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
Outline� Introduction
Hard vs. Superhard coatings
� Experimental
Combined PE PVD technology
Nanoindentation
Results and Discussion
Microstructure & morphology
Chemistry
Nanohardness
� Conclusions
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)
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)
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
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)
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
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/
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
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...
Morphology of the coating#20: 200 nm
strong delamination, ?? layered structure??
1 Pa / 5 kV/ 1 mA.cm-2
Microstructure and morphology of the
coatings#24, 700 nm, 2 Pa/4.5 kV /1.2 mA.cm-2
Partial delamination
Si substrate
Microstructure of the WC/C coating
Close to optimum conditions
Steel substrate Si substrate
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
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
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
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
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)
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