镍及镍基合金的离子辐照效应研究

发布时间：2018-08-16 08:15

【摘要】：镍基合金由于其优异的耐熔盐腐蚀性以及高温力学性能被选为熔盐堆的结构材料。熔盐堆中结构材料面临中子辐照,这将影响结构材料的微观组织及力学性能,进而影响反应堆的安全性及服役寿命。然而,结构材料的中子辐照研究费用高昂,中子辐照后材料被活化具有放射性。为此,本论文通过离子辐照来模拟镍基合金的中子辐照效应,采用纳米压痕仪、透射电子显微镜及慢正电子淹没装置研究镍基合金辐照后的力学性能及微观结构演化,并以单质镍为模型分析镍基合金辐照后的力学性能及微观结构演化机理。采用7MeV Xe~(26+)及650°C高温He~+辐照研究了镍及镍基合金辐照后的力学性能,研究表明,单质镍、GH3535合金以及Ni-W-Cr合金在离子辐照后发生了明显的辐照硬化现象,辐照产生的位错环、缺陷团簇以及氦泡是导致镍及镍基合金发生辐照硬化的主要原因。Makin-Minter方程能够用来描述单质镍、GH3535合金以及Ni-W-Cr合金离子辐照诱导的硬化随辐照损伤的变化关系,且有效体积常数可用于表征合金的抗辐照性能。另外,与GH3535合金相比,Ni-W-Cr合金具有较好的抗辐照硬化能力。采用30 keV He~+及1MeV Xe~(20+)辐照研究了单质镍及镍基合金中辐照诱导的微结构演化。研究表明,Hastelloy N合金中Xe~(20+)辐照使得固有位错周围出现位错环修饰现象。另外,随辐照剂量的升高,固有位错的密度减少,这是由于间隙原子的吸收使得固有位错线向样品表面的攀移而引起的。高温原位退火实验说明,退火温度低于600°C时,Hastelloy N合金中辐照产生的缺陷是稳定的。在30 keV He~+辐照下,氦原子的存在导致单质镍中形成柏氏矢量为1/2110的间隙性位错环。随辐照温度的升高,由于单质镍中小位错环或团簇的长大及合并,位错环尺寸增大、密度减少。另外,采用30 keV He~+辐照研究了镍基二元合金(Ni-Cr、Ni-W,Ni-Mo)中溶质原子对镍基合金辐照性能的影响。研究表明,Cr、Mo固溶元素能够抑制合金中位错环的生长。溶质原子的体积尺寸因子以及合金化效应与合金中辐照产生的位错环的密度和尺寸有密切关系,这可能是由于Cr、Mo、W溶质原子的加入影响了合金的化学无序性、间隙/空位原子团簇和点缺陷在级联碰撞过程的扩散、缺陷在级联碰撞中的复合概率和缺陷向样品表面的逃逸概率。高温He~+辐照下,镍基二元合金中有氦泡出现且在基体中均匀分布;随辐照温度的升高,氦泡的尺寸增大。分析表明,固溶合金中杂质溶质原子的存在是导致合金中氦泡均匀分布的主要原因,杂质溶质原子与He原子结合能的不同导致了合金中氦泡的密度和尺寸的差异。
[Abstract]:Nickel-based alloys are selected as structural materials for molten salt stacks due to their excellent corrosion resistance and high temperature mechanical properties. The structure material in molten salt reactor is exposed to neutron irradiation, which will affect the microstructure and mechanical properties of the structure material, and then affect the safety and service life of the reactor. However, the neutron irradiation of structural materials is expensive, and the activated materials are radioactive after neutron irradiation. Therefore, the neutron irradiation effect of nickel-based alloy was simulated by ion irradiation. The mechanical properties and microstructure evolution of Ni-base alloy after irradiation were studied by nano-indentation instrument, transmission electron microscope and slow positron submergence device. The mechanical properties and microstructure evolution mechanism of Ni-based alloy after irradiation were analyzed by means of a simple nickel model. The mechanical properties of nickel and nickel base alloys after irradiation were studied by 7MeV Xe26 and 650 掳C high temperature he-irradiation. The results showed that the irradiation-hardening phenomenon of Nickel-HGH3535 alloy and Ni-W-Cr alloy was obvious, and the dislocation ring produced by irradiation was observed. Defect clusters and helium bubbles are the main causes of irradiation hardening of nickel and nickel-based alloys. Makin-Minter equation can be used to describe the relationship between irradiation hardening and radiation damage induced by the ions of Nickel-HGH3535 alloy and Ni-W-Cr alloy. The effective volume constant can be used to characterize the radiation resistance of the alloy. In addition, Ni-W-Cr alloy has better radiation hardening resistance than GH3535 alloy. The microstructure evolution induced by irradiation in nickel and nickel-based alloys was studied by means of 30 keV He~ and 1MeV Xe20 irradiation. The results show that Xe20 irradiation causes dislocation ring modification around inherent dislocation in Hastelloy N alloy. In addition, with the increase of irradiation dose, the density of intrinsic dislocation decreases, which is caused by the inherent dislocation line climbing toward the surface of the sample due to the absorption of interstitial atoms. High temperature in-situ annealing experiments show that the defects produced by irradiation in Hastelloy N alloy are stable when annealing temperature is below 600 掳C. The existence of helium atoms at 30 keV He- irradiation results in the formation of a 1 / 2110 interstitial dislocation ring in nickel. With the increase of irradiation temperature, the size of dislocation ring increases and the density decreases due to the growing and merging of small and medium dislocation rings or clusters of nickel. In addition, the effects of solute atoms on the irradiation properties of Ni-based binary alloy (Ni-Cr-Ni-WN-Ni-Mo) were studied by 30 keV He-irradiation. The results show that the solid solution element of Cr-Mo can inhibit the growth of dislocation ring in the alloy. The volume size factor and alloying effect of solute atom are closely related to the density and size of dislocation ring produced by irradiation in the alloy, which may be due to the influence of the addition of Cr-MoW solute atom on the chemical disorder of the alloy. The diffusion of gap / vacancy clusters and point defects in cascade collisions, the recombination probability of defects in cascade collisions and the escape probability of defects to the surface of samples. Under high temperature He-irradiation, helium bubbles appeared in Ni based binary alloys and distributed uniformly in the matrix, and the size of helium bubbles increased with the increase of irradiation temperature. The analysis shows that the existence of impurity solute atoms in the solid solution alloy is the main reason for the uniform distribution of helium bubble in the alloy. The difference of binding energy between the impurity solute atom and he atom leads to the difference of the density and size of the helium bubble in the alloy.
【学位授予单位】：中国科学院研究生院(上海应用物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TL341

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