- Abstract The instability of boron carbide in contact with liquid copper triggers the interaction between B 4 C and the melt. In a silicon-free melt, this interaction leads to the dissolution of boron in the liquid Cu with a concomitant release of free carbon. The compositions of the substrate and of the melt are adjusted according to the equilibrium requirements in the three-phase (B 4 C–graphite–liquid solution saturated with carbon) system. In the course of the interaction between boron carbide and the Cu–Si melt containing less than 13 at.%Si, no silicon carbide is formed and the liquid does not wet the substrate. For a silicon content higher than 13 at.%, the presence of graphite particle agglomerates within a crater, which is formed as a result of the initial decomposition of boron carbide, offers appropriate sites for the nucleation and subsequent growth of SiC particles. The interaction between the Si-containing melt and the B 4 C substrate leads to an enrichment of the melt with boron released from the substrate. In the vicinity of the triple line, the composition of the near-surface substrate layer is shifted to higher boron content and the conditions for wetting the substrate are met.