Gradient plasticity in gradient nano-grained metals

Gradient nano-grained (GNG) metals are a unique class of materials with spatial gradients in grain size, typically from the surface to the bulk. Here the gradient mechanical behavior in GNG copper is studied by a crystal plasticity finite element model that accounts for grain-size-dependent yield strengths. The associated finite element simulations reveal both the gradient stress and gradient plastic strain in the cross section of GNG copper subjected to axial tension. These spatial gradients arise due to progressive yielding of gradient grains under an overall uniform deformation. They stand in stark contrast to the widely studied strain gradient plasticity induced by imposing a non-uniform deformation such as torsion, bending, and indentation. Our work suggests a new material strengthening mechanism through the introduction of plastic strain gradients via gradient microstructures.