ABSTRACT
Boundaries play a crucial role in mechanical behaviors of both laminated and gradient structured materials. Heterogeneities exist in chemical composition, grain size, hardness and texture across the boundaries. Simultaneous improvement of strength and ductility with decreasing boundary spacing is found in tensile tests. Early literatures have linked microstructural heterogeneity with strain gradient evolution and subsequent generation of geometrically necessary dislocations (GNDs) during plastic deformation. It has been a grand challenge to investigate the aforementioned issues through direct experimental observations in gradient structures. The microstructural and compositional difference across the boundary led to sharp difference in hardness. Dislocation pile-up will produce hetero-deformation-induced (HDI) stress, which is a long-range stress field that prohibits further dislocation emission from the dislocation source. The copper/bronze laminates were produced by means of ARB/annealing with varying boundary spacing but similar heterogeneity across the boundaries including chemical composition, grain size, micro-hardness and texture.
