Papers

ICMCTF2004 Session B7-1: Properties and Characterization of Hard Coatings and Surfaces

Monday, April 19, 2004 10:30 AM in Room Golden West

Monday Morning

Start	Invited?	Item
10:30 AM		B7-1-1 Stability of Nano-Layered Hard Coatings S.A. Barnett (Functional Coating Technology LLC and Northwestern University) This talk describes nano-layered coatings deposited by reactive magnetron sputtering that are stable at elevated temperatures. Two types of coatings are discussed: nitride/boride nano-layers such as TiN/TiB₂ and ZrN/ZrB₂, and metal nitride nano-layers such as W/ZrN. As a result of the low-energy interfaces and the immiscibility of the layers, these structures show excellent high-temperature stability. For example, W/ZrN nano-layers with thicknesses down to 1 nm showed no detectable change in structure after annealing at 1000°C for several hours. Hardnesses were generally observed to increase after annealing the as-deposited coatings. Annealed nano-layered coatings showed hardness enhancements compared to the constituent materials, with maximum hardness values of ~~50 GPa. Initial results on the application of these coatings for cutting tools will be described.
11:10 AM		B7-1-3 Characterization and Wear Properties of Industrially Produced Nanoscaled CrN/NbN Multilayer Coating E. Bemporad (University of Rome, Italy); C. Pecchio, S. De Rossi (Istituto Scientifico Breda, Italy); F. Carassiti (University of Rome, Italy) Present work deals with morphological, microstructural, compositional and tribological characterisation of new industrially produced nanoscaled multilayer CrN/NbN coating. Nanoscaled multilayer structures usually show high hardness and better wear resistance, correlated with grain refinement, coherency strain hardening, inhibition of dislocation motion, together with an excellent corrosion resistance, due to the interruption of coating columnar pinholes and to the combined metal element effect. This application deals with the coating of cutting tools for plastics, where friction coefficient and corrosion resistance are critical. To satisfy industrial requirements, a standard CA-PVD deposition chamber, already available and routinely used to produce conventional CrN coatings, has been used. To obtain multilayer structure a non conventional Reactive Arc Physical Vapour deposition technique has been set up, consisting of triggering alternatively on Cr or Nb cathodes with appropriate time constant so to obtain layers of about 4-5 nanometers each. During process optimisation, microstructural and compositional properties were investigated and reported hereby. Low Angle X-ray Diffraction, Optical and Atomic Force Microscopy, Electron Probe Microscopy (SEM, TEM, SAD, EDS) and Focussed Ion Beam techniques has been used. Defects were also investigated, particularly microdroplets (shape, dimension, density, clustering and other process-sensitive features). Mechanical and tribological properties were characterized by micro and nano hardness measurements, scratch test, ball on ring, ball crater and sin²ψ residual stresses evaluation. Salt spray corrosion test were performed to appreciate corrosion resistance with respect to conventional CrN coatings. Finally, performances results (e.g. wear rate and degradation behaviour) obtained by operating in line two different sets of cutting tools (respectively CrN and CrN/NbN coated) are presented.
11:30 AM		B7-1-4 Correlation between Constitution, Properties and Machining Performance of Tin/Zrn Multilayers S. Ulrich, C. Ziebert, P. Schlossmacher, M. Stüber, H. Holleck (Forschungszentrum Karlsruhe, Germany); E. Schweitzer, M. Göken (University Erlangen-Nürnberg, Germany) A new concept for wear protective coatings in the area of machine cutting applications on the basis of nanoscaled TiN/ZrN multilayers is presented. So far a columnar growth morphology was not desired, since along the columnar grain boundaries fracture can be formed under high load, which lead to the failure of the layer. However, the new concept adjusts this morphology to use the cavities between the columns as a depot for cooling lubricant. The challenge was to optimize the deposition parameters in order to increase the adhesive strength sufficiently to reach values which usually are only possible with a compact morphology (critical failure load in the scratchtest > 40 N). Nanoscaled TiN/ZrN multilayers were deposited by reactive dc-magnetron sputtering of metallic titanium and zirconium targets in an argon nitrogene plasma. In these multilayers periodic stress-strain fields are produced, because even if TiN and ZrN exhibit cubic-face-centered crystal lattices, the difference of the lattice parameters of 7.1 % should lead to stress peaks in the interfaces. These multilayers were a model system for a complete characterization of multilayers and their interfaces from the micrometer down to the nanometer scale to correlate their constitution (SEM, XRD, TEM, AFM), their properties (hardness: 2000 - 2600 HV0.015, reduced elastic modulus: 330-420 GPa, internal stress: < 1 GPa, critical failure load in the scratchtest: 30 - 85 N) and their machining behavior (cutting S-containing Fe-alloys with coated HSS saw blades, tool lifetime, friction coefficient). In addition, on the TiN/ZrN multilayers the small angle cross section method for measuring depth profiles of the mechanical properties of multilayers was developed and preliminary results will be presented.
11:50 AM		B7-1-5 Structural Properties and Thermal Stability of Nanometric Cr/CrN Multilayers J. Romero (Universitat de Barcelona, Spain); J. Esteve (Universitat de Barcelona, Catalunya, Spain); A. Lousa (Universitat de Barcelona, Spain) Polycrystalline Cr/CrN multilayers were deposited on silicon and hardened steel substrates by r.f. magnetron sputtering from a pure Cr target alternating a pure Ar atmosphere and a N₂/Ar reactive mixture. Bilayer period values varied from nanometric range (2-20 nm) to higher values. Coatings structural properties were analyzed by X-ray diffraction and cross-sectional transmission electron microscopy. The multilayer period and relative thickness were clearly determined, and a polycrystalline epitaxial cube-on-cube structure was found on Cr/CrN multilayers. This epitaxial relationship between layers inside each columnar crystallite is given by Cr(001)\|\|CrN(001) and Cr[100]\|\|CrN[110]. Nanoindentation measurements showed multilayer hardnesses reaching 30 GPa in the nanometric range, more than two-times higher than the expected from rule-of-mixtures. The thermal stability of multilayers was studied by post-deposition annealing at temperatures up to 1000°C. Changes in microstructure and hardness were also investigated.