Abstract
Anodic oxide layer was formed on A5052 aluminum alloy, and subsequently DLC was deposited on it to fabricate DLC/anodic-oxide hybrid coating. Rotating bending fatigue testes have been performed using the hybrid-coated specimens with different thicknesses of anodic-oxide interlayer. The interlayer thicknesses were 10 and 50μm, where the thickness of DLC film was fixed as 3μm. 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 oxide layer were lower than those of the base metal without coating because oxide layer had pin-hole defects and the defects could be fatigue crack initiation sites. However, when DLC was deposited on the oxide layer to fabricate DLC/anodic-oxide hybrid coating, fatigue strengths were improved. The hybrid-coated specimens with the interlayer thickness of 10μ had higher fatigue strength than the base metal and those with the interlayer thickness of 50μm. Thin DLC layer with the thickness of 3μm could have suppressed the cracking in interlayer, and led to the improvement of fatigue strengths than the base metal. When the interlayer became relatively thicker compared with the DLC film, such as 50μm, DLC film could not suppress the cracking in interlayer, resulting in the lower fatigue strengths.
