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Evaluation of alumina as protective coating for carbon fibers in aluminum-based composites

: Krug, Mario; Abidin, Alfaferi Zainal; Höhn, Mandy; Kozera, Rafał; Malczyk, Piotr; Endler, Ingolf; Michaelis, Alexander

European Society for Composite Materials:
17th European Conference on Composite Materials, ECCM 2016. Proceedings : 26-30th June 2016, Munich, Germany
Munich, 2016
ISBN: 9783000533877
Art. 126913
European Conference on Composite Materials (ECCM) <17, 2016, Munich>
Fraunhofer IKTS ()
Cf / Al-MMCs; Al2O3 coating; 2D-textile preform; Al-alloy (239D); GPI

Carbon fiber reinforced aluminum metal matrix composites (Cf/Al-MMCs) have been considered as promising materials for lightweight applications. Especially for automotive and aerospace industry they offer outstanding mechanical properties combined with low density. Nevertheless, major obstacles in manufacturing of Cf/Al-MMCs are high reactivity and poor wettability of the carbon fibers with molten Al-alloy. Often an undesired formation of carbides (e.g. Al4C3) at the fiber-matrix interface is observed. Another issue is the sensitivity of carbon fibers to oxidation especially at temperatures of more than 400°C. In order to solve these problems alumina (Al2O3) protective coating was applied on carbon fiber-based high modulus (HM) 2D-textile preforms by means of atomic layer deposition (ALD). The influence of the coating on the carbon fibers was investigated by measurement of the tensile strength with single filaments and by determination of the oxidation behavior using TGA analysis. Alumina coated fibers show an enhancement of tensile strength of up to 700 MPa compared to uncoated fibers. An improved oxidation resistance of coated preforms was verified by TGA analysis. The Cf/Al-MMC using alumina coated HMfibers and alloy 239D as matrix material was prepared via gas pressure infiltration (GPI). In comparison to the alloy 226D the use of the alloy 239D allows an infiltration without formation of detrimental Cu2Al precipitations. SEM cross-section analysis of Cf(Al2O3)/239D-system revealed that the Al2O3 coating acts as an effective protective layer against the aggressive Al-melt. Furthermore it improves wettability with Al-melt and a dense composite structure can be obtained. Infiltration without alumina protective coating leads to many casting defects (e.g. uninfiltrated area) and carbide formation at the fiber-matrix interface. Interaction of alloying elements with alumina layer at the fiber-matrix interface is further studied by TEM analysis.