DEVELOPMENT OF CONTINUOUS SiC FIBER REINFORCED HfB2-SiC COMPOSITES FOR AEROSPACE APPLICATIONS

The fabrication of SiC/HfB2-SiC continuous fiber reinforced composites by polymer impregnation and slurry infiltration of partially densified SiC-SiC laminates was investigated. A polymer-based HfB2 precursor was synthesized and used to impregnate the preform panels via vacuum infiltration. Subsequent heat treatment at 1600 degrees C in argon carbothermally reduced the polymer to HfB2 and residual carbon. Slurry infiltration was performed via vacuum infiltration, pressure infiltration, vibration infiltration, vibration-assisted vacuum infiltration and vibration-assisted pressure infiltration using 5 vol % HfB2 slurries in ethanol. An additional pressure infiltration experiment was performed using a 15 vol % slurry. Subsequent heat treatment at 1600 degrees C was sufficient to initiate sintering of HfB2 particles, but not densification. Polymer impregnation resulted in poor infiltration due to the low ceramic yield of the polymer and poor adhesion to the preform. SEM analysis, Archimedes density measurements and computational image analysis showed some success for the slurry infiltration techniques, with the best results observed for pressure infiltration using the 5 vol % slurry.