ABSTRACT
Gradient structured metals have been reported to possess superior mechanical properties attributed to their mechanical heterogeneity. Recently, several promising strategies for achieving simultaneous high strength and high ductility have been proposed by tailoring microstructures through heterogeneous and/or hierarchical structures. Back-scattered electron imaging, electron backscattered diffraction and transmission electron microscopy were used to study the microstructures and their gradients. The gradient structures can be regarded as consisting of numerous thin layers with systematically varying mechanical behaviors. For the first time, the evolutions of the strain gradient and deformation anisotropy in a gradient structured sample during tensile loading were revealed by a series of quasi-static tensile tests, coupled with in-situ 3D strain contour measurements. Unlike the homogeneous deformation in the untreated coarse-grained sample, strain gradients in both lateral directions started to develop at the beginning of the tensile deformation and increased with increasing applied tensile strain, resulting in increasing geometrically necessary dislocations to sustain the uniform deformation for the gradient structured sample.
