Opto-acoustic and acoustic microscopy studies of microstructure, elasticity and defects in B$_4$C/C$_{60}$ and c-BN/C$_{60}$ nanocomposites

Carbon-ceramic nanocomposites based on boron carbide with fullerene C$_{60}$ (B$_4$C/C$_{60}$) and cubic boron nitride with C$_{60}$ (c-BN/C$_{60}$) were prepared by a high-energy ball milled pre-treatment of the initial mixture of components with the addition of a CS$_2$ solvent followed by a high-pressure/high-temperature consolidation. Elastic properties of the composites were characterized by the elastic moduli calculated on the bases of the experimentally measured density and values of velocities of the longitudinal and transverse bulk acoustic waves (BAW) in the samples. The BAW velocities were measured with a pulse-echo method by laser optoacoustic excitation of ultrasonic pulses. Acoustic microscopy was used to visualize the bulk microstructure and internal defects, and to measure the local values of BAW velocities of specimens on which the elastic moduli were calculated.