Effect of Interlayer Thickness on Fatigue Behavior in A5052 Aluminum Alloy with Diamond-Like Carbon/Anodic-Oxide Hybrid Coating

Abstract

Anodic oxide layer was formed on A5052 aluminum alloy, and subsequently diamond-like carbon (DLC) was deposited to fabricate DLC/anodic-oxide hybrid coating. Plane bending fatigue testes have been performed using the hybrid-coated specimens with different thicknesses of anodic-oxide interlayer. The interlayer thicknesses were 10 and 50 µm, where the thickness of DLC film was fixed as 3 µm. The specimens without coating, with DLC single layer and with anodic-oxide single layer were also used for comparison. The fatigue strengths of the specimens with anodic-oxide single layer were lower than those of the substrate without coating because the corner edge cracking or pin-hole defects could be fatigue crack initiation sites. However, when DLC was deposited on the anodic-oxide layer, fatigue strengths were improved. The hybrid-coated specimens with the interlayer thickness of 10 µm had higher fatigue limit than the substrate and specimens with the interlayer thickness of 50 µm. Thin DLC layer with the thickness of 3 µm could have suppressed the cracking in interlayer, and led to the improvement of fatigue strengths than the substrate. When the interlayer became relatively thicker compared with the DLC film, such as 50 µm, DLC film could not suppress the cracking from the corner edge defects, resulting in the lower fatigue strengths in spite of the presence of hybrid coating.