目的 针对航空发动机可磨耗封严涂层对结构完整性与高温摩擦学稳定性的严苛要求,旨在解决镍包石墨涂层制备中石墨高温烧损与致密化之间的矛盾。通过优化等离子喷涂工艺参数,实现对涂层微观组织与服役性能的协同调控。方法 采用化学镀法制备核壳结构镍包石墨粉末。基于L9(34)正交试验,系统考察喷涂功率、喷枪移速、送粉量及喷涂距离对涂层沉积效率、孔隙率、硬度及石墨烧损率的影响。结合极差分析与微观表征,揭示工艺参数的作用机制,并验证最优涂层的热震及宽温域（RT~500 ℃）摩擦学性能。结果 极差分析表明,不同工艺参数对涂层性能的影响具有明显差异。其中,送粉量对沉积效率和硬度的影响最为显著,喷枪移动速度主要控制孔隙率,而喷涂功率对石墨烧损率起主导作用。基于中等热输入策略,确定的最优工艺为功率24.4 kW、移速200 mm/s、距离120 mm、送粉量3.3 g/s。在该条件下所制备涂层孔隙率为12.70%,硬度为28.75HR15Y,石墨烧损率为18.89%。该涂层经75次热震未失效,在RT~500 ℃下的摩擦系数稳定在0.26~0.35,比磨损率保持在4.95~10.79×10-6 mm3/(N·m)的低量级,表现出较好的热震稳定性和宽温域摩擦学稳定性。结论 优化的等离子喷涂工艺通过中等热输入有效平衡了涂层致密化与石墨保留的冲突。高温下生成的NiO致密膜与残留石墨构建了“氧化物-石墨”协同润滑体系,赋予了涂层良好的结构可靠性与宽温域耐磨性,显示出在发动机中低温封严部位应用的潜力。
Abstract
Abradable seal coatings for aero-engines are required to maintain structural integrity and stable tribological performance over a wide temperature range. However, during the atmospheric plasma spraying (APS) process, a critical trade-off exists between coating densification and severe high-temperature burnout of the graphite functional phase. In this study, APS parameters are systematically optimized to achieve synergistic regulation of coating microstructure and service performance. Core-shell structured nickel-coated graphite (Ni@C) composite powders are successfully synthesized by in-situ electroless plating using nickel sulfate and hydrazine hydrate at 80 ℃. The continuous nickel shell significantly improves the powder flowability to 94.5 s/50 g and the apparent density to 0.91 g/cm³, providing favorable feedstock characteristics for thermal spraying. To establish the intrinsic relationship between spraying parameters and coating properties, an L9(34) orthogonal experimental design is employed. The effects of spray distance (80, 100, and 120 mm), gun traverse speed (200, 250, and 300 mm/s), spraying power (17.8, 24.4, and 28.0 kW), and powder feed rate (2.0, 3.3, and 4.6 g/s) on deposition efficiency, porosity, Rockwell hardness, and graphite burnout rate are systematically investigated. Range analysis and microstructural characterization are further conducted to clarify the governing mechanisms of these parameters. In addition, the high-temperature reliability of the optimized coating is evaluated through water-quench thermal shock testing, prolonged isothermal aging at 400 ℃, and friction and wear tests over a temperature range from room temperature (RT) to 500 ℃.
Range analysis shows that different process parameters predominantly control different coating properties. Powder feed rate exerts the strongest influence on deposition efficiency and Rockwell hardness, whereas gun traverse speed mainly governs coating porosity by regulating the splat overlap behavior. Spraying power is identified as the dominant factor affecting graphite burnout. Microstructural observations indicate that excessive heat input promotes particle melting, splat spreading, and matrix densification, but simultaneously intensifies graphite oxidation, leading to large burnout cavities, local collapse defects, and reduced abradability. To address this trade-off, an optimized medium-heat-input strategy is proposed. A well-structured Ni@C composite coating is obtained under the optimized parameter combination of 24.4 kW spraying power, 200 mm/s gun traverse speed, 120 mm spray distance, and 3.3 g/s powder feed rate. Under these conditions, the coating achieves a balanced microstructure, exhibiting a porosity of 12.70%, a Rockwell hardness of 28.75 HR15Y, and a significantly reduced graphite burnout rate of 18.89%.
The coating prepared under the optimized parameters exhibits excellent service performance. During thermal shock testing, it withstands 75 cycles between 400 °C and room-temperature water quenching without visible macro-cracking or delamination, demonstrating superior thermal shock resistance. Isothermal aging at 400 ℃ for 100 h reveals a three-stage hardness evolution behavior involving stress relaxation, oxidation strengthening, and dynamic equilibrium, with the hardness eventually stabilizing within a favorable abradable range of 21.5±1.0 HR15Y. Tribological tests demonstrate excellent wear resistance over a wide temperature range. From RT to 500 ℃, the average friction coefficient remains stable between 0.26 and 0.35, while the specific wear rate is maintained at a low level of 4.95 to 10.79×10-6 mm3/(N·m). The optimized medium heat input effectively balances matrix densification and graphite retention. The high-temperature tribological stability is mainly attributed to the synergistic lubrication system formed by the protective NiO oxide film and the continuous release of retained graphite. This structure effectively suppresses crack propagation and severe adhesive wear, indicating promising application potential in medium- and low-temperature gas-path sealing sections of advanced aero-engines.
关键词
镍包石墨 /
可磨耗封严涂层 /
等离子喷涂 /
正交试验 /
摩擦学性能 /
微观组织 /
抗热震性能
Key words
Ni-coated graphite /
abradable seal coating /
plasma spraying /
orthogonal experiment /
tribological performance /
microstructure /
thermal shock resistance
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基金
国家自然科学基金（52571111）; 国家重点研发计划（2022YFC3902001）; 河南省自然科学基金杰出青年科学基金项目（252300421050）
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