DE3310750A1 - METHOD FOR COATING A HEAT-RESISTANT ALLOY BASE - Google Patents

Description

Method of coating a heat-resistant

The present invention relates to a method for forming coating layers with excellent Heat and corrosion resistance on the surface of a heat-resistant iron alloy base, which used primarily in a low-carbon, fuel-burning atmosphere.

Light fuels such as natural gas, petroleum gas and naphtha were used in heating stoves, which are used for distilling, reforming or cracking materials such as hydrocarbons in Oil refining or chemical plants are used. A main reason for this is that when a fuel other than the above-mentioned light fuels, such as one containing a still residue Heavy oil such as obtained at a petroleum refining stage, coal or a mixture thereof is used

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becomes, the problem of high temperature corrosion of the metallic Material of the heating furnace occurs. Especially when burning poor quality fuel propose compounds of heavy metals, such as δ vanadium, sulfur compounds, or sodium chloride the like., which are contained therein, on the inner Metal surface of the furnace as so-called. Fuel ash down, which corrodes at a speed odej * is eroded, which is unusually higher than that Corrosion rate of the metallic material when it is at a high temperature in the surrounding air is exposed. This phenomenon is called "heat corrosion".

Previously known methods for avoiding heat corrosion can roughly be classified as follows:

(i) the resistance of the metallic material per se to high temperature oxidation is improved;

(2) the corrosive effect of the heavy oil combustion gas is reduced; and

(3) the metallic material is surface treated, so as to improve its resistance to high temperature corrosion.

As a concrete example of (1), an oxidation-resistant material with a high chromium content was used as an alloy component developed. The oxidation resistance of the alloy is increased by increasing the chromium content significantly improved from this. However, if the chromium content is increased above a certain value, this will be metallic material becomes brittle and its strength is reduced at room temperature and higher temperatures, whereby its practical value as a construction material

35 is deposited.

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At present, a metallic material of this kind which is excellent as a practical construction material is made of an alloy comprising chromium and nickel in substantially equal amounts and a very small amount of TJb. However, when using this alloy, a hot corrosion occurs even when the metal surface temperature exceeds in the combustion atmosphere of a heavy fuel 900 ⁰ C, and the metal-w ill be useless. Furthermore, this material is very expensive, as can be seen from its composition. The cost of this material is at least several times higher than that of iron alloys commonly used to make pipelines for reforming furnaces, such as an alloy comprising 25 wt% chromium, 35 wt % nickel and the rest essentially iron. Thus, the measures in which the oxidation resistance of the material per se is improved have the disadvantages that the furnace temperatures which can be used for inferior fuel combustion are limited and that the material is very expensive.

As a concrete example of (2), calcium oxide, magnesium oxide, magnesium carbonate or the like becomes the inferior one Fuel is added so as to form calcium vanadate, magnesium vanadate or the like and to reduce it to prevent the melting temperature. The lowering of the melting temperature comes about through formation eutectic mixtures of vanadium pentoxide from the combustion of organic compounds of vanadium, v / which were contained in the inferior fuel, with a thin layer of heavy metal oxides, i.e. Nickel oxides, chromium oxides and the like. These metal oxides completely cover and protect the metal surface effectively the metal surface, since the eutectic

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Mixture of vanadium pentoxide with a thin layer made of heavy metal oxides to protect the metal surfaces is not effective.

δ These measures cause many problems by increasing the melting point of fuel ash and increasing its amount is increased, and by making the ashes uneven precipitates on the metal surface, and finally by inhibiting heat transfer and making uniform heating impossible. Furthermore, it is difficult to mix the above-mentioned additives homogeneously into the inferior fuel, and an increase the fuel cost is inevitable.

As a concrete example of (3), the surface of the metallic material is covered with a substance that has a high Has heat and corrosion resistance, coated by means of a surface treatment process. It different coating materials and

20 drives suggested.

However, the coating layers still have unsatisfactory corrosion and peeling resistance, if the coated bases are repeatedly exposed to temperature fluctuations. Such a thing repeated heating and cooling is hereinafter referred to as "heat history".

The attached drawings show: 30

1 shows the results of corrosion tests; Figures 2 and 3 show the results of peeling and peeling tests, respectively; and

4 shows the shape of the test specimens used in the examples. ;

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From extensive research and studies on the For the purpose of improving the corrosion and peeling resistance of coating films produced according to the The present invention resulted. First of all coating processes according to the invention are described.

"" The present invention provides a method of coating the surface of a heat-resistant alloy base with two or three protective layers. The base has sufficient strength at high temperatures for practical use as a construction material for various parts of the furnace. The base comprises 18 to 35 wt. % Chromium, 18 to 50 wt.% Nickel, up to 0.6 wt.% Carbon and the remainder essentially iron. In particular, the remainder of this heat-resistant alloy base consists essentially of iron and can furthermore optionally contain a small amount of one or more of the elements molybdenum, tungsten and niobium. The first coating layer comprises an alloy of 20 to 80% by weight of chromium, 20 to. 80 Gev.% Nickel and up to 3 wt.% Of another element. The first coating layer is formed on the surface of the base by means of the plasma flame spraying method, also known as plasma fuel spraying. Then the second coating layer,

70 to 30 wt.? o of materials of the same composition. like the alloy used in the first layer

tion and 30 to 70 wt.% Alumina comprises, on the Outer surface of the first layer, again by means of the plasma flame spraying method, formed.

The third coating layer, which is optionally formed, is made of alumina, has a

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Thickness of up to 100 / urn. and is formed on the outer surface of the second layer by the plasma flame spraying method to thereby further improve the coating effects.
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According to the method of the invention described above. becomes a coated, heat-resistant alloy base with improved peeling and corrosion resistance, compared with that obtained by means of the above-mentioned known methods. Another advantage of the process according to the invention is that disadvantages, such as acceleration of corrosion and deformation of the coating films during high-temperature heat treatments, which are carried out in an oxidizing atmosphere, as in some of the previous ones Descriptions mentioned can be prevented.

Although the precise reasons for the excellent peeling and corrosion resistance of the coating layer formed by the process of the present invention have not yet been explained, it is believed that this is due to the following causes. As described above, it is well known that the high-temperature corrosion resistance of an alloy increases ■ as the chromium content increases. However, if the coating layer of an alloy having such a high chromium content is formed on a base which has a thickness greater than that of the coating layer and is higher in high temperature resistance than that of the coating layer, and it is further subjected to a heating history as defined above , the high chromium coating layer tends to crack because a high chromium alloy is brittle. However, if a basis of the above-mentioned

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used th, erfindungsgeraäßen composition and the coating layer formed directly thereon is an alloy according to the invention comprising 20 to 80 wt.% chromium, 20 to 80 wt.% "nickel and up to 3 wt.% eines.anderen element, the thermal expansion difference is between the base and the coating layer obtained when the heating history is applied to the coating layer side, also the thermal stress caused in the coating layer is reduced. This is considered to be a reason for the excellent peeling resistance which can be obtained. even when an alloy with such a high chromium content is used to form the first layer

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The above-mentioned conventional methods differ from the method according to the invention in that that the difference in metal composition between the first layer and the base in conventional, heat-resistant, coated alloy bases is excessive. Becomes an alumina layer insoluble in the alloy phase in the first Layer used in the form of a two-phase mixture, as described in some of the known processes, so the brittleness of the first layer is further increased in order to achieve that the first layer is one of the desired Effect of preventing cracks of the first layer shows opposite effect. The-'according to the invention Alloy used to form the first layer, which has a high chromium content, has a has high corrosion resistance, although even its corrosion resistance is still insufficient. Furthermore, their formability and other properties required for a construction material are not

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satisfactory. Although this alloy is hardly suitable as a base, it can be used to form a dense, first coating layer on a base can be used, the base having sufficient malleability and the other for a construction material has necessary properties, so that a crack formation is prevented, the peeling and Corrosion resistance can be significantly improved as a result. As a result, the remaining unsolved problem is to prevent the components of the combustion gas, which the first Corrode layer, come into contact with this layer. For this purpose, according to the invention, the second Layer and, optionally, the third layer in a row

! 5 coated on the first layer.

The second layer according to the present invention is a coating layer comprising a mixture of (1) an alloy having a composition within the same ranges as in the first layer, and (2) Alumina. One reason why an alloy that has a composition is used in the second layer is within the same ranges as in the alloy used for the first layer in minimizing the formation of cracks in the second layer, as above with respect to the first layer described. Alumina is incorporated into the second layer for the corrosion resistance of the second Layer to increase, and if a third coating layer formed from aluminum oxide thereon, ■ the adhesion of the third layer to the second Layer to improve. If the second layer is exposed to the course of heat, as defined above, it forms some cracks, as this second layer of aluminum oxide

holds which is insoluble in the alloy (metal) phase

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is. However, the second layer will not peel off from the first layer even if cracks are formed, since the composition of the alloy phase of the second layer is similar to that of the first layer. δ Thus, even if there are very fine cracks mainly at the interface between the alumina phase and the alloy phase in the second layer may form the contact of corrosive constituents largely prevented with the first layer. The method of forming a second layer comprising a mixture of (1) an alloy composition similar to that of the first layer and (2) aluminum oxide, is not known from the prior art. In this regard, the present invention differs

¹ ^ finding conventional methods.

According to the present invention, a third coating layer made of alumina can be formed on the second layer. Compared with coated bases, in which an aluminum oxide layer is formed on an aluminum oxide-free layer according to conventional methods, the { third coating layer of aluminum oxide formed according to the invention has very good adhesion to the second layer, and the third layer 5 is exposed to a Essentially not detached from the second layer in the course of heat. Remarkable effects are obtained when the alloy phase formed on the surface of the second layer is prevented from coming into direct contact with the corrosive components. The thickness of the third layer made of aluminum oxide is preferably up to 100 / tim. If the thickness _t of the third layer more than 100 / um, it can be easily peeled off. The aluminum oxide content of the second layer is more suitable->

^a °, wise 30 to 70% by weight. According to the present invention,

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in which the compositions of the three coating layers are specially adjusted, v / ground, compared with the conventional methods, far more excellent Effects achieved. These effects are obtained through the synergistic interaction of the combination from the two or three coating layers and the basis.

It is desirable that the layers concerned have dense, fine structures with only low porosity. If the fine structures are highly porous, then a satisfactory effect is not expected. That used to form the first coating layer High chromium alloy and the metal alloy component the second coating layer have a high melting point. To a coating layer with a dense, fine structure underneath Using a chromium alloy with a high melting point by means of the plasma flame spraying process, are high flame spray temperature and pressure, i.e. a high impact speed of the fine particles of the molten alloy and the base flame sprayed alumina is required. Therefore, to form the coating layers according to the invention Process a plasma flame spraying process in which a particularly high flame spraying temperature is achieved, preferred over other, known flame spraying processes. It is the same for Formation of a coating layer to a high degree

of adhesion to the surface of a substrate · effective to carry out flame spraying during a oxidized film that can be formed on the substrate is reduced to metal by being drawn into it during plasma flame spraying used, inert gas hydrogen

°° is performed.

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The method of the present invention can be practically carried out under the following conditions. The temperature is ⁰ 3000-50 00o C, preferably 10000-30000 ⁰ C. The flow rate of the gas δ is between 1/4 of the sound speed up to the speed of sound, preferably 1/3 of the speed of sound to the sound velocity. The coated base obtained generally has a porosity range between 0.01 and 5% by volume, preferably 0.01 and 1% by volume.

The preferred thickness of the first and second layers is 50 to 150 µm, and that of the third layer is according to the invention up to 100 μm. The total thickness of the two layers or the three layers is desirably up to 300 / µm. The method according to the invention can be used for the treatment of heat-resistant, iron alloy castings with a high chromium, high nickel content, rolled material and

20 welded products of various shapes.

Examples

Many specimens were prepared by cutting the body of a tube by means of a centrifugal casting process from a HK-40 steel alloy comprising 25 wt.% Chromium, 20 wt.% Nickel, up to 0.4 wt.% Carbon and the balance Iron, was produced, this tube having an outer diameter of 120 minutes and an inner diameter of 100 mm. The test specimens consisted of partial cylinders, as shown in FIG. 4, with a wall thickness a of 5 mm, a chord length b of 30 mm and a length c of 100 mm. The outer surface A of each part cylinder was the casting surface of the above-mentioned pipe. The test specimens were coated by various methods and then corrosive

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Sion resistance and peeling tests for the coating s shift. A commercially available plasma flame spraying device was used to coat the test specimens used. The spray gas used consisted of a mixture of 60 vol% argon and 40 VoI-Jo helium. The following spray conditions were used: DC current = 40 V and discharge current = 800 A. Coating layers of an alloy of the following described composition, a mixture of this alloy and aluminum oxide or aluminum oxide alone were on the entire surfaces of the corresponding test specimens with coating layer thicknesses applied from 50 to 150 / µm. The test specimens coated in this way were used as test pieces. 15th

A powdery mixture comprising 85% by weight of vanadium pentoxide and 15% by weight of anhydrous sodium sulfate was kneaded together with acetone to make a soft paste. This soft paste was applied to the surface of the test specimen as artificial fuel ash in an amount of 20 mg solids / cm of the test specimen surface. The acetone was evaporated to dry the paste by drying in air at ambient temperature.
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During the corrosion test, the test specimens to which the artificial fuel ash was applied were heated to 900 ° C in an electric furnace over 3 h. The test specimens were then removed from the electric furnace and cooled to room temperature for 5 h, then brushed in water to wash off the artificial fuel ash, and finally dried and weighed. The weight was compared with that before the application of the artificial fuel cell weight of the test specimen measured. The results of the corrosion test are shown in FIG.

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In Fig. 1, the ordinate indicates the values obtained by dividing the change in weight of the Test specimen after the test through the surface of the test specimen. Ordinates on the positive side mean . that the weight of the test body was increased by the test, and ordinates mean on the negative side, that the weight of the test specimen was reduced by the test. The digits 1, 2, 3 and 4, as in the Figure shown by the bars refer to the correspondingly numbered, coated bases with the structures given in Table 1.

The test results shown in Table 1 show that when a first alloy coating layer comprising 20 parts by weight of chromium and 80 parts by weight of nickel and a second coating layer comprising a mixture of (i) 70 parts by weight of the same alloy as that used in the first layer and (2) 30 parts by weight of aluminum oxide are formed (Experiment No. 2), the corrosion resistance improves but is still insufficient. If, however, a third coating layer made of aluminum oxide (thickness = 100 μm) is additionally formed on the second layer (test no. 4) or is the first layer made of an alloy comprising 50% by weight of chromium and 50% by weight of nickel , and the second layer comprises a mixture of (1) the same alloy as that used in the first layer and (2) at least 30 % by weight of aluminum oxide, the product can be used in practice

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° den, unless the layers are peeled off.

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Table 1

Second layer (layer formed on the first layer)

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Third layer (layer formed on the second layer)

1 (cf.) none

2 (Req.) Coating made of an alloy of 20% by weight of chromium and 80% by weight Nickel with a thickness of 100 µm

3 (Req.) Coating made of an alloy of 50% by weight of chromium and 50% by weight Nickel with a thickness of 100 µm

4 (Req.) Same as the first layer in experiment no. 2

5 (Req.) Coating made of an alloy of 20% by weight of chromium and 80% by weight Nickel with a thickness of 100 µm

6 (VgI.) The same as the first layer in experiment no. 3

no

Coating from a mixture of none of 70 parts of the alloy's first layer and 30 parts of 100 / µm thick aluminum oxide

Coating from a mixture of none of 70 parts of the alloy's first layer and 30 parts of 100 / µm thick aluminum oxide

same as the second layer in experiment no. 2

Coating of a mixture of 70 parts of an alloy of 50% by weight of chromium and 50% by weight Nickel and 30 parts of aluminum oxide with a thickness of 100 μm

Coating from a mixture of none of 20 parts of the alloy's first layer in experiment No. 3 and 80 parts of aluminum oxide with a thickness of 100 μm

Coating of "^ aluminum oxide with a thickness of 50 / µm

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Table 1. (continued)

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7 (VgI.) Coating of an alloy of 15% by weight of chromium and 85% by weight of nickel with a thickness of 100 μm

8 (VgI.) Coating made of an alloy of 20% by weight chromium, 10% by weight Silicon and 70% by weight nickel (JIS Z-3265-B Ni-5 filler metal for Brazing of nickel with a thickness of 100 µm

9 (VgI.) Coating made of an alloy of 85 % by weight of chromium and 15% by weight of nickel with a thickness of 100 / µm 10 (Req.) The same as the first layer in test no. 3

11 (cf.) same as the first layer at Experiment No. 10

Coating from a mixture of no 70 parts of an alloy of 50% by weight Chromium and 50 parts by weight of nickel and 30 parts of aluminum oxide with a thickness of 100 / µm

Coating from a mixture of no 70 parts of an alloy of 50% by weight Chromium and 50% by weight of nickel and 30 parts of aluminum oxide with a thickness of 100 μm

same as the second / second layer in experiment No. 7

same as the second layer in experiment 3, but with one Thickness of 150 µm

same as the second layer in experiment No. 10

no

Coating ^ ¹ ι made of aluminum - ^. oxide with an f thickness of 100

Coating of aluminum oxide with a thickness of 150 µm

The following additional tests were carried out to determine the degree of detachment caused by exposure to a heat profile, as defined above. The temperature of the δ test specimens produced according to the above description was increased from ambient temperature to 1000 ^° C. at constant speed over 10 h. After a temperature of 1000 ^° C. had been reached, the test specimens were ^{kept at 1000 °} C. for 1 h, and then cooled to ambient temperature at a constant rate over a period of 10 h. This procedure, which includes the previous stages, is referred to as "one cycle". After repeating a total of 5 cycles, the test specimens were weighed. After weighing, the same test specimens were subjected to the same treatment again, repeated 5 cycles and then weighed. The weight determination at 5 cycle intervals was repeated and the changes in the original weight were determined. The weight gains

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or -Losses per cm of the test specimen, determined according to 5, ·

10 and 15 cycles are shown in FIG.

The digits of the curve lines entered in FIGS. 2 and 3 relate to the test specimens listed in Table 1.

In Fig. 2, the ordinate shows the weight gain or

the weight loss per cm of the surface of the test specimen. Negative values mean that the coating layers were peeled off in the test, reducing the weight of the sample, and positive fourths mean that the weight was increased by an oxidation reaction or the like. Fig. 2 shows that the coating layers are impractically high peeled off when the chromium content of the base differs from that of

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The first layer is very different (experiment 9) if the first layer contains a substance that has different properties from metals, such as silicon (experiment 8), or if the aluminum oxide content of the second layer is excessive (experiment no .9). On the other hand, FIGS. 2 and 3 show that the coated layer structures of tests no. 5 and 5 according to the invention according to Table 1 are suitable for practical use.

FIG. 3 shows the results of peeling tests which are the same as the peeling tests of the examples of FIG Fig. 2 except that the thickness of the third alumina coating layer was varied. the Structures of the coated base materials are given as in Table 1 (experiments no. 10 and 11). The results shown in Fig. 3 illustrate that aluminum oxide layers with a thickness of over 100 / µm can easily be peeled off, even if the structures of the first and second layers are suitable are.

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Claims (1)

GRUNECKER. KINKELDEY. STOCKMAIR & PARTNER · PATENT LAWYERS A GRUNECKER o-f OR H KINKELOEY. Ct ^. OR W STOCKMAiR »* DR K SCHUMANN o * P M JAKOB t ^ v -ο OR G BEZOLO. O". O" W MASTER. O ^ -o M HILGERS o- ^ J OR H MEYER PLATH. March 24, 1983 P 17 899 TOYO ENGINEERING CORPORATION 2-5, Kasumigaseki 3-Chome, Chiyoda-ku, Tokyo, Japan . Method for monitoring a heat-resistant Alloy base Claims . 11 <Method of coating a heat-resistant Base made from essentially 18 to 35 wt. 96 chromium, 18 to 50 wt. # Nickel, up to 0.6% by weight of carbon and the remainder essentially of iron .consisting base alloy, characterized in that it comprises the following stages: Coating on the heat-resistant base by means of plasma flame spraying of a first coating layer, made from a first, essentially from 20 to 80 wt.% chromium, 20 to 80 wt.% Nickel and up to 3% by weight of different chromium and nickel Elements of existing coating alloy; and then COPY Coating on the first coating layer by plasma flame spraying a second coating layer which substantially consists of a mixture of (1) 70 to 30 wt.% Of a-second, essentially of 20 to 80 wt.% Chromium, 20 to 80 weight .%. Nickel and up to 3 % by weight of a coating alloy consisting of elements other than chromium and nickel; and (2) 30 to 70% by weight of aluminum oxide. 2. The method according to claim 1, characterized in that further on the second coating layer means Plasraa flame spraying has a third coating layer, consisting of aluminum oxide, coated on it the third coating layer having a thickness ¹⁵ of up to 100 / µm. 3. The method according to claim 1, characterized in that that the first coating layer has a thickness in the range of 50 to 150 / µm and the second coating layer have a thickness in the range of 50 to 150 µm. 4. The method according to claim 2, characterized in that the total thickness of the first, second and third Coating layer is not larger than 300 µm. 5. The method according to claim 3, characterized in that the difference between the chromium content, in% by weight , of the base and the chromium content, in% by weight, of the first coating layer is not more than 25% by weight. 6.. Method according to claim 2, characterized in that the plasma flame spraying using a Injection gas mixture, which consists essentially of hydrogen and an inert gas, is carried out. 7. The method according to claim 3> characterized in that the plasma flame spraying using a Injection gas mixture, which consists essentially of hydrogen and an inert gas, is carried out. 8. The method according to claim 3 _f, characterized in that the second coating layer consists of about 70% by weight of the second coating alloy and 30% by weight of aluminum oxide, the second coating alloy being identical to the first coating alloy. 9. The method according to claim 1, characterized in that the second coating alloy with the first 15 coating alloy is identical. 10. The method according to claim 1, characterized in that the base alloy is at least an effective amount an element selected from the group consisting of molybdenum, tungsten ²⁰ and niobium existing group. 11. A method of coating a heat-resistant base made up essentially of 18 to 35% by weight chromium, 18 to 50% by weight nickel, 0 to 0.6% by weight carbon and the remainder essentially off Iron existing base alloy, characterized by it that it comprises the following stages: Forming a first coating layer by plasma-flame spraying directly on the basis, said first coating layer from a first, essentially of 20 to 50 wt.% Chromium, 50 to 80 wt.% Of nickel and up to 3 wt.% Of chromium and nickel coating alloy consists of various elements, and these are the first. Coating layer has a thickness ranging from 50 to 150 µm; and then COPY \ S WI w «- - Forming a second coating layer by means of plasma flame spraying directly on the first coating layer, this second coating layer consisting essentially of a mixture of (1) 30 to 70% by weight of a second, essentially 20 to 50 % by weight of chromium, 50 to 50% by weight 80 wt.% of nickel and up to 3 Gevr.% of chromium and nickel various elements existing coating alloy and (2) 70 to 30 wt.% alumina, 'wherein di ^ö se second coating layer has a thickness in the range of 50 to 150 / um has . 12. The method according to claim 11, characterized in that in a further stage by means of plasma flame spraying a third coating layer made of alumina forms directly on the second coating layer, this third coating layer has a thickness of up to 100 µm, and wherein the total thickness of the first, second and third coating layers is not more than 300 µm. 13. The method according to claim 11, characterized in that the second coating alloy with the first coating alloy is identical. 14. Heat-resistant, coated bases, manufactured according to a method according to at least one of claims 1, 2, 11 and 12. 35 copy bad oric """i