Inelastic Deformation of Copper Nanoparticle Based Joints and Bonds

The inelastic deformation properties of sintered metal nanoparticle joints are complicated by the inherent nanocrystalline and nanoporous structures, as well as by dislocation networks formed in sintering or under cyclic loading. Creep rates of sintered nanocopper structures were found to be dominated by the diffusion of individual atoms or vacancies, while dislocation motion remained negligible up to stresses far above those of practical interest. Rapid sintering of one material led to unstable structures with particularly narrow necks between Cu particles and a dense network of dislocations. Creep rates were dominated by dislocation core diffusion within the necks to the nearest open pore surfaces. Exposure to elevated temperatures led to coarsening of the necks and, importantly, annihilation of dislocations, which reduced the creep strongly. Longer sintering of another material led to wider necks without excess dislocations and thus more stable structures. Creep rates were dominated by grain boundary diffusion within the necks and could be strongly enhanced by subsequent work hardening in mild cycling.