不同温度下bcc-Fe中螺位错滑移及其与^(1/2)[111]位错环相互作用行为

Screw dislocation slip and its interaction with ^(1/2)[111]dislocation loop in bcc-Fe at different temperatures

采用分子动力学方法模拟研究了不同温度下bcc-Fe中螺位错滑移行为和螺位错与^(1/2)[111]位错环相互作用机制.结果表明,螺位错在低温2 K剪切应力下主要沿(211)面滑移;随温度逐渐升高到823 K,它容易发生交滑移,该交滑移在(110)和(211)面之间交替进行,因此随温度升高,临界剪切应力逐渐降低.当螺位错滑移靠近位错环时,不同温度下螺位错与位错环相互作用机制不同:低温2 K时,螺位错与位错环之间存在斥力作用,当螺位错滑移靠近位错环过程中,螺位错发生交滑移,切应力比无位错环时有所降低;中温300 K和600 K时,螺位错与位错环间斥力对螺位错的滑移影响减弱,螺位错会滑移通过位错环并与之形成螺旋结构,阻碍螺位错继续滑移,切应力有所升高;高温823 K时,螺位错因热激活更易发生交滑移,位错环也会滑移,两者在整个剪切过程中不接触,剪切应力最低.

Reduced activation ferritic/martensitic(RAFM)steel,as a typical body centered cubic(bcc)iron based structure material,has become a candidate material for future fusion reactor.Nano-scale prismatic interstitial dislocation loops formed in irradiated RAFM have been studied for many years because of their significant influences on the mechanical properties(e.g.irradiation embrittlement,hardening,creep,etc.).Compared with edge dislocation,screw dislocation has very important influence on plastic deformation behavior because of its low mobility.Thus,the mechanism of interaction between screw dislocation and interstitial dislocation loops has become an intense research topic of interest.In this study,the slip behavior of screw dislocation and the mechanisms of interaction between screw dislocation and ^(1/2)[111]dislocation loop in bcc-Fe at different temperatures are investigated by molecular dynamics simulation.The results show that the screw dislocation mainly slides along the(211)plane at a low temperature of 2 K under the increase of shear stress.With the temperature increasing to 823 K,it is prone to cross slip,and then the cross slip occurs alternately in the(110)plane and the(211)plane.Therefore,with the increase of temperature,the critical shear stress decreases gradually.When the screw dislocation slips close to the dislocation loop,the mechanism of interaction between screw dislocation and dislocation loop is different at different temperature:at low temperature of 2 K,there is repulsive force between screw dislocation and dislocation loop,when screw dislocation slip approaches to the dislocation loop,the cross slip of screw dislocation can occur,and shear stress is lower than that from the model without dislocation loop;at medium temperatures of 300 K and 600 K,the influence of repulsive force on the cross slip of screw dislocation can be weakened,and screw dislocation will slip through the dislocation loop then form the new structure named helix turn,which further hinders screw dislocation slipping and results in the increase of shear stress;at a high temperature of 823 K,the screw dislocation is more likely to cross slip due to the thermal activation,and the slip of dislocation loop is also easier to occur,but the screw dislocation and the dislocation loop do not contact each other in the whole shearing process,therefore the shear stress is lowest.