Local indentation response of carbon fibers embedded in a harsh environment: The sintered ultra-high temperature ceramic matrix

Understanding the properties of the constituent elements within Ceramic Matrix Composites (CMCs) is of paramount importance. During manufacturing process, the properties of the starting phases can undergo changes or be influenced by their interactions. In this work, micro-indentation analysis was used to selectively characterize matrix and fiber of Ultra-High-Temperature CMCs (UHTCMCs) produced by slurry infiltration of unidirectional pitch-derived carbon fabrics and sintering. A loading pre-factor was exploited to differentiate between indentations made on the matrix and those made on the fibers. The ZrB2-based matrix showed typical elasto-plastic behavior, leaving a residual imprint, with hardness and a modulus of 11.5 GPa and 220 GPa, respectively, consistent with its porosity, cracks and fiber content. Conversely, the fiber displayed no residual imprint and displayed hardness and modulus values of 1.1 GPa and 40 GPa, respectively. These values were attributed to the graphitic sheets buckling and residual thermal stress. Furthermore, the indentations indicated a transition zone between the matrix and fiber affecting mechanical behavior.