氦泡在bcc钨中晶界处成核长大的分子动力学模拟

The nucleation and growth of Helium hubbles at grain boundaries of bcc tungsten:a molecular dynamics simulation

钨(W)是潜在的聚变堆面向等离子体材料.聚变反应中产生的氦(He)不溶于金属W,并在其中易聚集形成He泡,使W基体发生脆化,从而导致W基体的性能发生退化.在前人工作的基础上,本文采用分子动力学研究了He泡在单晶bcc-W中以及bcc-W中∑3[211](110)和∑9[110](411)晶界处He泡形核长大初期的演化过程.结果发现,晶界处He泡的长大机制和单晶W中有所不同.单晶W中He泡通过挤出位错环促进长大.而He泡在∑3[211](110)晶界处的长大机制为:首先挤出并发射少量自间隙W原子,而后挤出1/2⟨111⟩位错线,随后,该位错线会沿晶界面上[111]方向迁移出去;在∑9[110](411)晶界处,He泡在我们的模拟时间尺度范围内没有观察到W自间隙子的发射和位错的挤出.

Tungsten(W)is a potential candidate for plasma facing materials(PFMs)of fusion reactor.The helium(He)produced in fusion reaction is insoluble and easy to gather and form to He bubbles in W,resulting in embrittlement and degradation of the performance of the W matrix.In this paper,based on molecular dynamics,the nucleation and growth of helium bubbles in the bulk and atΣ3[211](110)andΣ9[110](411)grain boundaries of W was studied.As a result,the growth mechanism of Helium bubbles at grain boundary of W was different from in bulk.Helium bubbles in bulk W grow up by extruding dislocation rings.The growth mechanism of helium bubbles atΣ3[211](110)grain boundary was as follows:Firstly,a small amount of W interstitial atoms were extruded and emitted.And then the 1/2(111)dislocation line was extruded.Finally,the 1/2(111)dislocation line would migrate along the direction of[111]of the grain boundary interface.Moreover,the emission of W interstitial atoms and dislocation extrusion of the helium bubble were not observed in our simulated time scale at theΣ9[110](411)grain boundary.Then we used the NEB method to calculate the diffusion barrier of self-gap atoms in the bulk and atΣ3[211](110)andΣ9[110](411)grain boundaries of W,which explained the simulation results.The migration energy barrier of W self-gap atoms in the bulk and atΣ3[211](110)grain boundary was only a few to a few millielectron volts.So as long as W self-gap atoms dissociated from the surface of the He bubble in the thermal relaxation process,they can be easily migrated out.However,The migration energy of the W self-gap atom at theΣ9[110](411)grain boundary can be from a few tenths to a few electron volts.Even during the thermal relaxation process,the W self-gap atoms dissociated from the surface of the He bubble.It was difficult for the W self-gap atoms migrated out.Finally,the correlation between He bubble size and stress released was given.Either in bulk or atΣ3[211](110)andΣ9[110](411)grain boundaries of W,after the pressure of the helium bubble becomes stable with time,the radius of the helium bubble would increase rapidly whenever the pressure dropped sharply.So there was a small step on the curve of the evolution of the radius of the helium bubble with time.Thus,helium bubbles in W could promote growth by releasing pressure intermittently.