Papers

ICMCTF2006 Session B7-1: Properties and Characterization of Hard Coatings and Surfaces

Monday, May 1, 2006 10:30 AM in Room Golden West

Monday Morning

Start	Invited?	Item
10:30 AM		B7-1-1 TiN/SiN_x Multilayer Thin Films L. Hultman (Linköping University, Sweden) The ternary Ti-Si-N system is presently attracting a lot of attention for the growth of nanocomposites [1], multilayers (superlattices) [2], and solid solutions [3]. Outstanding questions are for how the physical properties of these advanced ceramics depend on their phase composition and microstructure. In this respect, multilayers are useful as a model system since they allow the design and study of interfaces not readily accessible in a 3-D structure. Thus, we could recently demonstrate initial pseudomorphic growth of cubic-phase SiNx on TiN template layers in TiN/SiN_x multilayers deposited by reactive dual magnetron sputtering [2]. There is a transition from epitaxial to amorphous layer growth as the layer thickness increases above one to a few monolayers. These results impacts on the models employed for describing a-Si₃N₄/c-TiN nanocomposites as the existence of a crystalline silicon nitride tissue phase now has also to be considered for explaining the material's mechanical properties. We propose, for example, that Koehler hardening can operate in such nanostructures. This presentation will review the work done on identifying the nature of the crystalline silicon nitride layer including in situ STM experiments and ab initio calculations of different polytypes. [1] S. Veprek, Thin Solid Films 476 (2005) 1. [2] H. Soderberg, et al., J. Appl. Phys. 97 (2005) 114327. [3] A. Flink, et al Surf. Coat. Technol. (2005) In press.
11:10 AM		B7-1-3 Role of Coherent Structures in Hardening of Nanolayers and Nanocomposite Thin Films G. Allidi, R. Sanjines, A. Karimi (EPFL, Switzerland) Lowering material dimensions is often accompanied by structural transitions in terms of length scales and their interactions, which can exert strong influence on final properties. In multilayered systems, both experimental and theoretical considerations showed that the effect of epitaxial and coherent structures exceeds that of image force on dislocations and grain boundary strengthening when the bilayer thickness decreases down to nm scale range. However, the formation of coherent structures and their influence on hardness enhancement of nanocomposites is less considered. For this purpose, Ti-Al-N system was chosen to produce AlN/TiN nanolayers with the layer thickness ranging from 1 nm to 50 nm, as well as nanocomposite TiAlN-AlN with grain size less than 10 nm. The samples were characterised in terms of structure-property relations using RBS, HRTEM, XRD, nanoindentation, and substrate curvature. Conditions to obtain coherent structures and different strengthening mechanisms operating in these nanostructured thin films will be discussed and compared. Particular emphasise will be made in nanocomposites developing coherent nanodomains.
11:30 AM		B7-1-5 Thermal Decomposition of CrN Hard Coatings W. Ernst, J. Neidhardt (University of Leoben, Austria); H. Willmann (Materials Center Leoben, Austria); B. Sartory (University of Innsbruck, Austria); C. Mitterer (University of Leoben, Austria) CrN-based coating systems are of great technological interest and already applied on a large scale on, e.g., combustion engine components. For many applications, their temperature resistance is of vital importance, which can be improved substantially by synthesizing ternary or even quaternary compounds with, e.g., Al, B, Si or even O. Further development of these complex coating systems requires a detailed understanding of the decomposition routes of the binary compound. Thus, in this study CrN was investigated by simultaneous thermal analysis (STA), a combination of thermo-gravimetric analysis (TGA) and dynamic scanning calorimetry (DSC), to monitor weight changes and heat flows connected to reactions in the material during annealing up to 1440°C in argon. A coupled mass spectrometer was used to identify desorbed gases. In parallel the decomposition-dependent evolution of the mechanical properties was monitored by nano-indentation on annealed samples. These results in combination with in situ high-temperature x-ray diffraction provide a good understanding of the decomposition routes of binary CrN. Furthermore, the different decomposition behavior, due to e.g. macro particles, of sputtered and arc evaporated CrN coatings will also be elucidated.
11:50 AM		B7-1-6 Stress Gradients in Cr and CrN Coatings G.C.A.M. Janssen, F.D. Tichelaar, C.C.G. Visser (TU Delft, Netherlands) Stress observed in hard films is the net sum of tensile stress generated at the grain boundaries, compressive stress due to ion peening and thermal stress due to the difference in thermal expansion of the coating and substrate combined with deposition at a higher temperature than the measurement temperature. Since grains usually are wider at the top of the coating than at the bottom the tensile part due to grain boundaries is thickness dependent. The other two contributions are not thickness dependent. Summation of the three components leads to a stress gradient in the coating. Dense chromium films can be deposited at room temperature, eliminating the contribution of thermal expansion. Also an ion bombardment is not necessary to deposit dense chromium films, eliminating the ion peening contribution. Therefore chromium was used to demonstrate the additive effect of tensile stress due to grain boundaries and compressive stress due to ion peening. Chromiumnitride is less experimentally accessible. Only at elevated temperatures and under a sufficient ion-bombardment dense films are deposited. The description developed for chromium can still be applied, although the contributions can not be isolated as in the case of chromium. A thickness series of CrN coatings showed a stress gradient from 600 MPa tensile for 12 nm thin coatings to 1100 MPa compressive for 3.5 µm thick coatings. A thermal stress of 800 MPa tensile at RT for CrN on Si (Tdep 450°C) was inferred from wafer curvature measurements after deposition both at room temperature and elevated temperature.