structure of a conventionally cast rotor blade
or a stator vane and a uni direction ally cast rotor blade or stator vane can
be revealed by macro-etching.
My process described
above features increased elevated temperature properties with excellent
ductility in a strong high temperature alloy as compared to the conventionally
cast properties of this same alloy. The notable feature is that all of the
results obtained on the directionally solidified material are above, and in
many cases, substantially above those of the conventionally solidified
material. This improvement in ductility is illustrated in the comparison of
tensile elongation. Again, it is notable that all the results obtained are
substantially above the average results of conventionally cast material. It is
notable that the maximum in tensile strength coincides with the minimum in
tensile ductility, as is customary for alloys of this type. Conventionally cast
material would exhibit no minimum in ductil-ity since the average values are
substantially below the minimum for the directionally solidified material, In
comparisons of the stress-rupture results of directionally solidified and
conventionally cast material, at all three temperatures (1400' F., 1800' F.,
and 1900' F.), the directionally solidified test alloy yields superior
properties.
Of major
significance is the stress-rupture fracture elongation, the average of the
conventionally the cast results 6 lie at 3 % elongation and below over the
whole temperature range, whereas the directionally solidified material yields
fracture elongations substantially above 3% elongation at all temperatures
tested. Third stage creep is present at all the temperatures tested, namely,
1400' F., 1800, F., and 1900' F. The advantageous effect of directionally
solidifying the test alloy on the rupture properties in terms of life time and
stress shows that in all cases, the directionally solidified material is
superior.
In addition to
the properties measured-by testing with the stress axis parallel to the
columnar grain axis, tests with the stress axis normal to the elongated,
columnar grain axis show that the grain structure of the conventionally cast
blade has-many boundaries normal to its principal stress axis, which is
vertical. The properties of directionally solidified material taken transverse
to the columnar direction are superior to the average properties of the
conventional cast material, as shown in the immediately following table, and it
was observed that the directionally solidified material properties fall above
the curve for the conventionally cast material. It is apparent then that there
is a sound technical basis for the substantial improvement in the properties
observed by directionally solidifying and testing with grain boundaries
parallel to the stress axis.
The following
table shows the times required to rupture specimens of conventionally cast
alloy SM 200 compared with specimens of directionally solidified alloy SM 200
when subjected to stresses of 95, 000, 90,000, and 85,000 pounds per square
inch at 1400' F.
Stress, k.s.i.
go Time to
rupture in Hours at 1400 F.
Conventionally
Cast Directionally Solidified SM 200 SM 200 0.1 15 155 200 245 Formation of gas
turbine, gas contacting blades according to the present invention, as described
compared to conventionally cast material, consistently yields the following
advantages: (1) Tensile properties: improved ductility at (at least) equivalent
strength levels over a wide temperature range.. (2) Creep rupture properties:
longer lifetimes at all temperatures, a 50-100' F. increase in potential
operating temperature or a high rupture strength at the same test temperature,
increased ductility at-all temperatures with minimization of low ductility
characteristics in the intermediate temperature range, TITm-=0. 5. (3)
Elimination of the intercrystalline failure mode.
(4) Development
of definite third stage creep. (5) Casting properties: a minimum of microporosity
in castings made by this process since solidification can occur only at the
liquid solid interface; substantially no macrosegregation in the casting since
the solidification-and cooling rate more nearly approximate equilibrium
conditions; substantially no entrapment of foreign matter since the moving
front will force such-foreign matter ahead of it into feeder heads provided for
the purpose. (6) Thermal shock resistance: uniformly high thermal shock
resistance is obtained compared to the widely varying and unpredictable thermal
shock characteristics of prior art conventionally cast products.
The gas turbine,
gas contacting blades according to the present invention are highly stable at
elevated temperatures since the texture developed in the columnar growth as
well as the more nearly equilibrium casting conditions tends to prevent
recystallization at elevated temperatures.
The following are
specific and preferred embodiments of the invention of the present invention.
3,260,505 7 Shell
molds for gas turbine, gas contacting blades, i.e., turbine rotor blades, were
prepared in electric resistance heating elements on their exteriors,
and-connected to a power supply so as to heat the upper portions of the molds
to temperatures of about 2500' F. to 2800' F. and at least 100' F. above the
melting point of the alloy.
Once the mold has
been assembled on the copper block in the furnace chamber, the furnace chamber
is closed and the internal pressure reduced until the pressure is less than
preferably about 501A and heating of the mold I begins. The heating of the mold
in the furnace chamber proceeds gradually so as to safely raise the temperature
of the assembly and assure outgassing the components, the melt stock of alloy
"SM 200" having been already charged into the furnace. The
temperature of the mold assembly I is gradually raised to approximately 1200'
F. A sufficient interval of time is allowed for continued outgassing of the
mold and the achievement of uniform temperature distribution in the mold assembly.
Subsequently, the temperature of the mold is raised in gradual steps until 2
the desired temperature of about 2500' F. to 2800' F. is achieved in the mold
assembly. The melt charge is then melted and outgassed and when both the
temperatures of the melt and of the mold assembly have been achieved, the melt
is poured at approximately 2700' F. Through-2 out the heat-up cycle, the water
to the water cooled copper block is controlled so that the outflowing water
temperature is approximately 180' F. Just prior to pouring of the melt, the
water is turned on full until the temperature of the outflowing water drops to
ambient and at that time themelt is poured. Subsequent to pouring, the power to
the mold assembly heater is reduced in a step-wise manner after a holding
period of approximately 20 minutes, after the furnace and casting are allowed
to cool, air or nitrogen gas is introduced into the furnace, and the castings
are removed from the furnace.
Thereafter, the
gas contacting blade, whether rotor blade or stator vane was finish machined to
the precise dimensions required.
Of the drawings:
FIGURE I is a
photographic reproduction, in side elevation, of a cast rotor blade for a gas
turbine power plant, according to the present invention, and showing the blade
in ",as-cast" condition after having been subjected to superficial
etching to reveal the crystalline structure of the metalof the blade;
FIGURE 2 is a
similar photographic reproduction of a conventional rotor blade cast from a
similar alloy, and also in its "as-cast," superficially etched
condition;
FIGURE 3 are
graphs showing the values for ultimate tensile strength and yield strength of a
blade material of the present invention compared with conventional blade
material of the same alloy, plotted against temperature;
FIGURE 4 are
other graphs showing the values for tensile elongation plotted against
temperature, for a blade material of the present invention compared with
conventional blade material of the same alloy, all plotted against temperature;
FIGURE 5 are
further graphs showing values for ultimate tensile strength, yield strength,
reduction of area and percentage elongation of a blade material of the present
invention;
FIGURE 6 are
graphs showing values for stress rupture life of directionally cast compared
with conventionally cast "SM 200" at 1400 F.;
FIGURE 7 includes
graphs showing stress-rupture data at 1800' F. and 1900-F. for a conventional
alloy, and data at the same temperatures with respect to one of the new
materials used in this invention;
FIGURE 8 is a
graph showing the creep curve for a material of the present invention at 1400
F. and 97,500 P.S.i.;
FIGURE 8A are
graphs showing creep curves for a malerial of the present invention at 1800' F.
with 29,000 p.s.i. loading and 1900 F. with a loading of 22,500 p.s.i.;
8 FIGURE 9 is a
graphical representation of fracture elongation data taken from stress rupture
tests of a material of the present invention at 1800' F. and 1900' F.;
FIGURE 10 is a perspective
view showing a preferred form of turbine rotor blade in accordance with the
present invention;
FIGURE 11 is a
photographic reproduction, in side elevation, of a cast stator vane for a gas
turbine power plant, according to the present invention, and showing the vane
in "as cast" condition after having been subjected to superficial
etching to reveal the crystalline structure of the metal of the blade;
FIGURE 12 is a
similar photographic reproduction of a conventional vane cast from a similar alloy,
and also in its "as cast," superficially etched condition;
FIGURE 13 is a
perspective view showing a preferred form of stator vane in accordance with the
present invention.
As is clearly
shown in FIGURES I and 11, the etched surface of the cast turbine rotor blade
or stator vane formed from alloy "SM 200," having a face centered,
cubic, crystal structure, by the shell-molding and vacuum-casting technique
reveals a rotor blade or stator vane which is directionally solidified with its
grain boundaries substantially parallel to the stress axis of the blade with
the substantial elimination of grain boundaries normal to the principal stress
axis of the rotor blade or stator vane. As shown in FIGURE 1, the crystals of
the alloy are of such a size, that the elongated, columnar crystals, for the
most part, extend from the root 2 of the rotor blade through the intermediate
airfoil portion 3, to the shroud 4 and extending through the shroud and root.
A similar effect
is shown in FIGURE 11.
In the rotor blade
structure shown in FIGURE 1 and similarly in the stator vane structure shown in
FIGURE 11, there are substantially no grain boundaries normal to the long
airfoil portion 3 of the rotor blade, and the principal stress axis of the
blade is along the length of this airfoil portion. Likewise, both the root
portion 2 4oand the shroud portion 4 of the rotor blade also have a similar
columnar grain structure of elongated, columnar crystals which extend in a
substantially parallel direction and extend into the intermediate airfoil
portion 3 from both the root and shroud. Preferably, the elongated, columnar
grains of the alloy have a length which is at least five times their maximum
width.
FIGURES 2 and 12
show similar side elevation view of a gas turbine rotor blade and a stator
vane, respectively, of identical contour, made from the same alloy "SM
200" as the FIGURES I and 11 structures, respectively. As in FIGURES 1 and
11, the photographs show the etched surface of the rotor blade and stator vane
as conventionally cast, and reveals their equi-axed polycrystalline structure
with their many grain boundaries substantially normal to the stress axis of the
rotor blade or stator vane.
FIGURE 3 is a
chart showing ultimate tensile strength and yield strength data from tests at
various temperatures on directionally solidified cast test specimens of alloy
"SM 200" having the grain boundaries parallel to the stress axis of
the specimen, compared with similar cast test specimens of the same alloy with
a conventional equi-axed structure. The data for the conventionally cast alloy
is shown by the fine line, while the data for the directionally solidified
alloy of the present invention is shown by the upper, heavy line.
FIGURE 4 are
graphs demonstrating the superiority of-gas turbine blades-of the present
directionally solidfied cast alloy "SM 200" compared with
conventionally cast test specimens of alloy "SM 20V in which values for
tensile elongation and percentage elongation are plotted against t6inpera-ture;
the heavy line indicating the values for the directionally solidified cast
alloy while the fine line represents comparable values for the conventionally
cast specimens;
FIGURE 5 gives
complete tensile results for directionally solidified cast alloy "SM
200" in which the stress in thousands-of pounds per square inch, values
for percentage elongation and percentage reduction of area are plotted against
temperature. Curve I shows the values for ultimate tensile strength in
thousands of pounds.
Curve 2 shows the
values of yield strength at 0.2% elongation. Curve 3 shows the percentage of
area reduction at various temperatures and stresses. Curve 4 shows values for
percentage elongation at various temperatures.
FIGURE 6 shows
graphs plotting stress rupture data at 1400' F. and showing stress rupture life
in hours plotted against stress in thousands of pounds per square inch. The
data for the directionally solidified alloy "SM 20V is shown by the upper
heavy line while the lower finer line shows comparable data for the
conventionally cast alloy "SM 200." It will be noted that the values
for the directionally solidified-material are consistently and substantially in
excess of those for the conventionally cast material;
FIGURE 7 are
graphs showing similar stress rupture data at 1800' F. and 1900' F., while the
small dots show comparable data for the directionally solidified specimens at
1800' F. and the small crosses show comparable data for the directionally
solidified material at 1900 F.;
FIGURE 8A is a
composite graph showing "creep curves" for directionally solidified
test specimens of alloy "SM 200" at:
1800 F. and
29,000 pounds/square inch stress;
1900' F. and
22,500 pounds/square inch stress.
As shown in
FIGURES 8 and 8A, the creep values are plotted in hours against percent
elongation of the test specimens. As will be noted, in each instance, creep or
elongation of the test specimen exhibits the unusual property of progressing at
a moderate rate over the major life of the part, after which the rate of elongation
increases and continues for a considerable period of time prior to failure,
thus giving rise to what may be called "third stage creep."
FIGURE 9 is a
graphical representation showing fracture elongation data from stress rupture
tests with the exception-of the extreme left-hand data point on each curve
which show tensile elongation values at room temperature. In the curves, values
for percentage elongation are plotted against temperature for directionally
solidified material according to the present invention.
In FIGURE 10, the
gas turbine rotor blade I has a substantially twist between the root 2 and the
blade shroud 4, as more fully described in the prior patent to Bodger No.
2,540,734 of June 6, 1950. In FIGURE 10, the elongated grains or crystals
extending longitudinally of the blade are of the type shown in FIGURE 1, but
are not shown in FIGURE L10.
While the gas
turbine rotor blade may be made in various other contours, as required by the particular
turbine construction, FIGURE 10 illustrates the preferred form, and a form to
which the principles of the present invention may be applied for their maximum
utilization.
In FIGURE 13, the
stator vane has an inner shroud 5 and an Outer shroud, 6 and an airfoil portion
7. The entire vane is a unitary casting which has been finish machined to
produce the desired shroud configuration.
In FIGURE 13, the
elongated grains or crystals extend parallel to the vertical axis of the
airfoil portion 7 and are of the type shown in FIGURE 11.
The following
comparison of rupture data for directionally solidified parts of alloy "SM
200," compared with equi-axed conventionally cast duplicate test parts,
also of alloy "SM 200," shows a wide range of values-obtained from
the conventionally cast alloy parts, and the minimum values obtained using the
directionally solidified alloy parts of the-present invention. (See PDF)
The following table shows the thermal shock resistance of
stator vanes prepared from equi-axed conventionally cast alloy "SM
200" compared with stator vanes prepared from directionally solidified
alloy "SM 20W' when tested at temperatures of 2000' F., 2100 F. and 2200
F. for, respectively, 600 cycles, 400 cycles and 400 cycles.
Each test cycle
involves heating the vane in a hot gas stream to the temperature indicated,
holding it at that temperature for one minute and then rapidly cooling it to
room temperature. (See PDF)
Two points become clear from the foregoing data.
First,
conventionally cast stator vanes have widely varying thermal shock resistance
and second, the stator vanes prepared by the directional solidification process
of this invention are both more uniform and better in thermal shock resistance
than the conventionally cast products.
The problem of
lack of uniformity in thermal shock resistance is a particularly serious one in
the case of stator vanes for gas turbine engines. There is no known method for
predicting the durability of any given stator vane. The following tabulation is
representative, again operating at 2000, ' F. for 600 cycles; 2100' F. for 400
11 cycles; and 2200' F. for 400 cycles. The test was stopped after 1400 cycles
or upon failure. In each instance, the blade was made of a standard alloy (B
1900, a competitive nickel base alloy) and conventionally cast under exactly
the same conditions. (See PDF)
Thus, with a conventionally cast vane, one could anticipate
some vanes to be reasonably resistant to thermal shock but also some to be very
poor and crack after only 100 cycles. In effect therefore, it is the poorest
spicemen that determines the useful life since every vane must be replaced on
the theory that its life expectancy is no better than the poorest resistant
product. Using the process of this invention with unidirectionally cast vanes,
uniformly high thermal shock resistance is insured.
While nickel base
alloys containing at least 35% nickel, preferably from 50 to 60% by weight of
nickel, and especially alloy SM 200 are preferred in carrying out the present invention,
generally similar results may be obtained by using the cobalt alloys with a
face centered, cubic, crystal structure above referred to which include at
least 35% cobalt and preferably 50% or more cobalt.
The invention in
its broader aspects is not limited to the specific steps, process and
compositions shown and described but departures may be made there from within
the scope of the accompanying claims without departing from the principles of
the invention and without sacrificing its chief advantages.
Claims:
What is claimed
is:
1. A gas
contacting blade for a gas turbine power plant formed as a unitary cast
structure from a strong, heat resistant and corrosion-resistant alloy, having a
face centered cubic crystal structure and a composition of Percent
Chromium---------------------------2 to Aluminum---------------------------0 to
9 Titanium-----------------------------0 to 6 Aluminum and titanium at
least----------3.5 Cobalt-------------------------------4 to
Carbon------------------------------0.1 to 0.5
Boron-------------------------------0.005 to 0. 1
Zirconium----------------------------0.05 to 0.2 Balance essentially nickel in
a quantity of at least 35% adapted to be axially stressed at high temperatures
in use, characterized by an elongated, columnar grain structure with grain
boundaries in the blade being substantially parallel to the principal stress
axis and with substantially no grain boundaries normal to the stress axis.
2. A gas contacting
blade as in claim I wherein the blade is a rotor blade having a root and a
relatively long integral airfoil portion extending from the root.
3. A gas
contacting blade as in claim I wherein the blade is a stator vane.
4. An integral
gas turbine rotor blade as claimed in claim I in which the elongated, columnar
grain structure of the airfoil portion extends into and through the root, with
substantially no grain boundaries normal to the length of the airfoil portion.
5. An integral gas turbine rotor blade as claimed in claim 4
in which the blade is provided with an integral shroud at the end of the blade
opposite the root and in which the elongated, columnar grain structure of the
airfoil portion also extends into and throughout the shroud with substantially
no grain boundaries normal to the length of the airfoil portion.
6. An integral
gas turbine rotor blade as claimed in claim 5 in which the elongated, columnar
grain structure of the airfoil portion extends into and through the shroud, with
substantially no grain boundaries normal to the length of the airfoil portion.
7. A gas
contacting blade for a gas turbine power plant formed as a unitary cast
structure from a strong, heat resistant and corrosion-resistant alloy, having a
face centered cubic crystal structure and a composition of Percent
Chromium---------------------------15 to 27 2o
Tungsten-----------------------------5 to 12 Titanium up
to------------------------I Carbon------------------------------0.40 to 1.20
Zirconium----------------------------0.05 to 2.5
Tantalum----------------------------3.0 to 10.0 Columbium and/or tantalum
to----------3.0 the balance being essentially cobalt in a quantity of at least
35% and containing not more than 12% nickel adapted to be axially stressed at
high temperatures in use, characterized by an elongated, columnar grain
structure with the grain boundaries in the blade being substantially parallel
to the principal stress axis and with substantially no grain boundaries normal
to the stress axis.
8. A gas
contacting blade as in claim 7 wherein the blade is a rotor blade having a root
and a relatively long integral airfoil portion extending from the root.
9. A gas
contacting blade as in claim 7 wherein the blade is a stator vane.
10. An integral
gas turbine rotor blade as claimed in claim 7 in which the elongated, columnar
grain structure of the airfoil portion extends into and through the root, with
substantially no grain boundaries normal to the length of the airfoil portion.
11. An integral
gas turbine rotor blade as claimed in claim 10 in which the blade is provide
with an integral shroud at the end of the blade opposite the root and in which
the elongated, columnar grain structure of the airfoil portion also extends
into and throughout the shroud, with substantially no grain boundaries normal
to the length of the airfoil portion.
12. An integral
gas turbine rotor blade as claimed in claim 11 in which the elongated, columnar
grain structure of the airfoil portion extends into and through the shroud,
with substantially no grain boundaries normal to the length of the airfoil
portion.