体心立方Fe中<100>位错环对微裂纹扩展影响的分子动力学研究

Effect of interstitial <100> dislocation loop on expansion of micro-crack in body centered cubic iron investigated by molecular dynamics method

在辐照环境下,载能粒子与材料相互作用导致材料中原子移位,造成辐照损伤.其中,由辐照形成的过饱和自间隙原子团簇形成的间隙型位错环,是体心立方Fe为基的材料中常见的辐照缺陷之一,其与材料中其他缺陷之间相互作用,是导致辐照硬化、脆化、肿胀及蠕变等辐照损伤的原因之一.除此相互作用外,在材料表面或内部沿晶界、沉积相、惰性气体形成的气泡所导致的微裂纹,是诱发辐照促进应力腐蚀开裂的重要原因.因此,理解辐照条件下间隙型位错环与微裂纹之间的相互作用,是理解辐照促进应力腐蚀开裂微观机制的重要一步.在本研究中,利用分子动力学方法,模拟了原子尺度微裂纹与间隙型位错环之间的相互作用,研究了位错环与微裂纹之间的距离、相对位置及位错环尺寸对二者相互作用的影响,揭示了位错环对微裂纹是否沿滑移面扩展的影响,发现当二者的相互作用起主导作用时(如在临界水平或垂直距离之内),形成的以<100>为主或高密度的1/2<111>位错网络可以抑制微裂纹沿滑移面的扩展.当位错环尺寸发生变化时,只有当位错环位错核与微裂纹尖端相互作用时,才能抑制微裂纹沿滑移面的扩展.这些结果为进一步理解辐照应力开裂提供了新的参考.

The interactions between the energetic particles and atoms in materials would result in the atomic displacements and the associated radiation defects.The interstitial dislocation loop,as one of the primary radiation defects,is formed by the clustering of the supersaturated self-interstitial atoms from the displacement damages in body centered cubic(bcc)iron based materials.The radiation hardening,embrittlement,swelling,creep,etc.are generally related to these loops and their interactions with other defects.In addition,the irradiation would also result in the formation of the micro-cracks from the surface of the materials and also from the interface of grains,precipitates,and gas-bubbles inside the materials,which would result in the irradiation assisted stress corrosion crack(IASCC).Therefore,to understand the interaction between interstitial dislocation loop and micro-crack under the irradiation,is one of key steps to understand the underlying mechanism of IASCC.In this work,the interaction between interstitial dislocation loop and micro-crack is simulated by molecular dynamics method on an atomic scale.The distance,relative position between them and radius of dislocation loop,as the main factors affecting their interactions,are studied to explore the underlying reason for inducing the micro-crack to expand on the slip plane.The simulation results indicate that when the interaction between them dominates the whole process with the distance between them within the critical value,the dislocation network containing the <100> and 1/2 <111> segments,would interact with the crack tip to inhibit the crack from expanding through the pinning effect.When the size of loop is different,the pining effect would be available only when the interaction between loop core and crack tip dominates with the distance between them within the critical value.All these results provide new understanding for further exploring the IASCC under irradiation.