Coupled motion of [10−10] tilt boundaries in magnesium bicrystals

Abstract

Magnesium bicrystals were grown with symmetric and asymmetric tilt boundaries about the [10-10] axis using the vertical Bridgman technique. Isothermal constant load tensile tests were conducted on these bicrystals in the temperature range 300-500 C and relative displacements of the two grains were measured to obtain an appreciation for grain boundary motion characteristics. Coupled grain boundary motion was noted in almost all cases with the degree of tangential motion versus migration changing with tilt misorientation, temperature and applied stress. Specifically, within the family of symmetric bicrystals evaluated, a minimum in grain boundary displacement in the specimen plane was observed at a tilt misorientation of 20 . In specific stress/temperature regimes, rigid body sliding was observed for the particular case of a 35 asymmetric tilt misorientation. The ease of basal and prism slip in magnesium at the temperatures considered and the consequential impingement of intragranular dislocations on the bicrystal boundary and their decomposition and motion along the boundary are thought to play an important role in the observed coupled motion of these tilt boundaries.

Coupled motion of asymmetrical tilt grain boundaries: Molecular dynamics and phase field crystal simulations

“…Initially observed experimentally for low-angle GBs in Zn [10,11], the coupling effect has recently been demonstrated for many high-angle GBs in a number of metallic and non-metallic materials [6][7][8][9][12][13][14][15][16][17][18][19][20]. The coupling can be responsible for the stress-induced grain growth in nano-crystalline materials [16,[21][22][23][24] and can influence the nucleation of new grains during recrystallization [25].…”

“…In fact, the impossibility of coupled motion of asymmetrical boundaries was suggested in the classical paper by Read and Shockley [46]. Yet, recent MD simulations [31,47,48], bicrystal experiments [6,9] and the observation of coupled GB motion in polycrystalline materials suggest that this may not be the case. Even less is known about geometric rules of coupling or migration mechanisms of large-angle asymmetrical GBs.…”

“…Recent research has led to the recognition that many grain boundaries (GBs) in crystalline materials can couple to applied shear stresses and are moved by them in a manner similar to dislocation glide [1][2][3][4][5][6][7][8][9]. During this "coupled" GB motion, the boundary produces shear deformation of the lattice and causes relative translation of the grains parallel to the GB plane.…”

“…bicrystal experiments [6,9] and the observation of coupled GB motion in polycrystalline materials suggest that this may not be the case. Even less is known about geometric rules of coupling or migration mechanisms of large-angle asymmetrical GBs.…”

A dual deformation mechanism of grain boundary at different stress stages

“…Therefore, the migration of asymmetric GBs was thought to be impossible, but recent observations of coupled GB motion in bicrystal experiments [25,26] has suggested that this may not be true. However, the geometric rules of coupling or migration mechanisms of asymmetric GBs are less known.…”