Abstract
Metallic thin films are now used as structural members of MEMS and electronic devices, and their fatigue properties may be different from bulk materials because of the difference in the crystalline orientation and grain size. In the present study, nickel nanocrystalHne thin films were produced by electrodeposition using sulfamate solution. Three types of thin films with different grain sizes were produced: CC films were made under constant current, PC films under pulse current, and CC-ally films under constant current with grain refinement additive. The grain size gets smaller in the order of CC, PC, and CC-ally films down to nanometers. The fracture strength and yield strength in tension tests follows the Hall-Petch relation. The fatigue strength increased with decreasing grain size, following the Hall-Petch relation down to lOnm. On the other hand, the resistance to fatigue crack propagation decreased for nano grain-sized films. The threshold stress intensity factor was the smallest for PC and CC-ally films. In the intermediate-rate range, the propagation rate increased with decreasing grain size when compared at the same stress intensity factor.
