Lattice preferred orientation and stress in polycrystalline hcp-Co plastically deformed under high pressure

The results of x-ray diffraction data of a polycrystal under nonhydrostatic compression are analyzed for lattice preferred orientation and stress using lattice strain theories with an application to hcp-Co deformed up to $42.6GPa$ in the diamond anvil cell. We obtain a pure [001] fiber texture that develops primarily between 0 and $15GPa$⁠. We also show that for hcp metals the hypothesis of uniform stress across grains and lattice planes cannot be applied. This implies that the effective single crystal elastic moduli deduced from x-ray diffraction under Reuss or geometric averages consistently differ from those measured with other techniques, even after including effects of lattice preferred orientations. These results can be interpreted as an $(hkl)$-dependent effective differential stress resulting from plastic deformation.