Microstructure-related anelastic and magnetoelastic behavior of nanocrystalline nickel

Nanocrystalline nickel was prepared by a planetary ball milling apparatus working in a vacuum of 10(-4) Pa in the 150-300 K temperature range. The kinetic of the milling process and the microstructure evolution upon annealing were followed by x-ray diffraction and mechanical spectroscopy measurements. It was observed that thermal annealing up to 600 K induces a strong reduction of the internal strains without significant grain growth. Measurements of elastic energy dissipation and dynamic elastic modulus as a function of temperature showed that in the nanocrystalline samples, anelastic relaxation processes occur, with the activation energy of grain boundary diffusion. A systematic study of the magnetic field dependence of the dynamic modulus (Delta E effect) revealed a correlation between the Delta E magnitude and the strain values obtained by x-ray diffraction analysis. (C) 1998 American Institute of Physics. [S0021-8979(98)06119-2].