U.S. patent application number 11/662689 was filed with the patent office on 2008-03-06 for process for obtaining protective coatings against high temperature oxidation.
Invention is credited to Georgiy Barykin, Ignacio Fagoaga Altuna, Carlos Vaquero Gonzalez.
Application Number | 20080057214 11/662689 |
Document ID | / |
Family ID | 36202697 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080057214 |
Kind Code |
A1 |
Fagoaga Altuna; Ignacio ; et
al. |
March 6, 2008 |
Process For Obtaining Protective Coatings Against High Temperature
Oxidation
Abstract
The invention relates to a process which allows obtaining
protective coatings against high temperature oxidation based on
MCrAlY in which M is selected from the group formed by Ni, Co or Fe
or their alloys, and comprises the thermal spray of MCrAlY-based
powders by high frequency pulse detonation (HFPD) techniques. A
high density ceramic layer is optionally deposited on the MCrAlY
layer by high frequency pulse detonation (HFPD) techniques.
Inventors: |
Fagoaga Altuna; Ignacio;
(San Sebastian, ES) ; Vaquero Gonzalez; Carlos;
(San Sebastian, ES) ; Barykin; Georgiy; (San
Sebastian, ES) |
Correspondence
Address: |
KATTEN MUCHIN ROSENMAN LLP
575 MADISON AVENUE
NEW YORK
NY
10022-2585
US
|
Family ID: |
36202697 |
Appl. No.: |
11/662689 |
Filed: |
September 14, 2004 |
PCT Filed: |
September 14, 2004 |
PCT NO: |
PCT/ES04/00399 |
371 Date: |
June 14, 2007 |
Current U.S.
Class: |
427/456 |
Current CPC
Class: |
C23C 28/3215 20130101;
C23C 4/126 20160101; C23C 4/073 20160101; C23C 28/3455 20130101;
C23C 28/36 20130101; C23C 4/18 20130101; C23C 28/345 20130101; C23C
4/02 20130101 |
Class at
Publication: |
427/456 |
International
Class: |
C23C 4/08 20060101
C23C004/08 |
Claims
1. A process for obtaining protective coatings against high
temperature oxidation based on MCrAlY in which M is selected from
the group formed by Ni, Co or Fe or their alloys, characterized in
that it comprises the thermal spray of MCrAlY-based powders by high
frequency pulse detonation (HFPD) techniques.
2. A process for obtaining protective coatings against high
temperature oxidation according to claim 1, characterized in that
the thermal spray is carried out using a mixture comprising at
least one fuel and one combustion agent.
3. A process for obtaining protective coatings against high
temperature oxidation according to claims 1, characterized in that
the thermal spray is carried out using a gaseous mixture formed by
methane or natural gas mixed with a dilution of inert gases
selected from nitrogen, argon, helium or others and oxygen or air
as a combustion agent.
4. A process for obtaining protective coatings against high
temperature oxidation according to claim 1, characterized in that a
heat treatment is applied in a controlled atmosphere after the
deposition of the MCrAlY layer to cause the diffusion.
5. A process for obtaining protective coatings against high
temperature oxidation according to claim 1, characterized in that a
high density ceramic layer is applied on the MCrAlY layer by
thermal spray, by means of high frequency pulse detonation (HFPD)
techniques, the dense ceramic layer forming an anchor for the
application of ceramic material thermal barriers, deposited by
means of any thermal spray technique.
6. A process for obtaining protective coatings against high
temperature oxidation according to claim 5, characterized in that
the thermal spray is carried out using a mixture comprising at
least one fuel and one combustion agent.
7. A process for obtaining protective coatings against high
temperature oxidation according to claim 6, characterized in that
the thermal spray is carried out using a mixture of gases selected
from propane, propylene, ethylene or acetylene, and oxygen as a
combustion agent.
8. A process for obtaining protective coatings against high
temperature oxidation according to claim 5, characterized in that a
heat treatment is applied in a controlled atmosphere before or
after the deposition of the dense ceramic layer to cause the
diffusion.
Description
OBJECT OF THE INVENTION
[0001] The present invention relates to a process for depositing
MCrAlY-based powders on a substrate to obtain a protective coating
against high temperature corrosion-oxidation.
[0002] The process of the invention allows obtaining quality
protective layers, with a high productivity and a low cost.
[0003] It is also an object of the invention that the MCrAlY layer
obtained is useful as an anchor for a thermal barrier.
BACKGROUND OF THE INVENTION
[0004] MCrAlY-based coatings, in which M is selected from Ni, Co
and Fe, are usually used for the protection of metal components in
high temperature environments, such as for example the blades or
casings of a gas turbine.
[0005] The purpose of these coatings is to protect the metal
substrate against high temperature corrosion and oxidation, for
which reason a layer formed by a ceramic thermal insulator or
thermal barrier is applied on them.
[0006] These coatings are deposited by means of different thermal
spray techniques, and especially by means of vacuum plasma spray
(VPS) techniques, air plasma spray (APS) technique, HVOF techniques
or detonation processes.
[0007] The validity of these coatings is directly related to their
density and internal cohesion and generally to a microstructure
preventing the presence of pores and cracks allowing the corrosive
attack on the substrate.
[0008] The chemical composition of MCrAlY and especially the
presence of aluminium and yttrium, which in the conditions of use
act by causing the formation of a well-adhered protective aluminium
layer, are also very important.
[0009] In this sense, the generation of oxides during the spray
deposition reduces the available amount of aluminium and yttrium
and therefore the protective behavior of the coating in use.
[0010] Vacuum plasma spray (VPS) techniques produce high quality
MCrAlY coatings and high thermal performance because they are
coatings with a high density and without the presence of oxides as
a result of the fact that they are made in a closed chamber with a
controlled atmosphere. However, they have the drawback that they
are expensive and have a low productivity, as well as the
dimensional limitations for the parts to be treated derived from
the need to use vacuum chambers.
[0011] Due to these drawbacks, vacuum plasma spray techniques are
not generally used in the industry to obtain this type of
protective coatings.
[0012] For this reason, alternative thermal spray techniques in
atmospheric conditions are used, such as APS or HVOF techniques for
example. Detonation techniques, known as D-Gun, according to U.S.
Pat. No. 2,714,563 are also used but none of them has been
successful due to their low density in the case of APS techniques
or the presence of oxides in the coating in the HVOF or D-Gun
techniques for example.
[0013] HVOF and detonation (D-Gun) techniques produce a high
velocity gas flow as a result of a continuous combustion or pulse
explosion process which can accelerate the spray particles and
obtain very dense coatings. However, it is extremely difficult to
control the oxidation of the obtained coatings given the oxidizing
nature of the fuel mixtures that are necessary to obtain high
velocity flows.
[0014] U.S. Pat. No. 5,741,556 describes a process for producing
MCrAlY coatings by means of detonation (D-Gun) processes, with an
oxide dispersion in the coating suggesting the modification of the
coating powders, increasing the initial presence of aluminium in
the powders to compensate for the loss thereof due to the formation
of oxides in the spray process.
[0015] U.S. Pat. No. 6,366,134 describes a family of MCrAlY powders
specifically designed for HVOF spraying with increased yttrium
levels to compensate for the oxygen-rich atmosphere of the HVOF
process and the subsequent formation of yttrium oxides, the
generation of which would reduce the availability of yttrium
necessary for the improvement of the durability and properties of
the protective oxides generated by MCrAlY layers in conditions of
use.
[0016] The drawback of the processes described in these two patent
documents is that they introduce modifications in the chemical
equilibrium of the different coating elements, it being difficult
to control the degree of oxidation generated during the spray
process, which finally affects the features of the coatings.
[0017] On the other hand, when MCrAlY coatings are used as an
anchoring layer for a ceramic coating acting as a thermal barrier
coating (TBC), the aluminium oxides formed in the MCrAlY during the
spray process can cause the ceramic layer to peel off or to come
off.
[0018] To solve this problem, a second MCrAlY coating with a
greater capability to form alumina is applied on the MCrAlY so as
to improve the adhesion and compatibility of the thermal barrier to
be applied on this second layer. A process of this type is
described for example in European patent no. 1 327 702. However,
this compositional modification of MCrAlY in this surface layer can
affect its protective capability against a corrosive medium at high
temperatures, and in any case it requires a specific deposition,
increasing the complexity of the process.
[0019] Treatments are sometimes carried out on MCrAlY coatings or
MCrAlY layers that are multi-stratum or have a gradual composition
the outer layer of which has a good adhesion for the thermal
barrier are used. This type of coatings are described in the
following patents for example: U.S. Pat. No. 5,894,053, DE19842417
and U.S. Pat. No. 5,942,337. However, any of these processes
introduces an additional complexity to the process, increasing the
costs and the application difficulties.
[0020] In any case, there is currently no known process which
allows simultaneously obtaining MCrAlY coatings with high
productivity, high quality and a reduced price and on which a
ceramic layer acting as a thermal barrier against high temperatures
can in turn be applied with good adhesion features.
DESCRIPTION OF THE INVENTION
[0021] The process object of the invention allows obtaining a
coating against high temperature corrosion and oxidation based on
the thermal spray of commercial MCrAlY powders using high frequency
pulse detonation (HFPD) techniques which allow obtaining a high
density, low oxidation coating with a high productivity and low
cost.
[0022] Furthermore, when the MCrAlY is to be used as an anchoring
layer for a thermal barrier, a ceramic layer can be sprayed on it
using the same HFPD technique, thus achieving a well-adhered, very
dense thin layer which prepares the MCrAlY with a ceramic outer
surface having good compatibility with thermal barriers. Said
porous thermal barriers can be deposited using any thermal spray
technique.
[0023] High frequency pulse detonation (HFPD) spray techniques are
described in the following applications for example: WO97/23299,
WO97/23301, WO97/23302, WO97/23303, WO98/29191, WO99/12653,
WO99/37406 and WO01/30506.
[0024] These techniques use the gas flows produced during the
cyclic explosions or detonations to accelerate and spray the
coating material and differ from the detonation techniques known as
D-Gun in the absence of mechanical valves or other mobile elements,
the pulsed behavior being achieved by the dynamics of the
detonation process, from a continuous gas supply.
[0025] Electronically controllable high frequency explosions which
can exceed 100 Hz compared to the frequencies of a D-Gun process
working between 1 and 10 Hz, are thus achieved.
[0026] This process allows generating explosions with a high
temperature range using combustion gases such as methane and
natural gas or propane, propylene, ethylene or acetylene type
gases, using oxygen-rich mixtures and controlling the amount of
gases involved in each explosion.
[0027] This technique allows the deposition of all types of
materials, from metallic to ceramic alloys achieving a good
adherence and compaction as a result of the detonation process.
[0028] The deposition of MCrAlY powders by means of the
aforementioned high frequency pulse detonation technique requires
optimizing the process parameters which allow obtaining a high
density, good compaction and adherence of the coating with minimal
internal oxidation, thus requiring a low temperature of the
detonation process and a low oxygen environment during the
spray.
[0029] Gases generating low temperature combustion such as methane
or natural gas mixed with a dilution of inert gases such as
nitrogen, argon, helium or others, are specifically used, using
oxygen as a combustion agent in order to achieve low oxygen-carbon
ratios.
[0030] Detonation frequencies exceeding 60 Hz are generally used to
improve the productivity of the process and optimize the volume of
gases used in each explosion.
[0031] The MCrAlY powders are introduced in the barrel of the
detonation gun in a point close to its exit, at a distance from the
detonation chamber between 100 and 500 mm so as to reduce their
residence time in the gaseous medium of the spray.
[0032] Generally, the MCrAlY coating obtained is later subjected to
a heat treatment in a controlled vacuum environment to promote the
diffusion process causing a suitable microstructure for protecting
against corrosion-oxidation.
[0033] When the MCrAlY coating is to be used as an anchoring layer
for a thermal barrier, a ceramic layer with a high density and
small thickness improving the adherence of the porous thermal
barrier on the MCrAlY is also sprayed on it by means of de high
frequency pulse detonation (HFPD) techniques.
[0034] This ceramic layer can be formed by Al.sub.2O.sub.3,
ZrO2-Y2O3 and mixtures of these elements, which can be applied as
single layers, multiple layers or gradual composition layers.
[0035] High detonation temperatures and oxygen-rich spray
environments are required for the spray of this dense ceramic layer
with a small thickness acting as an anchor for the thermal barrier,
in order to cause the complete fusion of the ceramic particles.
[0036] High temperature combustion gases such as propane,
propylene, ethylene or acetylene with high concentrations of oxygen
as a combustion agent are specifically used in order to achieve a
high temperature detonation and highly oxidizing environments
allowing the fusion of the ceramic powders.
[0037] The frequency of the explosions can be greater than 40 Hz
and the ceramic powders are introduced in a point of the barrel
close to the combustion chamber to force them to traverse the
entire length of the barrel, thus increasing the residence time and
favoring heat transfer from the gaseous mixture to the ceramic
powder.
[0038] The porous thermal barrier can be deposited on the obtained
coating by using any thermal spray technique such as VPS, APS or
HVOF, for example, or even other techniques, such as PVD for
example.
DESCRIPTION OF THE DRAWINGS
[0039] To complement the description which is being made and with
the aim of aiding to better understand the features of the
invention, a set of drawings is attached as an integral part of
said description, in which the following has been represented with
an illustrative and non-limiting character:
[0040] FIG. 1 shows a microstructure with a MCrAlY coating
according to the process object of the invention.
[0041] FIG. 2 shows a microstructure of a MCrAlY coating and a
dense ceramic layer with a small thickness on the latter obtained
according to the process object of the invention.
PREFERRED EMBODIMENT OF THE INVENTION
[0042] Two examples of MCrAlY coatings obtained according to the
process of the invention are described below.
Example 1
MCrAlY Coating
[0043] CoNiCrAlY (Amdry 9954) were used as powders for obtaining
the coating. The spray was carried out by means of high frequency
pulse detonation techniques with the following parameters: [0044]
Natural gas flow (slpm): 59 [0045] Nitrogen flow (slpm): 62 [0046]
Oxygen flow (slpm): 82 [0047] Frequency (Hz): 60 [0048] Nitrogen
carrier gas (slpm): 80 [0049] Spray distance (mm): 150
[0050] A coating was obtained with these parameters, and the
microstructure of such coating after a high temperature heat
treatment can be seen in FIG. 1.
Example 2
MCrAlY+Ceramic Coating
[0051] CoNiCrAlY (Amdry 9954) was used as a spray powder to obtain
the lower MCrAlY layer. The spray was carried out by means of high
frequency pulse detonation (HFPD) techniques with the following
parameters: [0052] Natural gas flow (slpm): 59 [0053] Nitrogen flow
(slpm): 62 [0054] Oxygen flow (slpm): 82 [0055] Frequency (Hz): 60
[0056] Nitrogen carrier gas (slpm): 80 [0057] Spray distance (mm):
150
[0058] Al2O3 (Metco 105SFP) was used as a spray powder to obtain
the upper ceramic layer. The spray was carried out by means of high
frequency pulse detonation (HFPD) techniques with the following
parameters: [0059] Propylene flow (slpm): 60 [0060] Oxygen flow
(slpm): 180 [0061] Frequency (Hz): 70 [0062] Nitrogen carrier gas
(slpm): 80 [0063] Spray distance (mm): 230
[0064] A coating was obtained with these parameters, and the
microstructure of such coating after a high temperature heat
treatment can be seen in FIG. 2.
* * * * *