微量合金元素对钒基合金性能影响的理论模拟

发布时间：2018-10-18 11:14

【摘要】：钒基合金因其低活化性、高热导率、优于其他材料的力学性能和抗辐照性能,而被认为是聚变反应堆中第一壁的首选结构材料,也因此引发了对钒基合金研究的热潮。本文分别采用第一性原理和分子动力学方法,从原子层面、微观结构角度探究合金元素原子在钒基合金中的分布及其对性能的影响,重点针对实验中观察到的富Ti析出相进行详细研究,并从微观角度分析富Ti析出相对钒基合金性能影响。通过第一性原理及分子动力学方法模拟表明,在钒基合金中,Cr原子在钒基合金中任意位置均可稳定存在,当Cr原子位于晶界处时,可有效强化钒基合金的晶界强度。而Ti原子易于晶粒内部偏析,并在晶粒内部形成一定的富Ti区,且Ti原子的存在,削弱了钒基合金的弹性变形能力,使得钒基合金的韧性减小。第一性原理模拟表示,Y的添加可通过钉扎晶界而细化晶粒,通过弥散强化作用改善钒基合金的力学性能。根据实验测定结果构建富Ti析出相的微观结构Ti(CNO)和Ti O,并对其进行一系列基本参数计算,从热力学、力学角度证明所构建富Ti析出相的微观结构可以稳定存在。又计算其基本力学参数,判断所构建富Ti相属于硬脆相,其硬度远高于纯V,且体现脆性材料特征。所得基本力学性质符合实验测试结果,这就进一步证明所建结构的准确性,同时也从微观角度解释了实验制备所得的钒基合金,因脆硬性富Ti析出相的存在大大降低了钒基合金的力学性能。对富Ti析出相与基体相所构成的界面进行研究发现,与纯钒界面相比,亚稳态下的富Ti析出相Ti O与基体之间界面强度增加,但是析出相自身晶粒内原子之间键合削弱。而稳态下的富Ti析出相Ti(CNO)与基体相之间界面上的O原子的存在,会明显削弱界面凝聚力,使其比纯钒界面更易发生断裂,显著降低其力学性能;但若界面上没有O原子而以C、N原子截止时,界面强度显著增加,因此,钒基合金中添加Y元素以吸O来改善由于富Ti析出相而降低的力学性能。综上所述:钒基合金中的Cr原子偏析于晶界时可视为晶界强化元素;Ti原子偏析于晶粒内部,易与杂质原子形成富Ti相析出,析出相的硬脆性及与基体界面上O的存在,使得钒基合金的力学性能下降;添加Y原子,一方面可吸收合金中渗入的O,改善由于富Ti相析出而降低的力学性能,另一方面,通过弥散强化作用细化晶粒以提高钒基合金的力学性能。
[Abstract]:Because of its low activation, high thermal conductivity, superior mechanical properties and radiation resistance of other materials, vanadium base alloy is considered as the preferred structural material in the first wall of fusion reactor. In this paper, first principles and molecular dynamics methods are used to investigate the distribution of alloying elements in vanadium-based alloys and their effects on the properties of vanadium based alloys from the angle of atomic level and microstructure. The effect of rich Ti precipitation on the properties of vanadium-based alloys was analyzed from the microcosmic point of view. The first-principles and molecular dynamics simulations show that Cr atoms can exist stably at any position in vanadium-based alloys. When Cr atoms are located at grain boundaries, the grain boundary strength of vanadium-based alloys can be effectively strengthened. However, Ti atoms are easy to segregate in grains and form a certain Ti rich region in the grains. The existence of Ti atoms weakens the elastic deformation ability of vanadium-based alloys and reduces the toughness of vanadium-based alloys. The first principle simulation shows that the addition of Y can refine the grain by pinning grain boundaries and improve the mechanical properties of vanadium based alloys by dispersion strengthening. According to the experimental results, the microstructures of rich Ti precipitates, Ti (CNO) and Ti O, were constructed, and a series of basic parameters were calculated. The thermodynamics and mechanics showed that the microstructure of the rich Ti precipitates could exist stably. The basic mechanical parameters were calculated, and it was found that the rich Ti phase was a hard brittle phase, and its hardness was much higher than that of pure V, and it reflected the characteristics of brittle materials. The obtained basic mechanical properties are consistent with the experimental results, which further proves the accuracy of the structure, and also explains the vanadium base alloys prepared from the microscopic point of view. The mechanical properties of vanadium-based alloys are greatly reduced due to the existence of brittleness rich Ti precipitates. The interface between rich Ti precipitated phase and matrix phase was studied. Compared with pure vanadium interface, the interfacial strength between Ti O and matrix increased in metastable state, but the bond between atoms in the precipitated phase itself was weakened. However, the existence of O atoms at the interface between Ti (CNO) and matrix phase in the stable state of rich Ti precipitates will weaken the cohesion of the interface, make it fracture more easily than the pure vanadium interface, and decrease the mechanical properties of the interface. However, if there is no O atom on the interface and the Con N atom is cut off, the interfacial strength increases significantly. Therefore, Y element is added to the vanadium base alloy to absorb O to improve the mechanical properties of the alloy due to the precipitation of rich Ti phase. To sum up, the Cr atoms in vanadium based alloys can be regarded as grain boundary strengthening elements when they are segregated at grain boundaries, and Ti atoms are segregated in the interior of the grains and are prone to precipitate with impurity atoms in the rich Ti phase, the hard brittleness of the precipitated phases and the presence of O at the interface with the matrix. The mechanical properties of vanadium-based alloys are reduced by adding Y atoms, on the one hand, the O infiltrated in the alloy can be absorbed, and the mechanical properties of the alloys due to the precipitation of rich Ti phase can be improved, on the other hand, The mechanical properties of vanadium-based alloys were improved by dispersion strengthening.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.413

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