Preparation of the Surfaces of High-Purity Polycrystalline Aluminum for the Mechanical Analysis by Means of Nanoindentation

The sample preparation and, in certain cases, the nanoindenter itself have an impact on the measurement results of a nanoindentation process on electropolished aluminum surfaces. In this work, the indentation hardness and the indentation modulus of recrystallized ultra-pure aluminum were determined. To this end, the surfaces were prepared by electrolysis. Two sources of influence were investigate drespectively: the sample preparation (roughness and deformed layer) and the nanoindenter (influence of the edge and damage to the sample caused by the measuring head). Very smooth (R-a <1 nm) surfaces could be generated. A statistical pop-in analysis revealed that the surfaces are virtually deformation free. The design of the measuring head of the used Picodentor HM500 considerably limits the available measuring surface. On a square ultra-pure aluminum sample with a dimension of 9.5 mm, only an area of 1.5 x 1.5 mm in the center of the sample can be measured by the indenter without any influences. The values for the indentation hardness and the indentation modulus of the suitably prepared samples were 240.1 MPa and 63.5 GPa, respectively, with a standard deviation of only 1 -2 %. The results can be obtained in a reproducible manner for several individual samples and fit well into data from literature.