Mechanical properties and microstructure of carbon fibre reinforced carbon materials produced by chemical vapour infiltration

Correlations between mechanical properties, fibre architecture, matrix texture and fracture behaviour of carbon fibre reinforced carbon CFC-materials produced by chemical vapour infiltration are investigated using results from tensile and four-point-bending tests, polarized light microscopy and scanning electron microscopy. Mechanical testing was performed at temperatures from 20 up to 1600 °C. Samples were tested in the as-received state and after heat treatment at T = 2200 °C. The heat treatment leads to an increasing Young’s modulus and brittleness, which corresponds with an increasingly distinct layer structure of high textured matrix carbon. A rise of test temperature up to 1400 °C also leads to a larger Young’s modulus and increasing brittleness. However, at T = 1600 °C the material shows a pronounced pseudoductile behaviour. Scanning electron micrographs show in this case a lot of concentric cracks between the sublayers of the high textured matrix. The fracture behaviour is explained by a multiple delamination between these layers.