U.S. patent number 3,819,338 [Application Number 05/181,600] was granted by the patent office on 1974-06-25 for protective diffusion layer on nickel and/or cobalt-based alloys.
This patent grant is currently assigned to Deutsche Edelstahlwerke Aktiengesellschaft. Invention is credited to Karl Bungardt, Gunter Lehnert, Helmut W. Meinhardt.
United States Patent |
3,819,338 |
Bungardt , et al. |
June 25, 1974 |
PROTECTIVE DIFFUSION LAYER ON NICKEL AND/OR COBALT-BASED ALLOYS
Abstract
Nickel and/or cobalt-based alloys are given a protective coating
by diffusing into the surface of the alloy metallic aluminum and
one or more metals of the platinum groups.
Inventors: |
Bungardt; Karl (Krefeld,
DT), Lehnert; Gunter (Krefeld, DT),
Meinhardt; Helmut W. (Krefeld, DT) |
Assignee: |
Deutsche Edelstahlwerke
Aktiengesellschaft (Krefeld, DT)
|
Family
ID: |
27181500 |
Appl.
No.: |
05/181,600 |
Filed: |
September 17, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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856539 |
Sep 10, 1969 |
3677789 |
Jul 18, 1972 |
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Foreign Application Priority Data
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Sep 14, 1968 [DT] |
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1796175 |
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Current U.S.
Class: |
428/652; 428/678;
428/938; 428/670; 428/926; 428/941 |
Current CPC
Class: |
C23C
10/52 (20130101); C23C 10/00 (20130101); Y10S
428/941 (20130101); Y10T 428/12931 (20150115); Y10T
428/12875 (20150115); Y10S 428/926 (20130101); Y10S
428/938 (20130101); Y10T 428/1275 (20150115) |
Current International
Class: |
C23C
10/52 (20060101); C23C 10/00 (20060101); B32b
015/00 () |
Field of
Search: |
;29/194,197
;117/130 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Weise; E. L.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Parent Case Text
This is a division, of application Ser. No. 856,539 filed Sept. 10,
1969 now U.S. Pat. No. 3,677,789 dated July 18, 1972.
Claims
What we claim is:
1. An object made of an alloy selected from the group consisting of
nickel based alloys, cobalt based alloys and nickel/cobalt based
alloy having a protective diffusion layer thereon and into the
surface thereof, said diffusion layer consisting of the nickel
based, cobalt based, or nickel/cobalt based alloy, aluminum and at
least one metal of the group consisting of platinum, palladium and
rhodium.
Description
This invention relates to the production of high-temperature
corrosion and scale-resistant protective diffusion layers on parts
made of high-temperature nickel and/or cobalt-based alloys, and to
methods of producing such layers.
Parts exposed to the action of corrosive media at high temperatures
as well as to mechanical stress, for example turbine blades, are
conventionally made of high temperature alloys based on nickel
and/or cobalt, and are provided with a protective layer produced by
diffusion to render them resistant to corrosion and scaling and
thereby to prolong their useful life. For the formation of the
protective layer aluminum is preferentially diffused into the
surface of such parts. Although parts that have been thus
aluminized are particularly resistant to corrosion and scaling,
their life, particularly turbine blades, is not as long as would be
desirable.
It is therefore the object of the invention to provide parts made
of high-temperature alloys that are based on nickel and/or cobalt
and that are to be subjected to high mechanical stress and to
attack by corrosive media, with a surface layer that will prolong
the life of such parts which, primarily due to scaling, will
otherwise have a restricted life.
For achieving this object, the present invention provides a
protective layer by diffusing into the surface of the parts that
are to be protected aluminum and one or more metals of the platinum
group of elements, particularly platinum, rhodium and palladium.
Tests have shown that parts provided with a protective layer
according to the invention have a longer life in service compared
with parts into which aluminum alone has been diffused in
conventional manner.
One or more metals of the platinum group can be diffused into the
parts at the same time as the aluminum, or alternatively in a
preferred method of producing the proposed protective diffusion
layer according to the invention, one or more metals of the
platinum group may first be applied to the surface of the part that
is to be protected in the form of a coating at least 7 .mu. thick,
and in a following diffusion heat treatment aluminum may then be
diffused into the surface together with the metal or metals of the
platinum group already deposited. Thus in the said preferred
method, the surface of the part that is to be protected is first
coated with a metal or metals of the platinum group, and this metal
or these metals of the platinum group are then diffused into the
surface simultaneously with the aluminum. The said coating of one
or more metals of the platinum group may be provided either
electrolytically, or by dipping, spraying, vapor deposition or by
mechanical plating. During the following diffusion treatment the
metal forming this coating together with the aluminum then diffuses
into the surface of the part that is to be protected and forms a
high-temperature scale-resistant protective layer on the part.
It is also possible to produce a diffused layer according to the
invention by first applying to the surface of the part that is to
be protected a coating of one or more metals of the platinum group
and then applying a further layer of aluminum covering the first
coating before the part is submitted to the diffusion treatment,
whereby both the metal or metals of the platinum group and the
aluminum diffuse into the said surface.
In a further preferred embodiment of the method of the invention
the parts that have been provided with a coating of one or more
metals of the platinum group may be embedded for the diffusion
treatment in a powder mixture containing metallic aluminum.
In general diffusion may be effected by heating between about
900.degree.C and about 1,200.degree.C for about 2 hours to about 10
hours.
The advantages that can be secured by the invention are illustrated
by the diagram of the accompanying drawing, wherein the amount of
scale formed in mg/sq.cm. is plotted against the time the part is
in operative use at 1,100.degree.C. Test pieces provided with a
diffusion layer according to the invention were compared with parts
having surfaces that were either left unprotected or that had been
protected with a conventional diffused layer of aluminum.
The test pieces consisted of an alloy containing 0.12 percent
carbon, less than 0.25 percent silicon, less than 0.25 percent
manganese, 13.5 percent chromium, 4.5 percent molybdenum, 6.25
percent aluminum, 2.3 percent niobium/tantalum, less than 1.0
percent cobalt, 0.9 percent titanium, less than 1.5 percent iron,
traces of boron and zirconium, the remainder being nickel.
The test pieces that had been provided with the protective
diffusion layer were first subjected to a preliminary treatment
consisting of wet blasting, degreasing in a cyanide bath 10 seconds
cathodically and 30 seconds anodically, followed by rinsing in
water and anodic pickling at 40.degree.C first 3 seconds in a 10
percent by volume H.sub.2 SO.sub.4 bath followed by rinsing in
water and then 30 seconds cathodically and 10 seconds anodically,
pickling in a 10 percent by weight solution NaOH bath, followed by
rinsing in water.
For the production of the diffusion layer according to the
invention the test pieces were then platinum coated in a bath
consisting of
13 g/l of hexachloroplatinic acid, H.sub.2 PtCl.sub.6,
45 g/l of triammonium phosphate, (NH.sub.4).sub.3 PO.sub.4,
240 g/l of di-sodium hydrogen phosphate, Na.sub.2 HPO.sub.4.
The temperature of the bath was 65.degree.C, the current density
9.0 amp/dm.sup.2 and the voltage 1.5 volts. Different thicknesses
of the platinum coating were provided by altering the treatment
times accordingly.
After having been platinum coated, the parts were heat treated
first for 2 hours at 260.degree.C and then for 3 hours at
400.degree.C to drive off hydrogen and to reduce the hardness of
the platinum coating. Finally the surface was degreased by rinsing
in methanol.
The test pieces which had thus been heated according to the
invention, together with the control pieces, were then submitted to
an aluminum diffusion treatment. The test pieces were packed into a
powder mixture consisting of 5 percent aluminum and 95 percent
Al.sub.2 O.sub.3 and diffusion treated for 21/2 hours at
1,100.degree.C under hydrogen as a protective gas.
The accompanying diagram reveals the difference in scale formation
between completely untreated parts, parts that had been merely
diffusion treated with aluminum and parts that had been provided
with the protective layer according to the invention, the
considerable superiority of which is apparent. Whereas the
untreated parts underwent considerable deterioration due to scaling
after 20 to 30 hours at the test temperature of 1,100.degree.C,
parts that had been subjected to aluminum diffusion in conventional
manner did not begin to scale until much later. However, the
scaling resistance of the parts provided with the protective layer
according to the invention was several times better than the best
of the comparative test pieces. Thus when a 7 .mu. platinum layer
had been applied the parts still disclosed no significant scaling
after 1,000 hours.
When considering the diagram it is to be noted that the areas
surrounded by full lines and by dashed lines are the areas of
scatter of the results achieved with untreated parts and with parts
that had been exclusively aluminized by diffusion, whereas the
other indicated lines for parts provided with the protective layers
according to the invention relate to individual tests and do not
comprise an area of scatter. However, the tendency of the test
pieces that had been provided with the diffusion layer according to
the invention to last longer is very clearly apparent.
Turbine blades made of the above-specified base material provided
with a 7 .mu. platinum coating by electro-deposition in the
above-described manner and then submitted to the above-described
aluminum diffusion treatment to form a layer having a total depth
of 65 .mu., were also subjected to thermal shock tests to examine
their liability to crack. For this purpose the turbine blades were
affixed to a wheel which was rotated. Two burners operated with
kerosene generated a peak temperature of 1,050.degree.C on the
surface of the turbine blades. After having passed through the
burner zones the turbine blades were quenched to about 150.degree.C
by exposing them to a blast of compressed air. The heating time in
each case was 60 seconds and the quenching time was also 60
seconds.
Simultaneously with this exposure to thermal stress, the turbine
blades were subjected to mechanical stresses by mounting them
eccentrically on the rotating wheel and thereby subjecting the
trailing edges of the turbine blades to tension.
After 10,000 temperature reversals, the turbine blades provided
with the protective diffusion layer according to the invention
showed no damage due to cracking or chipping. The appearance of the
protective surface layer when inspected by the naked eye was still
excellent after 10,000 temperature reversals, whereas after the
same number of temperature reversals blades that had been provided
with other conventional types of surface protection had scaled
surfaces as well as cracks.
* * * * *