Thermal stability of the engineered interfaces in [W.sub.f]/W composites

Application of tungsten as a structural material is severely restricted due to its inherent brittleness. Recently, a novel toughening method for tungsten was proposed by the authors using tungsten wires as reinforcement. The idea is analogous to the fiber-reinforced ceramic-matrix composites theory which utilizes the internal energy dissipation caused by the debonding and frictional sliding at the fiber/matrix interfaces to absorb strain energy and to redistribute stress concentrations over an extended volume. To maximize the energy dissipation, the interfaces need to be engineered by coating which can withstand thermal exposure during service. In this work, we studied the thermal stability of various interfacial coatings after heat treatment. Microstructural change and the effect on mechanical properties were investigated by means of electron microscopy and fiber push-out tests. The results show that the microstructural phases of the analyzed interfaces remained relatively stable under thermal exposure of 800°C for 10 h. Under such thermal exposure, the fracture energy of the Er/W multilayer and the Zr[O.sub.x]/Zr multilayer were affected by less than 10%, while it was increased by 40% for the Zr[O.sub.x]/W bilayer. The fracture energy of the C/W dual layer was decreased by a factor of 4, whereas for the Cu/W multilayer case it was increased by a factor of 2.