Heat treating a product material of prealloyed powders after shaping by superplastic deformation restores the ability of the material to resist deformation at high temperatures. Heat treating is accomplished by heating to a temperature between the solidus and liquidus with the application of isostatic pressure to close any voids. This pressure may be simultaneously applied while the material is at the heat treating temperature. The pressure may also be applied when the material cools to a temperature between that at which it is shaped and the solidus

Ashbrook, R. L.

Freche, J. C.

Waters, W. J.

English

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U.S. patent No. : 3. M^ ^ I /30
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https://ntrs.nasa.gov/search.jsp?R=19740002408 2020-03-17T14:20:57+00:00Z
United States Patent
Freche et al.
[ i i ] 3,765,958
[45] Oct. 16,1973
[54] METHOD OF HEAT TREATING A FORMED
POWDER PRODUCT MATERIAL
[75] Inventors: John C. Freche, Fairview Park;
William J. Waters, Cleveland;
' Richard L. Ashbrook, Berea, all of
Ohio
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics of Space
Administration, Washington, D.C.
[22] Filed: June 28, 1972
[21] Appl. No.: 266,928
Related U.S. Application Data
[ 62 ] Division of Ser. No. 29,917, April 20, 1970, Pat. No.
3,702,791.
[52] U.S. Cl 148/126, 29/420.5, 75/200,
75/226
[51] Int. Cl B22f 3/24
[58] Field of Search 75/226, 200, 214;
148/126; 29/420.5
[56] References Cited
UNITED STATES PATENTS
3,469,976 9/1969 Her 75/226
3,671,230 6/1972 Smytheetal 75/214
3,655,458 4/1972 Reichman 75/214
Primary Examiner—Carl D. Quarforth
Assistant Examiner—B. Hunt
Attorney—N. T. Musial et al.
[57] ABSTRACT
Heat treating a product material of prealloyed pow-
ders after shaping by superplastic deformation restores
the ability of the material to resist deformation at high
temperatures. Heat treating is accomplished by heat-
ing to a temperature between the solidus and liquidus
with the application of isostatic pressure to close any
voids. This pressure may be simultaneously applied
while the material is at the heat treating temperature.
The pressure may also be applied when the material
cools to a temperature between that at which it is
shaped and the solidus.
6 Claims, 3 Drawing Figures
PATENTED OCT161973 3.765,958
10
0
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3,765,958
• - . 1 2
METHOD OF HEAT TREATING A FORMED OBJFCTS OF THF INVFNTIONPOWDER PRODUCT MATERIAL OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to
RELATED APPLICATION
 heat treat artjcles of manufacture made from superal-
This application is a division of copending applica- 5 . loy compositions which are too highly alloyed to be
tion Ser, No. 29,917 filed Apr. 20, 1970 and now pa- cast without gross segregation,
tent No. 3,702,791. A further object of the invention is to provide a
noirMw r»u TUP IMVCMTIOU method of heat treating a superalloy article of manu-ORIGIN OF THE INVENTION
 facture in whjch significant deformation has been
The invention described herein was made by employ- 10 achieved with relatively low applied forces,
ees of the United States Government and may be man- A still further object of the invention is to provide a
ufactured and used by or for the Government for gov- method of making a superalloy article of manufacture
ernmental purposes without the payment of any royal- in which the microstructure of the formed material is
ties thereon or therefor. coarsened by heat treating at temperatures above the
BACKGROUND OF THE INVENTION IS ™*™1 "^ P°ilU °f the a"°y With°Ut VOid f°rma-
This invention is concerned with heat treating super- Another object of the invention is to provide superal-
alloy powder product meterials. The invention is par- loys having higher strength at intermediate or at high
ticularly directed to improving powder materials hav- temperatures than can be obtained by conventional
ing an ultrafine grain size for superplastic behavior at 20 cast and cast-wrought processes,
high temperatures by heat treating to increase the grain These and other objects of the invention will be ap-
size in the final product. parent from the specification which follows and from
Conventionally cast and wrought alloys are utilized the drawing. i
for the hot components of gas-turbine engines. Cast r>F<!rHiPTir»w OF THF no AwiNir
nickel-base alloys are generally used for turbine buck- 25 DESCRIPTION OF THE DRAWING
ets and stator vanes, whereas wrought alloys are used The figures are micrographs of HS-31 powder prod-
for turbine discs. In more advanced engines wrought uct at a magnification of 500.
nickel-base alloys are also used for compressor discs FIG. 1 shows the as-extruded alloy,
and blades in the latter compressor stages. FIG. 2 shows the material after the first step of heat
The operating cycle temperatures must be raised in 30 treatment, and
advanced engines to meet the demand for increased FIG. 3 shows the material after final heat treatment
performance. Nickel-base alloys that can be used at with the application of pressure,
high temperatures throughout the engine have been DESCRIPTION OF THE PRFFFRRFD
suggested. However, most high strength nickel-base al- DESCRI • !°J ° *™f ^ raRRED
loys are highly alloyed and metallurgically very com- 35 EMBODIMENT
plex. As a consequence, severe macro- and micro- The method of the present invention utilizes preal-
segregation can occur in castings, such as turbine buck- loyed powders of a highly alloyed superalloy composi-
ets and stator vanes, so that the full-strength potential tion. The powders are extremely fine and have a high
of the alloy is not realized. Also, in ingots, the usual purity. ,
starting stock for breakdown operations, segregation 40 The powders can be prepared by inert gas atomiza-
increases the difficulty of forming the alloys. tion or other methods, such as the rotating electrode
„.,.,.. ~-~.. . ^»,^-,^», method. To produce the powders by atomization re-
SUMMARY OF THE INVENTION melt stock is first melted under an inert gas or in vac-
Fine p real loyed powders of highly alloyed superalloy uum in an induction furnace, and the melt is then atom-
compositions may be consolidated and then shaped in ized under an inert gas. The resulting powders are
separate steps. Likewise these powders may be consoli- screened, and only suitable size powders are used for
dated and shaped simultaneously. During the shaping further processing in accordance with the invention,
operation the consolidated powders are heated to tern- The prealloyed powders are then consolidated in the
peratures at which the material exhibits superplastic form of either bar stock or preforms. More particularly,
behavior, and only relatively low pressures need be ap- the prealloyed powders can be made into bar stock by
plied to shape the material. At intermediate tempera- extrusion, or by a combination of hot pressing and ex-
tures significant increases in strength over the cast or trusion. These powders can also be made into preforms
wrought counterparts of the alloyed material can be for turbine buckets or other desired articles of manu-
obtained by alloys consolidated or shaped in accor- facture. These preforms are made by slip-casting, by
dance with the invention. pressing in a shaped die, or by enclosing the powder in
' Suitable heat treatments are utilized to improve ele- a suitably shaped container, such as a metallic can.
vated temperature properties compared to the cast or The consolidated powders are then heated to a tern-
wrought counterparts of the alloys. Heat treating at perature at which the material exhibits superplastic be-
temperatures between the solidus and liquidus with a havior. While a blank or preformed shape of these con-
simultaneous imposition of isostatic pressure is used to solidated powders is still hot, pressure is applied to
obtain a suitably coarse microstructure and a solidifi- form the powders into the desired configuration. This
cation structure resulting from partial melting at the pressure may be applied unidirectionally to suitably
grain boundaries that will provide good high tempera- shaped dies.
ture strength and a structure free from voids. In an al- ,, Because of the superplastic behavior of the material
ternate embodiment the isostatic pressure is applied at a very low pressure is required to shape the consoli-
a temperature between the shaping temperature and dated powders. The shaping may be accomplished at
the solidus. pressures as low as 1,000 psi.
3,765,958
3 4
An important feature of the invention is that the lively constant strain rate of between 0.03 to 0.07 inch
formed part or article of manufacture is then heat per inch per minute. This strain rate was used to ap-
treated to obtain suitably coarse microstructures for proximate the rate observed when superplasticity was
superior high temperature strength. Isostatic pressure encountered with the alloy in a stress rupture test. The
is imposed during heat treating and the temperature 5 upset specimen had a diameter of 1.1 inch and a thick-
may be either above the incipient melting point or be- ness of 0.175 inch after pressing,
tween the forming temperature and the solidus of the According to the present invention heat treatments
powder material. to effect solutioning and aging were performed in vac-
EXAMPLES uum or under argon on unmachined extruded bars of
10
 the nickel-base alloy. These heat treatments coarsened
In order to better illustrate the invention test samples
 the microstructure of extruded powder products and
of an experimental nickel-base superalloy were pre-
 substantiai|v improved stress rupture life for the alloy
pared and tested The nominal composition of the alloy
 compared to the life of the as.extruded powder product
is shown in TABLE 1.
 at an intermedjate temperature. At 1,200° F and
TABLE I — NOMINAL COMPOSITION OF ALLOY 105,000 psi the extruded and heat-treated powder
product of the alloy had a rupture life of 975 hours,
Tantalum *" 8 whereas the as-extruded powder product had a life of
Tungsten 4 374 hours.
CCo'lSnfbium 2.5 20 Heat-treated extruded samples of the alloy had sub-
Chromium 6 stantially lower rupture life at high temperatures of
Zirconium 0 75 l >800° to 2000° F than as-cast samples.JFor the heat
Carbon 0.125 treated, extruded powder product it was 2.2 against 90
Nickel Balance
 hours at 1,900° F and 15,000 psi.
_,.. . , , . „ ... 25 By simultaneously applying pressure and heatingThis cast nickel-base superalloy was melted under . .. . . . / i5 • . r .u . j j
• . . , ~, . above the incipient melting point of the as-extruded
vacuum in an induction furnace. The melt was atom- . . , . ., , °.r .., . .
ized under argon to spheroidal powders which were ".ckel-base alloy powder product void format.on is pre-
s^Hid with Tyle7icreeirs"to^0 mesh. Only the vented' Thls Product was successfully hea*d to 2,400
-<SO mesh fraction was used for further processing. F'which is about 50° above the incipient melting point,
The sieve analyses for the -60 mesh fraction for the 30 under a Pressure of 10,000 psi. This simultaneous ap-
alloy is shown in TABLE II plication of pressure and the high temperature coars-
ened the microstructure to a greater degree than by
TABLE II — PARTICLE SIZE DISTRIBUTION OF conventional heat treatments.
ATOMIZED POWDER Xest samples of a commerical cobalt-base alloy were
Tyler screen a'so prepared and tested to illustrate the beneficial ef-
size Percent feet of the heat treatment that utilized both high tem-
100/500 13^5 peratures above the incipient melting point and high
150/270 30.0 pressures. The cobalt-base alloy identified as HS-31
325/400 90 40 was mac'e bv l^e aforementioned prealloyed powder
400 35.5 process. The microstructure of as-extruded HS-31
powder product is shown in FIG. 1.
These fine powders were sealed in evacuated mild As extruded bars of the cobalt-base alloy were heat
steel cans. The canned powders were heated to 2,200° treated for 1 hour at 2,400° F at atmospheric pressure.
F in a furnace and transferred to an extrusion press.
 4J The microstructure after this heat treatment is shown
Here the powders were extruded into bars and the cans
 in FJG 2 This is about 60» F above ,he incipient mdt.
were reduced in size from 2 inches to approximately
 m_ pojnt
9116 inch in diameter by passing them through an ex-
 The grajn growth was accompanied by the formation
trus'on dle- - ... . j of large voids. Subsequent application of isostatic pres-
The bars were first tested in the as-extruded condi-
 5Q sufe of 30 OOQ . at 22QQO p the grains further
uon, The^ckeUbase _alloy had1 anelongation of_more
 and do§ed ^ vojds Thjs restored ^ Qf
than 600% after testing at ,900° F and 1,000 ps, for
 es shown jn operation at 13,000 psi
4.1 hours. These very h.gh elongations which occurred •"
 2Q £ which £
in elevated temperature tensile and stress rupture tests ' . „ ,-, .- 1 *, „„„ . .
indicated superjlastic behavior in this temperature re- „ h^°f H16 "f"1 a»^ Operations at 61,000 ps, and
•
 n
 5S
 1,200° F resulted in a 420 hour life compared to 10
Samples of the as^extruded powder product of the hours f6r" the cast alloy,
alloy were upset and formed to shapes in closed dies to What 1S claimed ls:
show that the material can be formed in compression »• A method of heat treating a dense formed powder
to take advantage of this superplastic behavior. A hy- product material selected from the group consisting of
draulically operated press with an in-place graphite sus- "'ckel and cobalt superalloys to coarsen the micro-
ceptor induction heating furnace was used. Bar speci- structure thereof comprising the steps of
mens approximately % inch high were heated to 2,000° heating the material to a temperature between the
F and pressed. Pressure was applied to the circular ends solidus and liquidus of the formed powdered mate-
of the specimens through high temperature alloy plates
 6J rial thereby promoting grain growth and void for-
which were heated to the same temperature as the mation, and
specimen. An initial load of 155 pounds was applied. imposing isostatic pressure on the material to close
The load was increased as necessary to maintain a rela- said voids.
3,765,958
2. A method of heat treating as claimed in claim 1
wherein the isostatic pressure is imposed simulta-
neously with the heating.
3. A method of heat treating as claimed in claim 1 in-
cluding the step of
cooling the material to a second temperature below
the incipient melting point before imposing the iso-
static pressure, said isostatic pressure being applied
at said second temperature.
4. A method of heat treating as claimed in claim 4
wherein the material is cooled to a temperature be-
tween that at which the material exhibits superplastic
behavior and the solidus temperature.
5. A method of heat treating as claimed in claim 1
wherein the formed powder product material is a nick-
el-base alloy.
6. A method of heat treating as claimed in claim 1
wherein the formed powder product material is a co-
balt-base alloy.
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Method of heat treating a formed powder product material

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