Effects of the fiber coating on interfacial phenomena in tungsten/nickel and tungsten/SUS316L (AISI 316L type stainless steel) composites were studied with special emphasis on the diffusion and the chemical reaction. A combination of tungsten fiber without doping and nickel matrix, in which recrystallization easily takes place at elevated temperature, was tested as a preliminary experiment. The combination is rather an extreme example with the recrystallization and interfacial reaction. Then, a composite with the tungsten fiber and 316L stainless steel matrix which would be more adoptable than pure nickel matrix for practical application was employed.
Oxides, carbides, and nitrides of such elements as aluminum, titanium, chromium, zirconium, and tantalum were examined as coating materials. The materials were selected on the basis of the chemical free energy of formation. The composites were exposed under the different kinds of thermal conditions. Effects of coating on the interfacial phenomena were evaluated by such characteristics of the composites as microstructure and mechanical behavior after the exposure.
Among all the coating materials tested, some of zirconium compounds were most effective in tungsten/nickel composites. Accordingly, zirconium dioxide and zirconium nitride coatings were mostly examined in a tungsten/316L stainless steel system. These coatings worked well as the reaction barrier at elevated temperature.