Dislocation structures in fatigued polycrystalline copper

The fatigue lives of a morphologically isotropic coarse grained cast duplex stainless steel (DSS) with 0.15 mass per cent nitrogen and of a morphologically anisotropic high nitrogen (0.35 mass per cent) fine and coarse grained DSS were examined. The comparison of their fatigue life curves with published literature data led to the conclusion that the fatigue behaviour of nitrogen containing DSS is influenced by a whole set of parameters including processing history, crystallographic texture, nitrogen content, morphological anisotropy and morphological scale. It was shown that increasing morphological anisotropy and decreasing morphological scale have an increasing effect on the fatigue life of DSS. The effect of nitrogen on the fatigue lives of DSS has apparently been overestimated in the past. Nitrogen seems to alter the extent of the deformation stages I, II and III and the slopes of the stress–strain and the Coffin–Manson fatigue curves. Despite these effects, nitrogen does not have a direct effect on the fatigue lives of DSS.