Mechanical Behavior of Bulk Ultrafine-Grained and Nanocrystalline Zn

摘要

Mechanical properties of bulk ultrafine-grained and nanocrystalline Zn produced by mechanical milling are reviewed. Dynamic recrystallization plays an important role in the microstructural evolution of cryomilled Zn during early milling times. The modulated oscillation of hardness during cryomilling is a combinational effect of dynamic recrystallization, average grain size, grain size distribution and dislocation density variations. Bulk ultrafine-grained and nanocrystalline Zn, synthesized by in situ consolidation during milling, possess high tensile ductility. Deformation mechanisms in larger grains (submicron) are different from that in nanoscale grains. Microstructure, ductility and deformation mechanisms in Zn and other ultrafine-grained and nanocrystalline elemental metals are compared. These comparisons indicate that the ductility of ultrafine-grained and nanocrystalline materials may be enhanced by the following ways (i) increasing strain hardening (ii) increasing strain rate sensitivity (iii) activating other deformation mechanisms such as twinning or stacking faults (iv) accommodating grain boundary sliding to postpone the generation of pores along the grain boundaries or triple junctions. The engineering design of materials with high strength and high tensile ductility can be achieved by optimizing the microstructures of ultrafine-grained and nanocrystalline materials.