A physical model revealing strong strain hardening in nano-grained metals induced by grain size gradient structure

A theoretical model has been developed, which reveals the underlying correlation between the strong extra strain hardening achieved in the nano-grained layers of the grain size gradient structure and the non-uniform deformation of the lateral surface in surface nano-crystallized materials, based on some existing experimental observations and the concept of geometrically necessary dislocations. The proposed model led to the establishment of a simple physical law that can be expressed as H^*=A^*, where H^* and A^* are two dimensionless parameters. The former represents the extra strain hardening, while the latter characterizes the non-uniform deformation of the lateral surface. The values of these two parameters can be measured through experiments.