INTERDIFFUSIONAL EFFECTS IN TUNGSTEN FIBER REINFORCED NICKEL-MATRIX COMPOSITES

The need for improved materials at elevated temperatures (1100-degrees-C) has stimulated research in many areas, including efforts to develop fiber-reinforced superalloy matrix compossites. In the tungsten-fiber-reinforced composites, having pure Ni-matrix, diffusion of Ni-atoms into the fiber has been observed which results in accelerated recrystallization of the fiber. Formation of intermetallic compound layer at the fiber/matrix interface has also been reported by some workers. This interdiffusional effects and aggressive fiber/matrix reactions degrades the mechanical properties of the fiber. In the present work, effect of tantalum as alloying element and barrier layer, on the kinetics and mechanism of interaction of thoriated tungsten fiber (Th2O = 1.6%) with Ni-base matrix has been studied. It has been found that addition of tantalum up to 2 at .% to the Ni-matrix decreases the rate of diffusion of Ni-atoms into the fiber and suppresses its recrystallization. Rapid heating and cooling (60-degrees-C/min) has been found successful in avoiding the formation of intermetallic compound layer at the fiber/matrix interface. A barrier layer of tantalum at the fiber/matrix interface, also suppresses the diffusion of Ni-atoms into the fiber up to 1300-degrees-C, and a thin layer of Ni3Ta(approximately 6-mu) is formed at the foil/matrix interface.