structural and mechanical properties of vanadium carbide obtained by dc reactive magnetron...
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Structural and mechanical properties ofvanadium carbide obtained by DC reactive
magnetron sputtering
E. Portolan(b), C. Aguzzoli (a), G. V. Soares (a,d), M. E. R. Dotto(c), M. E. H. Maia da Costa(c), I. J. R. Baumvol(a,d), and C. A. Figueroa(a)
(a)Centro de Ciências Exatas e Tecnologia, Universidade de Caxias do Sul, Caxias do Sul, RS, Brazil.(b)Tramontina S.A., Farroupilha, RS, Brazil.(c)Departamento de Física, Pontifícia Universidade Católica do Rio do Janeiro, Rio de Janeiro, RJ, Brazil.(d)Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil.
www.plasmartecnologia.com
Motivations1) Development of a single hard coating for tooling applications
The Caxias do Sul – Porto Alegre (RS) region concentrates the 2nd Brazilian metal-mechanic industrial pole. So, the main research focus is to support, technologycally, this productive chain.
Vanadium carbide (VC) is a single coating that has a relative high hardness (~ 30 GPa).(*) Many tooling problems can be resolved by this type of coating. Example: Die for metal conformation.
2) Understand the mechanical properties from an structural point of view
Hardness is one of the most important properties of functional coatings. However, the mechanical properties can be explained from structural aspects such as grain size, stress, defects, interstitial atoms, etc.
(*) Lu, Selleby, Sundman, Acta Mater. 55 (2007) 1215.
Experimental set up and characterization
Characterization: XRD, RBS, AFM, NanoIndentation measurements.
Magnetron sputtering chamber at LESTT (UCS)
ExperimentalParameters
1. DC reactive magnetron sputtering for VC deposition2. Substrate: Si.3. Target: V.4. CH4 as C source.5. Variable T = 100 to 500oC.6. P (dep.) = 3x10-1 Pa7. Power density = 5.5 W.cm-2
Structural properties: RBS-like carbon spectra from the 12C(,)12C resonant reaction(*)
15 % CH4 at 450oC
(*) Driemeier and Baumvol, Nuclear Instruments and Methods in Physics Research B 266, 2041 (2008).
The carbon content is homogeneous
along the VC coating
VCSi
0,40,8
1,2
1,6
1000
2000
42504300
4350
Yie
ld (a.
u.)
E beam (keV)
Scattering
energy (MeV)
(b)
Contam
ination
Film Substrate
Structural properties: Rutherford Backscattering Spectrometry
1 20
4
8
12
0.5 0.6
0
1
2
Interface C
Yie
ld (ar
b. u
nits
)
Energy (MeV)
Suface C
Interface V Surface V
100 200 300 400 500150
200
250
300
Thi
ckne
ss (nm
)
Temperature (oC)
(b)
100 200 300 400 500
0,6
0,9
1,2
1,5
C/V
ato
mic
rat
io
Temperature (oC)
The VC stoichiometry goes towards to 1:1 at higher temperatures
Aouni, Weibecker, Loi, and Bauer-Grosse, Thin Solid Films 469-470, 315 (2004).
Structural properties: X-ray diffraction experiments
15% CH4
VC has a FCC crystalline structure, independently of temperature, at 15 % CH4
30 35 40 45 50 550
2
4
6
8
10
Inte
nsity
(ar
b. u
nits
)2degrees)
Temperature
(oC)
100
200
300
400
500
(111) (200)
Portolan, Amorim, Soares, Aguzzoli, Perottoni, Baumvol, Figueroa, Thin Solid Films (2009), in press.
100°C
500°C
300°C
100 200 300 400 5000
1
2
3
4
5
Rou
ghne
ss R
a (n
m)
Temperature (°C)
There is a maximum of roughness at 300oC
Mechanical properties: Atomic Force Microscopy
Mechanical properties: hardness and Young’s Modulus
Both hardness and Young’s modulus increase at higherdeposition temperatures
100 200 300 400 500
20
25
30
35
Temperature (°C)
Har
dnes
s (G
Pa)
100
150
200
250Y
oung's Modulus (G
Pa)
HardnessYoung's modulus
The best plastic resistance parameters are achieved at higher deposition temperatures
Mechanical properties: plastic resistance parameter
100 200 300 400 5000,4
0,6
0,8
1,0
1,2H
3 /E2 (
GP
a)
Temperature (°C)
Physically, the intensity of XRD peaks depends on the constructive interference of outgoing X-ray radiation after scattering with atoms (essentially electrons) which form each atomic plane. So, the intensity must increase with the presence of more atoms in each plane.
Some comments from XRD analysis
Up to now, higher deposition temperatures (450 – 500oC) have providedthe best properties in terms of homogeneity, stoichiometry, and
mechanical properties (hardness, H3/E2, and roughness).
But, what about an structural point of view in order to explain the mechanical properties ?
30 35 40 45 50 550
2
4
6
8
10
Inte
nsity
(ar
b. u
nits
)2degrees)
Temperature
(oC)
100
200
300
400
500
(111) (200)
Planes (111) and (200)White dots are C atoms in octahedral sites.
(111)
(200)
Plane (200) crosses octahedral interstitial positions
Planes (111) and (200)White dots are C atoms in tetrahedral sites.
(111) (200)
Plane (111) crosses tetrahedral interstitial positions
Evolution of the intensity ratio from planes (111)/(200) as a function of deposition temperature
As more carbon is present in octahedral sites more the intensity of interference at plane (200) and less the intensity
ratio (111)/(200)
At lower T, C atoms are mostly in tetrahedral sites while thatat higher T, C atoms occupy octahedral sites
100 200 300 400 5000
2
4
6
8
10
Intensity ratio for stoichiometric VC
Inte
nsi
ty ratio
I 111/
I 200
Temperature (oC)
Intensity ratio I111/I200 for different stoichiometries and site occupancies for carbon in vanadium carbide interstitials sites
simulated with PowerCell
C in interstitials sites
VC stoichiometry Intensityratio I111/I200
All in tetrahedral V0.400C0.600 3.82All in tetrahedral V0.500C0.500 3.33Both, tetrahedral and octahedral
V0.500C0.500 2.32
Both, tetrahedral and octahedral
V0.455C0.555 1.87
All in octahedral V0.500C0.500 0.92All in octahedral V0.540C0.460 1.12
Structural properties: XRD simulations
The XRD simulations show that the intensity ratio I111/I200
decreases when C atoms goes from tetrahedralto octahedral sites.
Conclusions:VC coatings obtained at 15 % CH4 have a FCC crystalline structure in the whole deposition temperature range (100 to 5000C).
By XRD, the intensity ratio I (111) / I (200) analysis as a functionof T indicates that carbon atoms migrates from tetrahedral to octahedral sites at higher T. So, carbon in octahedral positionsincreases the VC resistance to plastic deformation.
By Nano-Indentation, the mechanical properties (hardness, Young’s modulus and H3/E2) are the best at higher temperatures.
By RBS, the VC coating is homogenous and the 1:1 stoichiometry is achieved at higher deposition temperatures.
Comparision between XRD simulations and measurements
(111) (200)
Raman spectra show that there is not amorphous C inthe VC coating
800 1200 1600 2000
6
8
10
12
14
500
400
300
Inte
nsi
ty (
u.a
.)
Raman shift (cm-1)
Temperature
(oC)
100
XRD measurements show that there is not graphite-typeC in the VC coating
VC
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