Structural and mechanical properties of vanadium carbide obtained by DC reactive magnetron sputtering
Structural and mechanical properties of vanadium 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
Motivations (*) Lu, Selleby, Sundman, Acta Mater. 55 (2007) 1215. 1) Development of a single hard coating for tooling applications The Caxias do Sul – Porto Alegre (RS) region concentrates the 2 nd 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.
Experimental set up and characterization Characterization: XRD, RBS, AFM, NanoIndentation measurements. Magnetron sputtering chamber at LESTT (UCS) Experimental Parameters 1. DC reactive magnetron sputtering for VC deposition 2. Substrate: Si. 3. Target: V. 4. CH 4 as C source. 5. Variable T = 100 to 500 o C. 6. P (dep.) = 3x10 -1 Pa 7. Power density = 5.5 W.cm -2
Structural properties: RBS-like carbon spectra from the 12 C( , ) 12 C resonant reaction (*) 15 % CH 4 at 450 o C (*) Driemeier and Baumvol, Nuclear Instruments and Methods in Physics Research B 266 , 2041 (2008). The carbon content is homogeneous along the VC coating VC Si
Structural properties: Rutherford Backscattering Spectrometry 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 VC has a FCC crystalline structure, independently of temperature, at 15 % CH 4 15% CH 4 Portolan, Amorim, Soares, Aguzzoli, Perottoni, Baumvol, Figueroa, Thin Solid Films (2009), in press.
There is a maximum of roughness at 300 o C Mechanical properties: Atomic Force Microscopy 100 °C 500 °C 300 °C
Mechanical properties: hardness and Young’s Modulus Both hardness and Young’s modulus increase at higher deposition temperatures
The best plastic resistance parameters are achieved at higher deposition temperatures Mechanical properties: plastic resistance parameter
Up to now, higher deposition temperatures (450 – 500 o C) have provided the best properties in terms of homogeneity, stoichiometry, and mechanical properties (hardness, H 3 /E 2 , and roughness). But, what about an structural point of view in order to explain the mechanical properties ? 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
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 that at higher T, C atoms occupy octahedral sites
Intensity ratio I 111 /I 200 for different stoichiometries and site occupancies for carbon in vanadium carbide interstitials sites simulated with PowerCell Structural properties: XRD simulations The XRD simulations show that the intensity ratio I 111 /I 200 decreases when C atoms goes from tetrahedral to octahedral sites. C in interstitials sites VC stoichiometry Intensity ratio I 111 /I 200 All in tetrahedral V 0.400 C 0.600 3.82 All in tetrahedral V 0.500 C 0.500 3.33 Both, tetrahedral and octahedral V 0.500 C 0.500 2.32 Both, tetrahedral and octahedral V 0.455 C 0.555 1.87 All in octahedral V 0.500 C 0.500 0.92 All in octahedral V 0.540 C 0.460 1.12
Conclusions : VC coatings obtained at 15 % CH 4 have a FCC crystalline structure in the whole deposition temperature range (100 to 500 0 C). By XRD, the intensity ratio I (111) / I (200) analysis as a function of T indicates that carbon atoms migrates from tetrahedral to octahedral sites at higher T. So, carbon in octahedral positions increases the VC resistance to plastic deformation. By Nano-Indentation, the mechanical properties (hardness, Young’s modulus and H 3 /E 2 ) 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 in the VC coating
XRD measurements show that there is not graphite-type C in the VC coating VC Graphite