Characterization of sputtered laboratory scale V-Al-C-N hard coatings and industrial scale-up for deposition on segmented forming tools for the automotive industry

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Abstract.
An emerging new approach is the design of carbon-based nanostructured
composite coatings being composed of nanocrystalline metastable hard phases
homogeneously dispersed in an amorphous carbon matrix or covered by an amorphous carbon
grain boundary phase. Such coatings could be used to locally tailor the friction coefficient of
forming tools in order to optimize the steel sheet forming process, to increase the manufacture
accuracy, to reduce the error rates and to increase the tool service life as planned in the related
publicly funded project IMAUF (‘‘Innovative methods for the design of forming tools in the
automotive industry’’). Nanocrystalline quaternary V-AI-C-N hard coatings were deposited
by reactive r.f.-magnetron sputtering in Ar/CH4 plasma on a laboratory scale Leybold Z550
machine using a combinatorial materials science approach. In each experiment, six coatings
of different composition and/or microstructure were obtained simultaneously by placing six
substrates in individual positions relative to a segmented target, composed of ceramic VC and
AlN half plates. The CH4 flow rate was systematically varied up to CH4 volume fractions of 8
... mehr% in the process gas. The chemical composition of the coatings was determined by electron
microprobe analysis and the topography, crystal structure and microstructure were
characterized by atomic force microscopy, X-ray diffraction, scanning as well as transmission
electron microscopy. By using nanoindentation and ball-on-disk tribometer tests against
100Cr6 steel balls the correlation with the mechanical and the tribological properties was
investigated. Significant changes in the coatings topography, microstructure and in the related
mechanical and tribological properties were observed both as a function of the sample
position and of the carbon content. In particular, a wide range variation of the friction
coefficient (0.15-0.45, s. Fig. 1) of the hardness (15-35 GPa) and of the reduced elastic
modulus (120-600 GPa) was achieved and correlated with constitution, microstructure and
effective wear mechanisms. After the successful development of V-Al-C-N coatings with
adjustable local friction coefficient on flat substrates on the laboratory scale the processes
have been scaled up to an industrial-scale CemeCon CC800/8 machine by using graphite and
VAl20-targets (metallic V target with 20 Al-plugs). Both non-reactive and reactive sputtering
in Ar/CH4 atmosphere has been applied in order to deposit the coatings on Si (100) substrates
and polished 1.2379 steel substrates. After a thorough characterization and optimization the
coatings have been deposited onto model forming tools from ThyssenKrupp Steel Europe AG
and segmented industrial forming tools from Volkswagen AG. These OEM’s will perform
model and production tests in order to validate the approach. The next step would be to
develop software that can predict the optimal local variation of the friction coefficient, which
could be realized afterwards by depositing the novel V-Al-C-N coatings.
Keywords: quaternary hard coatings, forming tools, scale-up
IDDRG 2010 Graz, 31.05.-02.06.2010
TOPIC: TOOL TECHNOLOGIES - Suptopic: surface and heat treatment
Key figure
0.6
0.5
0.4
μ
0% CH4
2% CH4
0.3
4% CH4
8% CH4
0.2
0.1
0.0
Pos 1 Pos 2 Pos 3 Pos 4 Pos 5 Pos 6
Fig.1 Dependence of the friction coefficient of V-Al-C-N coatings on sample position as a
function of CH4 content.