The possibilities of mechanical property control in fine grained structures

Grain refinement is one of the most effective strengthening mechanisms, improving mechanical properties without loss in ductility. It is well known, however, that proper prediction of mechanical properties of fine grained materials is much more complicated because of different deformation and strengthening mechanisms operating in these materials. When the strong grain refinement (below 1 μm) is achieved, some deviations compared to conventional materials have been reported, i.e. change in Hall–Petch slope, different deformation mechanism, enhanced strain rate sensitivity, lack of work hardening or different fracture mechanisms. Unfortunately, these phenomena and their physical basis are still poorly understood and most of the well known constitutive laws (i.e. Hall–Petch relationship) are no longer effective for a description of the deformation processes of such materials. This paper discusses selected problems relating to mechanical behavior of submicron/nano grain size materials.