Influence of W and Re Interlayers on the Interface between SiC Fibers and 9Cr Steel Matrix

S. Levchuk (Sp), S. Lindig, A. Brendel, H. Bolt, Max-Planck-Institut für Plasmaphysik, Garching (Germany) 
The future fusion power plant DEMO aims for structural materials which can withstand high heat fluxes and coolant pressure conditions at temperatures attractive for efficient thermodynamic energy production. The reduced activation ferritic martensitic steel EUROFER 97 is considered as a reference structural material for the first wall and structural components of DEMO. The efficiency of the fusion plant is strongly dependent on the operation temperature. Therefore, the limitation of the maximum operation temperature of EUROFER 97 to about 550°C is a significant disadvantage of this steel. The reinforcement of the steel with SiC-long fibres may allow the increase of the operation temperature of the composite up to 750°C. To investigate the processes at the fibre-matrix interface of such a material SiC-fibres were coated by magnetron sputtering with a fine structured steel interface layer. Then, a thick EUROFER matrix layer was deposited by arc deposition with high deposition rate. As a final step of the composite processing, hot isostatic pressing has to be applied to consolidate the coated fibres at 1000°C which is not subject of the present study. To simplify investigations of the interfacial reactions between the fibres and the matrix with a number of available analysis methods, planar SiC- and C-substrates were used. The samples with sputtered EUROFER layers were annealed at different temperatures ranging from 400°C to 1000°C and the strong diffusion at the interface between substrate and coating materials was found. To suppress this process, samples with different intermediate diffusion barrier layers (interlayers) of Re, W, and ZrO2 between the substrate and the EUROFER coating had been prepared. The interlayers were deposited by magnetron sputtering. The samples with the diffusion barriers were investigated before and after annealing using SEM, XRD and RBS analyses.