Hot Isotactic Pressing HIPing

Hot isostatic pressing can provide a uniform high density, to almost 100% of theoretical density, providing near net shape components without size limitations. Since the applied pressure is uniform, the density too is uniform. The process can be used directly, or in combination with a preforming step such as injection molding or sintering. The technique has been described in relation to carbon-carbon composites (Chapter 14, Section 14.3.3.3). 

Slip infiltrated, HlPed carbon fiber reinforced material, slip infiltrated SiC fiber reinforced nitrided SisN4, and polysilazane solution infiltrated pyrolyzed composites with SiC fibers have been fabricated [159]. All materials exhibited non-brittle fracture. 

Carbon fiber/Si3N4 composites were fabricated using slip infiltration of fiber bundles, subsequently stacked in a plaster mold, dried, glass encapsulated and HfPed to form unidirectional composite test bars. Neither chemical reactions between fiber and matrix, nor thermal mismatch cracks in the matrix were observed. The bend fracture behavior of the composites was non-brittle with extensive fiber pullout. 

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