Elastic moduli and strength of nanocrystalline cubicBC2Nfrom x-ray diffraction under nonhydrostatic compression

Abstract

The stress behavior of nanocrystalline cubic boron carbon nitride $(c{\text{-BC}}_{2}\text{N})$ was investigated using radial and axial x-ray diffractions in the diamond-anvil cell under nonhydrostatic compression up to ~100 GPa. The radial x-ray diffraction (RXRD) data yield a bulk modulus ${K}_{0}=276\ifmmode\pm\else\textpm\fi{}20\text{ }\text{GPa}$ with a fixed pressure derivative ${K}_{0}^{\ensuremath{'}}=3.4$ at $\ensuremath{\psi}=54.7\ifmmode^\circ\else\textdegree\fi{}$, which corresponds to the hydrostatic compression curve. The bulk modulus obtained from axial x-ray diffraction (AXRD) gives a value of $420\ifmmode\pm\else\textpm\fi{}11\text{ }\text{GPa}$. A comparative study of the observed compression curves from radial and axial diffractions shows that the ruby-fluorescence pressure scale may reflect the maximum stress under nonhydrostatic compression. It was found that nanocrystalline $c{\text{-BC}}_{2}\text{N}$ sample could support a maximum differential stress of ~38 GPa when it started to yield at ~66 GPa under uniaxial compression. Moreover, the aggregate elastic moduli of the nanocrystalline $c{\text{-BC}}_{2}\text{N}$ have been determined from the RXRD data at high pressures.