Paper number 715


Christine Mayencourt and Robert Schaller

Institut de Génie Atomique, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland

Summary C / Mg and SiC / Mg have been produced by gas pressure infiltration of fibre preforms by a Mg-Si alloy. The Young's modulus of these composites corresponds to the mixture law. The damping capacity of the magnesium matrix is preserved and is 10 to 100 times higher than in an industrial magnesium alloy (AZ63). Moreover, the mechanical loss spectra obtained by mechanical spectroscopy are modified by transitory phenomena which appear during thermal cycling. The transient response informs us about the thermal stress relaxation mechanism occurring at ceramic-metal interfaces and thereby about the interface quality and the fatigue behaviour. The comparison between the experimental results and a model of dislocation motion allows one to interpret the energy dissipation as due to reversible dislocation motion, which is controlled by a solid friction mechanism. This interpretation is confirmed by transmission electron microscopy observations during "in situ" thermal cycling. Furthermore, the composites do not exhibit thermal fatigue over more than 50 thermal cycles (100K-400K).
Keywords damping capacity, Young's modulus, fatigue, magnesium, unidirectional fibres, dislocations, microstructure.

Theme : Metal Matrix Composites ; Microstructure/Properties Relationship

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