强韧与微结构稳定一体化Al2O3–GAP共晶涂层的高PV值磨损服役行为

Oxide ceramics show high strength, high hardness, good high temperature and oxidation resistances. The corresponding coatings exhibit excellent application potential in the dynamic seal systems of aeronautical, astronautical and high-class civil fields. However, previous investigations were mainly focused on the mechanical properties of the coatings without taking account of their high temperature microstructure and mechanical performance stabilities under high PV (P: contact pressure; V: friction velocity) wear conditions accompanied by high temperature, serious oxidation and strong thermal shock. Based upon rapid directional solidification growth feature of Al2O3-based bulk eutectic ceramics, this study is to deposit the novel Al2O3–GdAlO3 (GAP) eutectic ceramic coatings via atmospheric plasma spraying. Simultaneously, strength-ductility synergy is achieved with multiscale distributions of Al2O3/GAP eutectic phases in the coatings. This project mainly investigates the coupled growth mechanism of interlocked Al2O3/GAP eutectic phases with network structure. Cooperatively strengthening and toughening mechanism of the coatings will be studied. The integration of strengthening, toughening and microstructure stabilization for Al2O3–GAP eutectic ceramic coatings will be realized. Additionally, the wear behavior and failure mechanism of the coatings will be elucidated under the above-mentioned severe conditions. These studies will provide theoretical basis and technical support for developing high performance Al2O3-based wear resistant coatings for high PV value applications.

氧化物陶瓷涂层因具有高强度、高硬度、耐高温和抗氧化等特点，可应用于航空、航天和高端民用等机械动密封领域。然而，以往研究着重关注涂层力学性能，对在高PV值（P：接触压强，V：摩擦速率）工况呈现的高应力、高温富氧和强热冲击服役环境，并未有效保证涂层的微结构及力学性能稳定性。本项目拟基于Al2O3基共晶陶瓷块体快速定向凝固生长特性，利用等离子体喷涂技术制备新型Al2O3–GdAlO3（GAP）共晶陶瓷涂层，获得交错分布网状结构Al2O3/GAP共晶组织，改善涂层高温微结构稳定性，引入共晶相尺寸多尺度分布设计思想进一步提高涂层强韧性，实现涂层强韧与微结构稳定一体化。研究Al2O3–GAP涂层共晶相之间相互交错、耦合生长形成机制，探明共晶相尺寸多尺度分布协同强韧机制，阐述涂层的高PV值磨损服役行为与失效机制，为开发在高PV值苛刻磨损条件下服役的高性能Al2O3基复合涂层提供理论依据和技术支持。

本研究以Al2O3/Gd2O3粉末为原料，基于深共晶凝固机制，利用大气等离子体喷涂首次原位沉积了Al2O3-GdAlO3（GAP）陶瓷涂层及其制备方法，不仅可以实现与Al2O3-YAG非晶陶瓷涂层类似的力学性能、耐磨性能及高温微结构稳定一体化，而且其喷涂粉体为原始物相组成（不需要进行高温固相反应），球形度佳、流动性好、沉积过程环节大大精简，同时大幅度提高涂层制备质量的一致性和可靠性控制。以亚微米Al2O3/Gd2O3粉末为原料，采用喷雾造粒技术制备并经900℃@2h煅烧处理（未发生固相反应），获得可喷涂Al2O3/Gd2O3粉体，球形度好，流动性佳，单颗粒中Al2O3和Gd2O3原料混合均匀。采用等离子体喷涂原位沉积Al2O3-GAP涂层，涂层中非晶相为主体相（非晶含量>90%），同时在非晶基体中均匀分布少量的α-Al2O3及GAP晶粒。Al2O3-GAP非晶涂层的晶化动力学研究显示晶化温度为1179.2 K，先后析出GAP、GAM和α-Al2O3相。基于Kissinger方程获得GAP和α-Al2O3的晶化激活能分别为847.6、915.8和868.7 kJ·mol-1。晶化激活能的计算显示，GAP晶相比GAM、α-Al2O3晶相更易形核，GAP和α-Al2O3的晶粒生长过程比形核过程更难，GAM的生长过程比形核过程更敏感。证实涂层的高温微结构稳定性良好，适于在较高的温度下（(1179.2 K）可靠服役。采用多组纳米压痕测试检测了三种涂层的纳米压痕硬度和弹性模量，其中Al2O3-GAP涂层的纳米压痕硬度为9.25±0.57 GPa，弹性模量为140.77±7.10 GPa，Al2O3-GAP涂层的微结构均一性优于Al2O3，Al2O3-YAG涂层。Al2O3-GAP涂层显示出优异的抗冲蚀性能。本研究中，还对比分析了Al2O3-GAP和Al2O3-YAG涂层的非晶形成机制、晶化动力学、高PV值磨损服役行为，为进一步提高Al2O3基复合涂层在高PV值苛刻磨损条件下的耐磨性能与工作寿命，为此类材料发展和应用提供理论依据和技术支撑。