热力耦合条件下自修复型MgO厚涂层体应力表征与微裂纹演化机理

MgO ceramic is usually used for fabricating crucible in the nuclear industry due to its high melting point, excellent alkali-resistant metal slag ability, and the MgO crucible can be used for smelting radioactive metal with high-purity, such as uranium, thorium and so on. However, the existence of large body stress under the thermal-mechanical coupling conditions will result in the generation of the micro-cracks at the inner of the ceramics and further limit its application. The use of magnesium oxide (MgO) thick coatings on superalloy crucible substrates is one of the most important means of replacing pure MgO ceramic crucibles. The author has investigated the thermal residual stress and dynamic behavior of the crack propagation for the plasma-spayed ceramic coatings under thermal-mechanical coupling conditions previously. Based on the previous research, the body stress of the self-repairing MgO thick coating (which can be regarded as 3D bulk material) will be characterized via the simulation and Raman testing, the position, magnitude and distribution of key body stress which could determine the crack propagation will be found. And the characterization method of the body stress for the ceramic will be established. And the dynamic behavior of the failure for the MgO thick coating under the thermo-mechanical coupling conditions will be studied. The in-situ acoustic emission technique will be used to monitor the crack propagation and self-repair signal under the thermo-mechanical loading conditions. Combining the analysis of the acoustic emission signal and the microstructure observation of the thick coating, the distinguish of failure modes of the thick MgO coating will be realized, and the evaluation mechanism of the cracks inside the self-repairing MgO will be pursued thoroughly. The investigation results will provide the theoretical guide and scientific basis for the optimization of the processing technique of the self-repairing MgO thick coating.

MgO陶瓷由于熔点高，抗碱性金属熔渣能力强, 通常用于核工业用坩埚,熔炼高纯度放射性金属铀、钍合金等。但由于在热力耦合条件下，内部存在较大体应力，从而导致其内部易出现裂纹，限制其应用。利用在高温合金坩埚基体上制备自修复型MgO厚涂层是替代纯MgO陶瓷坩埚重要手段之一。作者前期系统开展了陶瓷涂层在热力耦合条件下热应力及其内部裂纹的动态行为研究，在前期研究基础上，本项目拟采用模拟计算和拉曼测试对等离子体喷涂自修复型MgO厚涂层（可视为3D块体材料）进行体应力表征，找到决定裂纹扩展关键位置的体应力大小及分布，建立陶瓷材料的体应力表征方法。进一步采用原位声发射技术监测涂层在热力耦合条件下其内部裂纹扩展与自修复信号，结合声发射信号及MgO厚涂层微结构分析，实现其失效模式的识别，全面探究自修复型MgO厚涂层微裂纹扩展及止裂的演化机制，进一步为优化自修复型MgO厚涂层的制备工艺提供理论指导和科学依据。

MgO陶瓷由于熔点高，抗碱性金属熔渣能力强, 通常用于核工业用坩埚, 用来熔炼高纯度的放射性金属铀、钍合金等。但由于在热力耦合条件下，MgO陶瓷内部存在较大的体应力，从而导致其内部易出现裂纹，限制其在核能领域的广泛应用。利用在高温合金坩埚基体上制备自修复型MgO厚涂层是替代纯MgO陶瓷坩埚重要手段之一。 本项目首先针对包含粘结层，自修复层，MgO陶瓷面层的多层结构自修复涂层，采用有限元模拟计算系统研究并优化了自修复MgO陶瓷涂层的成分与结构，同时采用模拟计算对等离子体喷涂自修复型MgO厚涂层（可视为3D块体材料）进行了体应力表征，找到了决定裂纹扩展关键位置的体应力大小及分布，建立了陶瓷材料的体应力表征方法。结合热力学计算及有限元模拟，提出了三种机制有利于涂层的高温自修复：（1）自修复反应产生的自修复颗粒填充裂纹缝隙，堵塞裂纹，使得裂纹产生闭合; (2)裂纹面尖端应力减小，钝化了尖端应力集中，且裂纹面周围在涂层发生自修复反应后产生了更大的压应力，挤压裂纹面，有利于裂纹的闭合；（3）自修复反应产生的物质密度较小，体积发生膨胀，进一步对裂纹面产生挤压。此外，考虑到MgO一定温度下容易与水发生反应，采用无水乙醇作为溶剂，醇解度高的PVA作为粘结剂球磨制浆，并采用喷雾造粒技术制备了自修复层对应的复合粉体及陶瓷面层粉体，采用等离子喷涂制备了自修复多层结构涂层。采用XRD应力衍射测试了涂层的表层残余应力，并采用原位声发射技术监测了涂层在热力耦合条件下其内部裂纹扩展与自修复信号，通过对声发射信号参数进行聚类分析，快速傅里叶变换及小波变换等，结合MgO涂层微结构分析，实现了其失效模式的识别。在该项目资助下，共发表主要代表性SCI论10篇，申请专利2项，获中国稀土学会科学技术奖二等奖一项。该项目的研究为进一步优化自修复型MgO厚涂层的制备工艺提供理了理论指导和科学依据。