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The residual stress significantly influences the cyclic stress response of the hierarchical nanostructured materials. An obvious tension-compression asymmetry with minimum stress in compression larger than maximum stress in tension was observed in gradient nanograined (GNG) Cu under strain-controlled high-cycle fatigue tests, which gradually diminished with increasing cycles or after being annealed at a low temperature. The observed asymmetric response is primarily induced by the presence of the residual compressive stress in the GNG surface layer. The longer fatigue life can be achieved in GNG Cu with a higher residual stress, compared to that of annealed GNG Cu. Obvious tension-compression asymmetry was observed in cyclically deformed gradient nanograined Cu under strain control, caused by the residual compressive stress in the GNG surface layer.

The plastic co-deformation behavior at the homophase interfaces between the hard nanotwinned grain inclusions and the soft recrystallized matrix grains in a duplex-microstructured AISI 316L austenitic stainless steel is examined through the analysis of long-range orientation gradients within the matrix grains by electron backscatter diffraction and transmission electron microcopy. Our analysis reveals that the mechanical accommodation of homophase interfaces until a macroscopic strain of 22% is realized within a small area of soft grains (about four grains) adjacent to the homophase interface. The activation of deformation twinning in the first two grain layers results in the occurrence of a ‘hump’ in the orientation gradient profile. We ascribe this effect to the role of deformation twinning on the generation of geometrically necessary dislocations. The smooth profile of the orientation gradient amplitude within the first 10 grain layers indicates a gradual plastic accommodation of the homophase interfaces upon straining. As a consequence, damage nucleation at such interfaces is impeded, resulting in an enhanced ductility of the single phase duplex-microstructured steel.