Materials Frontier No.150
Title: Strain-induced Ultrafine Grain Formation in Mg alloys and Other Materials
Speaker: Prof. T. Sakai The UniversityofElectro-Communications
Date/Time: 2014-09-11, 09:00 —11：00
Inviter: Prof.Guangyin YUAN
Plastic deformation and annealing are basically important technology for microstructural control of engineering materials. The new grains evolve by nucleation and growth in materials with low to medium stacking fault energies (SFE). On the other hand, new fine grains can be produced in any material irrespective of the SFE by means of severe plastic deformation (SPD) at relatively low temperatures. The latter can result from the gradual transformation of the dislocation sub-boundaries produced at low strains into ultrafine grains with high angle boundaries at large strains. This process, termed in-situ or continuous dynamic recrystallization (cDRX), is still not perfectly understood. Recent studies of the deformation behavior of metals and alloys under SPD conditions are synthesized and the links between the microstructural and mechanical observations are examined carefully. Some models for grain formation under SPD conditions are discussed.
Next, the post-dynamic recrystallization behavior, i.e. that of annealing after both dDRX and cDRX, is described. The differing annealing behaviors result from the differences in the natures of the deformed microstructures. Finally, an integrated recrystallization model for these phenomena, i.e. dynamic and static recrystallization of both the continuous and discontinuous types, is presented and discussed.