The defect structures and mechanical properties of Cu and Cu-Al alloys processed by split Hopkinson pressure bar

Pure Cu, Cu-5 at%Al, Cu-10 at%Al and Cu-15 at%Al with different stacking fault energy (SFE) of 78, 37, 7 and 5 mJ/m2, respectively, were processed through split Hopkinson pressure bar (SHPB) with the strain rate of 103/sec. The influence of high strain rate on the evolution of microstructures and mechanical properties of Cu and Cu-Al alloys was investigated. X-ray diffraction measurements indicate that, the microstructures of Cu and Cu-Al alloys have been refined to the nano scale after deformed by SHPB, and with decreasing SFE, the average grain size decreases gradually from 72 to 40 nm, while the dislocation density increases from 0.55×1014 to 4.4×1014 m−2 and the twin density increases from 0.04% to 1.07%. The formation of deformation twins is an additional factor that contributes to the microhardness and strength of Cu and Cu-Al alloys except the solid solution strengthening effect. Cu-15 at%Al has the biggest strain hardening rate at larger strains due to its lowest SFE which results in the highest twin density. The results confirm that lower SFE improves both strength and strain hardening rate of materials.