BORON-CARBIDE BASED COATINGS ON GRAPHITE FOR PLASMA-FACING COMPONENTS

In the effort to evaluate boron-rich coatings as plasma-facing surface s in fusion devices, a new process for applying boron carbide (B4C) co atings to graphite was developed. The process entails eutectic melting of the carbon (C) substrate surface with a precursor layer of B4C par ticles. Adherent coatings were achieved which consisted of two layers: a surface layer and a graded penetration zone in the outer portion of the substrate. The surface-layer microstructure was multiphase and ra nged from reaction-sintered structures of sintered B4C particles in an eutectic formed matrix to that of hypereutectic carbon particles in a B4C-C eutectic matrix. Because of high surface energy, the coating ge nerally developed a nonuniform thickness. Quantitative evaluations of the coating were performed with limiters in the TEXTOR fusion device a nd with coupons in electron beam tests. Test results revealed the foll owing: good adherence of the coating even after remelting; and, during remelting, diagnostics detected a corresponding interaction of boron with the plasma.