Title of Invention	"A METHOD OF HARD SURFACING OF SUPERALLOYS"
Abstract	A method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components comprising the steps of; a) the super alloy samples are cleaned, shot blasted to ensure better absorption of laserbeam; b) the cleaned super alloy sample surface is exposed to laser source with a variable power'source and a powder feeder attached to the laser head at a predetermined angle using a special fixture; c) a defocused laser beam of sufficient energy density is used to melt a small layer of the base metal and the powder to be clad is fed into the laser beam simultaneously; d) the powder melts and mixes with the thin liquid layer of the base metal and freezes to form a clad layer with a very good metallurgical bond; e) the sample is moved under the laser beam to form a continuous clad layer of sufficient thickness without any porosity and defects; f) the clad thickness and width is increased by multiple over lapping passes.

Title of Invention

"A METHOD OF HARD SURFACING OF SUPERALLOYS"

Abstract

A method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components comprising the steps of; a) the super alloy samples are cleaned, shot blasted to ensure better absorption of laserbeam; b) the cleaned super alloy sample surface is exposed to laser source with a variable power'source and a powder feeder attached to the laser head at a predetermined angle using a special fixture; c) a defocused laser beam of sufficient energy density is used to melt a small layer of the base metal and the powder to be clad is fed into the laser beam simultaneously; d) the powder melts and mixes with the thin liquid layer of the base metal and freezes to form a clad layer with a very good metallurgical bond; e) the sample is moved under the laser beam to form a continuous clad layer of sufficient thickness without any porosity and defects; f) the clad thickness and width is increased by multiple over lapping passes.

Full Text	The invention relates to a method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components to combat severe high temperature fretting wear conditions. Conventionally hard surfacing of super alloys are being carried out using Tungsten Inert gas (TIG) welding process. There are disadvantages associated with the present system of hard surfacing of super alloys using Tungsten Inert gas welding process. The main disadvantage associated with the present system of hard surfacing of super alloys are that there are distortion in dimension due to high heat input. Another disadvantages associated with the present system of hard surfacing of super alloys is that there is excessive dilution of base metal with clad layers leading to poor wear resi stance. Yet another disadvantages associated with the present invention of hard surfacing of super alloys is that the heat affected zone cracking leads to high rejection rate of processed components. With the availability of Lasers capable of high power density, flexible operation and easy adaptability to working environment, the application range to laser seems to be unlimited. However in reality the laser assisted processing is predominantly used in low level applications such as sheet metal cutting, marking, micro drilling etc} Therefore the main objective of the present invention is to provide a simple and low cost means of hard surfacing of super #llPy» to combat »ev«re high temperature fretting wear conditions as experienced by gas turbine components. Yet another objective of the present invention is to utilize the precisely controllable high power CO2 laser source in hard surfacing of super alloys. Yet another objective of the present invention is to develop clad hard surface using cobalt based alloy with very fine grain micro structure and high hardness essential for high wear resistance at operating elevated temperatures. j Yet another objective of the present invention is to develop clad hard surfacing of super alloys with minimum distortion and reduced clad thickness to avoid excessive po*t machining operation still another objective of the present invention is to develop clad hard surfacing of super alloys with negligible dilution of base metal leading to better wear resistance properties. Further objective of the present invention is to develop hard surfacing of super alloys with negligible heat affected zone cracking of the base metal to avoid rejection of components. Yet further objective of the present invention is to develop hard surfacing of super alloys with minimum clad thickness to avoid wastage of costly cobalt based alloys. According to the present invention there is provided a method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components comprising the steps of\| a) the super alloy samples are cleaned, shot blasted to ensure better absorption of laserbeam; b) the cleaned super alloy sample surface is exposed to laser source with a variable power source and a powder feeder attached to the laser head at a predetermined angle using a special fixture; c) a defocused laser beam of sufficient energy density is used to melt a small layer of the base metal and the powder to be clad is fed into the laser beam simultaneously; d) the powder melts and mixes with the thin liquid layer of the base metal and freezes to form,a clad layer with a very good metallurgical bond; e) the sample is moved under the laser beam to form a continuous clad layer of sufficient thickness without any porosity and defects; f) the clad thickness and width is increased by multiple over lapping passes. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non limiting exemplary embodiments of the invention. Figure 1, photographs showing (a) single track clad layer and (b) multiple track Figure 2, shows graph 1. Variation of hardness from base into clad layer Figure 3 shows graph 2, EDX line scan analysis for the elements Cv, Co and Ni Figure 4 shows graph 3, Distance from interface (O)f mm The Hard surfacing of super alloys is illustrated by the results of a typical experiment as illustrated below. According to the present invention the hard surfacing of super allloys assisted by lack is simple and a low cut option which when clad with external powder feed produces surface with uniform high hardness and with uniform very fine micrestructure. In this process of hard surfacing the dilution of base material with that of clad is negligible and there is total absence of he'at affected zone and its consequent cracking. The process thereby results in negligible distortion and reduced rejection rate. The process also produces a hard surface results in near net shape dimension requiring minimal post machining operation. The process can also be automated with flexible and precise control of parameters which facilitates consistent quality and control over undesirable interactions. DETAILED DESCRIPTION OF THE PROCESS The super alloy samples are cleaned, shot blasted to ensure better absorption of the laser beam. A standard 5 kW laser source is used whose power can be varied. A special powder delivery system ensures uniform supply of hard surfacing powder into the laser beam at a predetermined angle. The powder feeder is attached to the laser head using a special fixture. The cleaned super alloy sample surface is exposed to laser source. A defocused laser beam of sufficient energy density is used to melt a small layer of the base metal and the powder to be clad is fed into the laser beam simultaneously. The powder melts and mixes with the thin liquid layer of base metal and freezes to form a clad layer with a very good metallurgical bod. The sample is moved under the laser beam to form a continuous clad layer of sufficient thickness without any porosity and defects. The clad thickness and width is increased by multiple over lapping passes. The following tables gives details of parameters used and the properties of the clad surface thus obtained. Table I : Details of Base metal, Alloy powder used for cladding and the Laser parameters. In the accompanying drawings Fig. 1 shows Photograph showing cross section of single track and multiple track clad layers Fig. 2 shows the Graph I: Variation of hardness from the base into the clad surface Table II: Composition of the clad surface with that of clad powder Figure 3 shows the Graph II: EDAX analysis indicating negligible dilution of base metal in the clad layer Figure 4 shows the Graph III: Comparison of multiple clad layer hardness values; Present invention Vs TIG welding Results: For our trials we used commercially available hard surfacing powder with characteristics as shown in Table I. The optimum laser parameters for successful cladding were obtained at 2 kW laser power as given in Table I belows Table I: Details of Base metal. Alloy powder used for cladding and Laser parameters. Base metal Ni base super alloy, Udimet 5QO Clad alloy1 Cobalt based alloy, stelite 694 Particle size:5O-12O u m Optimum laser parameters Laser power & Dia.:2kW,5mm Powder feed rate: 16 gms/min. Traverse speed of base metal: 10O mm/min. The photographs of both single pAss and multiple pass claddings show similar features (Figure 1). No porosity, no heat affected zone cracking and no other defects were observed. The low dilution of base metal into the clad layer as shown in Graph 1 wherein the nickel concentration in the clad layer is very low indicates the high purity of the clad layer deposited and the precise control of process parameters. Detailed chemical composition of the clad layer at different locations was carried out using EDAX facility and the results are given in table 2 below: Table 2.Composition of clad surface at different locations Major element Ch rom i um Powder (wt X ) Clad (wt X ) 26 - 3O 26.77 27.19 27.85 26.96 Tungsten IB - 21 18. O 18.14 2O. 14 18.32 Nickel 4-6 6.78 6.O8 6.43 6.41 Cobalt Min.38 4O.71 39.41 39. O7 4O.O From the results it can be seen that the clad layer at different locationS has the same composition to that of the stellite powder. Defect free, homogenous cladding of 1.2 mm maximum height and 3.5 mm maximum width could be obtained at 2 kW power level for single track samples, The micro hardness was uniform throughout the entire cross section and in the range of 69O —715 HV (Graph H) as against the base metal hardness of 45O IIV. In the case of multi clad samples, a maximum defect free clad thickness of 3 mm height and 2O mm width could easily be established. This validates that the hard surfacing can be obtained even for larger thickness even though for many applications thickness of the order of 1—1.5 mm is sufficient. The microhardness results were also satisfactory and a maximum value of 8OO HV could be achieved as against the base metal hardness of 45O HV. It is evident from the graph III that higher hardness could be achieved even with lower thickness as compared to TIG welded claddings. This becomes a direct evidence for the economics of the present invention. This hard surfacing can easily be automated to get reliable and consistent results on large components. The laser source makes it easy to adapt this process to different working envi ronments. The invention described hereinabove is in relation to a non-limiting embodiments and as defined by the accompanying c1aims. WE CLAIM: 1. A method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components comprising the steps of; a) the super alloy samples are cleaned, shot blasted to ensure better absorption of laserbeam; b) the cleaned super alloy sample surface is exposed to laser source with a variable power source and » a powder feeder attached to the laser head at a predetermined angle using a special fixture; c) a defoeused laser beam of sufficient energy density is used to melt a small layer of the base metal and the powder to be clad is fed into the laser beam simultaneously) d) the powder melts and mixes with the thin liquid layer of the base metal and freezes to form a clad layer with a very good metallurgical bond. e) the sample is moved under the laser beam to form a continuous clad layer of sufficient thickness without any porosity and defects; f) the clad thickness and width is increased by multiple over lapping passes. 2. A method of hard surfacing of super alloys using laser wherein a standard 5 KW CO2 laser having variable power is used with optimum laser parameter of power and dia of 2 KW and 5mm respectively. 3. A method of hard cur facing of super alloys where in the base metal is Nibase super alloy, Udimet 5OO and the clad alloy is cobalt base alloy, stilite 694 having a particle size of 50-120 urn. 4. A method of hard surfacing of super alloys wherein the powder in WtX comprises chromoum 26—3O, Tungsten 18—21, Nickel 4—6, cobalt minimum 38. 5. A method of hard surfacing of super alloys wherein the clad meterial in Wt.X comprises chromium 26, Tungsten 18, Nickel 7, Cobalt 41. 6. A method of hard surfacing 'of super alloys wherein a clad thickness of 3 mm and a maximum hardness value of BOO HV is achieved against the base metal hardness of 49O HV. 7. A method of hard surfacing of super alloys using lasvr for applications in high temperature wear resistance coatings particularly on gas turbine components as herein described and illustrated in the accompanying drawings.

Full Text

The invention relates to a method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components to combat severe high temperature fretting wear conditions. Conventionally hard surfacing of super alloys are being carried out using Tungsten Inert gas (TIG) welding process.
There are disadvantages associated with the present system of hard surfacing of super alloys using Tungsten Inert gas welding process.
The main disadvantage associated with the present system of hard surfacing of super alloys are that there are distortion in dimension due to high heat input.
Another disadvantages associated with the present system of hard surfacing of super alloys is that there is excessive dilution of base metal with clad layers leading to poor wear resi stance.
Yet another disadvantages associated with the present invention of hard surfacing of super alloys is that the heat affected zone cracking leads to high rejection rate of processed components.
With the availability of Lasers capable of high power density, flexible operation and easy adaptability to working environment, the application range to laser seems to be unlimited. However in reality the laser assisted processing is predominantly used in low level applications such as sheet metal cutting, marking, micro drilling etc}
Therefore the main objective of the present invention is to
provide a simple and low cost means of hard surfacing of super #llPy» to combat »ev«re high temperature fretting wear conditions as experienced by gas turbine components.
Yet another objective of the present invention is to utilize the precisely controllable high power CO2 laser source in hard surfacing of super alloys.
Yet another objective of the present invention is to develop clad hard surface using cobalt based alloy with very fine grain micro structure and high hardness essential for high wear resistance at operating elevated temperatures.
j
Yet another objective of the present invention is to develop clad hard surfacing of super alloys with minimum distortion and reduced clad thickness to avoid excessive po*t machining operation still another objective of the present invention is to develop clad hard surfacing of super alloys with negligible dilution of base metal leading to better wear resistance properties.
Further objective of the present invention is to develop hard surfacing of super alloys with negligible heat affected zone cracking of the base metal to avoid rejection of components.
Yet further objective of the present invention is to develop hard surfacing of super alloys with minimum clad thickness to avoid wastage of costly cobalt based alloys.
According to the present invention there is provided a method of hard surfacing of super alloys using laser for applications in high temperature wear resistance coatings particularly on gas turbine components comprising the steps of|
a) the super alloy samples are cleaned, shot blasted to
ensure better absorption of laserbeam;
b) the cleaned super alloy sample surface is exposed to
laser source with a variable power source and
a powder feeder attached to the laser head at a predetermined angle using a special fixture;
c) a defocused laser beam of sufficient energy density is used
to melt a small layer of the base metal and the powder to be
clad is fed into the laser beam simultaneously;
d) the powder melts and mixes with the thin liquid layer of the
base metal and freezes to form,a clad layer with a very good
metallurgical bond;
e) the sample is moved under the laser beam to form a
continuous clad layer of sufficient thickness without any
porosity and defects;
f) the clad thickness and width is increased by multiple over
lapping passes.
The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non limiting exemplary embodiments of the invention.
Figure 1, photographs showing (a) single track clad layer and (b) multiple track
Figure 2, shows graph 1. Variation of hardness from base into clad layer
Figure 3 shows graph 2, EDX line scan analysis for the elements Cv, Co and Ni
Figure 4 shows graph 3, Distance from interface (O)f mm
The Hard surfacing of super alloys is illustrated by the results of a typical experiment as illustrated below.
According to the present invention the hard surfacing of super allloys assisted by lack is simple and a low cut option which when clad with external powder feed produces surface with uniform high hardness and with uniform very fine micrestructure. In this process of hard surfacing the dilution of base material with that of clad is negligible and there is total absence of he'at affected zone and its consequent cracking. The process thereby results in negligible distortion and reduced rejection rate. The process also produces a hard surface results in near net shape dimension requiring minimal post machining operation.
The process can also be automated with flexible and precise control of parameters which facilitates consistent quality and control over undesirable interactions.
DETAILED DESCRIPTION OF THE PROCESS
The super alloy samples are cleaned, shot blasted to ensure better absorption of the laser beam. A standard 5 kW laser source is used whose power can be varied. A special powder delivery system ensures uniform supply of hard surfacing powder into the laser beam at a predetermined angle. The powder feeder is attached to the laser head using a special fixture. The cleaned super alloy sample surface is exposed to laser source. A defocused laser beam of sufficient energy density
is used to melt a small layer of the base metal and the powder
to be clad is fed into the laser beam simultaneously. The
powder melts and mixes with the thin liquid layer of base metal
and freezes to form a clad layer with a very good
metallurgical bod. The sample is moved under the laser beam to
form a continuous clad layer of sufficient thickness without
any porosity and defects. The clad thickness and width is
increased by multiple over lapping passes.
The following tables gives details of parameters used and the
properties of the clad surface thus obtained.
Table I : Details of Base metal, Alloy powder used for cladding
and the Laser parameters.
In the accompanying drawings Fig. 1 shows Photograph showing
cross section of single track and multiple track clad layers
Fig. 2 shows the Graph I: Variation of hardness from the base into the clad surface
Table II: Composition of the clad surface with that of clad powder
Figure 3 shows the Graph II: EDAX analysis indicating negligible dilution of base metal in the clad layer
Figure 4 shows the Graph III: Comparison of multiple clad layer hardness values; Present invention Vs TIG welding
Results:
For our trials we used commercially available hard surfacing powder with characteristics as shown in Table I. The optimum laser parameters for successful cladding were obtained at 2 kW laser power as given in Table I belows
Table I: Details of Base metal. Alloy powder used for cladding and Laser parameters.
Base metal Ni base super alloy, Udimet 5QO
Clad alloy1 Cobalt based alloy, stelite 694
Particle size:5O-12O u m
Optimum laser parameters Laser power & Dia.:2kW,5mm
Powder feed rate: 16 gms/min. Traverse speed of base metal: 10O
mm/min.
The photographs of both single pAss and multiple pass claddings show similar features
(Figure 1). No porosity, no heat affected zone cracking and no other defects were observed. The low dilution of base metal into the clad layer as shown in Graph 1 wherein the nickel concentration in the clad layer is very low indicates the high purity of the clad layer deposited and the precise control of process parameters. Detailed chemical composition of the clad layer at different locations was carried out using EDAX facility and the results are given in table 2 below:
Table 2.Composition of clad surface at different locations

Major element Ch rom i um Powder (wt X ) Clad (wt X ) 26 - 3O 26.77 27.19 27.85 26.96
Tungsten IB - 21 18. O 18.14 2O. 14 18.32
Nickel 4-6 6.78 6.O8 6.43 6.41
Cobalt Min.38 4O.71 39.41 39. O7 4O.O
From the results it can be seen that the clad layer at different locationS has the same composition to that of the
stellite powder.
Defect free, homogenous cladding of 1.2 mm maximum height and 3.5 mm maximum width could be obtained at 2 kW power level for single track samples, The micro hardness was uniform throughout the entire cross section and in the range of 69O —715 HV (Graph H) as against the base metal hardness of 45O IIV.
In the case of multi clad samples, a maximum defect free clad thickness of 3 mm height and 2O mm width could easily be established. This validates that the hard surfacing can be obtained even for larger thickness even though for many applications thickness of the order of 1—1.5 mm is sufficient. The microhardness results were also satisfactory and a maximum value of 8OO HV could be achieved as against the base metal hardness of 45O HV. It is evident from the graph III that higher hardness could be achieved even with lower thickness as compared to TIG welded claddings. This becomes a direct evidence for the economics of the present invention.
This hard surfacing can easily be automated to get reliable and consistent results on large components. The laser source makes it easy to adapt this process to different working envi ronments.
The invention described hereinabove is in relation to a non-limiting embodiments and as defined by the accompanying c1aims.

WE CLAIM:
1. A method of hard surfacing of super alloys using laser for
applications in high temperature wear resistance coatings
particularly on gas turbine components comprising the steps of;
a) the super alloy samples are cleaned, shot blasted to
ensure better absorption of laserbeam;
b) the cleaned super alloy sample surface is exposed to
laser source with a variable power source and
» a powder feeder attached to the laser head at a
predetermined angle using a special fixture;
c) a defoeused laser beam of sufficient energy density is used
to melt a small layer of the base metal and the powder to be
clad is fed into the laser beam simultaneously)
d) the powder melts and mixes with the thin liquid layer of the
base metal and freezes to form a clad layer with a very good
metallurgical bond.
e) the sample is moved under the laser beam to form a
continuous clad layer of sufficient thickness without any
porosity and defects;
f) the clad thickness and width is increased by multiple over
lapping passes.
2. A method of hard surfacing of super alloys using laser
wherein a standard 5 KW CO2 laser having variable power is
used with optimum laser parameter of power and dia of 2 KW and
5mm respectively.
3. A method of hard cur facing of super alloys where in the base
metal is Nibase super alloy, Udimet 5OO and the clad alloy is cobalt base alloy, stilite 694 having a particle size of 50-120 urn.
4. A method of hard surfacing of super alloys wherein the
powder in WtX comprises chromoum 26—3O, Tungsten 18—21,
Nickel 4—6, cobalt minimum 38.
5. A method of hard surfacing of super alloys wherein the
clad meterial in Wt.X comprises chromium 26, Tungsten 18,
Nickel 7, Cobalt 41.
6. A method of hard surfacing 'of super alloys wherein a
clad thickness of 3 mm and a maximum hardness value of BOO HV is
achieved against the base metal hardness of 49O HV.
7. A method of hard surfacing of super alloys using lasvr
for applications in high temperature wear resistance coatings
particularly on gas turbine components as herein described and
illustrated in the accompanying drawings.

Documents:

2997-del-1998-abstract.pdf

2997-del-1998-claims.pdf

2997-del-1998-correspondence-others.pdf

2997-del-1998-correspondence-po.pdf

2997-del-1998-description (complete).pdf

2997-del-1998-drawings.pdf

2997-del-1998-form-1.pdf

2997-del-1998-form-13.pdf

2997-del-1998-form-19.pdf

2997-del-1998-form-2.pdf

2997-del-1998-form-4.pdf

2997-del-1998-form-5.pdf

2997-del-1998-gpa.pdf

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Patent Number

224566

Indian Patent Application Number

2997/DEL/1998

PG Journal Number

44/2008

Publication Date

31-Oct-2008

Grant Date

17-Oct-2008

Date of Filing

12-Oct-1998

Name of Patentee

BHARAT HEAVY ELECTRICALS LTD.,

Applicant Address

BHEL HOUSE, SIRI FORT, NEW DELHI-110 049, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	KRISHNA RAO VENUGOPAL	BHARAT HEAVY ELECTRICALS LTD., CORPORATE RESEARCH & DEVELOPMENT, VIKASNAGAR, HYDERABAD-500593, INDIA.

PCT International Classification Number

B32B 3/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA