钨/石墨烷/钨第一壁材料缺陷与力学性能的第一性原理计算

托卡马克装置是实现可控热核聚变的主要装置之一, 而第一壁材料在确保托卡马克装置稳定运行的过程中起着至关重要的作用. 钨金属已被广泛使用作为第一壁材料, 但是聚变反应产生的氦原子在进入钨晶体后易形成氦气泡和点缺陷, 严重影响托卡马克装置第一壁材料的稳定性. 首次设计将钨/石墨烷/钨体系作为第一壁材料. 第一性原理计算结果表明, 钨/石墨烷/钨第一壁材料中的界面可以捕获氦原子和空位, 且能促进自填隙钨原子与空位复合, 从而降低钨体相中的缺陷密度; 弹性常数计算结果表明, 石墨烷层的存在可以提高钨金属的柯西压力值($C' $)和各向异性因子($A$), 使第一壁材料的延展性得以提高, 且不易出现裂纹, 但是在相同温度下钨/石墨烷/钨第一壁材料的力学模量有所下降; 利用准简谐德拜模型计算吉布斯自由能 $G^*$、定容热容$C_mathrm V$、熵($S$)等热力学函数结果表明, 钨/石墨烷/钨第一壁材料的热力学稳定性与纯钨金属相比有所下降.

First-principles calculation of defects and mechanical properties of tungsten/graphane/tungsten as a first wall material

A Tokamak is a primary device used to obtain energy from controlledthermonuclear fusion. The first wall material inside the device isthe key to its stable operation. Tungsten metal is widely used as afirst wall material, but the helium atoms derived from the fusionreaction generate helium bubbles and point defects after they enterthe tungsten crystal, which critically affect the stability of thefirst wall material. Therefore, we designed for the first time atungsten/graphane/tungsten system as a first wall material. Resultsof first-principles calculations showed that the interface of thetungsten/graphane/tungsten system can capture helium atoms andvacancies as well as promote recombination between self-interstitialtungsten atoms and vacancies, thereby reducing the defect density ofthe tungsten metal. An elastic constant calculation showed that thepresence of a graphane layer could increase the Cauchy pressurevalue ($C'$) and anisotropy factor ($A$) of the tungsten metal,indicating that the ductility of the material was improved andcracks were not likely to occur. The mechanical modulus of thetungsten/graphane/tungsten material decreased under the sametemperature. Using the quasi-harmonic Debye model to calculate theGibbs free energy ($G^ast$), heat capacity at constant volume($C_mathrm V$), entropy ($S$), and other thermodynamic functionsshowed that the thermodynamic stability of thetungsten/graphane/tungsten material decreasedas compared with that of the pure tungsten metal.