Experimental Study and Thermodynamic Analysis of High Temperature Interactions between Boron Carbide and Liquid Metals

Abstract

Fabrication of MCCs (Metal Ceramic Composites) and ceramic brazing requires improved wetting properties are often absent in various ceramic/metals systems. This report summarizes a comprehensive study concerning the wetting properties of boron carbide in contact with non-reactive metals such as Cu, Au, Ag, and Sn. In order to improve wetting, three different reactive elements were added to the melts; Si, which has relatively high affinity to C, leads to SiC formation and changes the stoichiometric boron carbide composition (B 4 C) towards lower carbon content; Ti, which displays high affinity to B, leads to TiB 2 formation and free carbon precipitation at the interface; and finally, Al, which forms borocarbide phases at the interface. It was found that Cu is unusual with respect to boron carbide compared the other non-reactive metals. The most important difference is its ability to dissolve ~25 at% of B, which makes B adequate as an additive to Cu in addition to Si, Ti, and Al. When boron was used as an alloying element, its effect on wetting behavior was attributed to altering the boron carbide composition in contact with boron-containing melts. It was concluded that the most important properties of boron carbide that affect wetting phenomena are the relatively low chemical stability and the existence of a wide composition range (B 4 C-B 10 C). The first property determines the possibility of boron carbide to react with liquid metals (by dissolution or formation of new phases) and the second offers an additional degree of freedom to improve its wetting by changing the composition of the ceramic phase.