DLC皮膜を被覆した展伸マグネシウム合金AZ61の疲労挙動に及ぼす膜弾性係数の影響

概要

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Plane bending fatigue tests were conducted using DLC (Diamond-like Carbon) coated magnesium alloy, AZ61, with two different kinds of film elastic moduli in order to investigate the effect of film rigidity on the fatigue behavior. From the experimental results, it was found that the DLC coating was effective to improve the fatigue strength when the film had larger elastic modulus and rigidity. Cracks and delamination of the film were observed near the crack initiation sites and they were prominent when the film elastic modulus was larger. By the DLC coating, the stress near the boundary between the base material and the DLC film was redistributed in a specimen and then the stress was relaxed at the base material and concentrated at the DLC film. The stress relaxation at the base material and the stress concentration at the DLC film near the boundary were evaluated by the FEM (Finite Element Method) analysis. From the stress analysis, it was quantitatively confirmed that the stress relaxation and the stress concentration were larger when the film elastic modulus was larger. It is considered that the DLC coating could improve the fatigue strength by the restraint of slip deformation in the base material by a film. The stress concentration at the DLC film could cause cracks and delamination after the film fracture but it would not give the negative effect on the fatigue strength.