On the mechanical properties of nanoporous anodized alumina by nanoindentation and sliding tests

Mechanical properties like hardness, Youngʹs modulus, and plastic deformation of nanoporous anodized alumina fabricated in the most used acid electrolytes (i.e. sulphuric, oxalic and phosphoric) were extracted from nanoindentation and sliding tests. The dependence of the mechanical properties on the porosity level was analyzed for each type of samples. Nanohardness, Youngʹs modulus and the coefficient of friction were related to the sample type and its porosity. Indents and scratches were inspected by FEG-SEM, which revealed that nanoporous anodized alumina undergo an elastoplastic behavior under the applied loads. The ductility is found to be higher for samples prepared in the phosphoric solution than for the ones obtained from oxalic and sulphuric solutions. This is associated with the high water content, the phosphate anions incorporated into the alumina structure during the anodization process and the aluminum nanopillar structure between those pores with irregular junctions located at the alumina–aluminum interface.