Shear stress- and line length-dependent screw dislocation cross-slip in FCC Ni

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• 作者：Shuozhi Xu^a ; ^{shuozhixu@gatech.edu" class="auth_mail" title="E-mail the corresponding author} ; Liming Xiong^b ; Youping Chen^c ; David L. McDowell^a ; ^d
• 关键词：Multiscale simulation ; Atomistic simulation ; Cross-slip ; FCC metal ; Plastic deformation
• 刊名：Acta Materialia
• 出版年：2017
• 出版时间：1 January 2017
• 年：2017
• 卷：122
• 期：Complete
• 页码：412-419
• 全文大小：1306 K

文摘

Screw dislocation cross-slip is important in dynamic recovery of deformed metals. A mobile screw dislocation segment can cross slip to annihilate an immobile screw dislocation segment with opposite Burgers vector, leaving excess dislocations of one kind in a crystal. Previous studies have found that the cross-slip process depends on both the local stress state and dislocation line length, yet a quantitative study of the combined effects of these two factors has not been conducted. In this work, we employ both dynamic concurrent atomistic-continuum (CAC) [L. Xiong, G. Tucker, D.L. McDowell, Y. Chen, J. Mech. Phys. Solids 59 (2011) 160–177] and molecular dynamics simulations to explore the shear stress- and line length-dependent screw dislocation cross-slip in face-centered cubic Ni. It is demonstrated that the CAC approach can accurately describe the 3-D cross-slip process at a significantly reduced computational cost, as a complement to other numerical methods. In particular, we show that the Fleischer (FL) [R.L. Fleischer, Acta Metall. 7 (1959) 134–135] type cross-slip, in which a stair-rod dislocation is involved, can be simulated in the coarse-grained domain. Our simulations show that as the applied shear stress increases, the cross-slip mechanism changes from the Friedel-Escaig (FE) [B. Escaig, J. Phys. 29 (1968) 225–239] type to the FL type. In addition, the critical shear stress for both cross-slip mechanisms depends on the dislocation line length. Moreover, the cross-slip of a screw dislocation with a length of 6.47 nm analyzed using periodic boundary conditions occurs via only the FL mechanism, whereas a longer dislocation with length of 12.94 nm can cross-slip via either the FE or FL process in Ni subject to different shear stresses.