【摘要】：釩基合金因其低活化性、高熱導(dǎo)率、優(yōu)于其他材料的力學(xué)性能和抗輻照性能,而被認(rèn)為是聚變反應(yīng)堆中第一壁的首選結(jié)構(gòu)材料,也因此引發(fā)了對釩基合金研究的熱潮。本文分別采用第一性原理和分子動力學(xué)方法,從原子層面、微觀結(jié)構(gòu)角度探究合金元素原子在釩基合金中的分布及其對性能的影響,重點(diǎn)針對實(shí)驗(yàn)中觀察到的富Ti析出相進(jìn)行詳細(xì)研究,并從微觀角度分析富Ti析出相對釩基合金性能影響。通過第一性原理及分子動力學(xué)方法模擬表明,在釩基合金中,Cr原子在釩基合金中任意位置均可穩(wěn)定存在,當(dāng)Cr原子位于晶界處時(shí),可有效強(qiáng)化釩基合金的晶界強(qiáng)度。而Ti原子易于晶粒內(nèi)部偏析,并在晶粒內(nèi)部形成一定的富Ti區(qū),且Ti原子的存在,削弱了釩基合金的彈性變形能力,使得釩基合金的韌性減小。第一性原理模擬表示,Y的添加可通過釘扎晶界而細(xì)化晶粒,通過彌散強(qiáng)化作用改善釩基合金的力學(xué)性能。根據(jù)實(shí)驗(yàn)測定結(jié)果構(gòu)建富Ti析出相的微觀結(jié)構(gòu)Ti(CNO)和Ti O,并對其進(jìn)行一系列基本參數(shù)計(jì)算,從熱力學(xué)、力學(xué)角度證明所構(gòu)建富Ti析出相的微觀結(jié)構(gòu)可以穩(wěn)定存在。又計(jì)算其基本力學(xué)參數(shù),判斷所構(gòu)建富Ti相屬于硬脆相,其硬度遠(yuǎn)高于純V,且體現(xiàn)脆性材料特征。所得基本力學(xué)性質(zhì)符合實(shí)驗(yàn)測試結(jié)果,這就進(jìn)一步證明所建結(jié)構(gòu)的準(zhǔn)確性,同時(shí)也從微觀角度解釋了實(shí)驗(yàn)制備所得的釩基合金,因脆硬性富Ti析出相的存在大大降低了釩基合金的力學(xué)性能。對富Ti析出相與基體相所構(gòu)成的界面進(jìn)行研究發(fā)現(xiàn),與純釩界面相比,亞穩(wěn)態(tài)下的富Ti析出相Ti O與基體之間界面強(qiáng)度增加,但是析出相自身晶粒內(nèi)原子之間鍵合削弱。而穩(wěn)態(tài)下的富Ti析出相Ti(CNO)與基體相之間界面上的O原子的存在,會明顯削弱界面凝聚力,使其比純釩界面更易發(fā)生斷裂,顯著降低其力學(xué)性能;但若界面上沒有O原子而以C、N原子截止時(shí),界面強(qiáng)度顯著增加,因此,釩基合金中添加Y元素以吸O來改善由于富Ti析出相而降低的力學(xué)性能。綜上所述:釩基合金中的Cr原子偏析于晶界時(shí)可視為晶界強(qiáng)化元素;Ti原子偏析于晶粒內(nèi)部,易與雜質(zhì)原子形成富Ti相析出,析出相的硬脆性及與基體界面上O的存在,使得釩基合金的力學(xué)性能下降;添加Y原子,一方面可吸收合金中滲入的O,改善由于富Ti相析出而降低的力學(xué)性能,另一方面,通過彌散強(qiáng)化作用細(xì)化晶粒以提高釩基合金的力學(xué)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.
【學(xué)位授予單位】：西南科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.413

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