U.S. patent application number 12/738945 was filed with the patent office on 2010-09-30 for process for producing body centered cubic (b2) nickel aluminide (nial) coating of controlled thickness on nickle-based alloy surfaces.
This patent application is currently assigned to The Secretary, Department of Atomic Energy,Govt. of India. Invention is credited to Arun Kumar Bhaduri, Srinivasan Ganesan, Baldev Raj, Gopal Venkatraman.
Application Number | 20100247793 12/738945 |
Document ID | / |
Family ID | 39598452 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100247793 |
Kind Code |
A1 |
Ganesan; Srinivasan ; et
al. |
September 30, 2010 |
PROCESS FOR PRODUCING BODY CENTERED CUBIC (B2) NICKEL ALUMINIDE
(NIAL) COATING OF CONTROLLED THICKNESS ON NICKLE-BASED ALLOY
SURFACES
Abstract
Aluminizing of nickel-base alloys and a process for producing
body centered cubic (B2) nickel aluminide (NiAl) coating of
controlled thickness on nickel-base alloys surfaces. Importantly,
the process of producing the nickel aluminide (B2 NiAl phase)
coatings on nickel-base alloys is directed to achieve high hardness
of 800-1100 VHN and dimensional tolerance of 80.+-.30 microns
coating thickness. The process achieves desired nickel aluminide
coatings with minimum environmental emission of toxic chemicals
fumes and is also environment friendly. Obtaining the nickel
aluminide coating is specifically possible without the need for
masking of the unwanted regions of the components and more
importantly can be attended both on flat and curved surfaces
thereby favouring wide scale utilities of such aluminizing process,
facilitate fabrication industries required to carry out surface
modifications and engineering (protective coating) on nickel-base
alloys desired for high service temperatures such as nuclear
industries, aircraft and gas turbine industries.
Inventors: |
Ganesan; Srinivasan;
(Kalpakkam, IN) ; Bhaduri; Arun Kumar; (Kalpakkam,
IN) ; Raj; Baldev; (Kalpakkam, IN) ;
Venkatraman; Gopal; (Chennai, IN) |
Correspondence
Address: |
The Law Office of Michael E. Kondoudis
888 16th Street, NW, Suite 800
Washington
DC
20006
US
|
Assignee: |
The Secretary, Department of Atomic
Energy,Govt. of India
Mumbai
IN
|
Family ID: |
39598452 |
Appl. No.: |
12/738945 |
Filed: |
October 26, 2007 |
PCT Filed: |
October 26, 2007 |
PCT NO: |
PCT/IN07/00514 |
371 Date: |
April 20, 2010 |
Current U.S.
Class: |
427/456 |
Current CPC
Class: |
C23C 4/08 20130101; Y02T
50/60 20130101; C23C 4/02 20130101; C23C 4/18 20130101 |
Class at
Publication: |
427/456 |
International
Class: |
C23C 4/08 20060101
C23C004/08; C23C 4/02 20060101 C23C004/02 |
Claims
1-10. (canceled)
11. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating of controlled thickness of 50 to 110
microns with high hardness in the range of 800-1100 VHN on
nickel-base alloy surfaces with minimum 40 weight % nickel content
comprising: activating the surfaces to be coated by grit blasting
preferably following dimensional check and degreasing; thermal
spraying of the required surfaces with commercial pure aluminium to
desired specific thickness in the range of 100 to 200 microns
preferably 100-120 microns; and subjecting the aluminium thus
sprayed onto the nickel-base alloy substrate to diffusion heat
treatment in vacuum atmosphere at a temperature in the range of
950.degree. C.-1100.degree. C. for a duration of 1.0 to 1.5 hours
such that the aluminium sprayed reacts with the nickel-base alloy
substrate to form the desired nickel aluminide coating of said
controlled thickness and hardness on said nickel-base alloy
substrate and subjecting the coated surface to surface
cleaning.
12. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating according to claim 11 wherein the said
surface activation by grit blasting is carried out using alumina
grit of specific size and distribution preferably in the range of
30-120 mesh size at an air pressure of 5.5+/-0.5 kg/cm.sup.2 and
more preferably with 50-80 mesh size at an air pressure of 5.0-5.1
kg/cm.sup.2.
13. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating according to claim 11 wherein said thermal
spray parameters comprise (i) aluminium wire diameter in the range
of 3.0 to 3.2 mm at a Wire Feed Rate in the range of 2.0-2.5
mm/sec; (ii) Pneumatic pressure in the range of 5.5+/-0.5
kg/cm.sup.2; (iii) Oxygen Pressure in the range of 2.5+/-0.3
kg/cm.sup.2; and Acetylene pressure in the range of 1.0+/-0.2
kg/cm.sup.2.
14. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating according to claim 11 wherein said
diffusion heat treatment in said vacuum atmosphere is carried out
at (10.sup.-5) millibar pressure preferably at temperature in the
range of 1010.+-.10.degree. C. with an aluminium spray thickness of
100-120 microns with the resultant coating thickness and hardness
being 80-90 microns and 980-1030 VHN respectively.
15. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating according to claim 11 wherein the said
surface cleaning of the coated surface comprise removing adherent
oxide scale using pickling solution following the steps of: (i)
providing the pickling solution preferably comprising (a)
concentrated nitric acid (specific gravity: 1.41 g/cm.sup.3) in
amounts of 16% (by volume); (b) Hydrofluoric acid (specific gravity
1.61 g/cm.sup.3) in amounts of 3.5% (by volume); and (c) Water in
amounts of 80.5% (by volume); (ii) soaking the diffusion treated
strips in the solution for a period of about 30 minutes; followed
by (iii) further cleaning the strips involving emery paper.
16. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating according to claim 11 wherein the NiAl
aluminide coating is carried out on nickel-base alloys involving
selectively flat and/or corrugated surfaces.
17. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating according to claim 11 adapted to produce
surface protective coatings such as to improve wear resistance on
nickel-base alloys with minimum 40 weight % nickel content for high
temperature applications.
18. A process for producing body centered cubic (B2) nickel
aluminide (NiAl) coating of controlled thickness on nickel-base
alloy with minimum 40 weight % nickel content surfaces
substantially as herein described and illustrated with reference to
the accompanying FIGURES.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to aluminizing of nickel-base
alloys and, in particular, to a process for producing body centered
cubic (B2) nickel aluminide (NiAl) coating of controlled thickness
on nickel-base alloys surfaces. Importantly, the process of
producing the nickel aluminide (B2 NiAl phase) coatings on
nickel-base alloys is directed to achieve high hardness of 800-1100
VHN and dimensional tolerance of 80.+-.30 microns coating
thickness. Advantageously, the process of the invention achieves
desired nickel aluminide coatings with minimum environmental
emission of toxic chemicals fumes and is thus also environment
friendly. Moreover, the nickel aluminide coating of the present
invention is possible without the need for masking of the unwanted
regions of the components and more importantly can be attended both
on flat and curved surfaces thereby favouring wide scale utilities
of such aluminizing process. The process of the invention would
facilitate fabrication industries required to carry out surface
modifications and engineering (protective coating) on nickel-base
alloys desired for high temperatures such as nuclear industries,
aircraft and gas turbine industries.
BACKGROUND ART
[0002] It is well known that nickel-base alloys are required to be
provided surface modified and engineered for protective coatings to
adopt such nickel-base alloys for high temperature application for
variety of industrial and allied uses.
[0003] Aluminizing on nickel-base alloys is usually known to be
carried out by processes such as pack cementations, slurry
spraying, brushing, dipping and chemical vapour deposition to
produce nickel aluminide (NiAl) layer over the substrate adapted
for providing a hard surface for fretting wear and galling
resistance (1-3).
[0004] It also known to carry out thermal spray processes alone for
deposition of metals on worn out surfaces of steel components (4,
5). Also, it is well known to achieve pack diffusion and vapour
phase diffusion coatings for protection against wear and fretting
of fast reactor components (6-7). Aluminium paint-based processes
for NiAl coating have also been used previously (8). While, the
above existing state of the art prevails for the nickel aluminide
coating on nickel base alloys there has been some inherent
limitations/disadvantages of such hitherto known processes and
devices.
[0005] Pack cementations is a process which has been widely used
for such aluminizing since it is inexpensive and ideally suited for
batch production of small components. In such pack cementation
process, the components to be aluminized are usually treated at
temperatures between 850.degree. C. and 1050.degree. C. in a pack
consisting of an aluminium source such as Ni--Al, Ti--Al, or
Cr--Al, an activator (halide) and some inert filler like alumina
(1). It is however, experienced that such pack cementation
technology involves handling of large quantities of alumina and
metal powders, long furnace time cycles due to a large thermal
inertia and inherently reduced throughput.
[0006] Vapour phase aluminizing (2) on the other hand largely
eliminates the disadvantages of the pack cementation processes, but
required specialized vacuum furnaces and fixtures. Moreover, both
these processes involve exposure of operator to corrosive halide
activators which is unsafe and undesired from the safety of the
operator.
[0007] Apart from the above discussed limitations and complexities
of the conventional methods of aluminizing on nickel-base alloys,
it is also important that following such processes of aluminizing
it has been always essential to mask the surfaces which were not
required to be coated requiring special precautions and added
complexities of such aluminizing processes.
OBJECTS OF THE INVENTION
[0008] It is thus the basic object of the present invention to
provide for a process for NiAl aluminide coating of nickel-base
alloys which would avoid the afore discussed limitations and
complexities of the present processes/devices for carrying out
surface modification and engineering (protective coating) of
nickel-base alloys.
[0009] Another object of the present invention is directed to a
process for NiAl aluminide coating of nickel-base alloys which
would on one hand be cost effective and at the same time on the
other hand would involve safe technology without the
problems/disadvantages of handling of large quantity of alumina and
metal powder, long furnace time cycle due to large thermal inertia
and inherent reduced throughput.
[0010] Further object of the present invention is directed to a
simple process for NiAl aluminide coating of nickel-base alloys
which would also not require any specialized vacuum furnaces and
fixtures and thus can be readily applied and used for producing
aluminide nickel-based alloys.
[0011] A further object of the present invention is directed to an
aluminizing process which would favour achieving NiAl aluminide
coating on nickel-base alloys and which would be suitable for mass
production of large sized components to a tolerance of 80.+-.30
microns with hardness range of 800-1100 VHN with reduced cycle time
than the conventional pack cementation and vapour phase diffusion
coating.
[0012] Yet another object of the present invention is directed to
favour production of selectively body centered cubic (B2) nickel
aluminide (NiAl) coated nickel-base alloys of desired thickness
without the complexities of masking of surfaces not to be coated
thereby facilitating controlled and simple production of such
nickel aluminide coated nickel-base alloys.
[0013] A further object of the present invention is to produce
ordered body centered cubic (B2) nickel aluminide (NiAl) coated
nickel-base alloys which can be advantageously used to form the
coating only on the desired surfaces without any special steps to
masking the areas where aluminizing is not desired.
[0014] Yet another object of the present invention is directed to,
produce ordered body centered cubic (B2) nickel aluminide (NiAl)
coated nickel-base alloys with higher productivity, environmental
cleanliness and suitability for mass production of large sized
components.
[0015] Yet another object of the present invention is directed to a
process which would achieve NiAl aluminide coating on nickel-base
alloys involving flat and/or corrugated surfaces to thereby favour
production of variety of NiAl aluminide coated nickel-base
alloys.
[0016] A further object of the present invention is directed to
produce surface protective coating for high temperature application
on nickel-base alloys with selectively desired coating thickness,
micro structure and hardness which can be consistently
reproduced.
[0017] Yet further object of the present invention is to provide
for a simple yet effective process for producing surface protective
coating for high temperature application on nickel-base alloys
which would favour overall reduction of time and cost for
aluminizing vis-a-vis the conventional processes of aluminizing of
such nickel-base alloys presently in use.
SUMMARY OF THE INVENTION
[0018] Thus according to the basic aspect of the present invention
there is provided a process for producing nickel aluminide (NiAl)
coating preferably body centered cubic (B2) nickel aluminide (NiAl)
coating of controlled thickness on nickel-base alloy surfaces
comprising:
thermal spraying of the required surfaces with commercial pure
aluminium wires to desired thickness; subjecting the aluminium thus
sprayed onto the nickel-base alloy substrate to diffusion heat
treatment such that the aluminium sprayed reacts with the
nickel-base alloy substrate and form the desired aluminum coating
on the entire nickel-base alloy substrate or selective required
surface thereof to be coated and with controlled thickness.
[0019] In accordance with a preferred aspect of the present
invention there is provided a process for producing nickel
aluminide (NiAl) coating body centered cubic (B2) nickel aluminide
(NiAl) coating of controlled thickness on nickel-base alloy
surfaces comprising:
activating the surfaces to be coated by grit blasting preferably
following dimensional check and degreasing; thermal spraying of the
required surfaces with commercial pure aluminium to desired
specific thickness in the range of 100 to 200 microns; subjecting
the aluminium thus sprayed onto the nickel-base alloy substrate to
diffusion heat treatment in vacuum atmosphere such that the
aluminium sprayed reacts with the nickel-base alloy substrate and
form the desired aluminum coating on the entire nickel-base alloy
substrate or selective required surface thereof to be coated and
with controlled thickness; and subjecting the coated surface to
surface cleaning.
[0020] Importantly, in the above process for producing body
centered cubic (B2) nickel aluminide (NiAl) coating the said
surface activation by grit blasting is carried out using alumina
grit of specific size and distribution preferably in the range of
30-120 mesh size at an air pressure of 5.5+/-0.5 kg/cm.sup.2.
[0021] In accordance with another aspect of the invention, the
thermal spray parameters comprise (i) aluminum wire diameter in the
range of 3.0 to 3.2 mm at a Wire Feed Rate in the range of 2.0-2.5
mm/sec; (ii) Pneumatic pressure in the range of 5.5+/-0.5
kg/cm.sup.2; (iii) Oxygen Pressure in the range of 2.5+/-0.3
kg/cm.sup.2; and Acetylene pressure in the range of 1.0+/-0.2
kg/cm.sup.2.
[0022] The said diffusion heat treatment in said vacuum atmosphere
is carried out preferably (10.sup.-5) level at temperature in the
range of 950-1100.degree. C. for a duration of 1.0 to 1.5
hours.
[0023] Preferably, in the above process for producing body centered
cubic (B2) nickel aluminide (NiAl) coating the said surface
cleaning of the coated surface comprise removing adherent oxide
scale using pickling solution following the steps of: [0024] (i)
providing the pickling solution preferably comprising (a)
concentrated nitric acid (specific gravity: 1.41 g/cm.sup.3) in
amounts of 16% (by volume); (b) Hydrofluoric acid (specific gravity
1.61 g/cm.sup.3) in amounts of 3.5% (by volume); and (c) Water in
amounts of 80.5% (by volume); [0025] (ii) soaking the diffusion
treated strips in the solution for a period of about 30 minutes;
followed by [0026] (iii) further cleaning the strips involving
emery papers of 400 grit size.
[0027] Following the above disclosed process of the invention it is
possible to carry out the NiAl aluminide coating on nickel-base
alloys involving selectively flat and/or corrugated surfaces.
Importantly, the said NiAl aluminide coating is carried out on
nickel-base alloys with minimum 40 weight % nickel content on both
flat and corrugated surfaces.
[0028] The process is adapted to produce surface protective
coatings selectively free of any masking of the uncoated regions
for desired high temperature applications on nickel-base alloys
with minimum 40 weight % nickel content and having hardness of
800-1100 VHN and a coating thickness of 80+/-30 micron
thickness.
[0029] Importantly, in the above process the surface activity,
spraying procedures and diffusion parameters are critical in
optimization of the coating thickness and hardness. Surface
activity is achieved by selection of suitable grade grit size
(30-120 mesh size) during grit blasting. Thermal spraying of
aluminium is carried out using 3.2 mm diameter aluminium wires and
by maintaining a torch-work distance of 200-300 mm and wire feed
rate of 2.0-2.5 mm/sec. Thickness of sprayed layer is monitored on
100% of the qualification strips and on a certain percentage of
production strips at random to ensure sprayed layer thickness of
100-200 microns. The optimized diffusion treatment is carried out
at 950-1100.degree. C. for 1.0-1.5 h.
[0030] It is thus possible by way of the present invention
discussed above to produce ordered body centered cubic (B2) nickel
aluminide (NiAl) coating of controlled thickness on nickel-base
alloys involving a selective thermal spray-diffusion process.
Importantly, the process of the invention achieves selective
advantages in producing such coated nickel-base alloys by involving
the thermal spraying which is a process in which molten or
semi-molten particles are applied by impact on to the surface at
uniform rate using mechanise or manually operated spray gun.
[0031] The selective diffusion treatment after thermal spray in
vacuum atmosphere is involved whereby the aluminium melts and
reacts with the nickel/iron base alloys to thereby form the desired
B2 phase.
[0032] Importantly, the major advantage in the above process of the
invention involving the combination of thermal spraying and
diffusion treatment is that the same avoids the complexities of
masking of uncoated surfaces and yet can favour achieving the
coating only on the desired surfaces of the nickel-base alloys.
This is an important advantage in the present process of producing
the nickel aluminide coated nickel-base alloys of the invention
since the conventional coating process of such alloys such as the
conventional pack cementation process essentially required coating
the entire strip unless special steps are taken to mask the area
where aluminizing is not desired.
[0033] The process being simple to operate and apply favours for
higher productivity and is importantly environment friendly and
safe from the operators point of view since the same does not
require the operator to be exposed to corrosive environment such as
corrosive halide activators involved in the conventional pack
cementation and vapour phase aluminizing processes.
[0034] The details of the invention, its object and advantages are
explained hereunder in greater detail in relation to non-limiting
exemplary illustration of the process of the invention as per the
following accompanying FIGURE and examples:--
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
[0035] FIG. 1: is a schematic illustration of the stages involved
in the aluminizing of Ni-base alloys in accordance with the present
invention involving thermal spray and diffusion treatment.
[0036] As shown in said FIGURE the basic steps involved in such
process of aluminizing comprises of carrying out sequentially (a)
dimensional checks, (b) degreasing, (c) grit blasting, (d) thermal
spraying, (e) diffusion treatment (f) surface finish and (g)
dimensional check. Such a process of aluminizing involving the
thermal spray and diffusion treatment of the invention is
illustrated further by way of the following example.
EXAMPLE
[0037] An Exemplary process of aluminizing of nickel-base alloys
following the process of the invention involving the thermal
spraying and diffusion treatment was carried out as detailed
hereunder: [0038] i) The nickel-base alloys surface to be coated
was first activated, after dimensional check and degreasing, by
grit blasting using alumina grit of specific size and size
distribution i.e., in the range of 30-120 mesh size at a air
pressure of 5.5.+-.0.5 kg/cm.sup.2; [0039] ii) thereafter thermal
spraying of the required surfaces using commercially pure aluminium
(dia 3.2 mm) to specific thickness in the range 100 to 200 microns
was carried out using the following thermal spray parameters [0040]
thermal spray parameters: [0041] a) wire feed rate: 2.0-2.5
mm/sec.; [0042] b) pneumatic pressure: 5.5.+-.0.5 kg/cm.sup.2;
[0043] c) oxygen pressure: 2.5.+-.0.3 kg/cm.sup.2; and [0044] d)
acetylene pressure: 1.0.+-.0.2 kg/cm.sup.2. [0045] iii)
subsequently diffusion heat treatment was carried out in vacuum
atmosphere (10.sup.-5) level at specified temperature in the range
950-1100.degree. C. for a duration of 1.0-1.5 h to enable the
aluminium sprayed to react with the nickel--iron--chromium alloys
substrate and form the aluminide coating; [0046] iv) subsequently
surface cleaning procedure was carried out to remove adherent oxide
scale using a pickling solution as per the following details:
[0047] a) concentrated nitric acid (specific gravity: 1.41
g/cm.sup.3): 16% (by volume); [0048] b) hydrofluoric acid (specific
gravity 1.61 g/cm.sup.3): 3.5% (by volume); and [0049] c) water:
80.5% (by volume).
[0050] The pickling solution obtained as above was used to soak the
diffusion treated strips for 30 minutes followed by hand cleaning
of the strips such as by using 400 grit size emery papers.
[0051] By way of the above disclosed process of the invention it
was possible to produce the ordered body centered cubic (B2) nickel
aluminide (NiAl) coating of controlled thickness on nickel-base
alloys involving the simple yet effective thermal spray-diffusion
process. Advantageously, the present aluminizing process can
achieve NiAl aluminide coating on nickel-base alloys with minimum
40 wt % nickel content on both flat and corrugated surfaces.
Moreover, the processes found suitable for mass production of large
sized components to a tolerance of 80.+-.30 microns of NiAl
aluminide coating with hardness range of 800-1100 VHN with reduced
cycle time as compared to the conventional processes such as the
pack cementation and vapour phase diffusion coating. Moreover, the
process of the invention involving the selective combination of
thermal spray and diffusion heat treatment would favour coating on
selected areas of the components both on flat and curved surfaces
without the need for masking and its related complexities. Thus,
the process offers overall reduction of time and cost of
aluminizing which is found to be four time faster than the
conventional processes of aluminizing nickel-base alloys.
[0052] The present process would thus enable producing surface
protective coatings for high temperature applications on
nickel-base alloys with desired coating thickness, microstructure
and hardness which importantly can be consistently reproduced.
Moreover, the process would favour the desired surface areas alone
to be aluminized without the need for complex masking of uncoated
areas. The process offers overall reduction of time and cost for
aluminizing. The duration of aluminizing for other conventional
processes is four times higher than the present invention and the
process would therefore favour much simpler and faster generation
of NiAl coated Ni-base alloys both on flat and/or corrugated
surfaces apart from being environment friendly and safe to carry
out.
* * * * *