Fatigue behaviour in AZ80A magnesium alloy with DLC/thermally splayed WC-12Co hybrid coating

WC-12Co was thermally sprayed on AZ80A magnesium (Mg) alloy as an interlayer, and then diamond-like carbon (DLC) film was deposited in order to fabricate DLC/WC-12Co hybrid coating. Rotary bending fatigue tests were conducted in laboratory air and the effect of hybrid coating on the fatigue behaviour was discussed. The thicknesses of WC-12Co interlayer were 15, 50 and 80 μm and those of DLC film were 3 and 15 μm. Thin hybrid coating (15 μm WC-12Co + 3 μm DLC) was detrimental to the fatigue strength because thin coating could not suppress crack initiation from the small notches introduced during thermal spraying process. Thick hybrid coating (80 μm WC-12Co + 15 μm DLC), however, could improve fatigue strength. Thick interlayer was effective for bearing fatigue loading, resulting in the higher fatigue strength than the substrate.