Bonding effect of liquid magnesium with open-celled carbon foam in interpenetrating phase composite

Abstract

Abstract The issue of bonding formation in liquid metal/open-celled carbon foam (Cof) systems was examined, taking into account the practical aspects of the synthesis of a new type of Mg-C metal material composite. The problem is complex due to the strong oxidation and intense evaporation of liquid magnesium, as well as the 3D geometry of the carbon component, where metal transport occurred through the foam cells’ windows. Laboratory experiments performed at 700°C in ceramic crucibles showed that spontaneous carbon foam infiltration by liquid metal is impossible under the applied conditions, either in an air atmosphere coupled with flux protection or under argon protection. Comparative tests performed in a UHV chamber filled with static pure Ar by a sessile drop method, coupled with non-contact heating and capillary purification at a test temperature of 700°C directly in the UHV chamber, showed non-wetting behavior of the Mg/Cof couple with a correspondingly high contact angle of about 135°. The graphite capillary was then moved down, the liquid drop being slightly pressed into the foam, but these changes did not induce effective foam penetration. Despite the short contact time for the sessile drop test under an argon atmosphere, SEM+WDS analysis of the solidified Mg/Cof couple revealed the formation of an MgO interlayer at the interface, with a thickness of approx. 1 µm. The experimentally demonstrated presence of oxygen in the carbon foam sample, both before and after its contact with magnesium, points to oxide-type bonding being established between Mg and Cof. This observation is in a good agreement with previous reports on the interface characterization of magnesium matrix composites reinforced with glassy carbon materials and carbon fibers by stir casting and pressure infiltration. Based on the findings of this study, a general structural scheme of the bonding process between carbon foam and liquid magnesium, as an important stage in the syntheses of Mg-C composites, was proposed.