Superhard materials based on the solid solution SiC–C

Superhard nanocrystalline silicon carbide films

“…Recently there has been a flurry of interest in superhard Si x C y ͑y ജ x͒ materials, where "superhard" is defined to mean hardness ജ40 GPa, well above the hardness of standard ␤-SiC, ϳ28 GPa. Several investigators [1][2][3][4][5][6] have synthesized SiC-diamond composites using high-pressure, hightemperature powder sintering, and have reported hardnesses ranging from 40-80 GPa. Recently it was reported that hydrogen-free amorphous C-Si films, synthesized by magnetron cosputtering of graphite and silicon, had hardness values of 45-55 GPa for Si mole fractions in the range 38-43 %.…”

Phase Segregation in Silicon Carbide−Carbon Solid Solutions from XRD and NMR Studies

“…The diffusion of superstoichiometric carbon atoms at the (4 GPa, 1800 °C) sintering changes the microstructure from planar long-range defects in the phase-segregated, as-synthesized SiC−C solid solution to point defects (C Si antisites) in the ideal solid solution, so that the average lattice parameter is not conserved during the process. Sintering the as-synthesized powder at a lower temperature of 1400 °C (when this diffusion process is not active) does not change the fine structure of the XRD pattern, and only a broadening of the peaks created by an increase of the dislocation density was observed …”

“…Subsequently, the as-synthesized SiC−C powder was annealed in a vacuum at different temperatures in the range of 1400−1900 °C and sintered under pressures in the range of 4−8 GPa and temperatures of 1400 and 1800 °C. The mechanical properties of these and other samples are reported elsewhere . To carry out the NMR measurements, the sintered samples were crushed in an agate mortar.…”

“…Thus, the superstoichiometric carbon atoms are located in the silicon carbide crystal structure as planar defects along {111}. These defects reduce the lattice parameter and produce strain anisotropy in the β-SiC crystal structure . It was revealed that a diffusion of the superstoichiometric carbon atoms during high-pressure and high-temperature sintering (4 GPa, 1800 °C) breaks down the planar defects producing an ideal solid solution of carbon in the silicon sublattice of the β-SiC crystal structure.…”

“…These defects reduce the lattice parameter and produce strain anisotropy in the β-SiC crystal structure. 5 It was revealed that a diffusion of the superstoichiometric carbon atoms during high-pressure and high-temperature sintering (4 GPa, 1800 °C) breaks down the planar defects producing an ideal solid solution of carbon in the silicon sublattice of the β-SiC crystal structure. The lattice parameter of this sintered sample has been used to estimate the composition through Vegard's law as Si 1-x C 1+x with x ) 0.007.…”