Study On Molecular Dynamics Of Grain Boundaries And Crack In Nano-alloys

In recent years,extensive studies have been made on the shear coupled grain boundary motions in pure nanoscale metals,while few work have focused on the behavior of those in nano-alloys.In this paper,by means of the molecular dynamics method embedded in LAMMPS,we systematically explored the motions of symmetrical tilted grain boundaries in Cu-Al alloys subjected to shear loading.It is found that the grain boundaries slides for Cu with high Al solute concentration(e.g.4at.%Al)at low temperature,however they show shear coupled grain boundary migration for those with low Al concentration.Furthermore,the transition concentration of Al atoms between the aforementioned grain boundary motions is found to depend on the tilt angels and temperatures.In particular,for those angles smaller than 50°,the transition concentration decreases with the increasing angle,whereas the opposite trend is obtained when the angles are greater than 50°.On the other hand,we also studied the grain boundary motions in nanoscale Cu-Al alloy in the presence of the pre-embedded elliptical crack.It is found that the deformation mechanism of alloy with both the grain boundary and the crack under the shearing load is different from that of the pure Cu bi-crystal.It is seen that there is no disclination quadrupole formed for Cu-Al alloy with 1 at.% Al,and no sub-grains were observed above the crack.However,the local grain boundary near the crack still conforms to the characteristics of the triple junction.During the application of shear loading,the crack will heal eventually because of the asymmetric deformation which is lower on the left and higher on the right.As the concentration of Al atoms increases,the mechanism of interaction between the crack and the grain boundary does not conform to the characteristics of the triple junction and the deformation mechanisms of the crack is also very uncertain.In this case,the crack is hardly to heal.The research results in this paper,although are in very preliminary stage,they may provide some insights for future research on the interaction between the grain boundary and crack propagation in those nano-alloy materials.