Mechanical spectroscopy of nanocrystalline metals: Structure and anelasticbehavior

Nanocrystalline aluminum and nickel were prepared by mechanical attrition i n a planetary ball-milling apparatus working under a 10(-4) Pa vacuum in th e 150-300 K range. A detailed investigation of the mechanical behavior in t he anelastic regime was accomplished by employing different mechanical spec troscopy apparatuses in the 0.01-10(3) Hz range. Measurements of the elasti c energy dissipation coefficient and of the dynamic elasticity modulus as a function of temperature and frequency have shown an enhanced damping at lo w temperatures and an anelastic relaxation peak tentatively assigned to the short range dynamics at the interfaces. Moreover the magnetic field depend ence of the dynamic elastic modulus in nickel revealed a strict correlation between the microstrains confined at the interfaces and the magnitude of t he magnetoelastic coupling.