高熵陶瓷在热障涂层与环境障涂层中的研究进展

Research Progress of High-Entropy Ceramic in Fields of Thermal Barrier Coatings and Environmental Barrier Coating

热障涂层(TBCs)和环境障涂层(EBCs)是航空发动机的关键技术之一。TBCs可以大幅提高发动机高温合金热端部件的工作温度,EBCs可以有效保护发动机陶瓷基复合材料高温部件。高熵陶瓷(HECs)一般指的是多种组分(5种或以上)以等原子比或接近等原子比形成的固溶体,其性能具有“鸡尾酒”效应,展现出常规陶瓷材料不具备的优异性能。HECs概念被提出以来已经在很多领域被广泛研究,成为陶瓷材料研究领域的热点。在TBCs与EBCs领域,研究者们对HECs也开展了大量的研究工作,取得了很多研究成果。对国内外已经报道可以用于TBCs和EBCs的新型HECs材料进行了分类总结,介绍了它们的制备方法、晶体结构、热导率、热膨胀系数、力学性能、环境沉积物(CMAS)腐蚀行为以及HECs涂层的制备与性能,并对HECs在TBCs与EBCs中的发展前景进行了展望。

Thermal barrier coatings(TBCs)and environmental barrier coating(EBCs)are key technologies for aero engines.Hotsections of aero engines are mainly made of superalloys and ceramic matrix composites.TBCs can significantly increase the operating temperature of the superalloy hot-sections,and EBCs can effectively protect the ceramic matrix composite.High entropy ceramics(HECs)generally refers to a solid solution formed by multiple components(five or more)in equal or near equal atomic ratios,and their properties have a"cocktail"effect,exhibiting superior performance as compared to the conventional ceramic materials.The concept of HECshas been widely studied in many fields since its introduction and has become a hot topic in the field of ceramic materials research.With the development of high-performance aero engines,the existing TBCs and EBCs materials are difficult to meet the requirements.HECs also have great application prospects in the field of thermal and environmental barrier coatings,and researchers have done a lot of research and achieved many results.This review summarizes a comprehensive classification of new HEC materials that have been reported for TBCs and EBCs at home and abroad,and introduces their preparation methods,crystal structures,thermal conductivity,thermal expansion coefficients,mechanical properties,CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)corrosion behavior,and the preparation and properties of HEC coatings,and provides an outlook on the development prospects of HECs in TBCs and EBCs.In recent years,researchers have proposed many new TBCs or EBCs materials,in which rare earth elements have played an important role,including rare earth zirconates,rare earth cerates,and rare earth silicates.The performance of these materials can be effectively improved by one rare earth element as the main element doping with other rare earth elements.By introducing the concept of"high entropy"into the design of new TBC and EBC materials,the synergistic effect of multiple rare earth elements is likely to yield unexpected attributes and make up for the performance deficiencies of single-component rare earth ceramics.This review first introduced HECs materials developed by scholars,including high entropy rare earth zirconates,high entropy rare earth cerates,high entropy rare earth tantalates,and high entropy rare earth silicates.These HECs were mainly prepared by conventional methods,such as chemical co-precipitation,solid-phase reaction method,and sol-gel method.Most HECs were single-phase solid solutions with good high-temperature phase stability and did not undergo phase transformation during cooling.In addition,their sintering resistance was also greatly improved compared to single-component rare earth ceramics,and the grain growth rate at high temperatures was very slow.All of HECs mentioned in the paper had lower thermal conductivity than single-component rare earth ceramics,and some of the high-entropy zirconates and high-entropy silicates had thermal conductivities even lower than 1 W·m^(-1)·K^(-1),which revealed a tremendous advantage as compared to the currently TBCs and EBCs materials.Their coefficient of thermal expansion(CTE)could be regulated bycomposition design,giving rise to improved CTE matching with the substrate.In addition,the high-entropy rare earth tantalates exhibited good mechanical properties,with improved fracture toughness and Vickers hardness.Resistance to CMAS attack was also a capability that should be available in the next generation of TBCs and EBCs materials,so this review also presented CMAS attack resistance of HECs.Rare earth elements were the key to inhibiting CMAS attack,and rare earth cations with different ionic radii had different interactions with CMAS.Due to the synergistic effect of multiple rare earth elements,the resistance of HECs to CMAS corrosion had been substantially improved.Then,this review presented some reports on high-entropy coatings.All coatings were prepared by atmospheric plasma spraying,which still had good high-temperature phase stability and low thermal conductivities,but the thermal cycle lifetimewaslow and cannot meet the requirements for TBCs and EBCs applications.Finally,it was concluded that HECs had great potential for applications in the field of TBCs and EBCs.However,there was still much room for the development of high entropy TBCs and EBCs.First,there was a lack of a clear underlying theory to guide material design.Secondly,the complexity of HECs composition and the large design space available were advantages,but they also resulted in a huge workload,especially with purely experimental methods.The introduction of methods such as first-principles calculations could significantly improve the design progress of HECs materials and should be an area of future research.Thirdly,the scientific aspects of HECs coating preparation.The current research mainly focused on the properties of HECs powders and bulks,but the crystal structure and properties of HECs in the coating state were significantly different from those of bulks and powders.Therefore,the preparation science of high-entropy TBCs and EBCs was a key issue that deserves further investigation.