U.S. patent application number 09/872272 was filed with the patent office on 2002-01-24 for roughened bond coats for a thermal barrier coating system and method for producing.
Invention is credited to Jackson, Melvin Robert, Johnson, Curtis Alan, Ritter, Ann Melinda.
Application Number | 20020009609 09/872272 |
Document ID | / |
Family ID | 22736066 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020009609 |
Kind Code |
A1 |
Ritter, Ann Melinda ; et
al. |
January 24, 2002 |
Roughened bond coats for a thermal barrier coating system and
method for producing
Abstract
A roughened bond coat comprises a screen that includes
interwoven wires defining openings and a metallic material disposed
on the screen. The screen and metallic material form a roughened
bond coat possessing an uneven, undulated, and irregular surface.
The metallic material may be one of a slurry and a powder, and
applied by coating and spraying, respectively. A thermal barrier
coating system, which is formed with and incorporates the roughened
bond coat, exhibits greater adhesion of a thermal barrier coating
and bond coat due to an increased interfacial surface area provided
by the uneven, undulated, and irregular surface.
Inventors: |
Ritter, Ann Melinda;
(Niskayuna, NY) ; Jackson, Melvin Robert;
(Niskayuna, NY) ; Johnson, Curtis Alan;
(Schenectady, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
22736066 |
Appl. No.: |
09/872272 |
Filed: |
June 4, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09872272 |
Jun 4, 2001 |
|
|
|
09199065 |
Nov 24, 1998 |
|
|
|
6264766 |
|
|
|
|
Current U.S.
Class: |
428/608 ;
416/241R; 427/287; 427/455; 428/609; 428/678; 428/937 |
Current CPC
Class: |
Y10T 428/12444 20150115;
C23C 4/12 20130101; Y10T 428/12931 20150115; C23C 4/04 20130101;
Y10T 428/12451 20150115; Y02T 50/60 20130101; C23C 4/18 20130101;
Y10S 428/937 20130101; Y10T 428/12063 20150115 |
Class at
Publication: |
428/608 ;
428/609; 428/937; 428/678; 416/241.00R; 427/287; 427/455 |
International
Class: |
B32B 015/14; B32B
015/16; B05D 005/00 |
Claims
1. A method of forming a bond coat, the method comprising:
providing a screen, the screen comprises interwoven wires defining
openings; providing a metallic material; and disposing the metallic
material on the screen to form an uneven, undulated, and irregular
surface.
2. A method according to claim 1, wherein said providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
3. A method according to claim 1, wherein said providing a screen
comprises selecting a screen with the wires having a diameter in a
range from about 50 .mu.m to about 240 .mu.m.
4. A method according to claim 3, wherein said providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
5. A method according to claim 1, wherein said disposing comprises
plasma spraying a layer of powder on the screen.
6. A method according to claim 5, wherein said plasma spraying
comprises providing a layer with a thickness in a range from about
5.0.times.10.sup.-3 cm to about 2.5.times.10.sup.-2 cm.
7. A method according to claim 1, wherein said disposing comprises
disposing a slurry on the screen.
8. A method according to claim 1, wherein said providing a metallic
material comprises selecting at least one of a slurry and a powder,
the metallic material comprises at least one of: MCrAlY; where M is
at least one of nickel (Ni), iron (Fe), and cobalt (Co);
Al--11.6Si; and Ni--20Cr.
9. A method according to claim 8, wherein the metallic material
comprises about 25% Al--11.6Si by weight and about 75% Ni--20Cr by
weight.
10. A method according to claim 1, wherein the metallic material
comprises a slurry comprising about 70% by weight of a metal powder
and about 30% by weight of a binder, and the metal powder comprises
about 90% NiCrAlY by weight and about 10% Al--11.6Si by weight.
11. A method according to claim 1, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 5.0.times.10.sup.-3 cm Ra.
12. A method according to claim 1, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface) with roughness in a range from about 2.5.times.10.sup.-4
cm Ra to about 10.sup.-3 cm Ra.
13. A method according to claim 1, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 7.5.times.10.sup.-4 cm Ra.
14. A method of forming a bond coat, the method comprising:
providing a screen, the screen comprises interwoven wires defining
openings; providing a powder; and plasma spraying the powder on the
screen to form an uneven, undulated, and irregular surface.
15. A method according to claim 14, wherein the providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
16. A method according to claim 14, wherein the providing a screen
comprises selecting a screen with the wire having a diameter in a
range from about 50 .mu.m to about 240 .mu.m.
17. A method according to claim 16, wherein the providing a screen
comprises selecting a screen with the openings having a diameter in
a range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
18. A method according to claim 14, wherein said plasma spraying
comprises providing a layer of powder on the screen.
19. A method according to claim 18, wherein said providing a layer
comprises providing a layer with a thickness in a range from about
5.0.times.10.sup.-3 cm to about 12.5.times.10.sup.-2 cm.
20. A method according to claim 14, wherein said providing a powder
comprises selecting a powder that comprises at least one of:
NICrAlY, where M is at least one of nickel (Ni), iron (Fe), and
cobalt (Co); Al--11.6Si; and Ni--20Cr.
21. A method according to claim 20, wherein the metallic material
comprises about 25% Al--11.6Si by weight and about 75% Ni--20Cr by
weight.
22. A method according to claim 14, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 5.0.times.10.sup.-3 cm Ra.
23. A method according to claim 14, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 10.sup.-3 cm Ra.
24. A method according to claim 14, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface, with roughness in a range from about 2.5.times.10.sup.-4
cm Ra to about 7.5.times.10.sup.-4 cm Ra.
25. A method of forming a bond coat, the method comprising:
providing a screen, the screen comprises interwoven wires defining
openings; providing a slurry; and disposing the slurry on the
screen to form an uneven, undulated, and irregular surface.
26. A method according to claim 25, wherein said providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
27. A method according to claim 25, wherein said providing a screen
comprises selecting a screen with the wires having a diameter in a
range from about 50 .mu.m to about 240 .mu.m.
28. A method according to claim 27, wherein said providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
29. A method according to claim 25, wherein said providing a slurry
comprises selecting a slurry that comprises about 70% by weight of
a metal powder and about 30% by weight of a binder.
30. A method according to claim 29, wherein the metal powder
comprises about 90% MCrAlY, where M is at least one of nickel (Ni),
iron (Fe), and cobalt (Co), by weight and about 10% Al--11.6Si by
weight.
31. A roughened bond coat comprising: a screen comprising
interwoven wires defining openings; and a metallic material
disposed on the screen, wherein the metallic material on the screen
forms the uneven, undulated, and irregular surface.
32. A bond coat according to claim 31, wherein the openings
comprise a size in a range from about 190 .mu.m.sup.2 to about 420
.mu.m.sup.2.
33. A bond coat according to claim 31, wherein the wires comprise a
diameter in a range from about 50 .mu.m to about 240 .mu.m.
34. A bond coat according to claim 33, wherein the openings
comprise a size in a range from about 190 .mu.m.sup.2 to about 420
.mu.m.sup.2.
35. A bond coat according to claim 31, wherein the metallic
material comprises a powder disposed on the screen.
36. A bond coat according to claim 35, wherein the powder comprises
a layer of powder plasma sprayed on the screen.
37. A bond coat according to claim 36, wherein the layer with a
thickness in a range from about 5.0.times.10.sup.-3 cm to about
12.5.times.10.sup.-2 cm.
38. A bond coat according to claim 31, wherein the metallic
material comprises a slurry disposed on the screen.
39. A bond coat according to claim 31, wherein the metallic
material comprises at least one of a slurry and a powder, the
metallic material comprises at least one of: MCrAlY, where M is at
least one of nickel (Ni), iron (Fe), and cobalt (Co); Al--11.6Si;
and Ni--20Cr.
40. A bond coat according to claim 39, wherein the metallic
material comprises about 25% Al--11.6Si by weight and about 75%
Ni--20Cr by weight.
41. A bond coat according to claim 31, wherein the metallic
material comprises a slurry comprising about 70% by weight of a
metal powder and about 30% by weight of a binder, and the metal
powder comprises about 90% MCrAlY, where M is at least one of
nickel (Ni), iron (Fe), and cobalt (Co), by weight and about 10%
Al--11.6Si by weight.
42. The bond coat according to claim 31, wherein the bond coat is
applied to a substrate comprising a turbine component.
43. A bond coat according to claim 31, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 5.0.times.10.sup.-3 cm Ra.
44. A bond coat according to claim 31, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 10.sup.-3 cm Ra.
45. A bond coat according to claim 31, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 7.5.times.10.sup.-4 cm Ra.
46. A method of providing a thermal barrier coating system, the
thermal barrier coating system comprises a roughened bond coat
disposed on a substrate, and a thermal barrier coating disposed on
the bond coat the method comprising: disposing a roughened bond
coat on the substrate; disposing a thermal barrier coating on the
roughened bond coat; wherein said disposing a roughened bond coat
comprises: providing a screen, the screen comprises interwoven
wires defining openings; providing a metallic material; and
disposing the metallic material on the screen to form a roughened
bond coat, wherein the roughened bond coat provides an uneven
undulated surface adjacent to the thermal barrier coating.
47. A method according to claim 46, wherein said providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
48. A method according to claim 46, wherein said providing a screen
comprises selecting a screen with the wires having a diameter in a
range from about 50 .mu.m to about 240 .mu.m.
49. A method according to claim 48, wherein said providing a screen
comprises selecting a screen with the openings having a size in a
range from about 190 .mu.m.sup.2 to about 420 .mu.m.sup.2.
50. A method according to claim 46, wherein said disposing
comprises plasma spraying a layer of powder on the screen.
51. A method according to claim 50, wherein said plasma spraying
comprises providing a layer with a thickness in a range from about
5.0.times.10.sup.-3 cm to about 12.5.times.10.sup.-2 cm.
52. A method according to claim 46, wherein said disposing
comprises disposing a slurry on the screen.
53. A method according to claim 46, wherein said providing a
metallic material comprises selecting at least one of a slurry and
a powder, the metallic material comprises at least one of: MCrAlY,
where M is at least one of nickel (Ni), iron (Fe), and cobalt (Co);
Al--11.6Si; and Ni--20Cr.
54. A method according to claim 53, wherein the metallic material
comprises about 25% Al--11.6Si by weight and about 75% Ni--20Cr by
weight.
55. A method according to claim 46, wherein the metallic material
comprises a slurry comprising about 70% by weight of a metal powder
and about 30% by weight of a binder and the metal powder comprises
about 90% MCrAlY, where M is at least one of nickel (Ni), iron
(Fe), and cobalt (Co), by weight and about 10% Al--11.6Si by
weight.
56. A method according to claim 46, the method further comprising
heat treating, wherein a portion of the metallic material melts
and, upon re-solidification, joins the roughened bond coat to the
substrate.
57. A method according to claim 46, the method further comprises
connecting the screen to the substrate prior to disposing the
metallic material to the screen.
58. A method according to claim 57, wherein said connecting
comprises welding the screen to the substrate.
59. A method according to claim 46, the method further comprises
disposing metallic material on the screen prior to disposing the
screen on the substrate.
60. A method according to claim 46, wherein the substrate comprises
a turbine component.
61. A turbine component according to claim 46, wherein the
disposing the metallic material forms the uneven, undulated, and
irregular surface with roughness in a range from about
2.5.times.10.sup.-4 cm Ra to about 5.0.times.10.sup.-3 cm Ra.
62. A turbine component according to claim 46, wherein the
disposing the metallic material forms the uneven, undulated, and
irregular surface with roughness in a range from about
2.5.times.10.sup.-4 cm Ra to about 10.sup.-3 cm Ra.
63. A turbine component according to claim 46, wherein the
disposing the metallic material forms the uneven, undulated, and
irregular surface with roughness in a range from about
2.5.times.10.sup.-4 cm Ra to about 7.5.times.10.sup.-4 cm Ra.
64. A thermal barrier coating system comprising: a roughened bond
coat disposed on a substrate; and a thermal barrier coating
disposed on the roughened bond coat, wherein the roughened bond
coat comprises: a screen comprising interwoven wires defining
openings; a metallic material disposed on the screen to form a
roughened bond coat possessing an uneven, undulated, and irregular
surface adjacent to the thermal barrier coating.
65. A system according to claim 64, wherein the openings have a
size in a range from about 190 .mu.m.sup.2 to about 420
.mu.m.sup.2.
66. A system according to claim 64, wherein the wire have a
diameter in a range from about 50 .mu.m to about 240 .mu.m.
67. A system according to claim 66, wherein the openings have a
size in a range from about 190 .mu.m.sup.2 to about 420
.mu.m.sup.2.
68. A system according to claim 64, wherein the metallic material
comprises a layer of metallic material that is plasma sprayed on
the screen.
69. A system according to claim 68, wherein said layer comprises a
layer with a thickness in a range from about 5.0.times.10.sup.-3 cm
to about 12.5.times.10.sup.-2 cm.
70. A system according to claim 64, wherein said metallic material
comprises a slurry disposed on the screen.
71. A system according to claim 64, wherein said metallic material
comprises at least one of a slurry and a powder, the metallic
material comprises at least one of: MCrAlY, where M is at least one
of nickel (Ni), iron (Fe), and cobalt (Co); Al--11.6Si; and
Ni--20Cr.
72. A system according to claim 71, wherein the metallic material
comprises about 25% Al--11.6Si by weight and about 75% Ni--20Cr by
weight.
73. A system according to claim 64, wherein the metallic material
comprises a slurry comprising about 70% by weight of a metal powder
and about 30% by weight of a binder and the metal powder comprises
about 90% MCrAlY, where M is at least one of nickel (Ni), iron
(Fe), and cobalt (Co), by weight and about 10% Al--11.6Si by
weight.
74. A system according to claim 64, wherein the system undergoes
heat treatment and a portion of the metallic material melts and
re-solidifies joining the roughened bond coat to the substrate.
75. A system according to claim 64, the system further comprises
connections that connect the screen to the substrate.
76. A system according to claim 75, wherein said connections
comprise welds.
77. A system according to claim 64, the system further comprises
the metallic material disposed on the screen prior to the screen
being disposed on the substrate.
78. A system according to claim 64, wherein the substrate comprises
a turbine component.
79. A system according to claim 64, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surfacer with roughness in a range from about 2.5.times.10.sup.-4
cm Ra to about 5.0.times.10.sup.-3 cm Ra.
80. A system according to claim 64, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 10.sup.-3 cm Ra.
81. A system according to claim 64, wherein the disposing the
metallic material forms the uneven, undulated, and irregular
surface with roughness in a range from about 2.5.times.10.sup.-4 cm
Ra to about 7.5.times.10.sup.-4 cm Ra.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to bond coats. In particular, the
invention relates to roughened bond coats for thermal barrier
coating systems.
[0002] Thermal barrier coating systems are used in hot-section
components in turbines, for example jet engine and gas turbines.
The thermal barrier coating system insulates the turbines from high
temperatures during thermal cycling. Thermal barrier coating
systems include a thermal barrier coating (TBC) disposed on a bond
coat, which in turn is disposed on a substrate. The thermal barrier
coating normally comprises zirconia, such as example at least one
of a stabilized zirconia and a partially-stabilized zirconia (PSZ).
The bond coat typically comprises an oxidation-resistant metallic
layer disposed between the TBC and substrate turbine component. The
TBC is adhered to the bond coat typically by mechanical
interlocking, so the bond coat provides oxidation resistant to the
substrate and a relatively rough surface. The bond coat surface
generally has Ra (Arithmetic Average Roughness (Ra) as determined
from ANSI/ASME Standard B461-1985) values over about 350 mainly by
mechanical interlocking. So the function of the bond coat is to
provide oxidation resistant to the substrate and a relatively rough
surface, preferably with Ra values over about 350 microinches, for
the TBC to adhere to the substrate. Thus, the TBC is disposed over
the turbine component can provide thermal insulation.
[0003] FIG. 1 is a schematic representation of a known thermal
barrier coating system 1. A substrate 10 comprises an underlying
part of a component, for example a turbine component. A bond coat
12 is disposed on the substrate 10. The bond coat is disposed on
the substrate 10 by any appropriate method, for example, but riot
limited to, thermal spray processes, such as vacuum plasma spray
(VPS), air plasma spray (APS) and hyper-velocity oxy-fuel (HVOF)
spray processes.
[0004] The structure and roughness of bond coat surface 13 are
dependent on the spray process. Bond coats deposited by a VPS
process are typically dense and free of oxides. Therefore,
VPS--applied bond coats provide protection at high temperatures
against oxidation. The VPS application process disposes fine
powders, and thus, VPS--applied bond coats are typically dense, for
example having a density greater than about 90% of its theoretical
density, but have relatively smooth surfaces. Consequently, a TBC
does not adhere well to a VPS bond coat.
[0005] An air plasma spray (APS) process produces rough bond coats
because of large powders used in APS. The large powders possess a
relatively high heat capacity; however, the APS--applied bond coats
contain high amounts of oxides. Also, APS--applied bond coats
possess a relatively low porosity due to the oxidation environment
and low momentum of the powders. Although APS--applied bond coats
provide better TBC adhesion due to their roughness, they are more
prone to oxidation because of their relatively high oxide levels
and relatively low porosity.
[0006] Bond coats deposited by HVOF are sensitive to particle size
distributions. Dense and oxide-free bond coats can be deposited by
HVOF using very lean conditions (low oxygen amounts) and finer
particles, for example particles with a size about -325+10 .mu.m.
The surface roughness of HVOF--applied bond coats is relatively
smooth. Rough bond coats can be deposited by HVOF using coarser
powders, for example particles with a size about -230+325, however
a low HVOF flame temperature is needed. The low flame temperatures
result in the bond coat comprising unmelted powders, therefore the
coating is porous and less dense.
[0007] A TBC 14 is disposed on the bond coat 12 and forms a surface
15 against the surface 13. The TBC 14 is disposed on the bond coat
12 by any appropriate process to adhere (bond) to the bond coat.
The TBC surface 15 and bond coat surface 13 define an interfacial
area 16 at their adjoining surfaces.
[0008] Effectiveness of a thermal barrier coating system during
thermal cycling is compromised by de-bonding of the TBC and bond
coat, for example at the TBC and bond coat interfacial area.
De-bonding can be caused by at least one of a poor TBC and bond
coat adhesion, and lack of accommodation of thermal expansion
mismatch between the TBC and bond coat. The lack of adhesion is
characteristic of smooth adjoining surfaces where a total surface
area is minimal. The thermal expansion mismatch between the TBC and
bond coat results from different coefficients of thermal expansion
of the materials used for these features. If the difference in
coefficients of thermal expansion of the adhered elements is large,
one element expands much more than the other, and separation and
de-bonding occur at the interfacial areas. De-bonding of the TBC
and bond coat is undesirable as the insulation effect of the
thermal barrier coating system will be lost at TBC separation.
[0009] Therefore, it is desirable to increase adhesion between the
TBC and the bond coat to prevent de-bonding. The adhesion between
the bond coat and TBC can be increased by roughening a bond coat,
thus increasing an area at an interfacial area mating surface of
adhered elements and enhancing mechanical interlocking adhesion
between the bond coat and TBC. Increasing a bond coat's roughness
provides an enhanced interfacial surface area for accommodation of
any thermal mismatch, with respect to non-roughened bond coats.
SUMMARY OF THE INVENTION
[0010] The invention overcomes the above noted deficiencies of
known thermal barrier coating systems. The invention sets forth a
method of forming a bond coat that comprises providing a screen,
where the screen comprises interwoven wires defining openings;
providing a metal material; and disposing the metal material onto
the screen to form an uneven, undulated, and irregular surface.
[0011] The invention also sets forth a method of forming a
roughened bond coat that comprises providing a screen, where the
screen comprises interwoven wires defining openings; providing a
powder; and plasma spraying the powder on the screen to form an
uneven, undulated, and irregular surface.
[0012] The invention also sets forth a further method of forming a
roughened bond coat that comprises providing a screen, where the
screen comprises interwoven wires defining openings; providing a
slurry; and disposing the slurry on the screen to form an uneven,
undulated, and irregular surface.
[0013] A roughened bond coat is set forth embodied by the
invention, and comprises a screen, where the screen includes
interwoven wires defining openings; and a metal material disposed
on the screen. The metal material on the screen forms an uneven,
undulated, and irregular surface.
[0014] An embodiment of the invention provides a method of forming
a thermal barrier coating system, where the thermal barrier coating
system comprises a roughened bond coat disposed on a substrate and
a thermal barrier coating disposed on the bond coat. The method
comprises disposing a roughened bond coat on the substrate and
disposing a thermal barrier coating on the roughened bond coat. The
roughened bond coat comprises a screen having interwoven wires
defining openings and a metal material disposed on the screen lo
form the roughened bond coat. The roughened bond coat possessing an
uneven undulated surface adjacent to the thermal barrier
coating.
[0015] A further embodiment of the invention provides a thermal
barrier coating system. The thermal barrier coating system
comprises a roughened bond coat and a thermal barrier coating
disposed on a substrate. The roughened bond coat comprises a screen
with interwoven wires defining openings and a metal material
disposed on the screen to form a roughened bond coat. The roughened
bond coat possessing an uneven undulated surface adjacent to the
thermal barrier coating.
[0016] These and other aspects, advantages and salient features of
the invention will become apparent from the following detailed
description, which, when taken in conjunction with the annexed
drawings, where like parts are designated by like reference
characters throughout the drawings, disclose embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic representation of a known thermal
barrier coating system;
[0018] FIG. 2 is a schematic representation of a thermal barrier
coating system including a roughened bond coat;
[0019] FIG. 3 is a plan illustration of a screen for use in a
roughened bond coat;
[0020] FIG. 4 is a plan illustration of a roughened bond coat;
[0021] FIG. 5 is a side, part sectional illustration of a roughened
bond coat;
[0022] FIG. 6 is a micro-photograph of a roughened bond coat;
and
[0023] FIG. 7 is a flow chart of one method for forming a thermal
barrier coating system.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Roughened bond coats enhance adhesion between a thermal
barrier coating (TBC) and a bond coat in a thermal barrier coating
system. Roughened bond coats prevent de-bonding and separation
between the TBC and bond coat of the thermal barrier coating
system. A roughened bond coat increases interfacial mating surface
areas of adhered elements, enhances mechanical interlocking between
the bond coat and TBC, and provides for accommodation of thermal
mismatches between the TBC and bond coat. Accordingly, expansion of
elements in a thermal barrier coating system with a roughened bond
coat does not lend to separation and de-bonding therebetween. An
effect of the roughened bond coat includes an enhanced life of the
TBC in the thermal barrier coating system.
[0025] In the following description, material compositions of
mixtures are provided in approximate weight percent unless
otherwise expressed. Further, individual compositions are provided
in weight percent, unless otherwise provided. For example, if a
mixture comprises about 70% of Constituent A and about 30% of
constituent B, the percents are in weight percents. Nomenclature
used for compositions is as follows. If Composition A comprises
Ni--23Cr--6Al--0.4Y, yttrium is provided at 0.4 weight percent,
aluminum is provided at 6 weight percent, chromium is provided at
23 weight percent, and nickel is provided as the balance weight
percent.
[0026] A thermal barrier coating system 100 including a roughened
bond coat, as embodied by the invention, is schematically
illustrated in FIG. 2. The thermal barrier coating system 100
comprises a substrate 10, a roughened bond coat 22 and a TBC 14. An
interfacial surface area 28 is located at adjacent, adjoining
surfaces 21 and 15 of the roughened bond coat 22 and the TBC 14,
respectively. The roughened bond coat 22 is attached to the
substrate 10, by at least one connection 110. The connection 110,
comprises a physical attachment, for example a weld, such as at
least one of a tack weld, laser weld, and ultrasonic weld. The
number of connections varies dependent on factors such as, but not
limited to, a screen's wire and mesh opening sizes.
[0027] A thermal barrier coating system 100 including a roughened
bond coat, as embodied by the invention, is schematically
illustrated in FIG. 2. The thermal barrier coating system 100
comprises a substrate 10, a roughened bond coat 22 and a TBC 14. An
interfacial surface area 28 is located at adjacent, adjoining
surfaces 21 and 15 of the roughened bond coat 22 and the TBC 14,
respectively. The roughened bond coat 22 is attached to the
substrate 10, by at least one connection 110. The connection 110
comprises a physical attachment, for example a weld, such as at
least one of a tack weld, laser weld, and ultrasonic weld. The
number of connections varies dependent on factors such as, but not
limited to, a screen's wire and mesh opening sizes.
[0028] The roughened bond coat 22 comprises a screen 24 provided
with a metallic material 26 disposed thereon. FIG. 3 illustrates a
screen 24, such as a metal screen, used to form a roughened bond
coat 22. The metal screen 24 comprises a material that is
metallurgically similar to the material of the substrate 12. For
example, if the substrate is a turbine formed of a nickel-based
superalloy composition, the screen 24 is formed from a nickel-based
material. This material is merely exemplary of screen materials,
and is not meant to limit the scope of the invention.
[0029] The screen 24 comprises interwoven wires 30 that define mesh
openings 34. The size of the wires 30 and openings 34 varies,
dependent on the ultimate desired roughness of the bond coat 22.
For example, the wires 30 of the screen 24 are provided with an
average diameter in a range between about 5 .mu.m to about 240
.mu.m. The openings 34 of the screen 24 are substantially
rectangular, such as square openings. The size of the openings 34
are provided in a range from about 190 .mu.m.sup.2 to about 420
.mu.m.sup.2. For example and in no way limiting of the invention, a
"fine" screen 24 provides an opening of about 200 .mu.m.sup.2 with
about 50 .mu.m average diameter wire; a "medium" screen 24 provides
an opening 34 of about 190 .mu.m.sup.2 with about 130 .mu.m average
diameter wire; and a "coarse" screen 24 provides an opening of
about 420 .mu.m.sup.2 with about 240 .mu.m average diameter
wire.
[0030] FIG. 4 is a schematic illustration of a roughened bond coat
22 with a metallic material 26 disposed on wires 30 of screen 24.
The metallic material 26 is disposed on the screen 24 by a method
appropriate for the metallic material 26. These methods include,
but are not limited to; spraying, such as, but not limited to,
plasma spraying; coating, such as by directly applying (painting);
and deposition, such as chemical vapor deposition and physical
vapor deposition. FIG. 4 illustrates one possible configuration of
the metallic material 26 on the wires 30 and in the openings 34 of
the screen 22, however this is merely exemplary and not meant to
limit the invention. An exact configuration of the metallic
material 26 on the screen 22 is dependent on various factors,
including, but not limited to, process variables used in applying
the metal material 26, the size of the wires 30 and openings 34,
and material characteristics of the metal material 26, such as
density and viscosity.
[0031] The metallic material 26 covers portions of the wires 30 and
extends into and at least partially fills the openings 34, as
illustrated in FIG. 4. For example, and in no way limiting of the
invention, the metallic material 26 totally covers the wires 30, as
at portion 33. The metallic material 26 also partially covers the
wires 30, as at portion 35. Further, the metallic material 26
totally covers the wires 30, while exposing other parts of the
wires 30. The metallic material 26 completely fills openings 34 in
the screen 22, as at portion 36. The metallic material 26 also at
least partially fills the openings 34, as at portion 37. Further,
the metallic material 26 completely fills some of the openings 34,
and partially fills other openings 34, as at portion 38. In other
words, the metallic material 26 covers at least part of wires 30
and fills parts of the openings 34.
[0032] The metallic material 26 possesses a thermal expansion
coefficient that is close to the thermal expansion coefficient of
the TBC 14. Close thermal expansions for the metallic material 26
and TBC 14 avoid one of these expanding much more than the other,
thus avoiding de-bonding.
[0033] The metallic material 26 is also an oxidation resistant
material. Oxidation of the thermal barrier coating system is
undesirable since it causes spalling, separation, de-bonding, and
possible failure of the thermal barrier coating system, and
oxidation is reduced by the addition of the metallic material 26.
The metallic material 26 comprises at least one oxidation resistant
material selected from NiCrAlY, where M is at least one of nickel
(Ni), iron (Fe), and cobalt (Co), AlSi (hereinafter "AlSi"), and
Ni--60Al--1B. The invention describes MCrAlY as NiCrAlY, however
this description is merely exemplary and is not meant to limit the
invention in any way.
[0034] The physical characteristics of the metallic material 26
facilitates its application on the screen 24. The metallic material
26 flows over and around the wires 30 to adhere to the wires 30.
The metallic material 26 also possesses a viscosity that enables
the metallic material 26 to fill the openings 34 in the screen 24.
Thus, the metallic material 26 comprises materials, such as but not
limited to slurries and powders.
[0035] A slurry as a metallic material 26 that is applied to the
screen 24 comprises a mixture of at least one oxidation resistant
material, such as a metal powder, plus a binder. The mixture
comprises about 70% by weight metal powder, and about 30% by weight
of a binder. The binder is selected from appropriate binders for
slurries, that are used to hold powders and similar materials
together.
[0036] One metal powder portion of a slurry mixture, as embodied by
the invention, comprises about 90% of NiCrAlY (Ni-23Cr--6Al--0.4Y)
by weight and about 10% of AlSi by weight. NiCrAlY is an
oxidation-resistant composition possessing a high melting point
(approximately 1350.degree. C.). AlSi is an oxidation-resistant
composition, and possesses a low melting point (approximately
577.degree. C.). Therefore, if the bond coat is subjected to a heat
treatment, AlSi melts prior to NiCrAlY melting, for example during
subsequent heat treatments of the thermal barrier coating system
100. Melted AlSi fuses and re-acts together elements of the
roughened bond coat. If the heat treatment is conducted at
temperatures higher than the melting point of AlSi, but lower that
the melting point of NiCrAlY, the AlSi melts before the NiCrAlY.
The melted AlSi joins (fuses) the un-melted NiCrAlY and structural
elements of the roughened bond together. NiCrAlY in the slurry
mixture is merely exemplary of the metal powders within the scope
of the invention, and other compositions, such as, but not limited
to Ni--20Cr (melting point about 1400.degree. C.) and Ni--60Al--1B
(melting point about 850.degree. C.), are within the scope of the
invention. The combination of different melting point powders
results in a higher density, for example a density of at least
about 95% of its theoretical density.
[0037] FIG. 5 is a side part-sectional schematic illustration of a
roughened bond coat 22 with the screen 24 having the metallic
material 26 disposed thereto. As illustrated, a surface 46 of the
metallic material 26 on the screen defines an interfacial surface
area 28. The surface 46 is uneven, undulated, and irregular, rather
than smooth as in known bond coat surfaces. Accordingly, the
surface 46 provides a larger surface area compared to known smooth
bond coat surfaces. For example, the interfacial surface area 28 is
greater than a known bond coat's surface area by at least about
25%.
[0038] The roughness of the bond coat 24 is sufficient to increase
interfacial surface areas at the interface, thus reducing
de-bonding and increasing accommodation of thermal expansion
mismatches. The bond coat 24, as embodied by the invention,
possesses a roughness in a range of about 100 microinches (about
2.5.times.10.sup.-4 cm) Ra (Arithmetic Average Roughness (Ra) as
determined from ANSI/ASME Standard B461-1985) to about 2000
microinches (about 5.0.times.10.sup.-3 cm) Ra. Alternatively, the
bond coat 24 possesses a roughness in a range of about 100
microinches (about 2.5.times.10.sup.-4 m) Ra to about 400
microinches (about 1.0.times.10.sup.-3 cm) Ra. Further, the bond
coat 24 possesses a roughness in a range of about 100 microinches
(about 2.5.times.10.sup.-4 cm) Ra to about 300 microinches (about
7.5.times.10.sup.-4 cm) Ra.
[0039] FIG. 6 is a micro-photograph of a roughened bond coat 22,
where the metallic material 26 is applied as a slurry. In FIG. 6,
some particles, such as NiCrAlY, that have a melting point higher
that another component of the slurry, such as AlSi, of the metal
powder portion of the slurry mixture remain un-melted after heat
treatments (as discussed above). These un-melted powder particles
sit on top of the screen and increase the localized roughness of
the bond coat 22, which, of course, is desirable.
[0040] Melting of the AlSi enhances adherence the metal powder
portion lo the screen 24. A larger volume fraction of a low-melting
point powder, such as AlSi, in the slurry mixture increases
adhesion of the slurry to the screen 24. Further, a larger volume
fraction of a low-melt powder, such as AlSi, decreases slurry
porosity, as more material is melted and less gaps between powder
particles remain. This reduced porosity enhances operation of the
resultant thermal barrier coating system 100, as there are fewer
gaps between powder particles for oxidation to initiate. Also,
metallic material comprising AlSi may be applied to reduce porosity
of the thermal barrier coating system at the screen, by applying
AlSi to the screen 24 prior to applying the metallic material 26.
Thus, the AlSi on the screen 24 will melt and reduce gaps at the
screen 24, further reducing porosity.
[0041] The metal material 26, which is disposed on the screen 24,
alternatively comprises a powder material. The powder material is
disposed on the screen 24 by an appropriate powder spraying
process, such as, but not limited to, plasma spraying, for example
air-plasma spraying. Therefore, a roughened bond coat 22, as
embodied by the invention, comprises a screen 24 with a powdered
metallic material 26 applied thereto, for example by spraying. This
process forms a metal material spray-formed overlayer, which
comprises the powdered metallic material 26 on the screen 24.
[0042] The spray-formed overlayer is provided in a range from about
5.times.10.sup.-3 cm to about 2.5.times.10.sup.-2 cm. One exemplary
overlay has an average thickness of about 1.27.times.10.sup.-2 cm
(0.005 inches). The powder for the metal material 26, in this
embodiment of the invention, comprises at least one powder selected
from: Al--11.6Si; NiCrAlY (Ni--23Cr--6Al--0.4Y); and a mixture of
about 25% AlSi by weight and about 75% Ni--20Cr by weight. NiCrAlY
is a known oxidation-resistant material. Thus, the mixture of AlSi
and Ni--20Cr provides the metal material with desirable
oxidation-resistant characteristics, especially after
heat-treatment.
[0043] FIG. 7 is a flow chart illustrating an exemplary process for
preparing a roughened bond coat 22 and thermal barrier coating
system 100, as embodied by the invention. In steps S1 and S1.1, a
screen 24 and substrate 10, respectively, are provided. The screen
24 is attached to the substrate 10 in step S2. The screen 24 is
attached to the substrate 10 at selected areas 110 (FIG. 2) by an
appropriate method, for example welding, such as tack welding,
ultrasonic welding, and laser welding.
[0044] Metallic material 26 is applied to the screen 24 in step S3.
If the metallic material 26 is a slurry, it is applied to the
screen 24 by a slurry liquid application process. If the metallic
material 26 is provided as a powder, the metallic material 26 is
sprayed onto the screen 24. Each of these processes results in a
roughened bond coat 22 on a substrate 10.
[0045] Once the roughened bond coat 22 is provided, a TBC 14 is
applied to the roughened bond coat 22 in step S4 to form a thermal
barrier coating system 100. The TBC is disposed on the roughened
bond coat 22 by an appropriate method, such as, but not limited to
spraying, deposition, and coating.
[0046] The roughened bond coat 22 and substrate 10, prior to the
TBC being disposed thereon, undergoes optional heat treatment, at
step S3.1. Further, the entire thermal barrier coating system 100
undergoes optional heat treatment at step S7. The heat treatment of
the thermal barrier coating system 100 comprises heat-treating at
about 1200.degree. C./1 hr in a vacuum and would generally be
performed only if optional heat treatment step S3.1 is performed at
a heat treatment temperature sufficient to melt the AlSi but not
NiCrAlY or Ni--20Cr, if provided, wherein upon re-solidification
the AlSi fuses the bond coat to the screen and its elements with
the roughened bond coat 22.
[0047] As discussed above, some metallic material 26 can be applied
to the screen 22 to reduce porosity of the roughened bond coat. The
application of the metallic material 26 to the screen 22 occurs at
step S1.2, which is prior to the attachment of the screen 22 to the
substrate 10.
[0048] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations or improvements therein may be made by those
skilled in the art, and are within the scope of the invention.
* * * * *