Dispersion-strengthened nickel alloys are sanded on one side and chemically polished. This is followed by a single-step welding process wherein the polished surfaces are forced into intimate contact at 1,400 F for one hour in a vacuum. Diffusion, recrystallization, and grain growth across the original weld interface are obtained during postheating at 2,150 F for two hours in hydrogen

Holko, K. H.

English

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https://ntrs.nasa.gov/search.jsp?R=19740012942 2020-03-17T14:48:24+00:00Z
United States Patent
Holko
tin 3,798,748
[45] Mar. 26, 1974
[54] DIFFUSION WELDING
[75] Inventor:
[22]
[21 ]
[63]
Kenneth H. Holko, Strongsville,
Ohio
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
Filed: Sept. 29, 1972
Appl. No.: 293,726
Related U.S. Application Data
Continuation-in-part of Ser. No. 289,033, Sept. 14,
1972, Pat. No. 3,758,741.
[52] U.S. Cl 29/487, 29/494, 29/498,
29/504
[ 5 1 ] Int. Cl B23k 31/02
[58] Field of Search 29/487, 498, 504, 494
[56] References Cited
UNITED STATES PATENTS
2;834.I02 5/1958 Pflumm et al 29/498 X
.-UI25.592 3/1962 Fischer et ul 29/498 X
3,530,568 - 9/1970 Owezarski et al 29/504 X
3^552.898 1/1971 ' Bird et al 29/504 X
3,646.591 2/1972 Thomas et al 29/487
3.672.031 6/1972 Kindlimann..'. 291504 X
3.680,197 8/1972 Blum et al 29/498 X
3,711,937 1/1973 Emley 29/487
3.714,702 2/1973 Hammond 29/504 X
OTHER PUBLICATIONS
Kaarlela et al., "Alloy Effects in the Low-Pressure
Diffusion Bonding of Superalloys," Welding Journal
Research Supplement, 6/67, pp. 283-S to 287-S.
Garrett et al., "Broad Applications of Diffusion Bond-
ing," NASA, CR^t09, March 1966, pp. 114-115,
Technical Library.
Primary Examiner—J. Spencer Overholser
Assistant Examiner—Ronald J. Shore
Attorney, Agent, or Firm—N. T. Musial; G. E. Shook;
J. P. Manning
[57] ABSTRACT
Dispersion-strengthened nickel alloys are sanded on
one side and chemically polished. This is followed by
a single-step welding process wherein the polished sur-
faces are forced into, intimate contact at 1,400°F for
one hour in a vacuum. Diffusion, recrystallization, and
grain growth across the original weld interface are ob-
tained during postheating at 2,150°F for two hours in
hydrogen.
8 Claims, No Drawings
^(TASA^Case-LEH-11188-2)
Patent (NASA) 4 p
"DIFFUSION WELDING
CSCL 13H
00/15
Unclas
33965 J
3,798,748
1 2
, >- " DIFFUSION WELDING tures around 2175°F. Therefore the two-step welding
'" cycle would be costly if applied to hardware manufac-
RELATED APPLICATION ture. The specially processed material is in the unre-
This application is a continuation-in-part of copend- "ystallized condition and is very difficult to form at
ing application, Ser. No. 289,033 which was filed Sept/ 5 room temperature. Also, the mat.ng surfaces requ.re an
14, 1972, now U.S. Pat. No. 3,758,741. involved sanding and electropohshmg procedure to in-
sure flatness and freedom of stored energy.
BACKGROUND OF THE INVENTION
 SUMMARy QF ^  ,NVENTION
The invention described herein was made by an em- _,
ployee of the United States Government and may be 10 The Present ""ention represents an improvement
manufactured and used by or for the Government for °ver 'h,e Process d.sclosed in application. Ser. No.
governmental purposes without the payment of any 289 033. One surface of each member is prepared by
royalties thereon or therefor. sandl"8 w"h 32°-8nt PaPer and chemlcal|y polish.ng.
Upon heating to 1,400 F in vacuum, a pressure be-
PRIOR ART 15 tween 20,000 psi and 40,000 psi is applied for one
This invention is concerned with using solid-state hour" Post-heating at 21 SOT for two hours in a hydro-
welding to achieve strong welds with metals that un- 8en furnace after Weldln8 ls recommended. By select-
dergo recrystallization upon heating. The invention is ln8 a Predetermined pressure in this range uncrystal-
particularly directed to improving the welding process ,ft llzed a ^ can be welded to themselves or to recrystal-
disclosed in copending application, Ser. No. 289,033. 2° llzed all°ys bv this Process'
This improved process has the advantages of shorter OBJECTS OF THE INVENTION
welding time, lower welding temperature, lower weld- . • • • , .
 f L
ing pressure, and a simpler and more reproducible sur- " IS' theref°re, an object of the present invention to
face preparation procedure. „ Pro"de a shorter Dingle-step method of solid-state
Conventional brazing and fusion welding methods, 2S Weldlm3 dispersion-strengthened materials at a lower
such as resistance spot welding, have been used to join temperature without losing strength ,n the parent mate-
certain alloys. Fusion welding and brazing methods re- , or at_lhe weld'
suit in weldments having approximately 50 percent of Another object of the invention is to provide an im-
the parent metal strength. 30 Proved method of welding dispersion-strengthened al-
Brazing dispersion-strengthened nickel alloys, such '°ys in which the mating surfaces are prepared in an im-
"as Ni-ThO2, Ni-Cr-ThO2, Ni-Mo-ThO2, and Ni-Cr- Proved manner.
Al-ThOa, involves degradation of parent metal A further object of the invention is to provide a
strength. Diffusion occurring between the braze method of solid-state welding unrecrystallized alloys to
alloy and parent metal at elevated temperatures 35 recrystallized alloys without producing a weld line at
causes porosity to form in the parent metal as well as the interface.
in the braze alloy. The thoria dispersion, which is, These and other objects of the invention will be ap-
critical to the development of strength, may be I parent from the specification which follows.
« °BSCR,PT,ONOFTHB "KnaRED EMBOD.BNT
braze alloy is not as strong at elevated temperatures Sheets of a nickel-base alloy, commercially desig-
as the dispersion-strengthened nickel alloy. All of nated as TD-NiCr, were welded in accordance with the
these factors can contribute to weak brazements. , present invention to illustrate the advantages of the im-
Fusion welding necessarily involves melting of the proved enhanced diffusion welding technique. Nor-
dispersion-strengthened nickel alloy, and the thoria dis- 45 malty commercial TD-NiCr is recrystallized, but spe-
persion is lost. Thus the strengthening effect of the tho- cially processed sheets of this material which were
ria is lost, and the weldment is relatively weak. unrecrystallized were obtained. The special processing
Solid-state welding using both direct resistance heat- consisted of omitting the final recrystallization heat
ing at the joint and indirect heating from a resistance treatment that is normally given to commercial TD-
heated element has been proposed for joining alloys. 50 NiCr after thermomechanical processing. Thus, the
Solid-state welding is desirable because melting is specially processed TD-NiCr was in the unrecrystal-
avoided and foreign material need not be introduced at lized condition in which the grain size is extremely fine,
the joint. However, conventional solid-state welds have The sheets had a nominal thickness of 0.4 millimeter
proven to be weak and brittle when tested at elevated (0.015 in.).
temperatures. A thin recyrstallized band of small grains Specially processed sheets were welded to each
forms at a continuous weld line which acts as a bound- .other. Commercial sheets were also welded to each
ary. The continuous weld line and the small grains other. Likewise the dissimilar combination of specially
cause weakness at elevated temperatures. This results processed and commercial TD-NiCr sheets was
in joint failure at low stresses. Typically, joint efficiency welded. The specially processed material welded to it-
is 0 to 60 percent. Also unwelded areas occur sporadi- self and the dissimilar material combinations were pre-
cally at the weld line. ferred over the commercial material welded to itself.
A two-step welding process described in copending ' This was because the weld line could be eliminated in
application, Ser. No. 289,033 has been satisfactory for the preferred weldments. Also creep-rupture fracture
welding specially processed dispersion-strengthed al-
 fi_ of weldments took place' in the parent material away
loys that have had their mating surfaces specially pre- from the weld line and the creep-rupture shear strength
pared. However, the two-step welding cycle used in- of the weldments was higher than commercial TD-NiCr
volves long times of over three hours and high tempera- weldments. With the commercial TD-NiCr, a semicon-
3,798,748
t inuous weld line resulted and creep-rupture shear frac-
ture took place in the weld line indicating a plane of
weakness.
TD-NiCr has a nominal composition of 20 percent
chromum, 2 percent thoria and the remainder nickel.
The alloy has good high temperature strength and oxi-
dation resistance. The TD-NiCr derives its high tem-
perature strength from mechanical working of the
Ni-20 weight percent Cr matrix which contains a fine
dipped in another polishing solution at 90°C for.*three
minutes. This solution comprised 40% HNOj, 20% HF,
and 40% H2O. Again all the compositions are in
volume percent's.
The specimens were finally rinsed in distilled water
and then rinsed with methyl alcohol. The specimens
were stored in trichlorotrifluorethane to minimize oxi-
dation. This surface preparation procedure was very
easy to perform, and the specimens were finished in a
dispersion of Th02 particles. Use of this metal has been 10 reproducible manner. The specimens were overlapped
suggested for applications where metal temperatures
may reach about 2,200°F in an oxidizing environment.
These metals have potential applications in jet engine
components and heat shield panels for space shuttle ve-
hicles.
The commercial TD-NiCr sheets which were also
welded for comparison purposes had the same thick-
ness. Commercial TD-NiCr is made from the special
processed material by recrystallization at 2,1 SOT for
two hours. This heat treatment is termed as stress re-
lieving.
The commercial material is more ductile at room
temperature than the specially processed material, and
15
approximately one-half inch, and a vacuum of 2 X 10 5
torr was attained in the weld chamber. The specimens
were heated to the welding temperature, the welding
force was applied, and diffusion welding was achieved.
A single-step weld cycle shown in TABLE I produced
the best welds. This cycle consisted of heating to
I400°F where both specially processed and commer-
cial TD-NiCr have adequate ducti l i ty for diffusion
20
 welding and forcing the surfaces together for one hour
in a vacuum of 2- x 10~5 torr.
Post heating at 21 SOT for two hours in hydrogen was
utilized to recrystallize the specially processed material
it is more formable. The specially processed material
 25
 and
 dissimilar material weldments causing grain growth
must be formed at elevated temperatures between
about 1,400T and 1,500T where the material has ade-
quate ductility. This hot forming is expensive, and the
preference is to form at room temperatures if possible.
Therefore the commercial material is preferred for use
 30
where shaping to a predetermined configuration is re-
quired.
The advantage of being able to diffusion weld spe-
cially processed to commercial TD-NiCr is twofold.
First, if in a two component assembly, such as a corru- 35
gation-stiffened heat shield, one component requires
extensive forming, e.g., the corrugation, it can be made
from the more formable commercial TD-NiCr. Like-
wise the component least formed, e.g., the face sheet,
can be made from the less formable specially processed 40
TD-NiCr. Second, in applications where all the mate-
rial or materials must be severely formed, the specially
processed TD-NiCr could be used as an interlayer be-
tween a severely formed commercial TD-NiCr.
A vacuum hot press was used to make diffusion weld- 45
ing lap welds in both the commercial and the specially
processed TD-NiCr. The weld specimens were radi-
antly heated by a tantalum resistance heater. Sintered
tungsten rams were used to transmit welding force from
a 25 ton hydraulic press to the weld specimens through 50
Inconel X or TD-NiCr weld tooling. A pressure of 2 x
10~9 torr was maintained in the vacuum chamber dur-
ing welding.
Both types of TD-NiCr sheets in the as-received con-
dition had 120-grit sanded surfaces with the surfaces
scratches parallel to the principal rolling direction..The
weld specimens were prepared by sanding only the side
to be welded with 320-grit paper and cleaning with a
detergent.
The surfaces were then chemically polished by dip-
ping the specimen in a polishing solution at 90°C for
three minutes. This solution contained 92% HC1, 3%
HNOj, and 5% H,S04. The compositions are in volume
percents.
 65
and elimination of the weld line. Post heating is be-
lieved to strengthen the commercial material weld-
ments by increased diffusion across the weld line.
TABLE I—WELD CYCLES
Material
Specially processed
Commercial
Specially processed
to commercial
Temp.
•F.
1400
1400
1400
Pressure
psi
20,000
40,000
30,000
Time Vacuum
hr torr
1.0 2x -»
1.0 2 X I O ~ S
1.0 2x -»
Other welds were made using the cycle shown in
TABLE II in a vacuum of 2 x 10~5 torr. The welds pro-
duced with these cycles were not as good as those using
the weld cycle shown in TABLE I.
TABLE II—OTHER WELD CYCLES
Material
Specially processed
Commercial
55
Specially processed
to commercial
Temperature
"F.
1400
1400
; 1400,
12175'
11400 I
'2175'
1400
Pressure
psi
10
20
25
30
35
30
35
40
45
50
1
 2 '
20
30
Time
hr
1
The weld cycles shown in TABLE I were used to pre-
pare diffusion weld specimens for creep-rupture shear
-testing at 2,000°F in air. The results of the creep-
rupture shear tests are shown in TABLE III. It is evi-
dent from TABLE III that diffusion welds in specially
processed materials and the dissimilar combination had
excellent creep-rupture shear strength and failure oc-
curred in the parent material, away from the weld line.
While diffusion welds in the commercial TD-NiCr were
After rinsing with distilled water the specimens were almost as strong, failure often occurred at the weld line.
3,798,748
TABIjEUll".—CREEP-RUPTURE SHEAR'STRENOTHS OF DIFFUSION LAP WELDS IN 0.4 MILLIMETER (0.016 IN.) THICK TIV
NiCr SPECIMENS AT 1,100° C. (2012° F.)
Shear stress.
Material
Socially processed
Commercial material
Specially processed to commercial
Surface preparation
320-nrit sanded
do
do
do
do
.. ..do
do
do
do
600-grit sanded
do
do
do
320-grit sanded
do
do
do
600-grit sanded
do -.
do .-
do
As reccived/600-grit sanded
600-grit sanded/as received
do
p.s.i.
3,100
3,100
. 2,500
3,080
2,400
2,500
2,300
2,350
2,980
2,770
2,980
2,810
3,200
2,500
2,800
2,500
2,700
1,800
3,090
3,020
2,760
2,680
2,720
2,690
Time (lirs.)
14.0
7.0
16.2
II. U
2U. 0
24.4
236+
310+
95.0
0.1
125.0
91. 0
0.25
310+
145.0
316+
0.1
164+
F.O.L.
1.7
18.6
160+
260+
138.4
Failure, locution/mode ol fracture
I'urent material/Umslle.
Do.
Do.
Do.
Do.
Do.
Test discontinued, no failure.
Parent material/tensile at R.T. on removal.
Parent material/shear.
Parent material/tensile and shear.
Parent material/tensile.
Do.
Parent metal/shear.
Weld/shear on cooling.
Weld/shear.
Weld/shear on cooling.
Weld/shear.
Parent material/tensile on cooling.
Weld/shear.
Do.
Parent metal/tensile and shear.
Do.
Do.
Parent material tensile.
Ail of the welded specimens in TABLE HI were post-
heated at 2,150°F for two hours in hydrogen prior to
testing. One of the welded specimens failed on loading
(F.O.L.).
All of the specimens were chemically polished after
sanding. In the last group in which the specially pro-
cesHcd material w welded to the commercial material
the surface preparation of the specially processed ma-
terial appears first.
While the preferred embodiment of the invention has
been described it will be apparent that various modifi-
' cations may be made to the disclosed process without
departing from the spirit of the invention or the scope
of the subjoined claims.
I claim:
1. A method of solid-state welding a pair of disper-
sion-strengthened nickel alloy members that undergo
recrystallization and grain growth upon heating com-
prising the steps of
providing mating surfaces on said members to be
welded that are flat and free of stored energy
thereby preventing the formation of small grains,
assembling said members with said mating surfaces in
intimate contact in a vacuum of about 2 X 10~5
torr,
applying a pressure to said assembled members in
said vacuum,
heating the assembled members to a temperature of
about 1400° F for about one hour to cause diffu-
25
35
45
50
sion welding, and
postheating at a temperature of about 2150° F for
about two hours after diffusion welding to cause
increased diffusion, recrystallization, and grain
growth across the original interface.
2. A method of solid-state welding as claimed in
claim I wherein the memhcrs are of a nickel alloy se-
lected from a group consisting of Ni-ThO2, Ni-Cr-
ThO2, Ni-Mo-ThOz, and Ni-Cr-AI-ThO*.
3. A method of solid-state welding as claimed in
claim 2 wherein at least one of the members is of a dis-
persion-strengthened nickel alloy that is unrecrystal-
lized prior to heating.
4. A method of solid state welding as claimed in claim
1 wherein the applied pressure is between about 20,000
psi and about 40,000 psi. '
5. A method of solid state welding as claimed in claim
4 wherein the members are postheated in hydrogen.
6. A method of solid-state welding as claimed in
claim 1 wherein both members are unrecrystallized
prior to welding and a pressure of 20,000 psi is applied.
7. A method of solid-state welding as claimed in
claim 1 wherein one of the members is uncrystallized
and the other member is recrystallized prior to welding
and a pressure of 30,000 psi is applied.
8. A method of solid-state welding as claimed in
claim 1 wherein both members are recrystallized prior
to welding and a pressure of 20,000 psi is applied.
55
60
65


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