DE2043952A1 - Process for aluminizing objects made of nickel, cobalt or their alloys - Google Patents

Description

to the patent application

HOWMET CORPORATION, 4-75, Steamboat Road, Greenwich, Connecticut, USA

• concerning:

Process for aluminizing objects made of nickel, cobalt or their alloys .

The invention relates to a method for aluminizing, that is for diffusing aluminum from a feedstock into the surface of a metal object for improvement the corrosion resistance and scale resistance at high temperatures and / or in a corrosive environment, such as those for example in internal combustion engines, turbines and the like. By diffusing aluminum into the surface of Such materials, such as alloys with a high nickel or cobalt content and high-alloy steels, can improve the thermal shock resistance, the corrosion resistance especially at high temperatures and other physical and mechanical properties are significantly improved.

During aluminizing, the object is packed into a powdery feedstock ^{at a temperature above 100O 0 O, this}

1098 U / U8S

1A-38 493 2U43952

contains aluminum and aluminum oxides, optionally preferably with a small proportion of a halide, such as Ammonium chloride or fluoride is used in this feed kept in a non-oxidizing atmosphere for about 4 to 10 hours. In doing so, aluminum diffuses into a depth of use from about 10 to 20 / U, depending on the diffusion time and - "temperature and the aluminum concentration in the input material" In the insert layer, the aluminum concentration decreases with increasing distance from the surface of the object proportionally.

The invention now relates to an improved method of all-iting in order to detect a progression during use Immigration of the aluminum from the insert layer into the object and therefore to prevent deterioration in surface properties. It has been shown that the aluminum should be kept in the shift without undue Diffusion into the interior of the object. There will be a good connection between the inset layer and the core of the object. 'This creates complex series of connections that are the cause of the particularly high Are corrosion resistance in the heat.

The method according to the invention is used in particular on special alloys, preferably nickel and cobalt alloys. According to the invention, a thin layer of nickel is applied to the object prior to the actual axiting. This is followed by the usual. Alitation. The intermediate layer of nickel acts as a barrier layer against the penetration of aluminum into the core of the metal object and therefore maintains the desired aluminum concentration in the insert layer. Often can . | the one atζschicht in the form of the diffused aluminum within the base material its high corrosion resistance, especially at high temperature and in the presence of strong

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_ 3 - maintain corrosive gases.

1A-38 493

2Ü439 52

According to the method according to the invention is initially a Nickel layer with a thickness of at least 2.5 / U ^ preferably produced between 2.5 and 25 yuan on the object.

The nickel layer of the appropriate thickness is deposited by conventional electroplating (ASM committee on Nickel Plating, Metals Handbook, Volume II, pp. 432 to 443). However, the nickel coating can also be produced in other ways (Metals Handbook, pp. 443 to 445).

The input material for the. The aluminizing stage should contain aluminum of small grain size in an amount of 0.1 to 10% by weight in a finely divided filler, preferably aluminum oxide. While it is not essential, an energy-providing agent such as aluminum chloride or fluoride can be used at a level of from 0.01 to 5% by weight of the feed. During the .Alitierung there is a hydrogen atmosphere or another inert atmosphere. The temperature is between 980 and 1100 ^° C. The insert layer with diffused aluminum should have a thickness of approximately 25 to 125 / U, preferably 38 to 76 / U ”. This generally takes about 9 to 10 hours.

The method according to the invention is particularly suitable for use on objects of the following composition: Alloy A: 70% by weight Ni
12 wt% Cr

5 wt% W

5 wt% Al

3.5 wt. % Mq

2.5 wt% Ti, Nb, Ta

Remainder Fe, C ₁ -Mn, Si

_ 4 _ 1098H / U85

1A-38 493 2 ü 4 3 9 5

Alloy B: 60 Wt% Co Wt% C 20th Wt% Cr Wt% Mn .10 Wt% W Wt% Si 2.0 Wt% Nb Wt% Cr "1.0 Wt% Ni Wt% Co Remainder Pe, C, Mn, Si Wt% Mo Alloy C: 0.08 Wt% Ti 0.75 Wt% Al 0.75 Wt% Fe 19.0 ■> Ni 19.5 Wt% C 4.0 Wt% Mn 2.9 Wt% Si 2.9 Wt% Cr 4.0 Wt% Mo rest Wt% Ti Alloy D: 0.12 Wt% Al 0.15 Wt% Fe 0.4 Wt% Cb 13.0 Ni 4.5 0.6 6.0 1.0 2.25 rest

Examples of the electrolytes for the deposition of the invention The nickel layer and its working conditions are given in Examples 1 to 5 below.

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10981 kl U85

1A-38

example

Nickel sulfate, NiSO ₄ nickel chloride, NiCl ₂ total Ni boric acid, H ₂ BO-, additives (antipitting)

30 to 4 to 8 (a) 7 »? to 14.2 4 to 6

This electrolyte has a pH between 1.5 and 5 _r 2 '

and is at a working temperature between 45 and 71 ⁰ G

(115 to 160 ° F) and a current density between 1 and 10 A / dm (10 to 100 A / sq.ft.).

example

Nickel chloride, NiCl ₂ .6H ₃ O Nickel sulfamate, Ni (SO ₃ NH ₂ ) ₂ total Ni
Boric acid, H ₂ BO ₂

up to 4 35 Ms 60 8.2 to 15 4 to 6

This electrolyte has a pH value between 3 and 5 and should be operated at a temperature between 38 and 60 ^° C. (100 to and a current density between 2.5 and 30 A / dm (25 to 300 A / sq.ft.) .

example

Ms 2 30 to 40 7.6 to 10.5 2 to 4

This electrolyte has a pH value between 2.5 and 4 and is at a temperature between 38 and 71 ⁰ C and a

Nickel chloride, nickel fluorate, Ni (BF ₄ ) ₂ total Ni
Boric acid, H.

2 '

■ 2 current density operated between 2.5 and 30 A / dm ·

1098H / U85

-.1-38 * 93 2U43952

The following two examples show baths for electrochemical nickel deposition.

Example 4 -

600 g / l nickel chloride (NiCl ₂ .6H ₂ O) and 30 g / l boric acid (H ₅ BO ₅ ),

This bath had a pH between 3 »5 and 4.5 and was operated at a temperature of 71 ° 0.

Example 5

A bath with a pH value between 4 and 6 was used at a temperature between 88 and 98 ^° C. for an approximate deposition rate of about 12.5 / um-h. The bathroom contained:

Nickel chloride 30

Nickel sulfate -

Sodium hypophosphite 10

Sodium acetate -

Sodium Hydroxyacetate '50

Sodium succinate -

Lactic acid (80%) ~

Propionic acid (100%) -

For the second stage of the process, namely alitizing even one can use a feedstock containing 5 & 6 aluminum powder Apply to 100 kg of alumina powder or 7 kg of aluminum powder, 100 kg of alumina powder with 0.2 kg of ammonium chloride.

In the electroplating with electrolytes according to Examples 1 to 3, the object is connected as a cathode and electrolyzed until a layer thickness of 2.5 to 25 µm (0.1 to 1 mil) is reached. The object is removed from the electrolyte and removed with water.

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to wash.

In the electrochemical deposition with baths of Examples 4 and 5, only thinner nickel layers, namely between 2.5 and 25 / tf ^{n, are achieved} with constant movement of the objects in the bath.

For the .Alitierung of the objects from the cobalt alloy B a diffusion time of 10 h "at 1065 ° C in water off atmosphere, packed in one of the input materials mentioned above, needed. Under the same conditions, the nickel alloys A, C and D .. had a layer thickness of 38 to 76 yum already reached after 9 h.

The method according to the invention can be applied to other special alloys Apply on the basis of nickel and cobalt, in which there is a destruction at high temperature in Presence of corrosive gases due to red brittleness or other phenomena caused by the sulfur in the atmosphere.

Under the term "powder" or "finely divided" in context the constituents of the feedstock mean an aluminum powder of preferably less than 5 / um. That means, that the grain size is below 100 / um, preferably between 5 and the filler or alumina is in the feed.

PATENT CLAIMS:

- 8 1098U / U85

Claims (3)

Claims 1 J Process for aluminizing objects made of nickel or cobalt or their alloys, characterized in that prior to the diffusion of the aluminum a nickel layer on the objects, in particular with a thickness of at least 2.5 μm, in particular up to 25 μm, is applied. 2. The method according to claim 1, characterized in that the nickel layer by electroplating or electrochemical deposition is applied. 3. The method according to claim 1 or 2, characterized g e k e η η draws that the Alitierung at a temperature between 980 and 1100 G in non-oxidizing Atmosphere carries out and an insert layer between 25 and 125 / um, in particular 38 to? 6 / um generated. k . Process according to claim 3t characterized in that a powder mixture containing 0.1 to 10 wt .- ^ aluminum in a filler, in particular aluminum oxide, optionally in the presence of an energy-supplying agent, is used as the starting material. 81XXIV95 109814 / 14B5