Fatigue behavior of nanoscale Mo/W multilayers on flexible substrates

Fatigue properties of Mo/W multilayers with individual layer thickness (lambda) of 5, 20, 50 and 100 nm on flexible polyimide substrates were investigated. The experimental results show that the fatigue resistance increases with decreasing lambda from 100 nm to 20 nm, and reaches the maximum at lambda =20 nm, and then decreases when further decreasing lambda. Fatigue cracks of Mo/W multilayers with different lambda were found to propagate along columnar grain boundary in the out-of-plane direction and along the boundary of cluster structures. The enhanced fatigue resistance is attributed to the larger cluster inclination angles and the more tortuous in-plane cracking paths.