原位协同强韧Cr2O3-Al2O3-YAG耐磨复合涂层研究

Oxide ceramics exhibit high strength, high hardness and anti-wear performance, as well as high temperature and good oxidation resistances. The corresponding coatings show excellent potential in the dynamic seal system in the turbine pumps of the rocket engines with the combined working conditions of high specific pressure (PV), including high temperature, strong oxidation and thermal shock. However, low toughness of oxide ceramics restricts their practical applications. It is difficult to combine conventional toughening methods with plasma spraying technology. Strengthening and toughening from grain refinement or solid solution are beneficial to the improvement of the strength and toughness of the ceramic coatings; however, these coatings have poor high-temperature stability of the microstructure and mechanical performance. The scope of this study is to deposit the Cr2O3-Al2O3-Y3Al5O12（YAG） wear-resistant composite coatings and investigate how plasma spraying process can be related to eutectic microstructure features that will enhance the strength and toughness of the coatings. Therefore, this type of composite coating may be suitable to serious work conditions, including high friction heat and strong thermal shock. Additionally, the wear-out-failure mechanism of the coatings will be elucidated under the above-mentioned severe conditions.

氧化物陶瓷具有高强度、高硬度、耐磨损、耐高温、抗氧化等特点，作为涂层材料应用于高比压（即高PV值，P是接触压强，V是摩擦速率）复合苛刻磨损工况（常伴随高温、强氧化、强热冲击）的火箭发动机涡轮泵动密封，具有较好的应用前景。然而，陶瓷涂层较低的塑韧性制约其实际条件下应用。传统增韧方法难与等离子体喷涂工艺有效结合。细晶强韧、固溶强韧在改善陶瓷涂层强韧性方面取得了进展，但较难保证涂层高温微结构和力学性能稳定性。本项目拟采用等离子体喷涂制备新型Cr2O3-Al2O3-Y3Al5O12（YAG）耐磨复合涂层。利用等离子体喷涂高热焓、大温度梯度和快速凝固的特点，设计工艺因素原位形成Al2O3/YAG共晶，并将Cr2O3-Al2O3复合强韧与Al2O3/YAG共晶组织调控相结合，以期获得有效复合强韧与高摩擦热、强热冲击条件下涂层微结构、热-机械性能稳定性之间的协调，并阐述涂层在苛刻磨损工况下的失效机制。

氧化物陶瓷具有高强度、高硬度、耐磨损、耐高温、抗氧化等特点，作为涂层材料应用于高比压（即高PV 值，P 是接触压强，V 是摩擦速率）复合苛刻磨损工况（常伴随高温、强氧化、强热冲击）的火箭发动机涡轮泵动密封，具有较好的应用前景。然而，陶瓷涂层较低的塑韧性制约其实际条件下应用。传统增韧方法难与等离子体喷涂工艺有效结合。细晶强韧、固溶强韧在改善陶瓷涂层强韧性方面取得了进展，但较难保证涂层高温微结构和力学性能稳定性。本项目采用等离子体喷涂制备Cr2O3–Al2O3–Y3Al5O12（YAG）耐磨复合涂层。利用等离子体喷涂具有高热焓、大温度梯度和快速凝固的特点，设计工艺因素原位形成Al2O3/YAG共晶相，并将Cr2O3–Al2O3复合强韧与Al2O3/YAG 共晶组织调控相结合，获得有效复合强韧与高摩擦热、强热冲击条件下涂层微结构、热-机械性能稳定性之间的协调。以纳米级Al2O3和Y2O3粉体为原料，依据共晶相图确定原料组分配比，采用喷雾干燥法制备团聚Al2O3/Y2O3复合粉末，利用等离子体喷涂制备出Al2O3–YAG共晶涂层。对涂层进行1200℃恒温热处理，时间分别为24h、96h、240h、600h、800h及1000h，共晶间距从0.32µm增加至最大0.47µm，其微结构较为稳定。与纯Al2O3涂层相比，Al2O3–YAG共晶涂层的显微硬度提高了75%（15.64GPa），热导率提高了200%（10.75W/m•K）。将Al2O3、Al2O3–Cr2O3、Al2O3–Y2O3、Al2O3–YAG涂层分别与石墨配对，进行高承载端面磨损测试，试验条件为：2000N, 500/750rpm, 1h。结果如下：①Al2O3、Al2O3–Cr2O3、Al2O3–Y2O3涂层磨损表面均出现较多网状裂纹，而Al2O3–YAG涂层表面完整，无开裂、无剥落；②Al2O3–YAG涂层/石墨摩擦系数稳定性最优；③Al2O3–YAG涂层磨损表面温度较低。按照质量比1：1将喷雾造粒团聚Al2O3/Y2O3粉末与烧结团聚Cr2O3/Al2O3粉末进行机械混合，制备了Al2O3–YAG/Al2O3–Cr2O3复合涂层。在1200℃热处理240h和600h后，涂层晶粒尺寸变化较小，喷涂态复合涂层具有较好的力学与耐磨性能。