Fatigue Behaviour of DLC Coated Magnesium Alloy in Laboratory Air and Demineralized Water

摘要

Rotary bending fatigue tests were performed in laboratory air and demineralized water using DLC-coated wrought magnesium (Mg) alloy, AZ80. Two film thicknesses, 3.5μm and 25μm, were evaluated in order to investigate the effect of DLC coating on fatigue and corrosion fatigue behaviour. In laboratory air, the fatigue strengths of the DLC-coated specimens were higher than those of the bare ones and increased with increasing film thickness. This was because hard DLC film with high coating adhesion suppressed slip deformation on the specimen surface. In demineralized water, fatigue strengths were considerably decreased due to the formation of corrosion pits in the bare specimens. Thin DLC film could not improve corrosion fatigue strength due to the penetration of the solution through the pre-existed hole defects in the film, while thick DLC film could improve corrosion fatigue strength because penetrating paths were eliminated during long and two-step DLC deposition process of 26 hours.