swarm Effect of Film Elastic Modulus on Fatigue Behaviour of DLC-Coated Wrought Magnesium Alloy AZ61

Plane bending fatigue tests were conducted using DLC-coated magnesium alloy AZ61 with two different film elastic moduli in order to investigate the effect of film elastic modulus on fatigue behaviour. Fatigue strength was improved by DLC film where DLC film with larger elastic modulus was more effective to improve fatigue strength. Delaminations of DLC film from base metal were observed near crack initiation sites. The number of small cracks and delaminations was larger as film elastic modulus was larger. By DLC film, stress near the boundary between base metal and DLC film is redistributed in a specimen compared with parent material without DLC film. Stress is reduced at base metal but large stress occurs at DLC film due to the difference of elastic moduli of base metal and DLC film. Stress at base metal and DLC film near the boundary is calculated by FEM (Finite Element Method) analysis. FEM analysis showed that stress decreases at base metal, stress increases at DLC film and that the difference of stresses at base metal and DLC film becomes larger when film elastic modulus is larger. It is considered that firm restraint of slip deformation in base metal by DLC film is effective to improve fatigue strength and that large stress in DLC film would not give negative effect on fatigue strength. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11