ICMCTF2013 Session B6-2: Coating Design and Architectures

Tuesday, April 30, 2013 2:10 PM in Room Royal Palm 1-3

Tuesday Afternoon

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2:10 PM B6-2-1 Design of Novel Protective Coatings for High Temperature Applications
Michael Schütze (DECHEMA-Forschungsinstitut, Germany)
There is an increasing demand in high temperature technology for more cost-effective coatings and such that can provide protection under increasingly aggressive high temperature conditions. Powder-pack and slurry coatings have been widely used over the last 2 or 3 decades but still offer a significant potential with regards to these aspects. Recent research at DFI delivered a quantitative model based on thermodynamic and kinetic approaches to quantitatively design the powder pack process with regards to the optimum process parameters. Furthermore, ongoing research is directed towards the target-oriented development of a novel type of slurry coating including multi-element diffusion coatings and non-conventional coatings for extreme environments. The paper will discuss the manufacturing routes and parameters of all these types of coatings and will dwell to a limited extent also on their performance under high temperature conditions.

2:50 PM B6-2-3 Design of Diffusion Coatings Developed via Pack Cementation
Ammar Naji, Mathias Galetz, Michael Schütze (DECHEMA-Forschungsinstitut, Germany)

Aluminization of steels using Pack Cementaion entails the risk of crack formation within the coating. This is due to a detrimental combination of the brittleness of the aluminium rich intermetallic phases that form, the coating thickness and the mismatch of the coefficients of thermal expansion (CTE) between the substrate and the coating. By means of a new coating design the desired coating properties can be achieved by predicting the required coating manufacturing parameters such as the process temperature, process time and powder composition. Thus, coatings consisting of intermetallic phases (iron and nickel aluminides), which are less brittle and have a CTE which is closer to that of the substrate can be designed with a controlled coating thickness that guarantees the well known good oxidation behaviour of aluminides. Furthermore, a modification using co-deposition of aluminium and another element such as silicon is considered in this coating design.

3:10 PM B6-2-4 Inhomogeneous Structural and Mechanical Properties of Thin Films and Coatings Revealed at the Micro- and Nano-Scale
Jozef Keckes, Rostislav Daniel (Montanuniversität Leoben, Austria); Angelika Riedl, Mario Stefenelli (Materials Center Leoben Forschung GmbH, Austria); Christian Mitterer (Montanuniversität Leoben, Austria)

Nanocrystalline and nanostructured thin films with grain size below 100nm exhibit typically inhomogeneous depth gradients of microstructure, strain and physical properties varying at the nano-scale. Currently, however, it is not trivial to reveal how these gradients relate to the macroscopic film behaviour. One of the main reasons is the lack of reliable experimental techniques which can provide thickness-dependent data with sub-micron resolution.

In this contribution, our recent results from position-resolved synchrotron X-ray diffraction (XRD) studies of microstructure and strain in nanocrystalline films will be presented. The experiments are based on position-resolved XRD performed using monochromatic beams with diameters down to 100 nm. On the examples of CrN, TiN and TiAlN coatings, it will be demonstrated that the newly developed approaches can be used to analyse lateral- and thickness-dependent gradients of strain, crystallographic texture, phases and grain size with sub-micron resolution.

Additionally, results from mechanical tests obtained from bending experiments on micro-cantilevers and indentation will be used to illustrate variability and anisotropy of mechanical properties in nanocrystalline coatings.

Finally, it will be demonstrated that the scanning X-ray diffraction studies and local mechanical characterization can be used as an effective tool to reveal structure-property relationship in inhomogeneous thin films and coatings at sub-micron scale.

3:50 PM B6-2-6 The Effects of Bilayer Periods on the Mechanical Properties of Cr-B-N/Ti-B-N Multilayered Thin Films.
Wang-Ting Tsai, Jyh-Wei Lee (Ming Chi University of Technology, Taiwan, Republic of China)
In this study, the Cr–B–N/Ti-B-N multilayered thin films was deposited using CrB2 and TiB2 targets by a pulsed DC reactive magnetron sputtering system at 250 °C and −150 V substrate bias. The bilayer periods of the Cr-B-N/Ti-B-N multilayer coatings were controlled in the range of 3 to 30 nm. The structures and bilayer periods (L) of multilayer coatings were characterized by an X-ray diffractometer (XRD). The microstructures of thin films were examined by field-emission scanning electron microscopy (FE-SEM). The bilayer periods of the multilayer coatings was evidenced by transmission electron microscopy(TEM). The surface roughness of thin films was explored by atomic force microscopy (AFM). The nanoindentation, scratch tests, Daimler–Benz Rockwell-C (HRC-DB) adhesion tests, pin-on-disk wear tests were used to evaluate the hardness, adhesion, indentation toughness and tribological properties of thin films, respectively. It was observed that the hardness and tribological properties were strongly influenced by the bilayer period of the Cr-B-N/Ti-B-N multilayer coatings. An optimal combination of mechanical and tribological properties behavior was found for a coating with a critical bilayer period of 5 nm.
4:10 PM B6-2-7 Ion Energy Distributions in Cathodic Arc Plasma of AlCr Composite Cathodes in Inert and Reactive Atmosphere
Robert Franz (Montanuniversität Leoben, Austria); Peter Polcik (PLANSEE Composite Materials GmbH, Germany); André Anders (Lawrence Berkeley National Laboratory, US)
In the past, the energy distributions of ions in vacuum arcs have been studied in great detail under various conditions, including their dependence on arc current level, strength of a magnetic field (if present), pressure and kind of background gases, and the distance from the plasma-producing cathode spots. Most of the work was done using pure elementary cathodes since the presence of two or more elements in the cathodes would most likely further complicate the situation when studying the physics of cathodic vacuum arcs. However, in many practical applications ternary or quaternary thin films are used. For their synthesis it is common to employ composite cathodes consisting of the elements of interest.

In the field of hard and wear-resistant coatings, thin films based on the system aluminium and chromium represent the state of the art. With the addition of nitrogen and/or oxygen ceramic coatings covering a wide compositional range can be synthesised. In the present study, a mass-to-charge analyser was used to investigate the charge state resolved ion energy distribution functions of Al and Cr as well as the surrounding gases Ar, N2 and O2. The number of Al++ ions increased by changing the background gas following the sequence from Ar, N2 to O2 leading to a higher mean charge state of Al. In contrast, the Cr charge states were reduced. Cr+++ ions were only found in Ar atmosphere while the number of Cr++ ions strongly reduced in O2 as compared to Ar and N2 atmosphere. In terms of cathode composition, both Al ions, Al+ and Al++, showed an increase in energy as the Al content in the cathodes was increased. The highest energies of up to 120 eV were recorded in O2 atmosphere. The Cr ions showed a similar but less pronounced energy dependence on the cathode composition as the Al ions. The observed ion energy distributions were interpreted in the established framework of plasma generation at cathode spots and ion-gas interactions.

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