a b s t r a c tInterfaces play a crucial role in mechanical behaviors of both laminated and gradient structured materials. In this work, copper/bronze laminates with varying interface spacing were fabricated by accumulative roll bonding and subsequent annealing to systematically study the interface effect on mechanical properties. Heterogeneities exist in chemical composition, grain size, hardness and texture across the interfaces. Simultaneous improvement of strength and ductility with decreasing interface spacing is found in tensile tests. Extra geometrically necessary dislocations (GNDs) are found to accumulate in the vicinity of interfaces, which is due to mechanical incompatibility across the interfaces. Importantly, an interface-affected zone spanning a few micrometers was found, which is not affected by interface spacing. These observations suggest the existence of an optimum spacing, which may produce the highest hardening capacity and ductility without sacrificing strength.

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Gradient structured metals have been reported to exhibit high strength and high ductility. Here we report that the strength of gradient structured aluminum rod is much higher than the value calculated using the rule of mixtures. The mechanical incompatibility in the gradient structured round sample produced 3D stress states, extraordinary strengthening and good ductility. An out of plane {111} wire texture was developed during the testing, which contributes to the evolution of the stress state and mechanical behavior.

a b s t r a c tIn this study, the shear strain at various depths of a low carbon steel processed by Surface Mechanical Attrition Treatment (SMAT) was measured using deformed carbide bands as internal strain markers. The shear strain gradient is found to strongly correlate with the gradients of texture, microstructure and hardness. The microhardness increases approximately linearly with shear strain, but deviates at the top surface. In the top surface, the average ferrite grain size is reduced to 60 nm with a strong {1 1 0}//SMAT surface texture.Ó 2015 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.Gradient structures are known to produce a wide variety of interesting properties including improved wear resistance and fatigue life, and extraordinary mechanical properties [1][2][3][4][5][6]. In recent years, Surface Mechanical Attrition Treatment (SMAT) has gained attention for its ability to generate gradient structured materials through grain refinement of the surface layer to the nanometer scale [1,[7][8][9][10]. This technique is ideal for systematic investigations of gradient structures due to the gradients in strain, strain rate, hardness, grain size, and hardening mechanisms throughout the deformed layer. In order to refine grain sizes to the nanometer scale, large strains and strain rates need to be applied [11][12][13]. It is well known that the shear component of the applied strain is directly correlated with dislocation slip and microstructure evolution. However, quantitatively mapping a single component of the strain tensor is challenging [14][15][16]. Markers and photographic evidence have been reported to extract the effect of shear strain on microstructure evolution, but they are not suitable for measuring shear strain in SMAT, due to the complexity of the process [17][18][19].In this work, cementite bands are used as internal markers to quantify the shear strain at various depths of the surface, which is the first time shear strain has been quantitatively mapped in SMAT-processed samples. Additionally, the texture evolution is systematically characterized, which has rarely been studied in SMAT-processed structures but profoundly affects mechanical behavior [20][21][22][23]. The observations from this work elucidate the effect of shear strain on the development of texture gradient, microstructure gradient, and microhardness gradient in the SMAT-processed samples.Normalized steel plates with a composition of 0.14% C, 0.33% Si, 1.44% Mn, 0.08% Cr, 0.03% Ni, and balance Fe was used for this study. Samples were cut along the rolling direction so that the SMAT treatment would take place normal to the rolling direction. The pearlite was agglomerated into bands normal to the SMAT surface as shown in Fig. 1. The SMAT process was carried out using a SPEX 8000M Mixer/Mill by replacing the lid of the vial with 1/4 00 thick plates of the sample to be treated. Samples were polished to 1200 grit, sealed in ambient atmosphere, and processed with three ½ 00 440C steel balls for 120 min. Profilometry reve...

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