Search and Control of self-healing mechanism in fusion reactor materials

固体材料在粒子辐照下具有自愈特性；许多工程材料在经过几十dpa后仍能保持原来的形状，这正是材料自愈特性的结果。在本研究中，研究了这些材料的内在性质，以及通过添加沉淀等赋予这些材料的外在自愈性。首先，已知的钒合金在超过某个中间dpa值的峰值后会出现溶胀减少。对这些材料中的沉淀物进行了仔细的研究，通过利用成像板、EDS和PEELS拍摄的选定区域衍射来确定它们的性质。很明显，这些沉淀与基体之间的界面作为捕获位点，在那里发生界面催化的重组，并在抑制膨胀中起重要作用。然而，这一现象并不能解释所观察到的肿胀减少而dpa增加的现象。辐照诱导沉淀引起的沉淀密度随dpa的增加似乎是解释溶胀减少的机制。因此，即使在长时间高剂量照射后，使这些沉淀物具有良好的稳定性似乎非常重要。在高dpa辐照下表现出自愈性能的一个很好的例子是V-5Ti合金。在本实验中，试样首先在FFTF/MOTA中辐照至17dpa。在JMTR中进一步辐照至0.1dpa，比FFTF中的辐照小得多。在FFTF/MOTA中，17dpa后的微观结构与在JMTR中辐照到0.1dpa后的微观结构几乎没有区别。微观结构基本由细小的TiO2析出物组成。这意味着该微结构在0.1dpa以下已经饱和，即使在长时间照射至17dpa时也没有演变。这种观察结果是由于微观结构由细小的沉淀组成，具有显著的自愈机制；基体与析出相之间的界面对自间隙原子与空位之间的相互复合起催化作用。为了分析实验观察到的自愈特性，开发了基于化学速率理论的计算机代码。采用HVEM原位辐照技术获得了输入参数。模拟结果定性吻合较好，定量吻合较好。理论与实验不完全一致的部分原因可能是由于理论所采用的近似不够。据信，其他机制是导致这一现象的原因，这将是进一步研究的主题。少

Self-healing property under particle irradiation is not uncommon to solid materials; many of the engineering materials keep their original shape even after several tens dpa, and this is exactly the result of self-healing property of the material. In this research, this intrinsic property, as well as extrinsic self-healing property given to these materials by adding precipitates, etc. is studied.Firstly, vanadium alloys that have been known to exhibit swelling decrease after going over a peak swelling at some intermediate dpa value. Precipitates in these materials have been examined closely, identifying their nature by utilizing selected area diffraction taken with imaging plates, EDS and PEELS. It became clear that interface between these precipitates and the matrix act as trapping sites, where interface-catalyzed recombination occurs, and play an important role in suppressing swelling. However, this phenomenon only cannot explain the observed decrease in swelling while dpa increases m … More onotonically. Increase in the precipitate density with dpa, caused by irradiation induced precipitation appears to be the mechanism explaining the decrease in swelling. Thus, it seems very important to give these precipitates good stability even after prolonged irradiation to high doses.One of the good example of self-healing property demonstrated under high dpa irradiation is the one observed in V-5Ti alloy. In this experiment, the specimen was first irradiated up to 17dpa in FFTF/MOTA. The specimen was further irradiated in JMTR up to 0.1dpa, which is much smaller to the irradiation in FFTF. The microstructure after 17dpa in FFTF/MOTA was indistinguishable to those in the specimen irradiated to 0.1dpa in JMTR. The microstructure basically consisted of tiny TiO2 precipitates. This means that this microstructure had been saturated below 0.1dpa and did not evolve even during the prolonged irradiation up to 17dpa. This observation is the result of remarkable self-healing mechanism due to the microstructure consisting of fine precipitates; the interface between the matrix and the precipitates act as catalysis for mutual recombination between self-interstitial atoms and vacancies.Computer code based on chemical rate theory has been developed in order to analyze the self-healing property observed experimentally. The input parameters have been obtained by using HVEM in situ irradiation technique. The result of the simulation was in good qualitative agreement while quantitative agreement was fair. The reason for this insufficient agreement between the theory and the experiment may partly be because of the insufficient approximation adopted in the theory. It is believed other mechanism is responsible for this and will be the topic of further research. Less