FR2532664A1 - - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR FORMING A CORROSION-RESISTANT OXIDE LAYER ON A METAL SUBSTRATE BY SURFACE TREATMENT IN AN OXIDIZING ATMOSPHERE CONTAINING DECOMPOSABLE ALUMINUM COMPOUNDS, IN A STEAM STATE, AT HIGH TEMPERATURE. THE PROBLEM SOLVED CONSISTS OF CARRYING OUT EFFICIENT COATINGS UNDER HIGHLY CORROSIVE CONDITIONS, EVEN AT ELEVATED TEMPERATURES. THE PROCESS IS CHARACTERIZED IN THAT THE SURFACE TREATMENT IS CARRIED OUT IN TWO STAGES, DISTINCT IN TIME AND IN ATMOSPHERES OF DIFFERENT COMPOSITIONS, Namely: A. IN THE FIRST STAGE A SIMPLY OXIDANT ACTION ATMOSPHERE, B. IN THE SECOND STAGE STAGES AN ATMOSPHERE CONTAINING DECOMPOSABLE ALUMINUM COMPOUNDS INTO ALO. THE INVENTION IS APPLICABLE IN PARTICULAR TO PROTECTION AGAINST THE PENETRATION OF HYDROGEN AND ITS ISOTOPES AS WELL AS OF CARBON.

Description

"A process for forming a corrosion-resistant oxide layer

  on a metal substrate and application of this layer

as a protective layer ".

  The invention relates to a process for forming a corrosion-resistant oxide layer on a metal substrate by surface treatment in an oxidizing atmosphere containing decomposable aluminum compounds in the vapor state at a temperature of high (CVD process) The invention

  extends to the application of the layer produced.

  For their use in an oxy atmosphere

  or corrosive, especially at high temperature,

  need protective coatings. It is cer-

  that oxidation-resistant alloys form

  same, in an oxidizing environment, such coatings protecting them against the progression of the attack; but it is not

  not the case in corrosive atmosphere and at high temperature.

  Chemical devices operating at a

  high temperature and hot-working assemblies as well as the component parts of power plants, for example,

  from the service fluid a corro-

  resulting in more or less significant damage depending on the application conditions considered.

  structural steels resistant to fluaqe at high temperature

  this is frequently the case? case for the construction of the component elements of the thermal installations

  gas and exchanging heat, the operation is not

  only with adequate cooling, since

  However, corrosion would be of catastrophic importance. It would, however, frequently be desirable, precisely as regards

  concerning the elements of the price of primary energy,

  bet on the overall performance, to increase the level of the

  by reducing cooling and thus allowing

  better use of lost heat.

  Another area of application with

  very similar matters but similar problems is constituted by

  the blades of hot gas turbines.

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  To prevent corrosion, the temperature

  of matter is limited in some cases by a refrodiss-

  When cooling alone is not enough,

  high temperature oxidation resistant alloys are used.

  It is also possible to use a layer of aluminum or layers of chromium and aluminum to stop corrosion by hot gases. This does not mean that complete protection is obtained. More or less significant reductions must be taken into account.

  in their turn have other disadvantages

  they are destroyed in the long run by diffusion processes.

  With ferrous base materials, this can go very quickly at high temperatures In addition to the loss of corrosion protection, the diffusion of aluminum can lead to

  considerable damage to the mechanical properties of the material.

  It is further known that cracks occurring in the

  aluminum layer as a result of its fragility also cause

  cracks in the base material at the limit of

  his. The invention alpur purpose to create a method

  the type indicated in the preamble, with which we can

  coatings which ensure, even under highly corrosive conditions and at high temperatures, the most optimal protection possible of a metal material irrespective of the

Composition of this material.

  To this end, the invention relates to a method of the above type, characterized in that the part is subjected to

  oxidation and then coated with aluminum oxide

by the method C V D.

  In other words, the processing is done

  surface in two distinct steps in time and in atmospheres of different composition, namely a) in the first step a simply oxidizing atmosphere, b) in the second step, an atmosphere containing decomposable aluminum compounds. A 1203 * -3 -

  -The protective coating against corrosion

  according to the invention consists of a recumbent

  closed and homogeneous aluminum oxide cover which is de-

placed on an oxide base.

  The deposition of layers of A 1203 by means of the CVD process is known per se for the coating of hard metal tools. Essentially one or more

  intermediate layers of titanium nitride (Ti N and / or

  Titanium (Ti C) The prevailing view is that ia

  formation of another oxide phase before the deposit of A 1203 se-

  would be undesirable and should be deleted.

  taking into account that it has been found during appropriate tests that

  can obtain by means of the CVD process layers of aluminum oxide

  completely enclosed and remarkably adherent

  on a metal base carefully treated beforehand and then oxidized at high temperature

  Oxidation of the metal part to be coated

  the CVD process for the 6 t of A 1203 can be carried out in an apparatus during operations

succeeding immediately.

/

  The oxidation of the part is then advantageously

  carbon dioxide (C 02), which is anyway necessary when depositing A 1203 'according to the equation

  of global re-admission: 2 Al C 13 + 3 C 02 + 3 H 2 A 1203 + 3 C O + 6 H Cl.

  However, oxidation can also be effected

  The process is carried out according to known processes during a separate preliminary operation, the part being provided with an intermediate oxide layer. It is then recommended to carry out the oxidation with water vapor With chromium steels, this can be done in a similar way to the steam income in

  In all cases, it is important to form a homogeneous oxide phase

  gene with a uniform layer thickness and a structure to

fine grain.

  As an important advantage during the

  With the addition of the aluminum oxide coating layer by means of the CVD process to an intermediate layer of metal oxide, it has been found that deposition can occur in temperature, total pressure and partial pressure domains.

  which are extended under the conditions of the CVD process.

  More precisely, these domains are as follows: Temperature: 850 to 1050 ° C. Total pressure: 200 mbar at atmospheric pressure. Fractions of molecules-grams of gas: N AIC 13 = 3.7 × 10 3 1.7 × 101 n CO 2 = 9.9 x 10 3.1 x 10-1 n 2 = 5.2 x 10-1 9.9 x 10-1

  Hydrogen is essentially the

  is the most important from a qualitative point of view and is also

  as a carrier gas for aluminum chloride.

  The possibility of executing the deposit at V'in-

  other parametric domains is of decisive importance.

  with regard to the coating of large surface objects

  this, for example long objects One can thus have

  relatively high yields of Al C 13 and CO 2 at the gas inlet of the deposition chamber, without resulting in the formation of spongy layers or an undesirable powder deposit. It is thus possible to ensure, downstream, that concentrations in

  gases sufficient for the formation of the Al 203 layer.

  With regard to the growth of the layer, the deposition of A 1203 on intermediate oxide layers

  has the advantage of forming a uniform isotropic structure.

  So there is no growth in column or dendritic This

  is important for the protection against corro-

  desired for the coating.

EXEMPLARY EMBODIMENT 1

  A hot-melt-resistant 13 Cr Mo 44 structural steel object, carefully cleaned and subjected to a mechanical surface treatment such as molding, turning, honing, is subjected to an oxidation treatment at 650,700 C -5-

  corresponding to the income from steam, that is to say from a

  dry steam for 2 to 4 hours.

  A uniform and finely crystalline layer of magnetite (Fe 304) of about 1 to 3 d is formed. The oxidized part is then coated with A 1203 in a retort according to the process.

  CVD at 910, 9400 C With a coating time of about 30 minutes

  At this temperature, a layer thickness of 10 g is obtained depending on the position in the gas flow. The composition of the gas at the reactor inlet depends on the geometrical conditions, but it is always within the areas indicated above. The recoil condition is determined by an appropriate cooling rate from the CVD coating and by

  the choice of income treatment that follows.

EXAMPLE 2

  A hot-creep-resistant chrome steel article such as X 20 Cr Mos 12 1 steel, treated as in Example 1, is oxidized at 700, 7500 C for 2 to 4 hours with steam. under a pressure of 10 to 200 mbar in

  an inert gas (Ar He) is then obtained-a layer of spinel-

  finely crystalline iron of 1 to 3 o; The oxidized part is transported in the CVD retort and coated at 1000.degree.-1050.degree. C. with 5 to 10% of A.sub.1203, 15 minutes being necessary for this.

proceeds as in Example 1.

EXAMPLE 3

  An iron-based alloy object X 10 Ni Ci Ti Ti 3220, known under the trade name "Incoloy 800" creep resistant at very high temperatures, previously treated as in Example 1, is oxidized in the CVD retort with the mixture of CO 2 / H 2 gas used for the deposition of A 1203, at 950 C for 0.5 to 3 hours, depending on the amount of H 2 in the mixture. A layer of Cr 203 closed is then obtained. 0.3 to 2 g approximately, substantially pure with a very finely crystalline structure The deposit of A 1203 which follows is caused simply by addition of the Al C fraction 13 With a duration

6 2532664

  deposition time of 20 to 25 minutes, a layer of A 1203 of 5 to

thick.

EXAMPLE 4

  An IN 100 nickel-based alloy object commonly used as a fin material for gas turbines

  planes, previously treated as in Example 1, is oxy-

  in the CVD retort at about 1000 ° C, according to Example 3 A closed layer of A 1203 and Cr 203 or mixed crystals of these products is then formed with a thickness of 0.3 to

  2 g In this case as well, the filing of A 123 which follows is effec'c-

  killed simply by addition of Al Cd 3 After 15 to 20 minutes of

  deposition time, a layer of A 1203 of 5 to 10 is obtained.

  It has further been found that the aluminum oxide layer can be remarkably used as

  protective layer against the penetration of foreign elements

  gers. Due to the presence of the layer

  intermediate produced during the preoxidation, the

  the following aluminum oxide layer acquires a

  weaving the formation of a closed coating, free from pores and cracks, with remarkable adhesion This closed layer provides, in connection with the property found by measurements, an extremely low permeability to the elements

  foreigners, perfect and lasting protection against penetration

  foreign elements, in particular hydrogen and

  its isotopes, as well as carbon.

EXAMPLE 5

  A hot-creep-resistant chrome steel object such as X 20 Cr Mo V 12 1 steel, carefully cleaned and subjected to a mechanical surface treatment such as grinding, turning, honing, is oxidized at 8000 C with water vapor under a pressure of 10 to 200 mbar in an inert gas (Ar, He) for 2 to 4 hours A layer of finely crystalline iron-chromium spinel of about 2 g is then formed. The oxidized part is coated with A 1203 in a retort according to the CVD process at a temperature of 1000 to 10500 C. With a coating time of about 15 minutes, a layer thickness of 5 to 10 o is obtained at this temperature depending on the position in the

  gaseous flow The composition of the gas at the inlet of the reactor de-

  geometric conditions, but still remains in the

  within the areas indicated above.

  As a variant, it is possible to proceed as follows: the part is oxidized in the CVD retort with the mixture of CO 2 H 2 gas used for the deposition of A 1203 at a temperature of 1000 to 1050 C up to a duration of 30 minutes, depending on the amount of H 2 in the mixture. An oxide layer is then obtained.

  chromium (Cr 203) 'containing iron and having a thickness <1 g.

  The filing of A 1203 which follows is simply caused by the addi-

  Al C 13 in H 2 as a carrier gas With a deposition time of about 15 minutes, the layer of A 1203 formed has a thickness of

from 5 to 10 g.

  Tubular parts thus coated were exposed to a hydrogen atmosphere at temperatures up to 750 ° C. under pressures of up to 10 bar and the penetration of hydrogen was measured. the hydrogen was lower, by a factor of up to 2000, that of the uncoated parts and by a factor of up to about 1000, to that

  parts coated with a conventional oxide layer.

EXAMPLE 6

  A very high temperature creep resistant iron alloy object X 10 Ni Cr Al Ti 32 20, known under the trade name "Incoloy 800", previously treated as in Example 1, was first annealed in the CVD retort in a 95000 hydrogen atmosphere, then oxidized by addition of CO 2 The CO 2 fraction was chosen to correspond favorably to the deposition of A 1203 which follows (see above) The prior oxidation was carried out during a period of 0.1 to 3 hours, a closed layer of substantially pure Cr 203 was obtained, 0.1 to 2 g thick, with a structure

very finely crystalline.

  The subsequent deposition of A 1203 was also caused by the addition of Al C 13 to H 2. In a deposition time of 20 to 25 min, a layer of A 1203 was obtained.

at 10 u.

  -8 - Measurements made to determine the reduction in hydrogen penetration have given even

  for a temperature of 950 C, a reduction factor of 1000.

  In addition, tests were carried out in a carburizing atmosphere of -5 (0.1 to 3% by volume of methane or propane and -5% by volume of H 2 in argon). of

  the material, ie the coating prevents the penetration

carbon.

EXAMPLE 7

  An object previously treated as in Example 1, made of a nickel-based alloy, such as the alloys known under the trade names "Hastelloy X" or

  "Inconel 617", used for the construction of composite

  resistant to high temperature, is oxidised in the

  CVD retort at about 1000 ° C., as in Example 2.

  Then, a closed Cr layer 203 with a thickness of 0.1 to 2 at constant temperature, gives a layer of Al 203

from 5 to 10 thick.

  The penetration measurement results of

  hydrogen and carbon corresponded to those of Example 2.

  In the case of application, o on the one hand, the building elements to be coated-are very big for

  classic CVD retorts but o, on the other hand, the geo-

  metric building elements allows it can be used

  the building element itself as a retort of ex-

  Corresponding ples are given by: tubes, bundles

  tubes, boilers and similar elements.

  to be coated are then brought by means of a chamber oven or a shaft furnace under the conditions required for the duration of the

coating.

Claims (3)

  1) Process for forming an oxide layer   resistant to corrosion on a metallic substrate Dar treats   surface in an oxidizing atmosphere containing   decomposable aluminum, in the vapor state, at elevated temperature, characterized in that the treatment of   surface in two distinct stages in time and in   mospheres of different composition, namely: a) in the first stage an atmosphere with an action that is simply oxidizing, b) in the second stage an atmosphere   containing aluminum compounds decomposable to A 1203.   Method according to claim 1,   characterized in that the treatment of the first stage is carried out   in an atmosphere of water vapor.   3. Process according to claim 2, characterized in that the first stage treatment is carried out.   at a temperature between 600 and 800 C.   4) Process according to any one of   Claims 1 to 3, characterized in that the milking is carried out   of the second stage in an atmosphere containing   Al C 13 vapor and hydrogen.    Method according to claim 4, characterized in that the processing of the second step is effected.   in an atmosphere containing AlCl 3 vapor, hydrochloric acid, gene and carbon dioxide.   Process according to claim 5, characterized in that an atmosphere of gaseous phases of 3 × 10 3 to 2 × 10 -3 (fraction of gram AlCl 3 gas molecules), 9.5 × is used. 10-3 to 3.5 x 10 N CO 2 and 0.5 to 10 n H. 7) Process according to any one of   Claims 1 to 6, characterized in that the processing   second De at a temperature ranging from 800 to 10500 C.   - 8} 0) Application of the process according to one   any of claims 1 to 7 to a resistive oxide layer   both to corrosion formed on a metal substrate as a protective layer against permeation of foreign elements. 9) Application according to claim 8,   as a protective layer against the penetration of hy-   and its isotopes and against the penetration of carbon.