microstructure and properties of pvd wc/c coatings lofaj.pdf · 2007. 12. 6. · microstructure...
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Microstructure and properties
of PVD WC/C coatings
František Lofaj1, Milan Ferdinandy1, András Juhás2*
Institute of Materials Research of SAS, Košice
Eötvös Loránd Tudomány Egyetem, Budapešť
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Outline� Introduction
Hard vs. Superhard coatings
� Experimental
Combined PE PVD technology
Nanoindentation
Results and Discussion
Microstructure & morphology
Chemistry
Nanohardness
� Conclusions
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Introduction
Functional coatings ...
Potential of hard coating with low friction coefficients
- lower wear
- longer lifetime
- lower energy consumption
Hard ���� Superhard ���� Ultrahard coatings
<15 GPa ���� 15 – 40 GPa ���� >40 GPa
(Max. 105 GPa in nc-TiN/a-Si3N4)
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Basic Principles of Hard Coatings
Approaches to obtain hard coatings:
1. Intrinsically hard material for coatings –(diamond, DLC, c-BN)
limits – hardness of the material
2. High compressive stresses at the surface
frequent decohesion, stress relaxation at higher temperatures
3. Nanocrystalline structure (TiN nanoparticles in Si3N4 matrix and others)
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Superhard nanocrystalline coatings
Veprek’s model requirements:
- 2 immiscible components with
spinodal decomposition
dD
- D has to be nano (~ 5 nm) –
dislocation movement is
excluded
- d has to be around 1 nm,
amorphous, high E, continuous skeleton
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Experimental ProcedurePVD apparatus
Vacuum pump
ARE electrode 0-300 V
0-5 kV
Sublimation chamber
substrate
Main parameters: total gas pressure, bias, current density
Substrates: HSS, Si single crystal; (Ti sublayers)
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Microstructure and PropertiesSEM /EDX, X-ray
Nanohardness – UMIS 2000 (ELTE Budapest)
Berkovich
loading up to 1 mN
or 5 mN in 20 steps
5 s hold
Unloading in 10
steps
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ResultsPreparation conditions
1.2
0.8
1
1
Beam current
[mA/cm2]
2004.50.8#21
70052#24
20051#20
3003.84#13, Ar
Thickness
[nm]
Bias
[kV]
Total pressure
[Pa]
Sample/
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Microstructure of the coatings (OM)
Delamination of the coating
High contact stresses –
unsuitable conditions
#13, 300 nm: 4Pa (Ar)/ 3.8 kV / 1 mA.cm-2
Ti interlayer Without Ti
Limited delamination
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Microstructure morphology and
chemistry of the coatings#13/Ti #13/no Ti
Big W-rich clusters on the
surface
Fe substrate
Ti
WC/C+O,
Relatively high content of oxygen...
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Morphology of the coating#20: 200 nm
strong delamination, ?? layered structure??
1 Pa / 5 kV/ 1 mA.cm-2
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Microstructure and morphology of the
coatings#24, 700 nm, 2 Pa/4.5 kV /1.2 mA.cm-2
Partial delamination
Si substrate
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Microstructure of the WC/C coating
Close to optimum conditions
Steel substrate Si substrate
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Phase composition of the coatings
Position [°2Theta]
30 40 50
Counts
0
200
400
W C
; Si
C
Si
C; W
C; Si
C
Si
C
W C
; Si
C
wc-c_si_2.rd
Sample #13 /Si substrate
WC (PDF 05-0728 ) identified – possibility for nanocrystalline phases
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Repeatability of the measurements
at 1 mN load
0,000 0,005 0,010 0,015 0,020 0,025 0,030 0,0350,0
0,2
0,4
0,6
0,8
1,0 HSS 07924-1
2Pa/5 kV/0.8 mA/cm-2
Load, m
N
Penetration depth, µm
0,00 0,02 0,04 0,06 0,080,0
0,2
0,4
0,6
0,8
1,0 HSS 070913-1
4Pa/3.8kV/1 mA/cm-2
Load, m
N
Penetration depth, µm
Ti
Penetration depth ~ 30-80 nm ... << layer thickness
??Effect of residual stresses??, correlation with delamination
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Repeatability at 5 mN load
0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,140
1
2
3
4
5HSS 070920
1 Pa/5kV/1mA/cm-2
Load m
N
Penetration depth, µm0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,140
1
2
3
4
5
HSS 070924
2Pa/5 kV/0.8 mA/cm-2
Load, m
N
Penetration depth, µm
0,00 0,02 0,04 0,06 0,08 0,10 0,120
1
2
3
4
5
HSS 070921
0.8 a/ 4.5 k / 1.2 mA/cm2
Load, m
N
Penetration depth, µm
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Summary of the hardness and
elasticity
266 ± 128(106 – 350)
20.1 ± 11.9(7.1 – 38.9)
#21
265 ± 12(251-277)
19.9 ± 2.1(17.7-22.9)
#24
318 ± 24(297-355)
21.5 ± 3.1(18.0 – 25.7)
#20
323 ± 96(203-489)
24.1 ± 9.5
(16.9- 45.8)
#13
Elastic modulus [GPa]
(min. – max.)
Hardness [GPa]
(min. – max.)
Sample
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Conclusions
� Delamination of the coating is a problem..
� WC/C coating preparation conditions were optimized ....
� Thin “nanocrystalline –like” coatings obtained but their hardness is only 20-25 GPa ...
� Serious problems with the measurement of nanohardness of thin coatings - influence of the residual stresses and morphology...
� TEM of the coatings and AFM/nanoindentation combination necessary ( direction of our future work)