The microstructural refinement of metals during Severe Plastic Deformation (SPD) strongly depends on the stacking fault energy (SFE), which not only affects the deformation mechanisms but also the dynamic recovery behavior and storage of dislocations. Cu based solid solutions are good model materials to study these effects, as the SFE of Cu can be reduced significantly by adding Zn or Al. However, aside from a change in SFE, alloying also results in a solid solution strengthening which can also affect the microstructural response during SPD.
To investigate the effect of SFE and solid solution strengthening on the grain refinement and strength of Cu based alloys, three alloys with 5% Zn, 30% Zn and 5% Sn were subjected to SPD via ECAP and HPT. Microstructural investigations show that a low SFE (CuZn30) as well as strong solid solution strengthening (CuSn5) lead to an increase in grain refinement rate with imposed strain. The minimum achievable grain size shows a similar trend with lowest numbers for CuZn30 followed by CuSn5 and highest for CuZn5. The strength of the ultrafine grained (UFG) alloys after SPD shows interesting results, as the CuSn5 alloy exhibits the highest hardness in spite of neither having the lowest grain size nor the lowest SFE, i.e. dislocation mobility. The high hardness of UFG CuSn5 cannot be solely attributed to the solid solution strengthening of Sn, which is known from the coarse grained conditions. This indicates that further strengthening contributions other than grain size and solid solution strengthening need to be considered.