U.S. patent number 3,640,815 [Application Number 04/856,188] was granted by the patent office on 1972-02-08 for method for surface treatment of nickel and cobalt base alloys.
This patent grant is currently assigned to Howmet Corporation. Invention is credited to Richard W. Martini, Charles W. Schwartz.
United States Patent |
3,640,815 |
Schwartz , et al. |
February 8, 1972 |
METHOD FOR SURFACE TREATMENT OF NICKEL AND COBALT BASE ALLOYS
Abstract
The treatment of high nickel and cobalt base alloy to improve
the corrosion resistance of parts formed thereof by first applying
a coating of nickel and then subjecting the part to diffusion
coating to aluminize the surface.
Inventors: |
Schwartz; Charles W.
(Whitehall, MI), Martini; Richard W. (Scotia, NY) |
Assignee: |
Howmet Corporation (New York,
NY)
|
Family
ID: |
25323032 |
Appl.
No.: |
04/856,188 |
Filed: |
September 8, 1969 |
Current U.S.
Class: |
205/191;
427/252 |
Current CPC
Class: |
C23C
10/02 (20130101) |
Current International
Class: |
C23C
10/00 (20060101); C23C 10/02 (20060101); C23f
017/00 (); C23c 009/00 () |
Field of
Search: |
;204/38S ;117/17.2P
;148/187-188 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Andrews; R. L.
Claims
We claim:
1. A method for surface treatment to improve the corrosion
resistance of products having surface portions formed of a metal
selected from the group consisting of nickel base alloys, cobalt
base alloys, and super alloys, comprising the steps of applying a
first coating of nickel on surfaces of the product, and then
aluminizing the nickel coated surfaces by diffusion transfer.
2. The method as claimed in claim 1 in which the first coating of
nickel is applied in a coating thickness greater than 0.0001
inch.
3. The method as claimed in claim 1 in which the first coating of
nickel is applied by a nonelectrolytic system in a coating
thickness within the range of 0.0001 to 0.001 inch.
4. The method as claimed in claim 1 in which the first coating of
nickel is applied in a coating thickness within the range of 0.0001
to 0.001 inch.
5. The method as claimed in claim 1 in which the nickel coating is
applied by electroplating the product.
6. The method as claimed in claim 1 in which the nickel coating is
deposited by chemical deposition.
7. The method as claimed in claim 1 in which the aluminizing
coating is applied with the materials at elevated temperature.
8. The method as claimed in claim 7 in which the materials are
applied at elevated temperature within the range of 1,800.degree.
to 2,000.degree. F.
9. The method as claimed in claim 1 in which the aluminizing
coating is applied in a nonoxidizing atmosphere.
10. The method as claimed in claim 1 in which the aluminizing
coating is applied in an amount to provide an overall coating
thickness within the range of 0.001 to 0.005 inch.
11. The method as claimed in claim 1 in which the aluminizing
coating is applied in an amount to provide an overall coating
thickness within the range of 0.0015 to 0.003 inch.
12. The method as claimed in claim 1 in which the product is
aluminized by packing the nickel coated product in an aluminizing
composition containing aluminum metal in finely divided form in an
amount within the range of 0.1 to 10 percent by weight uniformly
distributed in a filler.
13. The method as claimed in claim 12 in which the filler is
alumina.
14. The method as claimed in claim 12 in which the aluminizing
composition contains an energizer.
Description
This invention relates to the art of aluminizing metal surfaces by
diffusion to provide a surface on the metal which is rendered more
resistant to corrosion or oxidation at high temperatures and/or in
corrosive atmospheres, such as exist in a combustion engine,
turbine, and the like. By diffusion of aluminum into the surface of
such metals as high nickel or cobalt alloys and high alloy steels,
heat shock erosion, corrosion resistance and other physical and
mechanical properties are markedly improved.
To the present, in the aluminizing treatment by diffusion coating,
the metal part is heated to a temperature above 1,000.degree. C. in
a pack formed of a powdered mixture of metallic aluminum and
aluminum oxides, without and preferably with a small amount of
halide salt such as ammonium chloride or ammonium fluoride, for
about 4 to 10 hours in a nonoxidizing atmosphere.
The aluminum diffuses into the surface, usually to a depth within
the range of about 10-20 microns, depending somewhat upon the time
and temperature of the aluminizing treatment and the amount of
aluminum in the pack, with the amount of aluminum in the diffusion
layer decreasing from the surface inwardly toward the center in
amounts somewhat proportionate to the distance from the
surface.
It is an object of this invention to provide an improved aluminized
article and method for preparation of same wherein the diffusion
coating of aluminum remains concentrated in a narrow layer on the
surface of the article without excessive diffusion into the
interior of the article; whereby a better bond is achieved between
the diffusion coating and metal substrate; and whereby a complex
series of compounds are formed in the diffusion layer to provide an
improved coating which offers higher temperature corrosion
resistance.
In accordance with the practice of this invention, the parts formed
of a super alloy, and preferably nickel and cobalt based alloys,
are first processed to provide the surface portions to be
aluminized with a thin coating of nickel, in a first coating step.
The coated parts are then packed in the conventional manner and
conventional compositions for aluminizing the surface by diffusion
transfer of aluminum. The presence of nickel as a precoat on the
metal surface is believed to operate as a barrier coat which
concentrates the diffused aluminum in the surface portions of the
metal parts to provide an aluminized surface having greatly
improved corrosion resistance, especially when measured at high
temperature and in the presence of highly corrosive gases.
In the described two-stage process of first nickel plating and then
diffusion coating to aluminize the plated surface by a pack
cementation process it is desirable to deposit a nickel coating in
the first stage having a thickness greater than 0.0001 inch and
preferably having a thickness within the range of 0.0001 to 0.001
inch.
The desired thickness of nickel coating can be deposited by
conventional electroplating processes, such as described in the
article published by the ASM Committee on Nickel Plating, entitled
Nickel Plating, published in the Metals Handbook, Volume II, pages
432-443, under general purpose plating baths. Instead, the desired
thickness of nickel coating can be deposited on the surface of the
parts nonelectrically, as described on pages 443-445 of the Metals
Handbook, Volume II, supra, under the heading Nonelectrolytic
Nickel Plating.
The aluminizing pack employed in the pack cementation process for
aluminizing the nickel-coated surfaces can be formulated to contain
aluminum metal in finely divided form in an amount within the range
of 0.1 to 10 percent by weight with the remainder formed of a
finely divided filler, preferably alumina. Although it is not
essential, use can be made of an energizer, such as ammonium
chloride or ammonium fluoride, in an amount within the range of
0.01 to 5 percent by weight of the pack. A hydrogen or inert
atmosphere is maintained during diffusion coating while the
materials are heated to a temperature within the range of
1,800.degree. to 2,000.degree. F. or a time sufficient to build up
a final coating thickness within the range of 0.001 to 0.005 and
preferably within the range of 0.0015 to 0.003 inch. The desired
coating thickness is obtained with a pack of the type described in
about 9 to 10 hours of heating.
The following examples are given by way of illustration, but not by
way of limitation, of the practice of this invention:
Alloy Compositions:
---------------------------------------------------------------------------
Example 1
Percent by Weight Ni 70.0 Cr 12.0 W 5.0 Al 5.0 Mo 3.5 Ti, Nb, Ta
2.5 Fe, C, Mn, Si Balance
---------------------------------------------------------------------------
Example 2
Percent by Weight Co 60.0 Cr 20.0 W 10.0 Nb 2.0 Ni 1.0 Fe, C, Mn,
Si Balance
---------------------------------------------------------------------------
Example 3
Percent by Weight C 0.08 Mn 0.75 Si 0.75 Cr 19.0 Co 19.5 Mo 4.0 Ti
2.9 Al 2.9 Fe 4.0 Ni Balance
---------------------------------------------------------------------------
Example 4
Percent by Weight C 0.12 Mn 0.15 Si 0.4 Cr 13.0 Mo 4.5 Ti 0.6 Al
6.0 Fe 1.0 Cb 2.25 Ni Balance
First stage of nickel coating:
---------------------------------------------------------------------------
Example 5
Composition of Electrolytic Bath
Nickel sulfate, NiSO.sub.4 6H.sub.2 O 30 to 55 Nickel chloride,
NiCl.sub.2 6H.sub.2 O 4 to 8(a) Nickel sulfamate, Ni(SO.sub.3
NH.sub.2).sub.2 -- Nickel fluoborate, Ni(BF.sub.4).sub.2 -- Total
nickel as metal 7.7 to 14.2 Boric acid, H.sub.3 BO.sub.3 4 to 6
Antipitting additives (b)
Operating Conditions
pH 1.5 to 5.2 Temperature F. 115 to 160 Current density, a. per sq.
ft. 10 to 100
__________________________________________________________________________
---------------------------------------------------------------------------
Example 6
Composition of Electrolytic Bath
Nickel sulfate, NiSO.sub.4 6H.sub.2 O -- Nickel chloride,
NiCl.sub.2 6H.sub.2 O 0 to 4 Nickel sulfamate, Ni(SO.sub.3
NH.sub.2).sub.2 35 to 60 Nickel fluoborate, Ni(BF.sub.4).sub.2 --
Total nickel as metal 8.2 to 15 Boric acid, H.sub.3 BO.sub.3 4 to 6
Antipitting additives (b)
Operating Conditions
pH 3 to 5 Temperature F. 100 to 140 Current density, a. per sq. ft.
25 to 300
__________________________________________________________________________
---------------------------------------------------------------------------
Example 7
Composition of Electrolytic Bath
Nickel sulfate, NiSO.sub.4 6H.sub.2 O -- Nickel chloride,
NiCl.sub.2 6H.sub.2 O 0 to 2 Nickel sulfamate, Ni(SO.sub.3
NH.sub.2).sub.2 -- Nickel fluoborate, Ni(BF.sub.4).sub.2 30 to 40
Total nickel as metal 7.6 to 10.5 Boric acid, H.sub.3 BO.sub.3 2 to
4 Antipitting additives (b)
Operating Conditions
pH 2.5 to 4 Temperature, F. 100 to 160 Current density, a. per sq.
ft. 25 to 300
__________________________________________________________________________
---------------------------------------------------------------------------
Example 8
Composition Nonelectrolytic Bath
Nickel chloride (NiCl.sub.2 6H.sub.2 O 80 oz. per gal. Boric acid
(H.sub.3 BO.sub.3) 4 oz. per gal. Operating Conditions pH 3.5 to
4.5 Temperature 160.degree. F.
__________________________________________________________________________
---------------------------------------------------------------------------
Example 9
Composition Nonelectrolytic Bath
Nickel chloride 30 Nickel sulfate -- Sodium hypophosphite 10 Sodium
acetate -- Sodium hydroxyacetate 50 Sodium succinate -- Lactic acid
(80%) -- Propionic acid (100%) --
Operating Conditions
pH 4 to 6 Temperature, F. 190 to 210 Plating rate (approx.), mil
per hr. 0.5
__________________________________________________________________________
---------------------------------------------------------------------------
Example 10
Aluminizing Pack: 5 pounds powdered aluminum metal 100 pounds
powdered alumina
__________________________________________________________________________
---------------------------------------------------------------------------
Example 11
7 pounds powdered aluminum metal 100 pounds powdered alumina 0.2
pound ammonium chloride
__________________________________________________________________________
In the electrolytic plating systems of examples 5 to 7, the part is
suspended as a cathode in the electrolyte until a coating thickness
within the range of 0.0001 to 0.001 inch has been deposited. The
part is then removed and rinsed with water to remove
electrolyte.
In the nonelectrolytic systems of examples 8 and 9, a thinner
nickel coating is deposited on the metal surfaces. In practice, the
parts are immersed in the bath with continuous movement until a
nickel coating having a thickness within the range of 0.0001 to
0.001 inch is deposited and the part is then removed and
rinsed.
The nickel plated parts are packed with the pack composition of
examples 10 and 11 in a retort. The parts formed of the cobalt
alloy of example 2 are heated in a hydrogen atmosphere for 10 hours
at 1950.degree. F. while the parts formed of the nickel-based
alloys of examples 1, 3 and 4 are heated in a hydrogen atmosphere
for 9 hours at 1,950.degree. F. to form parts having a final
coating thickness within the range of 0.0015 to 0.003 inch.
Instead of making use of the nickel or cobalt based alloys of
examples 1 to 4, use can be made of parts formed of nickel or
cobalt based superalloys in which corrosion resistance at high
temperature and resistance to deterioration by the sulfides present
in corrosive gases is greatly improved.
The term "powdered" or "finely divided" form, as applied to the
elements in the pack composition, is meant to refer to aluminum
metal particles of preferably less than 5 microns and is meant to
refer to particles of less than 100 microns and preferably within
the range of 5-100 microns for the filler or alumina component of
each pack.
It will be understood that changes may be made in the details of
formulation and operation without departing from the spirit of the
invention, especially as defined in the following claims.
* * * * *