Polymer derived carbon ceramics are highly desirable for lightweight, high strength, extreme environment material architectures, but their mechanical performance as a function of structure and processing is not currently understood and cannot be predicted. In this study, the mechanical behavior for bulk-scale pyrolytic carbons (PyCs) made via polymer pyrolysis of phenolformaldehyde precursors are established as a function of heat treatment temperature and the resulting average nano-and meso-scale order and disorder via X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. The PyCs exhibit crystallite evolution on both the atomic-and meso-scale for pyrolysis temperatures of 600 • C to 1000 • C, whereas only atomic-scale crystallite evolution is observed for pyrolysis temperatures of 1000 • C to 1400 • C. The measured Vickers hardness of the PyCs is observed to scale non-monotonically as a function of the pyrolysis temperature reaching a peak at ∼ 4 GPa for samples prepared at 1000 • C. New modeling results, based on the elastic constants of disordered graphite, indicate that this counter-intuitive Vickers hardness scaling, which is a decades-old open question, originates from the PyC inter-layer shear elastic constant and the crystallite aspect ratio evolution with processing temperature. PyCs studied here are shown to be the lightest super-hard materials, having Vickers hardness-to-density ratios that are comparable to super-hard carbides, oxides, nitrides, and phosphides.

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high strength low density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano-and meso-scale structural evolution of phenol-formaldehyde derived PyCs is established as a function of pyrolysis temperature (T p) using x-ray diffraction, Raman spectroscopy, and