Mechanical spectroscopy of nanoparticle reinforced, electrodeposited ultrafine grained nickel

The grain size of electrodeposited ultrafine grained nickel can be reduced from ∼300 nm down to ∼60–150 nm by adding ceramic nanoparticles such as Al2O3 or SiO2. The first results are presented using temperature-dependent mechanical spectroscopy (vibrating reed technique at ∼200–800 Hz) applied to pure Ni as well as to Ni nanocomposites with very small (7 nm) SiO2 or larger (25 nm) Al2O3 particles, respectively. The mechanical spectra reveal several different elastic and anelastic phenomena: a high temperature damping background, irreversible changes in Young’s modulus, magneto-mechanical effects, and two low temperature loss peaks attributed to dislocations and to absorbed hydrogen, respectively. These phenomena and their different annealing characteristics are discussed in terms of underlying physical mechanisms and related processes of recovery and grain growth. The Ni/Al2O3 nanocomposite differs from the two other materials by effective suppression of matrix grain growth as manifested in the stabilisation of high temperature damping and absence of magneto-mechanical effects, and by the properties of the matrix/ceramic interfaces – with the incorporation of hydrogen and generation of dislocations by thermal stresses – as detected by the low temperature loss peaks. On the other hand, the annealing-induced increase in Young’s modulus, being more sensitive to the early stages of recovery, seems to be smaller with SiO2 than with Al2O3 particles (in spite of a lower stability against grain growth), which is not yet fully understood.