Papers by Keyword: Micro-Particles

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Authors: G. Bonnet, M. Mollard, B. Rannou, J. Balmain, F. Pedraza, X. Montero, M. Galetz, Michael Schütze
Abstract: Novel, unconventional type of high temperature coating systems can be elaborated by depositing Al micro-particles on nickel base substrates, using an appropriate binder, and converting them into a thermal barrier type coating by a two-step heat treatment under argon. Final result is a coating structure consisting of a quasi-foam top coat, constituted by spherical hollow alumina particles, surmounting a β-NiAl diffusion layer able to form during high-temperature oxidation a protective alumina scale. In this work, pure nickel was employed as a model material to evaluate the effects of moderate temperatures (550-700°C), dwelling times and Al particle size on the final characteristics of the coatings. Almost no diffusion occurred below 600°C. In contrast, a Ni2Al3 layer very quickly formed at 650 or 700°C. The rapidity of coating formation was attributed to the appearance of a liquid phase at the coating/substrate interface. The increase of dwelling time did not provide any significant thickness increase as the Al particles got practically emptied after 2h. In addition, the use of different micro-sized particles resulted in similar Al diffusion coatings under the investigated conditions.
Authors: Geng Rong Chang, Fei Ma, Da Yan Ma, Ke Wei Xu
Abstract: Micro-particles and nano-wires, small outgrowths were found to appear on upper film surface when metal thin film is confined between two Si3N4 layers deposited by magnetron sputtering and is annealed at an appropriate temperature. The stress evolution during this process is monitored by multi-beam optic stress sensor, and is qualitatively interpreted in terms of elastic and plastic deformation, as well as bulk diffusion. Additionally, the interface constraint effect among different layers is explored. Stress relaxation of nano-sandwiched thin films behaves in different stress modes. As a comparative study, Si3N4/Zn/Si3N4 sandwiches were prepared and studied by the same method. Experimental results show that the pertinent geometry is strongly dependent on material types and stress states of the substrates. Finally, an appropriate mode was suggested to interpret this phenomenon.
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