Characteristic features of diffusion induced grain boundary migration for #SIGMA#9 (110) asymmetric tilt boundaries in the Cu(Zn) system

摘要

The characteristic features of diffusion inducedgrain boundary migration (DIGM) in the Cu(Zn) system wereexperimentally studied for (110) asymmetric tilt boundaries usingCu bicrystals at 693 K for various times by a capsule zincificationtechnique. The experiment was carried out for the boundaries withinclination angles of ? = 0,20,35,55,65 and 90 deg and with aconstant misorientation angle of #theta#= 39 deg (#SIGMA#9).During annealing, the grain boundary migrates towards a crystalgrain of larger coherency strain energy with higher probability dueto DIGM. Taking elastic anisotropy of each crystal grain intoconsideration, the difference between the probabilities of grainboundary migration towards both side grains can be accounted forby the coherency strain model proposed by Hillert. The migrationrate v of the moving boundary is almost constant regardless of theannealing time t between t =72 and 384 h (2.59 x 10~5 and 1.38 x10~6 s). The value of v monotonically decreases with increasinginclination angle. This implies that the boundary diffusioncoefficient of Zn in Cu is a monotone decreasing function of theinclination angle. The experimental results on the kinetics at thesteady state stage were theoretically analyzed using the energybalance model proposed by Kajihara and Gust (Scripta mater.,1998, 38, 1621. The analysis indicates that the effective drivingforce #DELTA#~(ef)G for the grain boundary migration is merelyone-thirtieth of the chemical driving force, whereas it still remainsthree times greater than the minimum value corresponding to thecoherency strain energy during DIGM under the presentexperimental conditions. The mobility of the moving boundarywas evaluated to be M = 3.77 x 10~ (-17) m~4/Js from the valuesof v and #DELTA#~ (ef)G according to the relationship M =v/#DELTA#~(ef)G. This value of M is close to the resultsestimated by Yamamoto et al. (Acta mater., 1999, 47, 1757) forthe (100) twist and random boundaries in the Cu(Zn) system.