Controllable gradient and concurrent improvements of strength-ductility in gradient-structured sheet fabricated by plastic flow machining

Abstract

This paper reports a controllable gradient microstructure sheet fabricated at room temperature conditions by a severe plastic deformation method, called plastic flow machining (PFM). The forming mechanism, microstructure evolution, and mechanical properties of the gradient-structured sheet for different machining parameters were investigated in detail. Results show that the prepared sheet by the PFM process is stratified into three structured surface layers, deformed grains layer (DGL), transition layer (TI), and ultrafine grains layer (UGL) from top to bottom, whereas microstructures present layer-by-layer refinement. The gradient structure can be controlled by adjusting the constraint tool angle and extrusion thickness in PFM. The gradient-structured sheet exhibits the concurrent combination of strength and ductility by comparison with homogeneous counterparts. It confirms that the extraordinary strength-ductility balance comes from the gradient structural effect. The insights in this study show that the continuous sheet production by PFM has superior performance and application perspectives in the structural materials, which can offer an effective and practicable one-step approach for low-cost fabricating the gradient-structured material.