耐事故包壳材料FeCrAl基合金中Laves相析出行为及其对高温力学强度的作用机制研究

As the core of the future advanced nuclear reactor, accident tolerant fuel (ATF) still keeps or even improves the performance for a long time under normal operation condition after the loss of coolant, which will significantly improve the safety of nuclear power. As a popular candidate for ATF cladding material, FeCrAl-base alloy features better irradiation resistance and corrosion resistance, higher thermal conductivity stability after irradiation as well as better high temperature steam oxidation resistance than that of traditional zirconium alloy. However, its high temperature mechanical strength is not high enough to meet the requirements for the performance in emergency situations. Doping elements, such as Nb, significantly improves the high temperature mechanical strength of FeCrAl-base alloy, but there are still disputes over the influencing mechanism of precipitated Laves phases (Fe2Nb) during high temperature aging on high temperature mechanical strength. In order to solve this problem, this project intends to study the precipitation behavior of Laves phases in FeCrAl-base alloy through regulating and controlling doped elements and heat treatment process. In-situ observation by internal friction technique, which is extremely sensitive to microstructure changes, was conducted to show the changes of internal friction and mechanical performance in the process of precipitation of the second phase containing Nb. The project carried out a systematic research on the effect and mechanism of Laves phases precipitation characteristics on high temperature mechanical strength. The findings will improve the high temperature mechanical strength of FeCrAl-base alloy and finally provide a scientific basis for its application.

作为未来先进核反应堆的核心，耐事故核燃料（ATF）在冷却剂丧失后仍能长时间保持或提高其在正常运行工况下的性能，这将显著地提高核电的安全性。作为热门的候选ATF包壳材料，FeCrAl基合金的抗辐照和耐腐蚀性能较好，辐照后热导率稳定，而且具有比传统的锆合金更出色的抗高温水蒸气氧化能力，但其高温力学强度较低不能满足事故状态下的性能要求。通过添加Nb等元素可提高FeCrAl基合金高温力学强度，但其高温时效时析出的Laves相（Fe2Nb）对材料高温强度的影响机制还存在较多争论。针对这一问题，本项目拟通过调控添加元素和热处理工艺研究FeCrAl基合金中Laves相的析出行为，采用对微观结构变化极为敏感的内耗技术原位观察含Nb第二相析出过程中内耗与力学性质的变化，系统研究Laves相析出特征对高温强度的影响规律和作用机制，为提高FeCrAl基合金的高温力学强度并最终应用提供科学据。

安全可靠是核能发展的生命线，日本福岛核事故后，具有一定事故包容能力的包壳材料（ATF包壳）成为国际研究重点。作为最重要候选的ATF包壳材料，FeCrAl基合金的抗辐照和耐腐蚀性能较好，辐照后热导率稳定，而且具有比传统的锆合金更出色的抗高温水蒸气氧化能力，但其高温力学强度较低不能满足事故状态下的性能要求。通过添加Nb等元素可提高FeCrAl基合金高温力学强度，但其高温时效时析出的Laves相对材料高温强度的影响机制还存在较多争论。因此，系统研究Laves相析出行为规律是掌握其对高温强度影响规律和作用机制的关键。所取得的主要研究结果总结如下：.（1）利用真空感应熔炼、均匀化退火、高温锻造、热轧、温轧、中间退火、冷轧及最终热处理等方法制备出了成分均匀且第二相可控的四种不同Nb含量的FeCrAl基合金，获得了含Nb的FeCrAl基合金的最佳优化制备工艺参数。.（2）掌握了Fe2Nb型Laves相在不同热时效条件下的析出、溶解与长大行为规律：极其细小的第二相颗粒发生溶解温度范围为700℃~800℃，发生熟化的温度起点约为800℃，当温度超过800℃，第二相颗粒尺寸长大的趋势明显增加。.（3）建立了内耗技术作为表征合金内第二相粒子与位错、晶界等微观缺陷相互作用的新手段，获得不同Nb含量下Laves析出相的析出特征对材料内耗特征谱的影响，研究结果为从原子尺度揭示Laves相析出特征对FeCrAl 基合金力学性能，尤其是高温力学强度的影响机制提供科学依据。.（4）项目执行过程中，共接受发表基金标注的重要科技论文共11篇（SCI论文9篇），获得国家发明授权专利2件，培养青年技术人员和研究生4名，依托本项目取得的部分研究内容作为支撑，获得了2020年四川省科技进步三等奖，较好的完成了项目预期目标。