Evaluation of Micromechanical Properties of Carbon/Carbon and Carbon/Carbon-Silicon Carbide Composites at Ultralow Load.

2D carbon fiber (C-fiber)-reinforced carbon/carbon (C/C) composites were prepared by vacuum infiltration with coal-tar pitch followed by carbonization and graphitization in inert atmosphere. Liquid silicon infiltration was done in controlled atmosphere at 1600°C to convert the matrix carbon of the C/C composites into silicon carbide. The 2D C/C and carbon/carbon-silicon carbide (C/C-SiC) composites had density of ∼1.65 and ∼2.32 g/cm, respectively with corresponding flexural strength of ∼70 and ∼169 MPa, respectively. The local mechanical properties like hardness, Young's modulus, contact pressure, relative stiffness, relative spring back, and indentation energies of the two composites under different loading conditions were measured at an ultra low load of 10 mN using a nanoindentation instrument with a Berkovich indenter. The scatter in the data was treated in terms of the two-parameter Weibull statistical analysis. The maximum characteristic Young's modulus (∼16 GPa) and hardness (1.20 GPa) was obtained for the C/C-SiC composites in parallel direction of fabric stacking. The elastic rebounce was also the maximum (0.77) for the C/C-SiC composites when loaded in parallel direction of fabric stacking. The extent of structural anisotropy was higher in the C/C-SiC composite than that of the C/C composite. [ABSTRACT FROM AUTHOR]