难熔合金用超高温玻璃陶瓷复合涂层的硼化物改性研究

Glass-ceramic coatings possess high resistance to oxygen permeability, well interfacial bonds and low thermal expansion coefficient mismatch to the alloy substrates, and high resistance to thermal fatigue except poor resistance to thermal erosion at ultra-high temperatures. Aiming at improving their thermal erosion resistance, glass-ceramic coatings are modified by adding particles of ultra-high temperature diboride ceramics, e.g., HfB2, ZrB2 or TiB2. By this incorporation, a multi-oxide scales composed of a refractory crystalline oxide (skeleton) and a borosilicate glass component could form in-situ during the high-temperature oxidation process, which are able to exhibit excellent resistance to thermal erosion and provide protection for the substrates at any temperature stage during service. In this project, the effect of the interactions between glass-ceramic matrix and the diboride inclusions on the oxidation behavior of borides, the regulation of interfacial reactions between refractory alloys and glass-ceramic coatings, in addition to the high temperature oxidation process of the coated refractory alloy systems are systematically investigated. Based on these studies, the methods of preparing the glass-ceramic composite coatings in-situ and controlling the coating/alloy interfacial structure are acquired, and the protection mechanisms of glass-ceramic composite coatings for refractory alloys against high temperature oxidation are illustrated as well, which will establish the theoretical foundation for the application of glass-ceramic composite coatings on refractory alloy components of the next generation of orbit and attitude control rocket engines and hypersonic vehicles.

玻璃陶瓷涂层阻氧能力强，与合金基体界面结合和热膨胀系数匹配良好，抗热疲劳性能优异，但在超高温条件下抗热冲刷性能差。本项目拟开展难熔合金基体上超高温玻璃陶瓷复合涂层的硼化物改性研究，通过添加超高温硼化物陶瓷（HfB2、ZrB2或TiB2）颗粒对硅酸盐玻璃陶瓷涂层进行改性，在高温氧化环境中原位生成以MO2（M为Hf、Zr或Ti）为“骨架”、硼硅酸盐玻璃为填充剂的复合氧化膜，有望在全服役温度范围内为难熔合金提供防护，同时显著提高玻璃陶瓷涂层抗高温高速气流冲刷的能力。本项目将阐明玻璃陶瓷基质对硼化物高温氧化的影响机理，确定玻璃陶瓷基质与不同种类难熔合金的高温界面反应过程，掌握界面结构的调控方法，并揭示原位合成的复合涂层对难熔合金的高温防护机理，为新一代高比冲姿、轨控火箭发动机和高超声速飞行器难熔合金用新型超高温防护涂层的设计与实现提供理论依据。

本项目针对高温条件下玻璃陶瓷涂层抗热冲刷性能不足的问题，开展了合金基体上玻璃陶瓷复合涂层的硼化物改性研究。明确了SiO2-Al2O3-ZnO-ZrO2-TiO2玻璃基质中Zr元素的分相形核机制，该玻璃基质析出的晶相强烈取决于烧结温度，且其晶化行为对其热膨胀性质影响明显：t-ZrO2的析出使玻璃陶瓷的热膨胀系数增大，而ZrSiO4的生成使玻璃陶瓷的热膨胀系数降低。添加YSZ颗粒能显著影响玻璃的晶化；高温下YSZ与玻璃发生界面反应生成锆石，且其具有内生长和外生长两种生长机制，烧结初期锆石的快速生长主要由外生长机制决定；添加YSZ能提升玻璃陶瓷的热膨胀系数，而锆石的生成会降低热膨胀系数。在900-1100 °C温度范围内，氧化铝与玻璃陶瓷的反应产物为锌铝尖晶石和钠长石；氧化铝的添加能抑制玻璃陶瓷自身的析晶行为；向YSZ/玻璃陶瓷复合材料中添加氧化铝能显著降低YSZ与玻璃陶瓷的界面反应速率。90wt.%TiB2-玻璃陶瓷涂层材料(G90T)在1200℃的氧化动力学符合抛物线-直线规律，但其氧化膜随氧化进行发生开裂，使得G90T作为高温防护涂层材料使用氧化速率过快。90wt.%ZrB2-玻璃陶瓷涂层材料(G90Z)在1000℃的氧化符合抛物线规律，而在1200℃和1400℃，70wt.% (G70Z)和90 wt.%ZrB2添加的玻璃陶瓷涂层材料的氧化规律均为抛物线-直线规律；1200℃的温度条件下，G70Z的氧化防护性能优于G90Z；而在1400℃的温度条件下G70Z的氧化防护性能优于G90Z；建立了不同成分ZrB2-玻璃陶瓷复合材料各温度下氧化模型。通过研究玻璃陶瓷与K438G、0.5%Hf改性Ni3Al粘结层、Ni+CrAlYSiN金属陶瓷、TC4钛合金的高温界面反应过程，确定了典型的界面反应方程式，实现界面层的生长与结构控制，首次阐述了双层热生长氧化物（TGO）α-Al2O3/ZnAl2O4的形成机制，掌握了合金基体上玻璃陶瓷复合涂层原位合成的科学方法，并揭示了玻璃陶瓷涂层通过改变合金基体高温氧化行为从而提高抗氧化性能的新机理。本项目的研究结果有望满足新一代高比冲姿、轨控火箭发动机和高超声速飞行器用难熔合金的超高温防护需求。