Production of net-shaped dense metal-carbide-based composites through an infiltration process at intermediate temperature

Abstract

Tungsten composites are interesting materials for high temperature applications. These composites are conventionally produced by solid state reaction, where elevated temperatures and long sintering processes are inevitable, and generally produce volatile components that increase defects and impair the properties of the composites for high temperature applications. In the present paper, synthesis of dense near net-shaped transition metal–metal carbide by reaction casting is studied, which creates a potential application for the composite at 2000°C. Since the pores of the ceramic preform are filled with reaction products, this technique is referred to as displacive compensation porosity (DCP). The effects of sintering and infiltration parameters on composition of ZrC/W composites produced by DCP were studied. For this purpose, porous WC preforms were first uniaxially pressed and then sintered at 1400°C for 2h leading to preforms with various porosities (54 to 57%). Unidirectional and spontaneous infiltration of the sintered preform by ZrCu liquid was performed at 1200°C for 1, 2 and 3h. The resulting specimens were then analyzed via X-ray diffraction. Scanning electron microscopy (SEM) was used to examine the microstructure and diffusion of molten phase into porous preforms. The microstructures show that grains of the WC are being surrounded with infiltrated eutectic melt, thereby promoting reaction between the melts and the preform components. Furthermore, the extent of incorporation of ZrCu melt into the preform was investigated as a function of time. It was concluded that infiltration time has a limited influence on residual unreacted reagent and the percentage of the resulting product. On the other hand, improvement in wettability/contact angle with reduction in either particle size or presence of additive can increase the efficiency of the infiltration process.