【作者】 李佳；

【导师】 刘波；

【作者基本信息】 四川大学 ， 能源动力， 2023， 硕士

【摘要】 随着核技术不断发展,亟需研发出能在更高运行温度和辐照剂量环境中应用的新型反应堆结构材料。难熔高熵合金由于其优异的性能,引起了广泛的研究兴趣。目前关于难熔高熵合金辐照响应行为的相关研究已取得部分成果,但其辐照响应行为仍未形成统一的规律和定论,为更系统、深入理解难熔高熵合金的辐照响应行为及相关机制,仍需继续探索研究新型难熔高熵合金的辐照响应行为及相关机理。非晶合金由于缺乏传统晶体结构缺陷如晶界、位错等,且具有各向同性的特征,在核结构材料方面具有巨大潜在的应用价值。本论文分别研究了He离子和Au离子对非晶TiTaNbZr难熔高熵合金微观结构和性能的影响,进一步阐明了其在辐照条件下的结构变化与力学性能演变之间的关联机制和两种离子辐照条件下不同结晶行为的原因,并在此基础上通过添加过渡元素Y和调控合金结构制备出具有显著区别的非晶和晶态TiTaNbZrY_x难熔高熵合金,综合评价TiTaNbZr和TiTaNbZrY_x难熔高熵合金的抗辐照性能,获得了抗辐照性能优异的非晶TiTaNbZrY_x难熔高熵合金。这为系统了解难熔高熵合金的辐照响应行为及相关机制提供了更多的基础和参考,并为开发可靠核结构材料提供了新的思路和前景。主要内容和结论如下:（1）探究了He离子辐照对TiTaNbZr难熔高熵合金微观结构和力学性能的影响。He离子辐照增强了TiTaNbZr难熔高熵合金内原子的短程扩散迁移和重排,该合金呈现出非晶-BCC单相的结构转变现象。结构转变过程中,增加的晶界作为缺陷汇为缺陷提供了有效的重组位点,抑制了晶体内的He泡,且原子的短程扩散没有显著破坏元素的均匀性。He离子辐照后,TiTaNbZr难熔高熵合金的力学性能显著提高,进一步详细阐明了该难熔高熵合金的结构转变与力学性能演变之间的关联机制。即使辐照剂量高达2×10¹⁷ cm^-2,力学性能也没有退化,归因于增加的晶界和自修复机制。且该TiTaNbZr难熔高熵合金的抗辐照肿胀和表面损伤性能优于其他研究所报道的传统W合金和Ta Ti WVCr难熔高熵合金。综上所述,TiTaNbZr难熔高熵合金表现出杰出的抗辐照性能,在核结构材料应用方面具有巨大潜能。同时,本研究探索的低能He离子辐照下TiTaNbZr难熔高熵合金的微观结构和力学性能演变为非晶难熔高熵合金的辐照效应提供了更多的理解和认识,为开发具有自修复能力的合金开辟了新前景,对第四代核电的发展具有重要意义。（2）探究了Au离子辐照对TiTaNbZr难熔高熵合金微观结构的影响,基于能量沉积理论揭示了与He离子辐照时的不同结晶行为。Au离子辐照时更强的原子扩散迁移使TiTaNbZr难熔高熵合金内发生明显的Ta元素偏析现象,形成了BCC双相结构。Au离子辐照时的结晶行为是辐照（热效应、自由体积）增强的扩散和级联碰撞无序化的竞争结果。辐照过程中增强的原子扩散促进了纳米晶生长,但级联碰撞会破坏晶格结构,这使Au离子辐照时纳米晶随辐照损伤增加的生长较于He离子辐照更缓慢,当辐照损伤为～47 dpa时,TiTaNbZr难熔高熵合金基体BCC相纳米晶平均尺寸仅为4.1 nm,其峰值损伤区域内仍可观测到大量非晶区域。本研究中探讨的不同离子辐照条件下难熔高熵合金的不同行为对于准确预测非晶难熔高熵合金在辐照环境中的行为,甚至通过优化辐照参数（离子、能量、通量）来准确调控其相结构和性质至关重要。（3）为进一步优化TiTaNbZr难熔高熵合金性能,通过添加过渡元素Y和调控合金结构制备出具有显著区别的非晶和晶态TiTaNbZrY_x难熔高熵合金,对比研究了其抗辐照性能。对于非晶TiTaNbZrY_x难熔高熵合金,添加的少量Y元素提高了其相稳定性,辐照后该合金内形成少量纳米晶;且由于Y元素与He原子、空位、间隙原子间均存在强结合作用,辐照后该合金内的位错、He泡等缺陷较小,没有观测到明显的气泡、破裂剥落等表面损伤,体积肿胀率较小,其随辐照剂量增加仅从0.48%增加到6.84%,表现出优异抗辐照性能。对于晶态TiTaNbZrY_x难熔高熵合金,辐照后其相结构保持稳定,但该晶态合金内晶界处形成了大量大尺寸的He泡团簇、位错,表面产生大量气泡,体积肿胀率随辐照剂量的增加从6.86%增加为14.24%。综合对比发现与TiTaNbZr和晶态TiTaNbZrY_x难熔高熵合金相比,非晶TiTaNbZrY_x难熔高熵合金具有更优异的抗辐照性能。更多还原

【Abstract】 With the development of nuclear technology,it is urgent to develop novel reactor structural materials which can be used in the environment of higher operating temperature and irradiation dose.So far,relevant researches on the behavior of refractory high-entropy alloys under irradiation have achieved a number of achievements,but there is no unified law and conclusion about this not yet.In order to systematically and deeply understand the irradiation response behavior and related mechanisms of refractory high-entropy alloys,it is still necessary to continue to explore the irradiation response behavior of novel refractory high-entropy alloys.In this paper,the effects of He ions and Au ions on the microstructure and properties of TiTaNbZrrefractory high entropy alloy were studied.The detailed correlation between the crystallization transformations and irradiation tolerance and the different crystallization behaviors under different ions irradiation in the refractory high entropy alloy films was further clarified.On this basis,by adding Y elements and adjusting the structure,the amorphous and crystalline TiTaNbZrY_x refractory high entropy alloy films was prepared and evaluated comprehensively with TiTaNbZrrefractory high entropy alloys.We have obtained the amorphous TiTaNbZrY_x refractory high entropy alloy which better excellent irradiation resistance.These can provide more references and basis for the systematic understanding of the irradiation response behavior and related mechanisms of refractory high entropy alloys,and provides a new prospect for the development of reliable nuclear structural materials.The main conclusions are summarized as follows:（1）The effects of He ions irradiation on the microstructure and mechanical properties of TiTaNbZrrefractory high entropy alloy were investigated.After irradiation,a structural transformation of amorphous-BCC single phase in TiTaNbZrrefractory high entropy alloy films was revealed on account of the enhanced diffusion and redistribution of atoms,which could also lead to a decrease of defects.In this process,increased grain boundaries,acting as effective defect sinks,have inhibited the He bubbles within crystals.The short-range migration of atoms did not destroy the uniformity of elements dramatically.After He ions irradiation,the mechanical properties of TiTaNbZrrefractory high entropy alloy are significantly improved,the correlation between the structural transformation and mechanical properties evolution in the refractory high entropy alloy films was also further clarified.No degradation of mechanical properties even for irradiation fluence as high as 2×10¹⁷ cm^-2due to the increased grain boundaries and self-healing mechanism.These results all indicate that the TiTaNbZrrefractory high entropy alloy have outstanding irradiation resistance and potential applications in reactor structural materials.Meanwhile,the microstructural transformation and performance evolution of the TiTaNbZrrefractory high entropy alloy explored in this study could provide more understanding of irradiation effect and a new perspective for the development of the alloys with self-healing ability in refractory high entropy alloys.（2）The effect of Au ions irradiation on the microstructure of amorphous TiTaNbZrrefractory high entropy alloy was studied.Based on the energy deposition theory,the crystallization behavior different from that of He ions irradiation was revealed.The results showed that the stronger atomic diffusion and migration during Au ions irradiation caused significant segregation of Ta elements and forms a BCC biphase structure in the TiTaNbZrrefractory high entropy alloy.The crystallization behavior during Au ions irradiation was the result of competition between the diffusion enhanced by irradiation（thermal effect,free volume）and disordering caused by cascade collision.The enhanced atomic diffusion during irradiation promoted the growth of nanocrystals,but the cascade collision would destroy the lattice structure,which makes the growth of nanocrystals with the increase of irradiation damage under irradiation of Au ions was slower than that of He ions.As Au ions irradiation damage was up to～47 dpa,the nanocrystalline size of matrix BCC phase in TiTaNbZrrefractory high entropy alloy was only 4.1 nm,and a large number of amorphous regions could still be observed in the damage peak region.The different crystallization behaviors of alloys under different ions irradiation conditions discussed in this study are very important for accurately predicting the behavior of amorphous refractory high entropy alloys in irradiation environment,and even regulating the phase structure and properties by optimizing the irradiation parameters（ion,energy,flux）.（3）In order to further optimize the properties of the TiTaNbZrrefractory high entropy alloy,significantly different amorphous and crystalline TiTaNbZrY_xrefractory high entropy alloy films was prepared by adding Y elements and adjusting alloy structure,and their irradiation resistance was studied comparatively.For the TiTaNbZrY_x amorphous refractory high entropy alloy,the added Y elements have improved the phase stability,and a small number of nanocrystals were formed in the alloy after irradiation.And due to the strong binding energy between Y elements and He atoms,vacancies and interstitials,the defects such as He bubble and dislocations in the alloy after irradiation are small,no obvious superficial damage such as bulging,cracking can be observed on the surface,and the swelling ratio only increases from 0.48%to 6.84%with the increase of irradiation fluence,showing excellent irradiation resistance.For the crystalline TiTaNbZrY_x refractory high entropy alloy,the phase structure remained stable after irradiation,bu a large number of large-size He bubble clusters were formed at the grain boundaries and plenty of bulges were generated on the surface after He ions irradiation.The swelling ratio increased from 6.86%to 14.24%with the increase of irradiation fluence.Compared with the amorphous TiTaNbZrand crystalline TiTaNbZrY_x refractory high entropy alloys,the amorphous TiTaNbZrY_x refractory high entropy alloys have better irradiation resistance.更多还原