DE1948031A1 - Improved process for the treatment of superalloys that are provided with an aluminum-containing coating - Google Patents

Description

United Aircraft Corporation p «yyALjgg NIELSCH

4-00 Main Street Patent Attorney

East Hartford 1948031 _ωβ ? " ⁰ ^ ⁰ I ⁹ J ° _in01 ,

I V "τ W ν« -f ι SdiloBstraBe 112 P.O. Box 10914

Connecticut 06108 long distance: 652 97 07

UNITED STATES.

IMPROVED PROCESS FOR TREATMENT OF SUPER ALLOYS WITH A COATING CONTAINING ALUMINUM.

Priority USA 765,777
Patent application dated October 8, 1968

The present invention is generally concerned with coatings, which withstand high temperatures and oxidation, especially with the aluminum-containing coatings on the superalloys be applied. The process is particularly applicable to the treatment of coated gas turbine engine parts made from nickel-based superalloys.

The increased resistance of the superalloys for gas turbine engines was mostly only at the expense of the oxidation resistance attained. The aluminum-containing coatings were developed to protect the alloys at higher temperatures to be able to apply.

The aluminum-containing coatings protect the alloys through intermetallic compounds from aluminum, which in turn are protected by a layer of aluminum oxide, which was formed by oxidation of the coating at high temperatures. The oxide gradually goes through erosive disintegration? "? .- ¥ ©, ä? Lorerj., / But a whale oxidation provides protection again Oxidation zs®. AlusiniiHE ^ s ^ rcl i ^ guarantee. The protection of the U ^ bsr ^ ugeo is: -v; m: U; <a function of the aluminum content, the higher the? «? .üwdslu2; ~ ^ Go alΐ the longer the life of the connection in Besr / ag on the

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progressive oxidation-erosion-reoxidation mechanism.

The typical aluminum-containing coating may be prepared in various ways, aper the best-known methods are those of the diffusion from the cement slurry or the block denial augmentation ₀ In a typical ZementbrülienHiethode applied to a base layer of Udimet 700, a mixture of aluminum and silicon Powder in a ratio of 9 to. 1 suspended in a cellulose acetate carrier and sprayed onto the mechanically roughened surface of a molded and heat-treated article. After volatilization of the support material and reacting the mixture of the base layer to which the whole is subjected to a few minutes to an elevated temperature, the article is as follows in the heat treated: Diffusion at 1079 · 5 ° C (1975 ⁰ F) for 4 hours; and 843 ° C (155O ⁰ I ¹ ) for 24 hours; and 760 ° 0 (1400 ⁰ F) for 16 hours.

In a typical block cementing method, the desired aluminum-containing coating is formed by dipping the parts in a block of 15% aluminum poodle, 3% ammonium chloride and 82% aluminum oxide and bringing the whole to a temperature of about 982 ° 0 (1800 ⁰ F) will.

Both mechanisms are mainly in le <c diffusion of aluminum into the base layer solos. Obsclion formed the «protective

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the surface loading properties must be improved to ensure maximum performance. The fatigue resistance of the coated connection is directly related to the properties of the coating. In the covered Udimet 700 system, which is much used for gas turbine blades, the most determining factor of integrity is often the stress fatigue of the engine as it accelerates and decelerates. An examination of the isothermal fatigue, with a small change at temperatures between 21.1 ⁰ O (70 ⁰ F) and 927 ° G (170O ⁰ I) has shown that the cracks, in fact, first on the outer surface Odei * in the coating is of course different in composition and structure from the base layer.

In this particular basic coating system, which is typical of a conventional aluminide superalloy system, the aluminum-containing coating comprises a polycrystalline matrix with a high aluminum content (, NiAl phase) interspersed with a number of secondary phases. These ß-phase aluminides having an aluminum content of between 30-40 weight percent aluminum is characterized by a low conductivity at temperatures below 816 ° C (1500 ⁰ IP), and is thus rapidly cracked. This low conductivity is a puncture with a high aluminum content and results in a high transition temperature with brittle conductivity, which is normally above the planned critical stress on the connection.

Furthermore, by applying the coating, the composition of the substrate near the coating is changed by the removal of species by diffusion into the coating. In the case of a typical nickel-based superalloy, there is an enrichment of cobalt and chromium and a subsequent treatment in the heat or the working of the engine results in an undesired sigma ( <h ) phase on the base layer surface.

The present invention aims at the fatigue properties of aluminum-containing Ueterz-ügen and of to improve coated articles, especially in their application to nickel-based superalloys and the resulting

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produced gas turbine engine parts.

The foregoing and other objects of the invention are achieved by changing the composition and / or structure of the Coating, especially through the formation of a larger number of optimal types, the number and distribution of the different ones Phases in the coating and / or by reducing the harmful phases. In contrast to the usual methods, the Treatment carried out so that the local aluminum content in the coating is reduced, thereby reducing the brittle aluminide phases, and / or the formation of a conductive JNi ^ Al ^ 'grain boundary layer phase, and better distribution the secondary phase in the structure is reached. For a further improvement, the base coat surface is presented the application of the coating mechanically cleaned by such a Obtain surface roughness below 28.5 microns / cm (65 microns / inch).

The preferred treatment includes an intermediate treatment at high temperatures between the application of the coating and the Treatment in the heat to suppress the substrate, this intermediate heat treatment is carried out in a temperature range carried out in which the sigma or other adverse phases are not stable.

This heat treatment attracts a beneficial homogenization of the aluminide and the secondary phases in the coating and a reduction in the local aluminum content in the Coating after itself. The special temperature level of this intermediate treatment in the heat or the annealing at high Temperature is a puncture of the composition of the base layer the working environment of the protected article and coincides with the decomposition temperature range of the base layer. this causes there is a second economic advantage of the method, in contrast to the conventional coating methods in which the protective layer often on the article that has been treated in the heat is applied, the present invention a method for the production of improved coatings on the cast, forged or mechanically treated articles, and

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the previous heat treatments of the unprotected base layer can be omitted.

The present method thus comprises the coating of a base layer with or without prior heat treatment, it usually, but not necessarily, includes the normal brief heat treatment to apply the coating; an annealing in the heat at the decomposition temperature of the Base layer; and a heat crackdown treatment.

A particularly "preferred coating method for Udimet 700, which includes intermediate annealing at high temperature, is thus: application of the protective layer on a base layer, a diffusion treatment in the heat at 1079.5 ⁰ G (1975 ⁰ I ¹ ) for 4 hours; an intermediate treatment in the heat at 1171 ° C (2140 ⁰ P) for 4 hours; air cooling at 1079.5 ° C for 4 hours; air cooling at 84-3 ⁰ C (1550 ⁰ P) for 24 hours; air cooling at 760 ⁰ G (14 -00 ⁰ P) for 16 hours; and air cooling.

Applying diffusion treatment of the protective layer to an acceptable base layer, in which heat at 1079.5 ⁰ G (1975 ° P) for 4 hours ·; when applied to the alloy MAH M200, the preferred method is composed of Intermediate treatment in the heat at 1204- ⁰ G (2200 P ⁰⁾ during 2 hours; Air cooling at 871 ⁰ O (1600 ⁰ P) for 32 hours; and air cooling.

The drawing is a graphical representation of the results of the experiments on the fatigue properties of Peststellung hammered Udimet 700 at low change at 927 ° G (1700 ⁰ P) and to which the Udimet was treated variously 700th

The term nickel-based superalloy used herein refers to those multiphase alloys of the ν - ^ type, characterized by a high resistance in the temperature ranges of 871 ⁰ O (1600 ⁰ P) - 1149 ⁰ C (2100 ° P) or higher. Some of the commercially available alloys of this type are recorded below.

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- 6 panel I.

Designation Nominal Composition; (Percent by weight) TTdimet 7OO 15% Cr, 18.5% Co, 3.3% Ti, 4.3% Al, 5% Mo,

0.07% C, 0.03% B, balance Ni MAE M200 9% Cr, 10% Co, 2% Ti, 5% Al, 12th, 5% V, 1%

Co, 0.15% C, 0.015% B, 0.05% Zr, Eestli IN-IOO10% Or, 15% Co, 4.5% Ti, 5 ° 5% Al, 3% Mo,

0.17% C, 0.75% V, 0.015% B, 0.075% Zr,

Remainder Ni -

TRW 1800 13% Gr, 9% W, 1.5% Nb, 0.6% Ti, 6% Al,

ι 0.07% B, 0.07% Zr, 0.09% C

MAR-M246 9% Cr, 1.5% Ta, 10% Co, 2.5% Mo, 10.0% ¥,

1.5% Ti, 3. ^% Al, 0.15% C, 0.10% Mn,

0.015% B, 0.05% Zr

The different methods by which the aluminous The coverings on which the super alloys are manufactured include Block cementing, heat immersion, cement broth method, Precipitation from the steam, electrolysis in molten salt, and flame or plasma spray. Of these, the Blockzemerfetion and the cement broth nmetho de most needed. All of the methods described involve the reaction of aluminum or aluminum-rich materials with the surface of the alloys of the base layer at elevated temperatures, and the Protective properties of the aluminum-containing coatings produced in this way all depend on the formation of an outer layer of aluminum oxide, which by treating the coating in one oxidizing atmosphere is formed at high temperature. The specific composition of the coating, and less that The morphology of the secondary phases (carbides, etc.) changes somewhat as a function of the composition of the base layer Interdiffusion of the species during the coating process. These Changes in the microstructure and composition change the basic principles of the protective mechanism of the coatings not.

It has been found that a change in the heat treatment of the coated nickel-based superalloys leads to a

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increased bite formation due to "fatigue due to low alternation, which, as already mentioned, is an undesirable factor for excessive Gas turbine engine parts is as it reduces their service life. The new method is primarily limited to the reduction the local aluminum content in the coating. By the conventional coating methods obtained local aluminum contents of 30-40%, whereas in this case the Aluminum content is between 20 and 25%. In a certain sense, the aluminum content of the coating is thus reduced. However, this only relates to the local aluminum content, because in reality there is roughly the same volume Aluminum in the cover made by the present method, but it is far better distributed in the cover.

With the reduction of the local aluminum content of the alloy and the subsequent formation of a small but important amount of conductive Ni, Al ^ ¹ aluminide phase, which surrounds the brittle phase, there is also an important change in the grain size and morphology in the coating achieved. The structure becomes more homogeneous; fine secondary phases are dissolved and the grain size becomes larger. Furthermore, the preferred method eliminates or reduces the segregation of the base alloy which can be determined by metallographic examination of the conventionally coated articles. The transition temperature of the improved coating, which is brittle-conductive, is also reduced to a less critical temperature range.

All of these advantages of the present invention are obtained primarily through an improvement in the heat treatments of the coated article. It has been found that the resistance to cracking by fatigue can be greatly increased by small changes of coated Udimet 700, ie the heat treatment. In this particular system, it has been found that an annealing at a high temperature at 1171 ° C (214-0 ⁰ J?) For 4 hours, between the coating and the treatment in the heat to ITi the deposition of the base layer, a big improvement of the conductivity of the over-

0098 1 7/1 346

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added to itself. The treatment cylus for Udimet) OO -comprises thus: a coating of the alloy followed by an optional one Diffusion treatment in the heat at 1079.5 ° C

I ¹ ) for 4 hours; an annealing in the heat at 1171 ⁰ O (2140 ⁰ F ^ for hours; treatments in the heat at 1079.5 ° O (1975 F) for 4 hours, at 843 ° C (1550 ⁰ Jj ¹ ) for 24 hours and at 760 ° 0 (1400 ⁰ F) for 16 hours.

In the "past, the coatings were in practice on the fully heat treated blade or propeller blade applied. Of course, this meant that the article had to be read beforehand Treatment cycle subjected to heat. In accordance With the present invention, it is possible to use a high temperature anneal after coating The coating and the base layer can be treated simultaneously in the heat and therefore the previous treatments of the Base layer can be omitted. In other words, the coatings can be applied to the freshly hammered, treated or smoother ones Blades or propeller blades are applied. Not only does it increase the resistance to signs of fatigue increased, but also the whole treatment cycle is greatly simplified and the manufacturing cost of the coated articles become smaller. In the practice of the new method it is generally possible to use the diffusion treatment in the Eliminate heat that the normal overdraft cycle normally does included, since the high annealing temperature serves at the same time to apply the coating and to carry out the desired diffusion mechanism.

The temperatures, times and sequences described above are of course only representative and do not limit the invention, this will be apparent to all those familiar with the Material are familiar. These parameters change from Legiaung to Alloy and are primarily a function of the basic composition, although other factors, such as intended use, are often taken into account. In particular is the The least treatment time at a certain temperature specific and is the less critical element that plays a role. The intermediate treatment in the heat between the

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draw and heat treatment for deposition of the base layer, or annealing at high temperature usually carried out at a temperature which corresponds to the decomposition temperature of the base coat. Decomposition temperatures for a number of nickel-based superalloys are summarized in the table below.

Plate II

Designation Normal decomposition temperature ⁰ Q ( ⁰ F)

Udimet 700 1149 - 1177 (2100 - 2150)

MAR-M200 1204 - 1221 (2200 - 2230)

IN-100 1171 (2150)

MAR-M246 1204 - 1232 (2200 - 2250)

TRW 1800 1204 - 1232 (2200 - 2250)

Nimonic "115 II9O.5 (2175)

Udimet 7IO II70 (2150)

Rene 41 II70 (2150)

TRW I9OO 1204 - 1232 (2200 - 2250)

In summary, the treatment sequence is: a coating of the Base layer; annealing the coated base coat at the decomposition temperature of the base coat; and treatment of the coated article in the heat to depress the base layer.

As is clear from the drawing, following the above procedures results in greater resistance to cracking and consequently greater resistance to fatigue at 927 ° 0 (1700 ⁰ I ¹ ). The improvement over metal articles coated by conventional methods is by a factor of 3 at 76O ⁰ O (1400 ⁰ F) and by a factor of about 2 at 927 ° C (1700 ⁰ F). The buckling limit of the coated article is almost not changed by using this method.

The majority of experimental.en articles have been the best one at 816 ° C (1500 ⁰ F) go, and the fatigue of various Grundachichben different thicknesses when bending with a small change and an applied force measured by a percent. the

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Dimensions of the coating varied between 0.00508-0.01270 cm (Ö.002-0.OO5 inches) and corresponded to the normal dimensions used to protect gas turbine blades and propeller blades. A comprehensive comparative assessment the properties of such articles are shown in Table III.

Plate III

Base layer thickness . Number of changes until crack formation cm (inch) Conventional method New method

O.2O32 (0.080) 1148 295O

0.1016 (0.040) 538. 1836

• 680

The drawing further shows that when the surface of the Grundschidi; is treated and a surface roughness of less than 28.5 microns / cm (65 microns / inch), a coating is obtained whose resistance to crack formation; by Fatigue is greater.

From the foregoing description, it will be clear that the improved treatment methods of this invention will increase the useful life of protected superalloy oil doubled 001 tripled can be. But this invention not only achieves the primary goal, but also the cost of manufacturing coated ones Superalloy items can be discounted.

The drawing shows a graph of the results for forged Udimet 700 alloy fcei 927 · C. The vertical dinate includes the total change in ferrule.

Number 1 represents the eventualities for uncoated alloy. Number 2 shows the results with a commercially available aluminum duct. Number 3 shows the results with the aluminum duct and high

temperature-tempering action number ¹ V shows the results with aluminide coating, Hechtempe * - tempering treatment and smooth substrate »* surface ·.

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Claims (3)

Claims 1. A method for the production of an aluminum-containing coating on a superalloy base layer on nickel base, characterized by the combination of the following levels: Coating the base layer surface with an aluminum-containing alloy; Treating the coated base coat with heat at the decomposition temperature of the base coat; and treating the coated base layer at the deposition temperature. 2. Method according to claim 1, characterized in that the annealing reduces the local aluminum content in the coating and thereby the conductive Ni ^ Alu ¹ phase of the aluminide is formed in the coating. 3. Method according to claims 1 and 2, characterized in that that the local aluminum content does not exceed a maximum of 25%. 4 ·. Method according to claims 1-3? characterized, that the surface roughness of the superalloy base layer before coating is a maximum of 28.5 microns / cm (65 microns / inch). 5 · Method according to claims 1-4 to produce an 'alumini to obtain a comprehensive coating on a gas turbine article made of a nickel-based superalloy, characterized in that that coating at least a portion of the surface of the article with an aluminum-containing alloy; the article is treated in the heat at the decomposition temperature of the base layer in order to reduce the local aluminum content in the coating and in order to obtain a conductive ITi ₂ -Al v 'phase of the aluminide at the grain boundary; a treatment in the heat to knock down the Base layer follows. 009817/1346 Empty elf