LOW-COST FABRICATION PROCESSES FOR HAFNIUM BORIDE AND HAFNIUM NITRIDE MATRIX COMPOSITES

The proposed Phase I project will examine potential low-cost, high-rate processes for synthesizing hafnium boride and hafnium nitride composite matrices from liquid precursors. Several of the most cost-effective precursor material combinations will be comparatively evaluated in terms of product yield and physicochemical characteristics when pyrolyzed as neat materials. The most promising precursor material combinations will be impregnated into woven carbon fiber preforms and pyrolyzed, the cycle being repeated multiple times, to produce prototype composite materials for preliminary evaluation of physical and mechanical properties for comparison with CVI-processed hafnium carbide matrix composite materials. The feasibility of a hybrid process achieved by using the liquid processing methods to complete the densification of partially CVI-processed materials will also be investigated. An option task will examine the feasibility of integration of the densification material with the fabrication process, for example by liquid impregnation of yarns with matrix precursors prior to weaving preforms. The developed materials and processing techniques are expected to significantly reduce fabrication times, and thus cost, for carbon fiber reinforced hafnium boride or hafnium nitride matrix composites. The processing techniques should also be applicable to other refractory borides and nitrides, including alloy compositions, of interest to the NSWC.