Morphology and Tribological Behaviour of Amorphous and Crystalline Aluminum Oxide Layers

Anodization of aluminum (Al) is a well-known process for the production of oxidized Al surfaces. Within the scope of the present work, three different Al-oxide layers, produced with different electrochemical methods, were investigated in view of their layer morphology and tribological properties. For this purpose, a newly developed PCO layer (Innovent e.V.), and two commercially available layers, Ematal and a CERANOD®, were compared. Al-oxide layers produced on flat samples were tested against cylindrical DIN 100Cr6 rings under dry sliding conditions. It was observed that under the selected conditions, the frictional behavior of the Al-oxide layers can be influenced by their structural composition and their surface topography, i.e. is different when their structure is amorphous or crystalline. The newly developed Al-oxide layer, which possesses the lowest surface roughness and a very uniform porosity, provided the longest lasting low friction period. Since γ-Al2O3 was also observed in this layer, it is believed that the structural composition of the Al-oxide layer has additionally influenced the frictional response of these samples.