Fatigue properties and crack behavior of ultra-fine and nanocrystalline pure metals

The fatigue behavior of metals is strongly governed by the grain size variation. As the tensile strength, the fatigue limit increases with decreasing grain size in the microcrystalline (mc) regime. A different trend in mechanical properties has been demonstrated in many papers for metals with ultra-fine (<1 μm) (ufg) and nanocrystalline (<100 nm) (nc) grain size in particular in the yield stress and fatigue crack initiation and growth. In the present paper the fatigue properties of pure metals (Al, Ti, Ni and Cu) produced via equa-channel-angular pressing (ECAP) is shown. The mechanical properties and in particular the fatigue behavior of electrodeposited nanocrystalline Ni (20 and 40 nm mean grain size) has been analyzed in the present paper by means of stress- and strain-controlled tests and the results compared with those of the ultra-fine grain counterpart (270 nm mean grain size). The fatigue crack initiation and growth of the described materials were studied. The high cycle fatigue and crack behavior of nanocrystalline electrodeposited cobalt has been analyzed in this paper by means of stress-controlled tests and the results compared with those of the microcrystalline counterpart. The fatigue crack initiation and growth of the described materials was studied over a broad range of stress levels.