DE1621303B2 - PROCESS FOR THE SIMULTANEOUS DIFFUSION OF CR, AL AND IF ANY SI INTO THE SURFACE OF HEAT-RESISTANT METALS - Google Patents

Description

The invention relates to a method for the simultaneous diffusion of Cr, Al and optionally Si into the surface of refractory metals to form a protective layer by wrapping and heating in a powdery reaction mass which, in addition to Cr, Al and optionally Si, is an inert filler material and contains a halogen component.

From the French patent 1 297 235 is the simultaneous diffusion of chromium, aluminum and optionally known silicon in the surface of heat-resistant metals to form a protective layer. However, the inventive method allows the working temperatures and increases a surprising increase in the service life of the treated workpieces.

The aim of the present invention is to create high-temperature-resistant workpieces in a Corrosive gas atmosphere can be exposed to temperatures that are significantly higher than Working temperatures to which the workpieces treated according to the known method are exposed can.

For a clear explanation of the invention, let us first consider the meaning of some that are used repeatedly Expressions set.

The expression "heat-resistant metallic workpieces" here refers to all workpieces that are in their whole mass or on the surface of an alloy based on iron, nickel, cobalt, tungsten,

ίο consist of molybdenum or more of these metals. With regard to the type and proportions of the totality of its components, this alloy is designed in such a way that that the alloy is already in itself, d. H. in the absence of any protective treatment, a resistance against mechanical stresses in a hot state and in general also a certain amount Has resistance to the effects of corrosion at high temperatures, especially in oxidizing or oxidizing and reducing or sulfur-containing atmospheres, e.g. B. by combustion gases of internal combustion engines. According to the current state of the art, you can Such alloys can be divided into four main classes, namely:

The stainless steels, for example, of the following composition (Fe 83, Cr 17) or the steel 18-8 (Fe 74, Cr 18, Ni 8) or the steel 25-20 (Fe 55, Cr 25, Ni 20);

the heat-resistant steels, for example, of the following composition Cr 25, Ni 25, C 0.10 to 0.4, Remainder Fe;

the heat-resistant alloys based on nickel, for example, of the following compositions Cr 20, Ti 0.4, Al 0.06, Fe 2.4, C 0.10, balance nickel, or Cr 20, Ti 2, Al 2 C 0.10 balance nickel, or Cr 9.5, Mo 3, Co 15, Ti 5, C 0.20, Al 5.5, W 1, remainder nickel,

or Co 10, Cr 13.5, Ti 2, Al 5.5 Mo 5, Nb 2.5, C 0.10, remainder nickel,

or Co 10, Cr 8, Ti 1, Mo 6, Ta 4.4, remainder nickel, or Ni 98, ThO _? 2,

and the Kpbalt-based heat-resistant alloys, of which, for example, the following compositions Cr 20, NiIO, W15, Fe 3, C 0.10, remainder cobalt,

or Cr 21, W11, Nb and Ta 2, Fe 2, C 0.50, remainder cobalt and Cr 21, WlO, Ta 9, FeI, C 0.85, Remainder cobalt

are listed.

The inventive method can also be used when the above heat-resistant metallic workpieces already have another diffusion treatment with a metal, in particular one Diffusion treatment with tantalum or chromium was made.

The term "magnesothermal chromium" denotes one produced by magnesothermal means ultra-fine chrome powder. Processes for producing such powders are particularly in the French patent specification 1123 326 and its additional patents 70 936 and 79 879 described.

When these definitions are taken into account, a Heat-resistant metallic workpiece a surface diffusion alloy by adding chromium and aluminum and optionally also formed by silicon.

3 4

The method according to the invention is thereby shown. 1 shows a chromating according to the invention

indicates that a reaction mass from a and aluminizing plant, the workpieces 1 in powder, the ultrafine Al powder and magnesother- the reaction mass 2 are embedded, which are in mixed Cr powder and optionally a very fine steel housing 3 with a partially gas Contains Si powder and the mean grain size of which is located 5 tight lid 3a, which is at most 1 μ in the chamber Aa , is used. a bell furnace 4 is housed by a

The workpiece with its entire upper line 5 becomes an at least partially hydrated protective surface brought into contact with the reaction mass. atmosphere is supplied.

The proportion of aluminum used as the reaction mass is expediently several independent

applied chromium-based alloy powder is from 5 to 25 percent by weight in the pendent treatment case 3 in the chamber Aa. If necessary, it is also prescribed that the silicon, which is then expediently turned by cross pieces, is separated in a proportion of 3 to 10, which contain a faster and more uniform weight percentage. Allow the reaction masses to be heated.

According to a preferred embodiment, FIG. 2 shows the stage of cooling of the

Alloy powder “in situ” through a previous heating housing3 and its use after the treatment are formed by the introduction of heat treatment, with cooling through pipes Workpiece precedes in the reaction mass. It can be sprinkled with water 6 after faster overflow The housing 3 is also presented under a protective cover 7 in an independent operation forms are. - takes place, which with at least one partially hydrogenated

As a chemically inert diluent, 20 th protective atmosphere is fed through a line 8 an oxide with a very high heat of formation, e.g. B. is, with the in the housing 3 by the cooling Roasted aluminum oxide in the form of a fine powder generated negative pressure the penetration of the protective (with a grain size, preferably in the size atmosphere, is favored in the housing. Order of a micron). Finally, a halo- At this point it seems useful to refer to the

ned constituent in liquid or finely divided addition to point out the essential role of the ultrafine stood (halogen, halide, hypohalite or Ge Character of the metallic component of the reaction mixture this body) added. tion mass (alloy powder with a grain size

In the alloy powder, the weight percentages are at most one micron for the components of the invention for the metallic component preferably plays according to the method.

5 to 50% and for the halogenated component 0.05 30 The ultrafine grain size of the alloy powder bebis 1% · The rest is made up of the indifferent dilution- acts a large surface development, which apparently resources. is favorable for the exchange reactions. In addition,

The reaction mass formed in this way and the work that as a result of the very small dimensions of the wall piece the surface layer of each grain is placed in a partially gas-tight housing brought, which in turn is quickly prescribed in a heating chamber with aluminum from the inside of the grain is. In the heating chamber there is at least one thing that ensures the aluminum-chromium ratio partially hydrogenated protective atmosphere, which remains constant especially for the alloy. Because aluminum has by ordinary electrolytic hydrogen, the tendency to penetrate more quickly into the crystal lattice of the plant a mixture of hydrogen and argon or pieces as in the crystal lattice of the alloy grains can be formed by cracked ammonia. 40 diffuse / This impoverishes the surface of the

The heating chamber is sandwiched between a fraction of grains of aluminum, which compensates for an hour and about 20 hours, and preferably migration of the aluminum atoms from the interior of the alloy grains to the surface for a period of several hours, at a temperature between 750 and 1200 ⁰ C forward, this takes place the faster the shorter the path of preferably 1050-1100 ⁰ C, maintained. Tem- 45 is aluminum atoms.

The temperature and duration of the treatment depend in particular. The preferred supply of aluminum to the

that of the workpiece used for the diffusion alloy layer (due to the greater electropositivity wanted thickness from. this metal) can be easily compensated for

The partially gas-tight housing will then be so that, after each treatment process, the protective atmosphere used in a protective atmosphere that adds some aluminum powder to the reaction mass during heating can be cooled, with this addition of aluminum powder about 0.5 to. The cooling is expediently BE DONE 1% of ^it can be reaction mass men that the below 750 ⁰ C temperature-lying the gradual but slower depletion of the

rature areas where the protective atmosphere is less effective is to be stepped through quickly. 55 will resemble that of the reaction mass from time to time

Will the formation of the ultra-fine chrome and aluminum time (e.g. after four or five work steps) one made of aluminum alloy powder "in situ", so a certain amount of ultra-fine chromium powder in one the reaction mass described above is also added in the amount of 0.5 to 1%, under the same working conditions defined above, the ultra-fine grain size of the metallic constituent

conditions treated in the absence of the workpiece. The invention is described below with reference to the size of the indifferent diluent. The grain on the drawing explained by way of example. however, the size of the indifferent diluent is F i g. 1 and 2 schematically show an apparatus for less substantial use than that of the metallic stock for the method according to the invention, sometimes and can therefore, for example, be smaller or larger in FIG. 1 of the actual heat treatment to be 65 than 1 micron, the proportion of the indifferent chromizing and aluminizing corresponds, while th diluent in the latter case must be greater than Fig. 2 on one of this heat treatment.
the following cooling process. It is also interesting to note that the

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weight ratio between the indifferent dilution - also against the action of the most violent thermal

medium and the metallic component of the visual or mechanical impacts completely insensitive

Reaction mass has no critical character and lent,

can practically vary between 1 and 20. Tests on the corrosion resistance in yourself

The treated according to the method works 5 high-sulfur combustion gases which have a dense shell without porosity and crack formation for 300 hours at 1100 ⁰ C with inserted dung and an excellent surface state of thermal shocks have been made have shown up. The workpieces show a plasticity of the surface layers that the exfoliated surface layers determined at the end of the tests are practically negligible in both cold and warm degrees of temperature (smaller than the state which gives the workpieces an exceptional 2 mg / cm ² ), while the same workpieces with lent resistance to thermal shocks he shares a corrosion resistance test without a previous one. Due to the increased chromium content, the upper protection is severely damaged and a flaky surface layers, the workpieces show a degree of corrosion of about 30 to 40 mg / cm ² ,
more resistant to sulphurous combustion gases. Practically equivalent results in terms of the reaction masses used do not experience any »aging of the workpieces, the homogeneity and the aging« and are not exposed to any hindrance (their plasticity of the sheaths, the resistance to nitrogen content can achieve high values without risk of corrosion and thermal shocks were thereby achieved), which has a practically unlimited use, that under the same conditions workpieces lasts for these masses as a consequence, these reacting were treated, the intermetallic compounds never brittle from other heat-resistant materials, nickel-based alloys from the following, for example Contains chrome and aluminum. Compositions passed:

The following application examples are used for

Explanation of the invention. After that, .. " _o _.; .., _ , _{λ η} . _xr

different heat-resistant alloys with an ^{A: Co 10} ' ^{Cr 8} > ^Tl *' ^{Mo 6} > ^{Ta 4} > ⁴ > ^{remainder Nl}

Reaction mass of the following composition 25 ° ^er

treated, which changed within fairly wide limits B: Cr 9.5, Mo 3, Co 15, Ti 5, C 0.20, Al 5.5, Wl,

can be. Remainder Ni

Weight percent or

LJltrafeines powder magnesothermi- _"o C: Ni 98, ThO _2. 2

see chrome 40

very fine aluminum powder 10 Here, too, they are fine in corrosion tests Annealed aluminum oxide 49.2 observed high temperature combustion gases

Ammonium chloride (or bromide) 0.8 degree of exfoliation in all cases practically unaffected

35 for the protected workpieces, while those for the same previously unprotected workpieces

It should be noted that in the case of strongly carbonized substances, it may be useful to observe degrees of exfoliation in the general material to be treated; ) can correspond to about 0.5 to 1 percent by weight of a connec- tion 4 °,
formation of the type of aluminum fluoride (AlF ₃ · 0.5 H ₂ O

or AlF ₃ · 3.5 H ₂ O) to be added, which at the beginning of the. ''

Operation the role of a superficial decarburization ■ Example2

by means of plays. ·

This reaction mass is used in Examples 1 to 7 45. In this example, the same workpieces are used. The chromium-aluminum alloy is treated as in Example 1; the treatment is carried out situ "by a preceding so-called" blind but for 20 hours at 900 ⁰ C.
Process «formed at 1000 ° C for about The properties regarding the appearance of the

one hour while maintaining the diffusion surface, the homogeneity of the diffused envelopes, sion process is carried out under the conditions provided for 5 ° of plasticity in the cold state or at high temperatures. . temperature, the insensitivity to thermal shocks

B e i s ρ i e 1 1 are the properties described in Example 1

",, ... _,. , analogously, the thickness of the diffusion shells produced

However, protection of moving turbine blades _{is less and depends on the nature of the be} _

Made of a heat-resistant alloy (CoIO, 55 materials between about 25 and 35 microns. Cr 13.5, Ti 2, Al 5.5, Mo 5, Nb 2.5, C 0.10, remainder Ni)
existing workpieces to be protected become one

Treatment for 6 hours at the temperature of Example 3
1080 ⁰ C subjected.

After treatment, the workpieces show a 60 In this example, the treatment

selir smooth surface and a semi-glossy very conditions and the treated materials dem

homogeneous sky blue appearance. The thickness of the Example 1; However, there were chromizing and aluminum

held difliisional covers reached about 65 microns. minimization reserves at the blade roots

Dicse rides protective covers rich in chrome and aluminum.

are free of any porosity, inclusions or 65 For this purpose, the blade roots are included at the beginning

Pillow. They are clearly plastic, even in cold layers of iron or nickel fabric

stood, and ΜίκιΜιΓιη; !!}! of the degree of deformation, coated and placed in cups, the powdery

what because pieces are exposed to. They contain calcined aluminum oxide, which is

if necessary iron powder or nickel powder is added. The cups containing the alumina are like this worked so that they fit pretty much into the upper rectangular part of the blade roots.

The thickness of the casings obtained on the unreserved surfaces is increased by the change the treatment conditions are not affected, the blade roots previously provided with reserves on the other hand are practically not chromed and aluminized.

. Example 4

Protection of distribution blades

made of a heat-resistant alloy, based on cobalt (Cr 20, Ni 10, W 15, Fe 3, C 0.10, remainder Co)

The protected workpieces are subjected to a treatment of 8 hours at a temperature of 1080 ⁰ C.

After the treatment, the workpieces have a very smooth surface and a light, semi-glossy one very homogeneous beige-orange appearance. The thickness of the diffusion shells obtained reaches about 55 microns. These protective covers, rich in chrome and aluminum, are of porosity, inclusions or Cracks completely free. You are cold yourself. stood at any given work piece Degree of deformation clearly plastic and completely insensitive to the action of the most violent mechanical or thermal shocks.

Corrosion tests in high temperature combustion gases corresponding to those described in Example 1 Tests have shown that the use of the plastic chromating and aluminizing treatment on these materials made possible the workpieces exposed to these tests without protection observed degree of exfoliation by more than 95%.

B e i s ρ i e 1 5

Protection of distribution blades made of heat-resistant

carbon-based alloys based on cobalt
(Cr 21, W 11, Nb and Ta 2, Fe 2, C 0.50, remainder Co)

The protected workpieces to a treatment of 10 hours, exposed to a temperature of 1050 ⁰ C.

After the treatment, the workpieces show a very smooth surface and a light beige-orange color Appearance. The thickness of the diffusion sheaths obtained reaches about 45 microns, and the sheaths are free of porosity, inclusions or cracks and are resistant to the most violent mechanical effects insensitive to thermal shocks.

Corrosion tests in combustion gases of high temperature according to Example 1 have shown that the use of the plastic chromizing and aluminizing treatment allowed that normally Reduce the degree of flaking observed on unprotected workpieces by more than 97%.

Example 6

Protection of combustion chambers from brazed

Arrangements made of stainless steel »18/8«,

Nickel and cobalt alloys

The workpieces are made of 18/8 steel (foot parts), a nickel alloy D (Cr 20, Ti 0.4, Al 0.06, Fe 2.4, CO ₁ IO, remainder Ni) [actual combustion chambers] and a Cobalt alloy E (Cr 20, Ni 10, W 15, Fe 3, C 0.10, remainder Co) [flame tubes] formed, which were previously hard soldered in a vacuum with the help of hard solders made of nickel-chromium-boron-silicon.

The workpieces to be protected are ^{exposed to a treatment at 98O 0} C for 15 hours. After the treatment, the thickness of the diffusion shells reaches 120 microns on the 18/8 stainless steel parts, 50 microns on the alloy D parts and 40 microns on the alloy E parts, these shells in all cases of inclusions, porosity or cracks were completely free and clearly plastic in the cold and warm state.

In the case of particularly difficult conditions

. The tests carried out on the test bench and during use on engines have not resulted in any failure of the Casings even with the use of strong sulfur

ao containing fuels observed, the degree of flaking of the treated workpieces in all Cases remained practically insignificant.

as example 7

Protection from before through tantalum diffusion

clad moving blades

made of nickel-based alloys F: CoIO, Cr 13.5, Ti 2, Al 5.5, Mo 5, Nb 2.5, C 0.10, balance Ni

Before using the chromizing and aluminizing process according to the invention, the Blades surrounded by tantalum diffusion with shells, this tantalum treatment the significant Improvement of the flow properties of the treated materials allowed.

To carry out this tantalization pretreatment, the workpieces were heated for 4 hours 30 minutes heated to 1080 ° C in partially gas-tight boxes placed in a hydrogenated protective atmosphere, wherein the workpieces were embedded in a powdery mixture made of fine, annealed aluminum oxide (97.5 percent by weight) and very fine tantalum powder (2.5 percent by weight) with an additive of 0.5 weight percent ammonium chloride.

This pretreatment led to the formation of very tantalum-rich diffusion shells with a thickness of 30 microns with a preferred deeper penetration of the tantalum at the joints between the grains of the material.

The previously tantalized blades made of alloy F were subjected to a treatment in a chromizing and aluminizing compound to which 5% silicon had been added, which was previously in a "blind treatment". was homogenized, the protective treatment for 8 hours at a temperature of 1080 ⁰ C

was made. ''

After the protective treatment by simultaneous diffusion of aluminum, chromium and silicon be the workpieces have a very smooth surface and a very homogeneous, semi-glossy him melblue appearance. The received protective cover! are about 55 to 60 microns thick. You sini free of porosity, cracks or inclusions and even clearly plastic when cold. The protective treatment provided excellent protection treated workpieces of very long lasting

209 647/17

Duration against the effects of combustion gases up to temperatures of 1100 ° C.

Example 8

Chromating and aluminizing

from before by tantalum diffusion with a protective cover provided workpieces made of alloys

based on nickel (alloy C, example 1)

The workpieces for test turbine wheels to be protected by plastic chromium plating and aluminizing were subjected to a pretreatment for cladding by tantalum diffusion. This pretreatment should allow too deep a back diffusion of the aluminum during the use of the protected workpieces impede. It also allows a reaction between the nickel alloy and thorium oxide the aluminum supplied in statu nascendi during the chromizing and aluminizing treatment to avoid.

The tantalization pretreatment is carried out by placing the workpieces in partially gas-permeable Nickel boxes with an intimate mixture of tantalum in the form of a very fine powder (5 percent by weight) and annealed alumina in the form of a fine powder (95 percent by weight) with an addition of 1 weight percent ammonium chloride. The arrangement is for 6 hours at 1080 ° C under a Hydrogen protective atmosphere heated. This treatment produces tantalum diffusion claddings Workpieces with a shiny appearance, which are plastic in the cold and warm state and one have a uniform thickness of about 35 microns.

The so tantalisierten workpieces are then subjected to a plastic chroming and Aluminisierungsvorgang for 8 hours at 1080 ° C, wherein a reaction mass following average composition is used: Chromium 30% Aluminum 5%, alumina 65 ° / o ^»m ^ an addition of 0 , 5% ammonium chloride (cement powder based on ultra-fine powder of magnesothermal chromium, fine aluminum powder and fine annealed aluminum oxide), this mass being homogenized beforehand during a "blanking process".

The workpieces obtained have a homogeneous, semi-glossy surface. The by the two consecutive Protective covers formed by treatments are plastic and possess when cold a uniform thickness of about 50 microns. They allow a particularly effective one to be achieved Protection of the treated workpieces against the corrosive effects of combustion gases at high temperatures even if very severe thermal shocks occur.

10

Example 9

Chromating and aluminizing
from before by chrome diffusion with covers
provided workpieces made of heat-resistant
Nickel alloys (alloy F, example 7)

In this example, on the one hand, the pretreatment for the production of a coating by chromium diffusion is intended and better behavior of the protected workpieces in combustion gases with a high sulfur content ensure and, on the other hand, reduce the penetration of aluminum between the grains, which ■ n the surface zones of the workpieces during use chromizing and aluminizing treatment can occur.

The pretreatment for chroming is carried out under such conditions that the formation of surface zones is avoided, which by

ao too strong a chromium enrichment has become brittle. The workpieces are chromed with a treatment compound, in which ultra-fine nickel-chromium powder can be used, which is obtained by preheating a mixture of ultra-fine powder of

»5 magnesothermal chromium (25 percent by weight), fine nickel powder (10 percent by weight) and fine Annealed aluminum oxide (65 percent by weight), to which 1 percent by weight ammonium chloride was added was made. The reaction masses prepared in this way for chromating are made by addition of 1% by weight chromium powder and 0.5% ammonium chloride or bromide between various Maintain operations. In the present case, the workpieces undergo a chroming treatment of 6 hours at 1050 ° C under a protective hydrogen atmosphere. The treatment results in the formation of smooth chrome diffusion shells with a homogeneous semi-glossy appearance, which, due to their limited chromium content, are plastic in the cold state and are uniform About 35 microns thick.

The workpieces chromed in this way then undergo an additional treatment for plastic chromizing and aluminizing under the conditions described in the previous example. Own the workpieces then a homogeneous semi-gloss surface appearance and are made of diffusion alloys, encased, which at the same time have a high chromium and aluminum content and their total thickness about Reached 65 microns. These covers are plastic when cold and warm and offer workpieces up to around 1050 ° C a very effective protection against combustion gases from fuels, their sulfur content Can reach 3 to 4%.

1 sheet of drawings

Claims (5)

Patent claims: 1. Process for the simultaneous diffusion of Cr, Al and optionally Si into the surface of heat-resistant metals to form a protective layer by packing and heating in a powdery reaction mass which, in addition to Cr, Al and optionally Si, contains an inert filler material and a halogen component, characterized in that, that a reaction mass composed of a powder which contains ultrafine Al powder and magnesothermal Cr powder and optionally extremely fine Si powder and the mean grain size of which is at most 1 μ is used. 2. The method according to claim 1, characterized in that the powder consists of the individual components is formed in situ by a previous heat treatment before the workpiece is in the reaction mass is introduced. 3. The method according to claim 1, characterized in that the preferred supply of aluminum to the workpieces is compensated by the fact that the reaction mass after each treatment process some aluminum powder is added, this aluminum powder addition 0.5 to 1 percent by weight of the reaction mass. 4. The method according to claim 1, characterized in that the gradual but slower depletion of the chromium in the reaction mass is compensated for by the fact that the reaction mass from time to time a certain amount of chromium in the form of an ultrafine powder in a proportion of 0.5 to 1 percent by weight of the reaction mass is fed. 5. The method according to claim 1, characterized in that the method is based on heat-resistant metallic workpieces on which another diffusion treatment with tantalum or Chromium was made is applied.