U.S. patent application number 14/767795 was filed with the patent office on 2015-12-24 for method for depositing a corrosion-protection coating.
This patent application is currently assigned to L'Air Liquide, Societe Anonyme pour l'Etude et Exploitation des Procedes Georges Claude. The applicant listed for this patent is CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE, L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLA, UNIVERSITE DE LORRAINE. Invention is credited to Stephane MATHIEU, Thierry MAZET, Nicolas RICHET, Michel VILASI.
Application Number | 20150368782 14/767795 |
Document ID | / |
Family ID | 48570257 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150368782 |
Kind Code |
A1 |
RICHET; Nicolas ; et
al. |
December 24, 2015 |
METHOD FOR DEPOSITING A CORROSION-PROTECTION COATING
Abstract
The use of a cement in a process for pack cementation deposition
on a substrate having cavities of minimum equivalent diameter
e.sub.cm, characterized in that the cement consists of spherical
particles each having a diameter d such that
d.ltoreq.e.sub.cm/10.
Inventors: |
RICHET; Nicolas;
(Fontenay-Le-Fleury, FR) ; MAZET; Thierry; (Nancy,
FR) ; VILASI; Michel; (Bouxieres Aux Dames, FR)
; MATHIEU; Stephane; (Villers Les Nancy, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'ETUDE ET
L'EXPLOITATION DES PROCEDES GEORGES CLA
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
UNIVERSITE DE LORRAINE |
Paris
Paris Cedex 16
Nancy Cedex |
|
FR
FR
FR |
|
|
Assignee: |
L'Air Liquide, Societe Anonyme pour
l'Etude et Exploitation des Procedes Georges Claude
Paris
FR
Centre National De La Recherche Scientifique
Paris Cedex 16
FR
Universite De Lorraine
Nancy Cedex
FR
|
Family ID: |
48570257 |
Appl. No.: |
14/767795 |
Filed: |
February 4, 2014 |
PCT Filed: |
February 4, 2014 |
PCT NO: |
PCT/FR2014/050193 |
371 Date: |
August 13, 2015 |
Current U.S.
Class: |
148/537 ;
427/180; 427/201 |
Current CPC
Class: |
C23C 10/60 20130101;
C23C 10/56 20130101; C22F 1/04 20130101; C23C 10/52 20130101; C23C
10/48 20130101 |
International
Class: |
C23C 10/48 20060101
C23C010/48; C22F 1/04 20060101 C22F001/04; C23C 10/60 20060101
C23C010/60 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2013 |
FR |
1351227 |
Claims
1-19. (canceled)
20. The use of a cement in a process for pack cementation
deposition on a substrate having cavities of minimum equivalent
diameter e.sub.cm, characterized in that the cement consists of
spherical particles each having a diameter d such that
d.ltoreq.e.sub.cm/10.
21. The use of claim 20, wherein at least some of the spherical
particles are comprised of a precursor of the element to be
deposited, at least some of the spherical particles are comprised
of an activating agent and some of the spherical particles are
comprised of an inert diluent.
22. The use of claim 21, wherein: the precursor of the element to
be deposited comprises a metallic powder; 10% to 60% of the
spherical particles are comprised of the metallic powder; 5% to 40%
of the spherical particles are comprised of the activating agent,
and a balance of the spherical particles are comprised of the inert
diluent.
23. The use of claim 22, wherein the metallic powder consists of
aluminum or a mixture of aluminum with Ni.sub.xAl.sub.y particles
or Al.sub.xCr.sub.yparticles.
24. The use of claim 20, wherein: at least some of the spherical
particles are comprised of a precursor of the element to be
deposited; at least some of the spherical particles are comprised
of a pickling flux; and at least some of the spherical particles
are comprised of an inert diluent.
25. The use of claim 20, wherein at least some of the spherical
particles are comprised of an organic or inorganic binder.
26. The use of claim 20, wherein the substrate is a metallic heat
exchanger.
27. A process for depositing a coating by pack cementation on a
substrate having cavities of minimum equivalent diameter e.sub.cm,
comprising the following successive steps: a) preparing a cement
consisting of three types of spherical particles, a first of the
three types being comprised of an activating agent, a second of the
three types being comprised of an inert diluents, a third of the
three types being comprised of a metallic powder, each of said
three types of spherical particles having a diameter d such that
d.ltoreq.e.sub.cm/10; b) the prepared cement is introduced into the
cavities of the substrate by a vibrating system to produce a
substrate-cement assembly; c) the produced substrate-cement
assembly is heated at a temperature below a melting point of the
metallic powder for a duration of at least 6 h at around
650.degree. C. for aluminum; d) the substrate-cement assembly is
cooled to ambient temperature; e) the cement is subjected to a
vibration step so as to eliminate the cement residue; f) the
substrate-cement assembly is heated at a temperature of between
900.degree. C. and 1150.degree. C., preferably above 980.degree.
C.; and g) a substrate having a coating over its entirety is
recovered.
28. The process of claim 27, wherein the metal of the metallic
powder is aluminum.
29. The process of claim 28, wherein the temperature, at which the
produced substrate-cement assembly is heated, is around 650.degree.
C.
30. The process of claim 27, wherein the temperature, at which the
substrate-cement assembly is heated, is between 900.degree. C. and
1150.degree. C.
31. The process of claim 30, wherein the temperature, at which the
substrate-cement assembly is heated, is above 980.degree. C.
32. The deposition process of claim 27, wherein the particles of
the cement prepared in step a) are preactivated by
mechanosynthesis.
33. The deposition process of claim 27, wherein the coating
recovered in step g) comprises NiAl.
34. The deposition process of claim 27, wherein the coating
recovered in step g) has a thickness of between 15 and 25
.mu.m.
35. The process of claim 27, wherein the substrate is a metallic
heat exchanger.
36. A process for depositing a coating by pack cementation on a
substrate having cavities of minimum equivalent diameter e.sub.cm,
comprising the following successive steps: a) preparing a cement
consisting of a pickling flux, spherical particles of an inert
diluent and spherical particles of a metallic powder, each of the
spherical particles of inert diluents and metallic powder having a
diameter d such that d.ltoreq.e.sub.cm/10; b) introducing the
prepared cement into the cavities of the substrate by a vibrating
system to prepare substrate-cement; c) heating the prepared
substrate-cement assembly to a temperature above a melting point of
the pickling flux, under either a low vacuum or under an inert
atmosphere (Ar), for a duration of between 10 min and 2 hr, to
thereby produce a substrate-cement assembly having a coating of
cement residue; d) cooling the coated substrate-cement assembly to
ambient temperature; e) subjecting the coated substrate-cement
assembly to a washing step so as to eliminate a cement residue such
that an entirety of the coating is recovered from the
substrate-cement assembly.
37. The process of claim 36, wherein the washing step e) is carried
out using an acidified aqueous solution.
38. The process of claim 36, wherein the coating recovered in step
f) comprises NiAl.sub.3.
39. The process of claim 36, wherein said process comprises, before
step e) and after step d), a step of heating the coated
substrate-cement assembly at a temperature of between 900.degree.
C. and 1150.degree. C.
40. The process of claim 39, wherein the coated substrate-cement
assembly is heated to a temperature above 980.degree. C.
41. The process of claim 39, wherein the coating recovered in step
f) comprises NiAl.
42. The process of claim 36, wherein the coating recovered in step
f) has a thickness of between 5 .mu.m and 200 .mu.m, preferably
between 5 .mu.m and 80 .mu.m.
Description
[0001] The present invention relates to the production of a
corrosion-protection coating on a substrate that has cavities.
[0002] The techniques for producing coatings may be grouped into
three large families:
[0003] thermal spraying,
[0004] chemical vapor deposition, and
[0005] physical vapor deposition.
[0006] Thermal spraying techniques such as plasma or flame spraying
consist in sending molten or partially molten particles, at high
velocity, to the surface of the part to be protected. The coating
is constructed of successive layers. These techniques can only be
used on open or readily accessible surfaces.
[0007] The vapor deposition techniques use a gaseous precursor of
the coating to be produced. This precursor may be produced in
direct proximity to the surface to be coated (pack cementation) or
be transported via a gas to the surface to be coated (out of pack,
CVD using a gas cylinder or mixture, . . . ). The main difficulties
encountered for pack cementation are linked to the filling of parts
that have a complex geometry or very small dimensions (several mm)
with the cement powder (precursor mixture of the coating). The main
limitations of techniques that use gaseous precursors relate to the
rapid depletion of reactive species from the gaseous mixture
leading to heterogeneities of chemical composition and/or of
thickness of the coating. It is very difficult to obtain a uniform
coating on large surfaces or in complex geometries.
[0008] The physical vapor deposition techniques consist in
evaporating the constituent element(s) of the coating before
condensing them on the surface of the part to be coated. The
evaporation generally takes place by bombarding a target with a
high-energy (electron or ion) beam. The distance between the target
and the surface to be coated is a major parameter for the
uniformity of the thickness of the deposition. These techniques are
very difficult to use on parts of complex geometry or on
inaccessible surfaces.
[0009] The intensification of industrial processes leads to
materials being used under increasingly harsh conditions and to the
size of the parts used being reduced. In most cases, it is
necessary to protect the parts from their surroundings with a
coating. As presented in the preceding paragraphs, complex
geometries and inaccessible surfaces pose problems for producing
coatings using conventional techniques.
[0010] It is therefore necessary to develop new deposition
techniques or to adapt the existing techniques to the new
constraints.
[0011] Pack cementation is a very old process for producing a
coating on a part. The latter is placed in a bed of cement powder,
which is a mixture of products capable of generating a reactive
atmosphere at high temperature. This cement must be placed in the
vicinity of the surface to be coated in order to produce a coating
that is uniform in terms of thickness and chemical composition.
Coatings are conventionally produced on parts having cavities of
several centimeters by filling the part with the cement powder.
[0012] However, when the cavities have characteristic sizes of the
order of a millimeter, and high aspect ratios (length/width
ratios), introducing the cement is much more complex. This is why
processes using powder, of pack cementation type, are generally
used for parts that have no or few zones that are difficult to
access.
[0013] Hence, one problem that is faced is to improve the pack
cementation deposition processes in order to enable the use thereof
for coating a substrate that has cavities.
[0014] One solution of the present invention consists of the use of
a cement in a process for pack cementation deposition on a
substrate having cavities of minimum equivalent diameter e.sub.cm,
characterized in that the cement consists of spherical particles
each having a diameter d such that d.ltoreq.e.sub.cm/10.
[0015] The size of the cement particles may be measured by laser
particle size analysis or with the aid of a screen in order to
ensure that no cement particle or agglomerate of cement particles
exceeds the required maximum size.
[0016] A step of deagglomeration may be necessary in order to
"break" the agglomerates of individual particles that may exceed
the required maximum size.
[0017] The equivalent diameters of the particles are conventionally
between 1 .mu.m and 1 mm, preferably between 1 .mu.m and 100
.mu.m.
[0018] The equivalent diameter is defined as the diameter of the
cylinder or of the circle that is inscribed within the smallest
cross section giving access to the surface to be coated.
Specifically, the latter does not necessarily have a standard
shape.
[0019] Depending on the case, the use according to the invention
may have one or more of the following features:
[0020] the cement consists of spherical particles each having a
diameter d such that d.ltoreq.e.sub.cm/10;
[0021] the cement comprises a precursor of the element to be
deposited, an activating agent and an inert diluent;
[0022] the cement comprises 10% to 60% of metallic powder as
precursor of the element to be deposited, 5% to 40% of activating
agent, and a balance to 100% of inert diluent, the inert diluent
preferably comprising refractory oxides;
[0023] the metallic powder consists of aluminum or a mixture of
aluminum with Ni.sub.xAl.sub.y or Al.sub.x,Cr.sub.y, particles;
[0024] the cement comprises a precursor of the element to be
deposited, a pickling flux and an inert diluent;
[0025] the cement comprises an organic or inorganic binder. The
organic binder may be PVA (polyvinyl acetate) and the inorganic
binder may be SiO.sub.2. Specifically, the organic or inorganic
binder may be used during a step of atomization of the powder
mixture. This optional step makes it possible to improve the
flowability of the powder and therefore the filling of the part. It
is a matter of forming spherical agglomerates of the powder
mixture. This step will preferably be carried out under an inert
atmosphere in order to avoid surface oxidation of the metallic
powders which may be detrimental to the deposition.
[0026] The inert compound is not chemically involved in the
formation of the coating. Its main role is to avoid the
densification of the cement which would prevent the elimination
thereof after deposition. In general, it is a highly stable
refractory compound. The content thereof is the balance of the
other two compounds.
[0027] The solution according to the invention enables the
production of a pack cementation deposition on parts of complex
geometry and in cavities that are difficult to access.
[0028] The cement used within the context of the invention has a
very good flowability that makes it possible to fill the smallest
interstices (of diameter <1 mm) and to be uniformly distributed
inside the whole of the cavity to be coated. The particle size
distribution and the morphology of the cement particles are the
principal parameters for ensuring a good flowability of the
mixture.
[0029] The particle size distribution is adjusted as a function of
the equivalent diameter of the smallest passage of the cavity.
Regarding the morphology, the spherical shapes which may be
obtained by various techniques of grinding the powders or the
powder mixture are also favored. An atomization treatment of the
powder mixture could also be used to form spheres of the powder
mixture. In the latter case, organic additives could be used to
ensure a good cohesion of the spheres and a uniform dispersion of
the elements of the mixture.
[0030] The present invention also relates to two processes for
depositing a coating by pack cementation on a substrate having
cavities of minimum equivalent diameter e.sub.cm.
[0031] The first process for depositing a coating by pack
cementation on a substrate having cavities of minimum equivalent
diameter e.sub.cm comprises the following successive steps:
[0032] a) a cement consisting of spherical particles of an
activating agent, of an inert diluent and of a metallic powder is
prepared, said spherical particles each having a diameter d such
that d.ltoreq.e.sub.cm/10;
[0033] b) the cement prepared in step a) is introduced into the
cavities of the substrate by a vibrating system;
[0034] c) the substrate-cement assembly is heated at a temperature
below the melting point of the metallic powder for a duration of at
least 6 h at around 650.degree. C. for aluminum;
[0035] d) the substrate-cement assembly is cooled to ambient
temperature;
[0036] e) the cement is subjected to a vibration step so as to
eliminate the cement residue;
[0037] f) the substrate-cement assembly is heated at a temperature
of between 900.degree. C. and 1150.degree. C., preferably above
980.degree. C.; and
[0038] g) a substrate having a coating over its entirety is
recovered.
[0039] By way of example, if the metallic powder is an aluminum
powder, in step c) the substrate-cement assembly is heated at
around 650.degree. C. for at least 6 h.
[0040] Depending on the case, the first process may have one or
more of the following features:
[0041] the particles of the cement prepared in step a) are
preactivated by mechanosynthesis; the preactivation makes it
possible to increase the chemical reactivity of the precursor
particles. This treatment facilitates the reaction between the
precursor and the activator, and therefore the deposition;
[0042] the coating recovered in step g) comprises NiAl;
[0043] the coating recovered in step g) has a thickness of between
15 and 25 .mu.m.
[0044] The second process for depositing a coating by pack
cementation on a substrate having cavities of minimum equivalent
diameter e.sub.cm comprises the following successive steps:
[0045] a) a cement consisting of a pickling flux and spherical
particles of an inert diluent and of a metallic powder is prepared,
said spherical particles each having a diameter d such that
d.ltoreq.e.sub.cm/10;
[0046] b) the cement prepared in step a) is introduced into the
cavities of the substrate by a vibrating system;
[0047] c) the substrate-cement assembly is heated at a temperature
above the melting point of the pickling flux, under low vacuum or
under an inert atmosphere (Ar), for a duration of between 10 min
and 2 h;
[0048] d) the substrate-cement assembly is cooled to ambient
temperature;
[0049] e) the cement is subjected to a washing step so as to
eliminate the cement residue;
[0050] f) a substrate having a coating over its entirety is
recovered.
[0051] Depending on the case, the second process may have one or
more of the following features:
[0052] the washing step e) is carried out using an acidified
aqueous solution;
[0053] the coating recovered in step f) comprises NiAl.sub.3;
[0054] said process comprises, before step e), a step of heating
the substrate-cement assembly at a temperature of between
900.degree. C. and 1150.degree. C., preferably above 980.degree.
C.;
[0055] the coating recovered in step f) comprises NiAl;
[0056] the coating recovered in step f) has a thickness of between
5 .mu.m and 200 .mu.m, preferably between 5 .mu.m and 80 .mu.m.
[0057] FIG. 1 schematically shows the various steps of the first
process according to the invention.
[0058] The first process consists of the use of a pulverulent
mixture consisting of the activating agent (5%), of an inert
diluent (alumina, silica, etc.) and of a metal to be deposited, a
metallic powder (between 10% and 60%) which may be either pure
aluminum or an Al+NiAl or AlCr mixture and the particles of which
may or may not have been "preactivated" by mechanosynthesis.
[0059] The particle size of the mixture is then adjusted so that it
can be introduced into the channels by a vibrating system. The
assembly is then brought to a temperature below the melting point
of the metal to be deposited for a duration of at least 6 h.
[0060] After cooling, the assembly is again subjected to a
vibration step that enables the extraction of the residual powder.
At this stage, the coating consists of a surface enrichment in
aluminum of the substrate, the composition of which is close to
NiAl.sub.3. The thicknesses obtained vary between 5 and 10 .mu.m
depending on the time for which the first heating step was carried
out. After this step, the part thus coated is brought to a
temperature of between 900.degree. C. and 1150.degree. C.,
preferably above 980.degree. C. so as to obtain the composition
NiAl in a surface border having a thickness ranging from 15 to 25
.mu.m (FIG. 3).
[0061] FIG. 2 schematically shows the various steps of the second
process according to the invention.
[0062] The second process consists of the use of a pulverulent
mixture consisting of a low melting point pickling flux
(K.sub.3AlF.sub.6-KAlF.sub.4), this is the element that has the
lowest melting point of the mixture constituting the cement and
particles, of an inert diluent and of a pure or aluminum alloy
metallic powder (10% to 60% of metallic powders, 40% of pickling
flux and the balance of inert diluent).
[0063] Everything is introduced by vibration as in the case of the
first process and is brought to high temperature, below the melting
point of the metallic phase, but above that of the pickling flux
for a time that varies from a few minutes to one or two hours.
[0064] It should be noted that the coating is obtained either under
low vacuum or under a controlled inert (argon) atmosphere.
[0065] The residues are then extracted by washing directly after
the heat treatment step. In order to further improve the extraction
of the residues, the apparatus may be washed with a chemical
(acidified aqueous) solution. The coating thus obtained corresponds
to a phase having a composition close to NiAl.sub.3 which may be
converted into NiAl during a subsequent annealing step at a
temperature of between 900.degree. C. and 1150.degree. C.,
preferably at 980.degree. C. The appearance of the coating is shown
in FIG. 4.
[0066] The mixtures of powders may be stored over long durations in
a desiccator under low vacuum or even in a dry chamber under inert
gas flushing and are immediately ready to use.
[0067] Preferably, the inert diluent is selected from powders of
refractory inert materials, more preferably from refractory mineral
oxides, such as alumina, silica, magnesia and mixtures thereof,
which are commonly used in pack cementation treatments.
[0068] The substrate which may be provided with such a coating is
generally selected from metallic substrates, for example based on
iron or nickel, substrates made of alloy(s) or made of
superalloy(s), composite substrates comprising one or more metals
and/or alloy(s) and/or superalloy(s) containing Ni in order to
react with the Al deposited and form NiAl.
[0069] Depending on the desired coating thickness, the substrate
could be surface-enriched with Ni beforehand, for example by
electrolytic deposition.
[0070] As examples of parts on which it is possible to carry out
the deposition processes according to the invention, mention may be
made of the inside of tubes, turbine blades, heat exchangers, in
particular metallic heat exchangers, reactor exchangers, storage
vessels, etc.
[0071] The treatments are generally carried out under an inert or
reducing atmosphere, for example under a hydrogen and/or argon
atmosphere, preferably under an argon atmosphere, or else under an
argon atmosphere with for example 5% to 10% of hydrogen.
[0072] The pressure used during the treatment may be atmospheric
pressure or a reduced pressure, for example a pressure of 10.sup.-2
atm of argon.
[0073] The coatings obtained by the processes according to the
invention give the substrates excellent resistance to corrosion,
even within each substrate cavity independently of its size.
[0074] Consequently, the service life of these substrates is
substantially improved.
EXAMPLE
[0075] The photos from FIG. 3 show two samples of HR120 alloy, one
(the one on the right) coated with the coating produced according
to the second process according to the invention and the other (the
one on the left) being uncoated. These samples were subjected to a
corrosive atmosphere consisting of (in vol %): 15% CO, 5% CO.sub.2,
55% H.sub.2, 25% H.sub.2O, at a pressure of 21 bar absolute and a
temperature of 650.degree. C. After 4700 hours of exposure, it
clearly appears that the coating deposited according to the second
process of the invention makes it possible to protect the alloy
from corrosion.
* * * * *