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Metals 2017, 7(1), 16; doi:10.3390/met7010016

Vibration-Assisted Sputter Coating of Cenospheres: A New Approach for Realizing Cu-Based Metal Matrix Syntactic Foams

1
Rudolfs Cimdins Riga Biomaterials Innovations and Development Centre of Riga Technical University (RTU), Institute of General Chemical Engineering, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Pulka 3, LV-1007 Riga, Latvia
2
Department of Mechanical and Industrial Engineering, Tallinn University of Technology, 19086 Tallinn, Estonia
3
Sidrabe Inc., LV-1073 Riga, Latvia
4
MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Hugo F. Lopez
Received: 10 December 2016 / Revised: 30 December 2016 / Accepted: 4 January 2017 / Published: 7 January 2017
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Abstract

The coating of hollow alumino-silicate microspheres or cenospheres with thin layers of Cu by means of vibration-assisted magnetron sputtering yields a starting material with considerable potential for the production of new types of metal matrix syntactic foams as well as optimized variants of conventional materials of this kind. This study introduces the coating process and the production of macroscopic samples from the coated spheres via spark plasma sintering (SPS). The influence of processing parameters on the coating itself, and the syntactic foams are discussed in terms of the obtained density levels as a function of sintering temperature (which was varied between 850 and 1080 °C), time (0.5 to 4 min), and surface appearance before and after SPS treatment. Sintering temperatures of 900 °C and above were found to cause breaking-up of the homogeneous sputter coating into a net-like structure. This effect is attributed to wetting behavior of Cu on the alumino-silicate cenosphere shells. Cylindrical samples were subjected to conductivity measurements and mechanical tests, and the first performance characteristics are reported here. Compressive strengths for Cu-based materials in the density range of 0.90–1.50 g/cm3 were found to lie between 8.6 and 61.9 MPa, depending on sintering conditions and density. An approximate relationship between strength and density is suggested based on the well-known Gibson–Ashby law. Density-related strength of the new material is contrasted to similar findings for several types of established metal foams gathered from the literature. Besides discussing these first experimental results, this paper outlines the potential of coated microspheres as optimized filler particles in metal matrix syntactic foams, and suggests associated directions of future research. View Full-Text
Keywords: syntactic foam; spark plasma sintering; magnetron sputtering; fly ash; cenospheres; composite; metal matrix composite; metal matrix syntactic foam syntactic foam; spark plasma sintering; magnetron sputtering; fly ash; cenospheres; composite; metal matrix composite; metal matrix syntactic foam
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Shishkin, A.; Drozdova, M.; Kozlov, V.; Hussainova, I.; Lehmhus, D. Vibration-Assisted Sputter Coating of Cenospheres: A New Approach for Realizing Cu-Based Metal Matrix Syntactic Foams. Metals 2017, 7, 16.

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