Modified strain rate regime in ultrafine grained copper with silver micro-alloying

Ultrafine grained (UFG) copper with an average grain size of 115 nm was micro-alloyed with silver (UFG CuAg) to analyze its effect on strain rate sensitivity. The materials were prepared by sintering Ag microalloyed-Cu ultrafine powder, using the spark plasma sintering (SPS) technique and after H2 pre-annealing for oxide reduction. Mechanical tests show that UFG CuAg follows the law of behavior established for UFG Cu: m≈B(1−σ0/σ)m≈B(1−σ0/σ), relating the strain rate sensitivity mm and the applied stress, σσ. In this relation, σ0σ0 is a threshold grain size dependent stress and BB is characterizing the grain boundaries diffusion properties. Main difference compared to pure UFG copper is a large value of the parameter BB for UFG CuAg, indicating a dominant role of the grain boundaries structure and chemistry on the rheology of UFG metals.