Nanoscale Mechanical Properties of Ultrahigh-Purity Aluminum

Abstract

Nanoindentation data reveal interesting behavior in aluminum with various purities: 99.9999% (6N), 99.99% (4N), and 99% (2N). Nanoindentation is used to investigate the relationship between the purity and the mechanical properties of ultrahigh-purity aluminum at room temperature. The area subjected to nanoindentation would be expected to behave similarly to a perfect, dislocation-free single crystal. Nanoindentation data is also compared with results of conventional tensile and hardness tests. These results highlight the differences between microscopic and macroscopic properties. The tensile strength and the hardness of normal-purity aluminum, 99% (2N), are larger than those of ultrahigh-purity aluminum, 99.9999% (6N), and high-purity aluminum, 99.99% (4N). However, in the nanoindentation test, the penetration depth for ultrahigh-purity aluminum (6N) and high-purity aluminum (4N) is less than that for normal-purity aluminum (2N). Thus, microscopic mechanical properties differ from macroscopic mechanical properties. It is suggested that the surface of high-purity aluminum is harder than that of normal-purity aluminum on the micro-scale. The experimental result shows that the perfect crystals are harder than the imperfect crystals. Furthermore, some recovery of the indentation mark is observed in high-purity aluminum. It comes from the recovery of deformation by indentation due to the mobility of defects in the sample.