High Pressure Effects On The Properties Of Dislocation In Zn（Mg）CNi₃ And Surface Effects On The Properties Of Screw Dislocation In Nanofilms

It is widely accepted that defects, such as dislocations, play a key role in determining the mechanical properties of materials. The classical Peierls-Nabarro(P-N)dislocation model has been the most widely used model of dislocations in bulk materials.Although powerful in its simplicity, it cannot deal with the dislocations in nanofilm with free surfaces. Accounting for the free surface on the physical properties of dislocations in nanofilm is important, as the ratio of surface to volume is high. The effects of free surface on the dislocation properties cannot be neglected anymore, the dislocation behavior in thin films is different from that in bulk materials. Recently, Lee and Li constructed a half-space P-N model for dislocations near a free surface and they claimed that the mobility of the dislocation will be increased near the free surface. Cheng and Shen et al. investigated Peierls stress of a screw dislocation below a free surface via a self-consistent semidiscrete variational P-N model using image dislocation method. It is found that the free surface increases the Peierls stress and in consistent with the results obtained by molecular dynamics simulation. In this work, the image dislocation method is used to investigate the dislocation core structure and Peierls stress in nanofilm with double free surfaces. The image dislocations are introduced to satisfy the free surface boundary condition, namely the stress field acting on the surface should vanish. The governing equation for dislocations in nanofilm is constructed according to the procedure for P-N equation provided by Joos et al..In our work, we chiefly study that high pressure effects on the properties of dislocation in Zn(Mg)CNi3 and surface effects on the properties of screw dislocation in nanofilms.The main work and results of this paper as follows:(1)High pressure effects on the properties of <110>(001) dislocation in Zn CNi3 and Mg CNi3We have employed an improved Peierls-Nabarro(P-N) equation considering the discreteness effect of crystals to study the properties of <110>(001) dislocation in the(001) plane in Zn CNi3 and Mg CNi3 under different pressure. The generalized-stacking-fault energy(GSFE) curves were calculated by using first-principles density functional theory(DFT). The core structures and Peierls stress of the screw, mixed and edge dislocation in the pressure range 0-50 GPa have been systematically researched by solving the modified P-N dislocation equation using thevariational method. The charge density further reveals the underlying mechanisms for the effects of stacking fault energy of Zn CNi3 and Mg CNi3 on the electronic properties.(2)Surface effects on the properties of screw dislocation in nanofilmsThe image dislocation method is used to construct the governing equation of dislocations in nanofilms. The classical Peierls-Nabarro equation can be recovered when the thickness of nanofilm is taken to be infinite. We have studied the effects of the generalized-stacking-fault energy, the spacing between the dislocation and the surface(h), and the interplanar atomic spacing(d/b) on both Peierls stress and core structure parameter, respectively,and dilocations in Al and Cu nanofilms are researched systematically. It is found that surface effect can increase the Peierls stress of screw dislocations in Al and Cu nanofilms.