The Evolution of Strain Gradient and Anisotropy in Gradient-Structured Metal

Gradient-structured metals have been reported to possess superior mechanical properties, which were attributed to their mechanical heterogeneity. Here we report in-situ observation of the evolution of strain gradient and anisotropy during tensile testing of a gradient-structured metal. Strain gradients and anisotropy in the lateral directions were observed to increase with increasing applied tensile strain. In addition, the equivalent Poisson’s ratio showed gradient, which evolved with applied strain. The gradient structure produced higher deformation anisotropy than coarse-grained homogeneous structure, and the anisotropy increased with increasing tensile strain. The strain gradient and anisotropy resulted in strong back-stress hardening, large strain gradients, and a high density of geometrically necessary dislocations, which helped with increasing the ductility.