快重离子辐照3C-SiC材料蠕变效应的研究

3C-SiC ceramics are promising candidate materials for future advanced nuclear energy systems, due to the unique combination of the inherent attractive properties of SiC, including high temperature, chemical stability, low activation/low decay heat nuclear properties, low tritium permeation, and high thermal conductivity. However, until now there are many questions of mechanical properties of 3C-SiC under high temperature and strong radiation environment of the advanced nuclear energy systems. On the basis of the serious problems of 3C-SiC under high temperature irradiation, the purpose of the project is study of irradiation creep in 3C-SiC. Upon different stresses, irradiation temperatures and dose rates, 3C-SiC would be irradiated with swift heavy ions that supplied by Sector Focus using Cyclotron of Heavy Ion Research Facility in Lanzhou (HIRFL-SFC). Stress effects on migration of point defects, the process of nucleation and growth of Frank dislocation loops and cavities will be comprehensively studied. The prior work by our group has founded an advanced facility of in-situ swift heavy ions irradiation under high temperature and stress. We are going to establish models of defect nucleation and growth in 3C-SiC based on thoroughly analyzing the experimental results and data simulation, and the theory of swift heavy ions irradiation-induced damages. In addition, we are going to explain the relationship between the microstructural defects and macroscopic mechanical properties of 3C-SiC, and try to elucidate the law and reason of irradiation creep of 3C-SiC. The investigations will supply a scientific foundation of 3C-SiC that can be used in advanced nuclear energy systems.

3C-SiC材料以其优异的耐高温、耐腐蚀、低放射活性、低氚渗透和高热导率等性能而成为未来先进核能系统强有力的候选材料。但目前，该材料在先进核能系统工作环境中的力学性能研究还存在诸多不足。本项目针对该材料高温辐照存在的关键问题，提出辐照蠕变为研究对象。利用兰州重离子国家实验室SFC加速器提供的快重离子，在施加不同应力、温度和剂量率条件下，辐照3C-SiC材料，系统地研究应力环境中高温辐照，点缺陷的迁移、Frank位错环和空腔等缺陷的形核和生长机制。作为本项目前期工作，我们已经搭建了国内第一个在线高温-应力材料快重离子辐照实验装置。通过综合分析现有实验数据，借助辐照损伤理论和数值模拟，建立应力环境中辐照缺陷形核和生长模型，并探讨微观缺陷与宏观力学性能的关系，尝试阐明3C-SiC材料辐照蠕变产生的规律及其原因，为3C-SiC材料能够应用于先进核能系统提供科学依据。

碳化硅是重要的核能结构材料，评估应力加载作用下材料辐照损伤程度，这对于材料稳定性很重要。经过项目三年研究，主要研究内容包括：（1）高温应力加载下氦离子辐照碳化硅材料，辐照损伤机理与实验论证；（2）不同温度氦离子辐照碳化硅材料，氦泡形成情况；（3）硅、氪、氙离子辐照碳化硅材料，损伤效应研究。取得的重要结果包括：（1）利用第一性原理计算发现施加张应力，会导致空位迁移能增加，而间隙子迁移能降低；相反，施加压应力，空位迁移能减低，而间隙子迁移能增加。实验数据证实了这一点；（2）在750℃及以上高温氦离子辐照碳化硅，容易在密堆积面上形成二维盘状空腔，但也有少量的盘状空腔垂直于密堆积面；（3）比较相同dpa离子辐照，氦离子辐照对材料晶格损伤要小于硅离子；（4）氪、氙离子辐照碳化硅，高温退火后气泡生长规律不同于氦离子辐照碳化硅，并且高温退火期间材料容易发生开裂。（5）单晶碳化硅与多晶碳化硅辐照相比，氦泡更容易在多晶碳化硅中形核与生长。以上实验结果科学意义如下：（1）在应力加载下，缺陷迁移能会发生变化，这与材料高温辐照蠕变性能有直接联系。如在张应力加载下，材料蠕变速率要大于压应力情况。可以通过调节应力加载方向，降低材料辐照蠕变速率；（2）高温辐照，容易形成二维盘状空腔。这些盘状空腔连接在一起，会导致材料开裂，降低材料稳定性。有必要通过材料设计，抑制盘状空腔的生长；（3）增加级联碰撞密度，将导致材料中残留更多的缺陷。也就是说，剂量率会对辐照损伤有影响，高的剂量率会导致材料损伤更大；（4）氪、氙是铀裂变主要产物，研究高温下氪泡、氙泡生长规律对于评估碳化硅包壳材料稳定性很重要。研究发现气泡生长速度明显小于氦泡，并且气泡容易沿着层错周围形核。在层错内部，气泡密度很小。同时缺陷密度也较低，这说明了层错能够提高材料抗辐照性能；（5）多晶碳化硅中存在大量的晶界，这些晶界会捕获碳间隙子，导致晶粒内空位浓度增加，出现氦泡更容易形核。这对于评估多晶碳化硅抗氦脆有重要意义。