Damping capacity of nanotwinned copper

Copper with different twin densities was obtained by its deposition from the vapour phase in the form of coatings or separated condensates (foils) oil substrates kept at different temperatures. True values of the logarithmic decrement (LD) for copper were calculated from LD amplitude dependences, measured for the coating-substrate system in the range of coating deformation amplitudes 5 x 10(-5) < epsilon < 10(-3) at bending vibrations of 140-50 Hz of cantilever specimens. It is shown that with the reduction of the twin domain thickness to the nanosize range, the copper damping characteristics undergo a qualitative change. which is expressed in an abrupt weakening of the amplitude dependence of LD and in a considerable increase in LD values at its heating in the entire range of deformation amplitudes. The observed changes of the dissipative properties of copper are associated with the influence of twin boundaries oil its microplastic deformation. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.