Influence of electrical discharged machining and surface defects on the fatigue strength of electrodeposited nanocrystalline Ni

The influence of EDM and surface defects on the fatigue behavior of both conventional cold-rolled coarse grain (CG) and nanocrystalline (NC) Ni was investigated in the present work. The experimental results revealed considerable influence by EDM on the fatigue strength of NC Ni, while it has little or no effect on that for CG Ni. Specifically, EDM led to a 50–75% reduction in fatigue strength for NC Ni despite a relatively small depth of EDM affected material (∼1% of width). Rationale for this effect can be attributed to grain growth, pre-existing microcracks, and the presence of sulfur at the grain boundaries in the EDM affected zone. In addition, the pre-existing surface defects that appear to be due to impurity segregation near the electro-deposition substrate significantly reduced the fatigue resistance of ED NC Ni.