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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