Rapid spark plasma sintering to produce dense UHTCs reinforced with undamaged carbon fibres

Short fibre reinforced ceramic composites, based on ZrB2 with a carbon fibre content of 45 vol%, were produced by ball-milling and rapid Spark Plasma Sintering (SPS) at 1800–2300 °C by varying the holding times. Careful control of the sintering parameters, such as the heating rate, dwell temperature and holding time are required to produce a fully dense matrix and avoid fibre degradation. The sintered materials were characterized in terms of relative density, morphology of the fibres and microstructural features of the matrix. The final residual porosity ranged from 16 to 3 vol%. The carbon fibres maintained their original morphology and the matrix consisted of ZrB2, SiC and ZrC phases. In spite of the good adhesion between the fibre surface and the matrix promoted by SPS processing, extensive fibre pull-out was observed in the fracture surfaces of all of the composites sintered at or below 1900 °C.