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Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters
Available online at www.sciencedirect.com
ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2013, 20(2). 52-57
Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters LUO Fang 1 ' 2 ,
Lupoi Rocco 3 , Cockburn Andrew 4 , O'neill William 4 , YAO Jian-hua 2
Sparkes Martin 4 ,
( 1 . College of Zhijiang, Zhejiang University of Technology, Hangzhou 310024, Zhejiang, China;
2. College of
Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, China;
3. Department
of Mechanical and Manufacturing Engineering, Trinity College Dublin, Dublin 2 , Ireland;
4. Institute for
Manufacturing, Department of Engineering, University of Cambridge, Cambridge CB3 O F S , U K ) Abstract: Stellite 6 powders were deposited on low carbon steel using SLD (supersonic laser deposition) under opti mized parameters. T h e structure, line scan of elements and porosity of coating were examined and analyzed using SEM (scanning electron microscope) , OM (optical microscope) and XRD (X-ray diffraction). T h e adhesion strength between coating and substrate was tested by P A T - A D H E S I O N / T E N S I L E and E900STM adhesive. The results showed the deposition characteristics of optimized coating with N2 at a pressure of 3. 0 M P a , a temperature of 450 *C and a laser power of 1. 5 kW were compared with those of Stellite 6 coating deposited by the H V O F (high velocity oxygen fuel). Keywords; Stellite 6; supersonic laser deposition; deposition characteristic ; H V O F
The performance of Stellite 6 (registered trademark of Kennametal Stellite) coating deposited using a vari ety of processes has been investigated by many re searchers in recent years due to excellent wear re sistance and corrosion protection over a wide range of temperatures. Conventional Stellite 6 coatings are often prepared by several processes, such as HVOF (high velocity oxygen fuel), plasma spray process and laser cladding. Stellite 6 coating deposited by HVOF processes is widely used in many industries to protect the components against erosion, corrosion r[l-9] However the coatings deposited by and HVOF have been found containing oxides and porosities'-10-11-'. The residual porosity in plasma spray Stel lite 6 coatings requires post-deposition treatments to im prove their properties1-12-163. Meanwhile, Stellite 6 clad ding shows defects, such as porosities, cracks, unac ceptable distortions on the piece, component dilution and oxide film on the surface layer1-17-20-1. The poros ity and dilution of Stellite 6 coating [21-24] have been
studied by many researchers. In the cold spray, there is no bulk particle melting and the feedstock properties can be retained [25-27] . However, the material is deposited using a high pressure, high velocity gas (helium) jet for the de formation and bonding of particles, therefore the cost is very high, and it is difficult to deposit brittle or hard materials ( e . g . ceramics) unless they are deposited and mixed with a ductile matrix'-28-'. In order to exploit the advantages of cold spray but at a reduced cost, to improve the property of coatings, and allow the deposition of harder materi als, the University of Cambridge129-30-1 has success fully combined a laser source with cold spray to pre pare higher density coating of Ti and Ti alloy. The technology is named SLD (supersonic laser deposi tion) and uses N2 as carrier gas. In particular, the function of the laser (IPG Fibre Laser, with a maxi mum power of 4 kW) is to provide additional energy to the deposition site. This allows harder materials
Foundation Item: Item Sponsored by National Natural Science Foundation of China (51271170) ; National International Technology Cooperation Project of China (KM JD2011010) ; Natural Science Foundation of Zhejiang Province of China (Y4110594) ; Open Fund of Zhejiang Provincial Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology of China (2011EM009) Biography:LUO Fang( 1966—), Female, Doctor, Associate Professor; E-mail: [email protected]; Received Date: September 15, 2011
Issue 2
Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters
Table 1 Element contents of Stellite 6 powder (mass percent, %)
to be laid down while maintaining the key advanta ges offered by t h e solid state deposition r o u t e found in cold spray. Stellite 6 deposited onto low carbon steels by SLD is analysed under optimised p a r a m e t e r s . Depo sition characteristics of SLD-Stellite 6 are compared against those of Stellite 6 sprayed by H V O F method.
1
· 53 ·
Ni
Co
W
Cr
Balance
4.75
28.5
1.2
Mo
Fe
Si
Others
<2.0 <1.0 <2. 0 <2. 0
<1. 0
Experimental Procedure
Fig. 1 s h o w s t h a t the particles are uniform and spherical, with diameter of 35 — 50 μτη. Nominal com position of Stellite 6 powder is shown in T a b l e 1. Six overlapping tracks by S L D were deposited on a low carbon steel s u b s t r a t e in order to form a coating (Fig. 2 ) . T h e process parameters are shown in Table 2.
Fig. 2 Sample of SLD Table 2
Process parameter of SLD
N2
N2
Laser
Feeding velocity/
temperature/"C
pressure/MPa
power/kW
(mm-s-1)
500
3.0
1.5
10
2
Experimental Results and Discussion
2.1
1 10 Particle size/μιη
1000
Fig. 1 Stellite 6 particles and particle size distribution
(a) Deposition topography of SLDi
Fig. 3
Analysis of surface topography and cross section T h e surface t o p o g r a p h y of Stellite 6 is presen ted in Fig. 3. Fig. 3 ( a ) s h o w s coating topography of Stellite 6 deposited by S L D ; it shows craters with fluctuation and no melting topography; Fig. 3 (b) shows melting topography of Stellite 6 deposited by H V O F . Fig. 4 s h o w s t h a t the s t r u c t u r e of the s u b s t r a t e is ferrite ( F ) and pearlite ( P ) . As for SLD, during the hard particles impact on the relatively hot substrate, the plastic deformation of the substrate results in recrystallisation of the interface area close to the substrate, thereby improving t h e interface s u b s t r a t e s hardness.
( b ) Deposition topography of H V O F .
Surface topography of Stellite 6
• 54 ·
Journal of Iron and Steel Research, International
Fig. 4
Vol. 20
Structure of substrate and interface zone
T h e cross section in Fig. 5 ( a ) , etched by aqua regia, s h o w s many blisters on the s u b s t r a t e due to corrosion. T h i s is because t h a t F e of s u b s t r a t e r e acts with hydrochloric acid and nitric acid, and gen erates gas ( s u c h as H 2 and N z ) . T h e coating of Fig. 5 ( a ) is magnified, and the s t r u c t u r e after polis hing and etching is shown in Fig. 5 ( b ) . The deforma tion appears to be greater on the top surface of each particle, indicating t h a t cold, hard particles are e m bedding themselves into a h e a t e d , softened s u b s t r a t e during deposition, and the dendrites appear close re
ticulation distribution. T h e spherical particles appear ra diant dendrites from core of particle to boundary [ a s s h o w n in a r r o w of Fig. 5 ( b ) and Fig. 6 ( a ) ] . T h e black cross m a r k ( p o i n t of m e a s u r e m e n t ) is magnified and s h o w n in Fig. 5 ( c ) . It can be found that t h e boundary of reticulation is composed of many white grains along the boundary. T a b l e 3 shows chemical composition at m a r k s ( black cross m a r k and white triangle m a r k ) . T h e results show content of carbon is high com paring with contents of Stellite 6 powder, possibly form
imi μιη
(a) Etched cross section;
( b) Structure of coating ; ( c) Magnification of cross mark ( SLD) i Fig. 5 Analysis of cross section
(d) Distances of line scan.
Issue 2
Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters
· 55 ·
(a) Optical micrograph of Stellite 6 coating (SLD) ; (b) SEM micrograph of Stellite 6 coating deposited by SLD; (c) Porosity of Stellite 6 coating deposited by SLD; (d) Porosity of Stellite 6 deposited by HVOF. Fig. 6 Optical micrograph and porosity of Stellite 6 coating Table 3
Element content of mark
Black cross mark White triangle mark
C
Cr
Co
W
5.41 7.23
31.23 33.53
60.96 58.53
2.40 0.71
ing carbide resulting in high content of carbon. Fig. 5 (d) and Fig. 7 shows that the distances of line scan from substrate to coating in cross-section of SLD, and the length of test is 560 μπι. It appears that the elements of coating have hardly diluted, and initial composition is still retained ^
75
Coating
Substratey
65 »
'55
i
— '
\
■ C ♦ Co • Si « W ACr »Mn T Fe · Ni
45 35
\ 1
^25
S
g 15
-r-î-T-J
£= ^
■
1
200 400 Distance from surface/μιη
600
Fig. 7 Change of element from coating to substrate
comparing with composition of powder. This proves SLD results in no bulk particle melting. 2. 2
Porosity and adhesion strength This structure and porosity of coating were measured optically and reported in Fig. 6. The sur face of coating shows sphere particles with radiant dendrite distribution clearly. Fig. 6 ( a ) shows the typical hypo-eutectic structure consisting of complex wear resistant carbides dispersed in Co matrix. Po rosity is an important parameter for evaluation of coating quality, and measured to be of 0. 2% for SLD [Fig. 6 ( c ) ] , which is considerably lower than porosity of 2% - 3 % for HVOF [31] [Fig. 6 ( d ) ] counterpart. The phase structure of the coating by SLD was analyzed and it is shown in Fig. 8. One of the key characteristics of any coating material is its bonding ability or adhesion to other materials. Without sufficient· adhesion, a coating will fail. Therefore, adhesion strength objectively and accurately during research and quality control are vital. The adhesion strength between coating and sub strate is tested by PAT-ADHESION/TENSILE, using E900STM adhesive. Test diameter is 6 mm (Fig. 9). The
J o u r n a l of I r o n a n d S t e e l R e s e a r c h ,
• 56 ·
2 500
results in T a b l e 4 show t h a t t h e average adhesion s t r e n g t h is 6 1 . 8 M P a . T h e d a t u m of t h e third cir cle m a r k is ignored due to t h e a p p r o a c h edge of specimen.
Cr7C,T Co
2 000h .1500
I
CrrCs
Co
I looo &
W2C 500 0
>■-
20
30
CrrC, Co
CrjCa Co
\ K ., . , , A..-, .JUÂ, 50
Vol. 20
International
20/(°)
70
90
110
Fig. 8 XRD of Stellite 6 deposited by SLD
Adhesion s t r e n g t h of Stellite 6 coating deposi ted by H V O F has not been reported by any paper. Adhesion s t r e n g t h of other alloy deposited on the steel by H V O F is s h o w n in Fig. 10. It can be seen t h a t adhesion s t r e n g t h of coating deposited by H V O F is 7 5 - 9 8 M P a [ F i g . 10 ( a ) [ 3 2 ] and ( b ) [ 3 3 ] ] because t h e t e m p e r a t u r e of H V O F is enough to melt metal which results in metallurgy b o n d , however with this m e t h o d phase transformations are likely to o c c u r , i. e. poor coating properties and higher level of porosity. Table 4
Fig. 9 Sample of pull-off adhesion testing
Element content of mark
No.
1
2
Adhesion s t r e n g t h / M P a
62.4
3 61.2
4.8
(W Substrate/NiCr Subsrrate/Ni/NiCr Substrate/WC-Co Substrate/Ni/WC-Co Substrate/NiCr/WC-Co
·- ->
Subsöate/Ni/NiCr/WC-Co
2
3 4 Sample number
(a) 8 0 % C r 3 C z / 2 0 % N i - C r coatings;
2 000
4000 6000 Average/psi
8000
10000
( b ) Tensile bond strength of coatings.
Fig. 10 Adhesion strength by HVOF
3
sistance of H V O F WC-Co and TiC/Ni-Ti Coatings Sprayed on
Conclusions
1) T h e s t r u c t u r e of deposition coating is typical hypo-eutectic s t r u c t u r e consisting of complex wear resistant carbides dispersed in b a s e , and dilution of elements hardly exists. 2) T h e porosity of coating deposited by S L D is 0 . 2 % , and it is lower than coating porosity of 2 % — 3 % deposited by H V O F . 3) Adhesion s t r e n g t h b e t w e e n coating deposi ted by SLD and s u b s t r a t e is 6 1 . 8 M P a .
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[15]
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ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2013, 20(2). 52-57
Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters LUO Fang 1 ' 2 ,
Lupoi Rocco 3 , Cockburn Andrew 4 , O'neill William 4 , YAO Jian-hua 2
Sparkes Martin 4 ,
( 1 . College of Zhijiang, Zhejiang University of Technology, Hangzhou 310024, Zhejiang, China;
2. College of
Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, China;
3. Department
of Mechanical and Manufacturing Engineering, Trinity College Dublin, Dublin 2 , Ireland;
4. Institute for
Manufacturing, Department of Engineering, University of Cambridge, Cambridge CB3 O F S , U K ) Abstract: Stellite 6 powders were deposited on low carbon steel using SLD (supersonic laser deposition) under opti mized parameters. T h e structure, line scan of elements and porosity of coating were examined and analyzed using SEM (scanning electron microscope) , OM (optical microscope) and XRD (X-ray diffraction). T h e adhesion strength between coating and substrate was tested by P A T - A D H E S I O N / T E N S I L E and E900STM adhesive. The results showed the deposition characteristics of optimized coating with N2 at a pressure of 3. 0 M P a , a temperature of 450 *C and a laser power of 1. 5 kW were compared with those of Stellite 6 coating deposited by the H V O F (high velocity oxygen fuel). Keywords; Stellite 6; supersonic laser deposition; deposition characteristic ; H V O F
The performance of Stellite 6 (registered trademark of Kennametal Stellite) coating deposited using a vari ety of processes has been investigated by many re searchers in recent years due to excellent wear re sistance and corrosion protection over a wide range of temperatures. Conventional Stellite 6 coatings are often prepared by several processes, such as HVOF (high velocity oxygen fuel), plasma spray process and laser cladding. Stellite 6 coating deposited by HVOF processes is widely used in many industries to protect the components against erosion, corrosion r[l-9] However the coatings deposited by and HVOF have been found containing oxides and porosities'-10-11-'. The residual porosity in plasma spray Stel lite 6 coatings requires post-deposition treatments to im prove their properties1-12-163. Meanwhile, Stellite 6 clad ding shows defects, such as porosities, cracks, unac ceptable distortions on the piece, component dilution and oxide film on the surface layer1-17-20-1. The poros ity and dilution of Stellite 6 coating [21-24] have been
studied by many researchers. In the cold spray, there is no bulk particle melting and the feedstock properties can be retained [25-27] . However, the material is deposited using a high pressure, high velocity gas (helium) jet for the de formation and bonding of particles, therefore the cost is very high, and it is difficult to deposit brittle or hard materials ( e . g . ceramics) unless they are deposited and mixed with a ductile matrix'-28-'. In order to exploit the advantages of cold spray but at a reduced cost, to improve the property of coatings, and allow the deposition of harder materi als, the University of Cambridge129-30-1 has success fully combined a laser source with cold spray to pre pare higher density coating of Ti and Ti alloy. The technology is named SLD (supersonic laser deposi tion) and uses N2 as carrier gas. In particular, the function of the laser (IPG Fibre Laser, with a maxi mum power of 4 kW) is to provide additional energy to the deposition site. This allows harder materials
Foundation Item: Item Sponsored by National Natural Science Foundation of China (51271170) ; National International Technology Cooperation Project of China (KM JD2011010) ; Natural Science Foundation of Zhejiang Province of China (Y4110594) ; Open Fund of Zhejiang Provincial Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology of China (2011EM009) Biography:LUO Fang( 1966—), Female, Doctor, Associate Professor; E-mail: [email protected]; Received Date: September 15, 2011
Issue 2
Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters
Table 1 Element contents of Stellite 6 powder (mass percent, %)
to be laid down while maintaining the key advanta ges offered by t h e solid state deposition r o u t e found in cold spray. Stellite 6 deposited onto low carbon steels by SLD is analysed under optimised p a r a m e t e r s . Depo sition characteristics of SLD-Stellite 6 are compared against those of Stellite 6 sprayed by H V O F method.
1
· 53 ·
Ni
Co
W
Cr
Balance
4.75
28.5
1.2
Mo
Fe
Si
Others
<2.0 <1.0 <2. 0 <2. 0
<1. 0
Experimental Procedure
Fig. 1 s h o w s t h a t the particles are uniform and spherical, with diameter of 35 — 50 μτη. Nominal com position of Stellite 6 powder is shown in T a b l e 1. Six overlapping tracks by S L D were deposited on a low carbon steel s u b s t r a t e in order to form a coating (Fig. 2 ) . T h e process parameters are shown in Table 2.
Fig. 2 Sample of SLD Table 2
Process parameter of SLD
N2
N2
Laser
Feeding velocity/
temperature/"C
pressure/MPa
power/kW
(mm-s-1)
500
3.0
1.5
10
2
Experimental Results and Discussion
2.1
1 10 Particle size/μιη
1000
Fig. 1 Stellite 6 particles and particle size distribution
(a) Deposition topography of SLDi
Fig. 3
Analysis of surface topography and cross section T h e surface t o p o g r a p h y of Stellite 6 is presen ted in Fig. 3. Fig. 3 ( a ) s h o w s coating topography of Stellite 6 deposited by S L D ; it shows craters with fluctuation and no melting topography; Fig. 3 (b) shows melting topography of Stellite 6 deposited by H V O F . Fig. 4 s h o w s t h a t the s t r u c t u r e of the s u b s t r a t e is ferrite ( F ) and pearlite ( P ) . As for SLD, during the hard particles impact on the relatively hot substrate, the plastic deformation of the substrate results in recrystallisation of the interface area close to the substrate, thereby improving t h e interface s u b s t r a t e s hardness.
( b ) Deposition topography of H V O F .
Surface topography of Stellite 6
• 54 ·
Journal of Iron and Steel Research, International
Fig. 4
Vol. 20
Structure of substrate and interface zone
T h e cross section in Fig. 5 ( a ) , etched by aqua regia, s h o w s many blisters on the s u b s t r a t e due to corrosion. T h i s is because t h a t F e of s u b s t r a t e r e acts with hydrochloric acid and nitric acid, and gen erates gas ( s u c h as H 2 and N z ) . T h e coating of Fig. 5 ( a ) is magnified, and the s t r u c t u r e after polis hing and etching is shown in Fig. 5 ( b ) . The deforma tion appears to be greater on the top surface of each particle, indicating t h a t cold, hard particles are e m bedding themselves into a h e a t e d , softened s u b s t r a t e during deposition, and the dendrites appear close re
ticulation distribution. T h e spherical particles appear ra diant dendrites from core of particle to boundary [ a s s h o w n in a r r o w of Fig. 5 ( b ) and Fig. 6 ( a ) ] . T h e black cross m a r k ( p o i n t of m e a s u r e m e n t ) is magnified and s h o w n in Fig. 5 ( c ) . It can be found that t h e boundary of reticulation is composed of many white grains along the boundary. T a b l e 3 shows chemical composition at m a r k s ( black cross m a r k and white triangle m a r k ) . T h e results show content of carbon is high com paring with contents of Stellite 6 powder, possibly form
imi μιη
(a) Etched cross section;
( b) Structure of coating ; ( c) Magnification of cross mark ( SLD) i Fig. 5 Analysis of cross section
(d) Distances of line scan.
Issue 2
Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters
· 55 ·
(a) Optical micrograph of Stellite 6 coating (SLD) ; (b) SEM micrograph of Stellite 6 coating deposited by SLD; (c) Porosity of Stellite 6 coating deposited by SLD; (d) Porosity of Stellite 6 deposited by HVOF. Fig. 6 Optical micrograph and porosity of Stellite 6 coating Table 3
Element content of mark
Black cross mark White triangle mark
C
Cr
Co
W
5.41 7.23
31.23 33.53
60.96 58.53
2.40 0.71
ing carbide resulting in high content of carbon. Fig. 5 (d) and Fig. 7 shows that the distances of line scan from substrate to coating in cross-section of SLD, and the length of test is 560 μπι. It appears that the elements of coating have hardly diluted, and initial composition is still retained ^
75
Coating
Substratey
65 »
'55
i
— '
\
■ C ♦ Co • Si « W ACr »Mn T Fe · Ni
45 35
\ 1
^25
S
g 15
-r-î-T-J
£= ^
■
1
200 400 Distance from surface/μιη
600
Fig. 7 Change of element from coating to substrate
comparing with composition of powder. This proves SLD results in no bulk particle melting. 2. 2
Porosity and adhesion strength This structure and porosity of coating were measured optically and reported in Fig. 6. The sur face of coating shows sphere particles with radiant dendrite distribution clearly. Fig. 6 ( a ) shows the typical hypo-eutectic structure consisting of complex wear resistant carbides dispersed in Co matrix. Po rosity is an important parameter for evaluation of coating quality, and measured to be of 0. 2% for SLD [Fig. 6 ( c ) ] , which is considerably lower than porosity of 2% - 3 % for HVOF [31] [Fig. 6 ( d ) ] counterpart. The phase structure of the coating by SLD was analyzed and it is shown in Fig. 8. One of the key characteristics of any coating material is its bonding ability or adhesion to other materials. Without sufficient· adhesion, a coating will fail. Therefore, adhesion strength objectively and accurately during research and quality control are vital. The adhesion strength between coating and sub strate is tested by PAT-ADHESION/TENSILE, using E900STM adhesive. Test diameter is 6 mm (Fig. 9). The
J o u r n a l of I r o n a n d S t e e l R e s e a r c h ,
• 56 ·
2 500
results in T a b l e 4 show t h a t t h e average adhesion s t r e n g t h is 6 1 . 8 M P a . T h e d a t u m of t h e third cir cle m a r k is ignored due to t h e a p p r o a c h edge of specimen.
Cr7C,T Co
2 000h .1500
I
CrrCs
Co
I looo &
W2C 500 0
>■-
20
30
CrrC, Co
CrjCa Co
\ K ., . , , A..-, .JUÂ, 50
Vol. 20
International
20/(°)
70
90
110
Fig. 8 XRD of Stellite 6 deposited by SLD
Adhesion s t r e n g t h of Stellite 6 coating deposi ted by H V O F has not been reported by any paper. Adhesion s t r e n g t h of other alloy deposited on the steel by H V O F is s h o w n in Fig. 10. It can be seen t h a t adhesion s t r e n g t h of coating deposited by H V O F is 7 5 - 9 8 M P a [ F i g . 10 ( a ) [ 3 2 ] and ( b ) [ 3 3 ] ] because t h e t e m p e r a t u r e of H V O F is enough to melt metal which results in metallurgy b o n d , however with this m e t h o d phase transformations are likely to o c c u r , i. e. poor coating properties and higher level of porosity. Table 4
Fig. 9 Sample of pull-off adhesion testing
Element content of mark
No.
1
2
Adhesion s t r e n g t h / M P a
62.4
3 61.2
4.8
(W Substrate/NiCr Subsrrate/Ni/NiCr Substrate/WC-Co Substrate/Ni/WC-Co Substrate/NiCr/WC-Co
·- ->
Subsöate/Ni/NiCr/WC-Co
2
3 4 Sample number
(a) 8 0 % C r 3 C z / 2 0 % N i - C r coatings;
2 000
4000 6000 Average/psi
8000
10000
( b ) Tensile bond strength of coatings.
Fig. 10 Adhesion strength by HVOF
3
sistance of H V O F WC-Co and TiC/Ni-Ti Coatings Sprayed on
Conclusions
1) T h e s t r u c t u r e of deposition coating is typical hypo-eutectic s t r u c t u r e consisting of complex wear resistant carbides dispersed in b a s e , and dilution of elements hardly exists. 2) T h e porosity of coating deposited by S L D is 0 . 2 % , and it is lower than coating porosity of 2 % — 3 % deposited by H V O F . 3) Adhesion s t r e n g t h b e t w e e n coating deposi ted by SLD and s u b s t r a t e is 6 1 . 8 M P a .
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