DE3104112A1 - METHOD FOR PRODUCING PROTECTIVE OXIDE LAYERS - Google Patents

Description

gli / sd

M.A.N. MASCIIINEMARRIK AUGSBIJRn STANDARDS Corporation

Munich, February 4, 1981

Process for the production of protective oxide layers

The invention relates to a method of manufacture protective oxide layers on a metallic Object for which the object after a pretreatment is subjected to an oxidation process at an elevated temperature.

This plays a role in the processes of nuclear coal gasification Permeation plays an important role. For security reasons it is necessary that the components come into contact with the hydrogen or tritium-containing working gases to provide protective layers to prevent these elements from penetrating.

A well-known method of protecting materials or objects against the entry of foreign elements is to to provide the surface of the corresponding object with an oxide layer.

In the known method, the oxide layer on the object is obtained simply by exposing the object to the atmosphere of the gasification process in question under the physical conditions on which the process is based.

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However, such a method is not suitable for use in cases where the object is extreme Conditions, especially hydrogen at high temperatures, is exposed, such as is the case with nuclear Coal gasification is the case.

The layers produced with the known method do not have sufficient tightness and, moreover, do not have sufficient mechanical stability. Under relative Cracks form in the protective layer or the layer even bursts when there is little stress away.

The invention is based on the object of improving the known method to the effect that the oxide layer a v / i rkungsvol 1 en protection against the permeation of foreign elements, in particular offers hydrogen or tritium even at high temperatures.

^xu The object is achieved according to the invention in that the object is subjected to a mechanical and / or chemical pretreatment using an object made of high-temperature alloys, and that the subsequent oxidation process using a low oxidation

^J potentials and a temperature between about 900 and 1000 ° C is carried out.

Due to the low oxidation potential, it is selective Oxidation possible, with the appropriate choice of

Partial pressure of the oxidizing agent can be achieved can that only individual F.lemente, preferably only one element from the material to be treated in the Oxidation process enters.

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Hoi lioclii et) i orl.cn steels sow it; Ni ck ο I have i r> l egi oriations could by using the method according to the invention observed that oxidation of that component which is the oxide with the lowest decomposition pressure forms, namely chromium. The slow growth of the chromium oxide results in a uniform formation of the oxide layer achieved. This layer formation was also promoted by the fact that in these alloys a relatively good Chrome mobility is given. Through this chrome path

There is a certain thrust of power from chrome the inner area to the surface, which contributes to the formation of a much more compact Cr ^ protective layer.

Investigations have shown that this Cr ₉ O layer produces a uniformly dense coating that satisfactorily inhibits the permeation of hydrogen or tritium and other elements into the material, even at very high temperatures. It could

also found that this oxide layer is on

at the same time provides good protection against high-temperature oxidation, against carburization, and against hydrogen sulfide, sulfur oxide and halogen corrosion. The cr _? 0 layer also shows an versus state of the

Technique improved mechanical stability. 25th

The quality of the. Protective layer can still be improved by subjecting the object to mechanical pretreatment, such as cold forming and then is subjected to an annealing treatment under hydrogen.

Mechanical treatment, grinding, honing, turning or shot peening, causes, related with the subsequent temperature treatment a refinement the grain sizes on the object surface, and there- ■ with an increase in chrome mobility. This will

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'Exploited in the subsequent chemical pretreatment to the effect that the Cr segregation of the alloy caused by the hydrogen in the annealing process brings about a remarkable enrichment of chromium in the surface area. On a chromium-enriched surface pretreated in this way and made directly accessible for the oxidation process, an almost homogeneously distributed oxidation takes place over the surface, which leads to a very dense and well-adhering and thus mechanically very stable barrier layer.

The annealing process is preferably carried out at a temperature carried out that of the temperature for the subsequent Oxidation process is approximately the same. This one has that 15- advantage that the two temperature-dependent process steps can be carried out in quick succession.

For the oxidation process, CO ₂ can be used as an oxidizing agent. This means that the Hi 1 f s equal weight 2C0 "= 2C0 + Q" can be used to reduce the oxygen partial pressure.

A preferred oxidizing agent is water vapor. With water vapor under the Hi 1 f sgl eichqowi cht? IL, 0 = ?. \\ +0 cci

an even lower oxidation potential than in the case of CO ₉ can be achieved. The use of this oxidizing agent in connection with the hydrogen reduction as a pretreatment has the further advantage that there is no rinsing process between the chemical pretreatment and the oxidation process

must be used. The excess of hydrogen present during the oxidation even has an effect has a positive effect on the process in that this hydrogen causes a further reduction in the oxygen partial pressure.

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To carry out the oxidation process under reduced pressure and thus the use of vacuum apparatus It is suggested to avoid the oxidizer in an inert carrier gas, preferably a noble gas, in particular helium or argon, via the to conduct the object to be coated. The oxidizing agent can preferably be in a closed Cycle but also in a partially closed or

open operation. 10

The use of C0 “as an oxidizing agent becomes a Oxidation potential of 'below 50 mbar, preferably about 10 mbar used while the water vapor partial pressure is lower than 100 mbar, whereby these values are set to normal

'5 conditions are related. That is particularly advantageous Application of the oxidation process with steam under a partial pressure of about 20 mbar. These conditions can be done directly at atmospheric pressure and room temperature reach.

It is advantageous if the oxide layer thickness is less than 4 / </ ^ Preferred v / ei se in the range of 2 ^ mi egt. Such a one Layer is against tension and otherwise

Resistant to stress and therefore stable. ·

Embodiments:

example 1

For coating a under the trademark "Haste! Oy X"

or "Inconel 625" known nickel-based coatings with the composition: 22% Cr, 9% Mo, 19% Fe, Si, Mn, remainder nickel or with the designation NiCr22Mo9Nb, the following process steps were carried out:

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'a) First, the surface was mechanically sanded (320 grit), pretreated honing or shot-peening.

b) Then the object was at 1000 ° C for 5 hours reduced with H ", and then flushed with argon,

c) thereupon the oxidation process was carried out at the same Temperature, ie 1000 "C with 20 mbar hydrogen in argon.

d) After a 4-hour oxidation process, a TO-dense Cr _? 0 layer from 1 to 2μ η obtained.

Example 2

An item made of high-alloy steel with 32% Ni, 20% Cr, 0.1% C, Al, Ti, remainder Fe was subjected to a pretreatment as in Example 1 (process steps a) and b) subjected.

c) Then the surface was oxidized at 900 to 950 ° C with up to 20 mbar of water vapor in argon.

d) In this case, too, a compact

Chromium oxide layer from 1 to 2 ^ .m can be produced.

Example 3 ■. ■

It became an object made of high-alloy steel as in Example 2 used with the same pretreatment, wherein

however, after the annealing treatment the hydrogen was not removed but retained for the oxidation process. The oxidation was initiated at 1000 ° C by adding steam in argon.

The water vapor partial pressure was between 10 and 20 mbar and that of the H ₂ was between 0.1 and 0.8 bar. The layer thickness after 4 hours of oxidation was also 1 to 2an.

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-10-

With this method, a higher level could be found compared to Example 2: fos I. ii) ki · it (\ t> r oxide layer, DdS Example 2 1 cifJt., On the other hand, can be carried out at lower temperatures.

In all cases, it was found that the oxide layer had high stability and was remarkable Protection against hydrogen resp. Tritium permeation caused.

(M Λ)? . 19H1

Claims (1)

gü / sd M.A.N. MACHINE FACTORY AUGSBURG-NORNBERG Corporation Munich, February 4, 1981 Claims e / - ■ 1'. Process for the production of protective oxide layers on objects, in which the object after a pretreatment subjected to an oxidation process at elevated temperature is, characterized in that to use the method for objects made of high temperature alloys the object is subjected to mechanical and / or chemical pretreatment and that the subsequent oxidation process using a low oxidation potential and a temperature between about 900 and 1000 ° C. 2. The method according to claim 1, characterized in that the pretreatment in a mechanical and a subsequent annealing treatment Hydrogen. 3. The method according to claim 2, characterized in that the chemical surface treatment at a Temperature is carried out which approximates the temperature for the subsequent oxidation process is equal to. 7.2041 4. The method according to any one of the preceding claims, characterized in that the oxidizing agent is CO ₂ . ^ '5. The method according to claim 4, characterized in that the CO _? ~ Partial pressure, based on normal conditions, is lower than 50 mbar, preferably about 10 mbar. 6. The method according to any one of claims 1 to 4, characterized characterized in that the oxidizing agent is water vapor. 7. The method according to claim 6, characterized in that that the water vapor partial pressure, based on Normal conditions, lower than 100 mbar, preferably is about 20 mbar. 8. The method according to any one of claims 4 to 7, there- characterized in that the oxidizing agent in an inert carrier gas, preferably noble gas such as argon or helium over the to be coated the subject is directed. 9. The method according to any one of the preceding claims, characterized in that the oxidation time depending on the desired layer thickness between 2 and hours. 10. The method according to any one of the preceding claims, characterized in that the oxide layer thickness is below 4M>"vorzugwei se below 3 ^ ¹ ""1. 7.2041
02/04/1981 11. Verfdhrah after πιηοιπ flor vorhortiohondon Arinpriichr », using an object made of nickel-based alloy, characterized in that the object is _{reduced after a mechanical pretreatment about • 5 3 hours with H 2} at 1000T and then a 4- to 8-hour oxidation process is subjected to water vapor in noble gas at 1000 * C with about 20 mbar. IQ. 12. The method according to any one of claims 1 to lo, and using an article made of high-alloy steel, characterized in that the article is _{reduced after a mechanical pretreatment for about 3 hours with H 2} at 10OCTC and then subjected to a 4 to 8 hour oxidation treatment at about 100OT, and that the oxidation atmosphere consists of water vapor, hydrogen and argon. 13. The method according to any one of claims 1 to 10, and using an object made of high-alloy steel, characterized in that the object is ^{reduced after a mechanical pretreatment for about 3 hours with H "at 1000 0} C and then a 4 to 8 hour oxidation process at 900 to 950 "C with steam in noble gas is subjected. 7.2041
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