摘 要

随着飞行器隐身性能要求的提高，基于磁性金属吸波剂的吸波涂层因具备轻薄、宽频且强吸收等特性而受到了较多的关注。但飞行器快速航行时，头锥、尾喷管与发动机部位的机体温度会陡然上升，这对磁性金属吸波剂的抗高温氧化性能提出严峻挑战。现阶段的研究主要聚焦于升温过程中原子热运动加剧对吸波剂磁性能的影响，缺乏高温氧化与吸波剂形貌、成分、结构与电磁性能间的系统研究。本文以具备高饱和磁化强度与高居里温度的纳米晶FeCo粒子为研究对象，研究了热处理温度对粒子形貌、结构、成分和电磁性能的影响规律及机理。本文获得以下结论：

1. 空气热处理后，纳米晶FeCo粒子的表面形貌、粒子结构和成分都发生了显著的变化。经过空气热处理后，粒子表面会逐渐生成凸起状的Fe₂O₃和CoO。相同空气热处理条件下，不同形貌的纳米晶FeCo粒子氧化程度不同。球状粒子生成的氧化物细小且紧密覆盖在粒子表面，一定程度上阻碍了氧化反应的进行；片状粒子因为其表面积较大，氧化反应活性位点多，生成的氧化物尺寸较大且不致密，无法对氧气进行有效的隔绝，导致其抗高温氧化性能弱于球状粒子。此外，不同温度热处理后，纳米晶FeCo粒子的晶粒结构不同。300℃下，纳米晶FeCo粒子在制备过程中引入的缺陷和内应变得以释放，晶粒结构变得规整；500℃下，粒子的氧化程度大幅度增强，随着质点热运动的加剧，粒子表面的氧化物无法抑制氧分子的扩散，氧化对粒子组成与结构的改变占主导地位，反应得到的氧化产物与基质金属的结合能力不佳，导致内应变回升。
2. 空气热处理对纳米晶FeCo粒子的静磁性能、电磁参数和吸波性能都会产生显著影响。随着空气热处理温度的上升，饱和磁化强度持续下降，矫顽力呈先下降后上升趋势。经过空气热处理后，复磁导率和复介电常数呈现下降趋势，并且不同温度下两者不同的下降趋势引起吸波性能变化趋势的波动。300℃热处理后，复介电常数下降明显、介电损耗角正切值下降幅度较大，介电损耗能力减退；复磁导率总体下降幅度不大，磁损耗角正切值仅在频段14-18 GHz局部明显下降，导致吸波剂的总损耗能力呈下降趋势，所以吸收性能有一定程度的下降。当温度提升至500℃时，纳米晶FeCo粒子的复介电常数和复磁导率在0.1-18 GHz频段内急剧衰减，介电损耗能力与磁损耗能力同步减退，厚度为1 mm且吸波剂体积填充分数28%的吸波涂层模拟反射率峰值仅为-2.01 dB，相较于室温条件下降低了73.3%，吸波性能大幅下降。

关键词：耐温吸波剂；纳米晶FeCo粒子；电磁性能 ；吸波性能

Abstract

With the improvement of the stealth performance requirements of aircraft,the wave-absorbing coatings based on magnetic metal wave-absorbing agents have attracted more attention because of their thin, wide-band and strong absorption characteristics. However, when the aircraft is sailing fast, the temperature of the nose cone, the tail nozzle and the body of the engine will suddenly rise, which poses a serious challenge to the high temperature oxidation resistance of the magnetic metal wave absorber. The research at this stage mainly focuses on the influence of the increased atomic thermal motion on the magnetic properties of the absorber during the heating process. There is a lack of systematic research between high temperature oxidation and the shape, composition, structure and electromagnetic properties of the absorber. In this paper, the nanocrystalline FeCo particles with high saturation magnetization and high Curie temperature are taken as the research object, and the influence law and mechanism of heat treatment temperature on particle morphology, structure, composition and electromagnetic properties are studied. This article obtained the following conclusions:

(1) After air heat treatment, the surface morphology, particle structure and composition of nanocrystalline FeCo particles have changed significantly. After air heat treatment, convex Fe2O3 and CoO are gradually formed on the surface of the particles. Under the same air heat treatment conditions, the nanocrystalline FeCo particles with different morphologies have different degrees of oxidation. The oxide produced by the spherical particles is small and closely covers the surface of the particles, which hinders the progress of the oxidation reaction to a certain extent; because of the large surface area of the flake particles, there are many oxidation reaction active sites, and the generated oxide size is large and not dense. Can not effectively isolate oxygen, resulting in weaker high-temperature oxidation resistance than spherical particles. In addition, after heat treatment at different temperatures, the grain structure of the nanocrystalline FeCo particles is different. At 300 ℃, the defects and internal strain introduced by the nanocrystalline FeCo particles during the preparation process are released, and the grain structure becomes regular; at 500℃, the degree of oxidation of the particles is greatly enhanced. As the thermal motion of the particles intensifies, the surface of the particles. The oxides cannot inhibit the diffusion of oxygen molecules. Oxidation dominates the composition and structure of the particles. The oxidation products obtained by the reaction have poor binding ability with the matrix metal, resulting in a rise in internal strain.

(2) Air heat treatment will have a significant effect on the magnetostatic properties, electromagnetic parameters and wave absorption properties of nanocrystalline FeCo particles. As the temperature of air heat treatment increases, the saturation magnetization continues to decrease, and the coercive force decreases first and then increases. After air heat treatment, the complex magnetic permeability and complex dielectric constant showed a downward trend, and the different downward trends of the two at different temperatures caused the fluctuation of the wave absorption performance. After heat treatment at 300℃, the complex dielectric constant decreased significantly, the dielectric loss tangent value decreased significantly, and the dielectric loss capacity decreased; the overall decrease in complex permeability was not large, and the magnetic loss tangent value was only in the frequency band 14-18. When the temperature is raised to 500℃, the complex dielectric constant and complex permeability of nanocrystalline FeCo particles attenuate sharply in the 0.1-18 GHz frequency band, and the dielectric loss capability and magnetic loss capability decrease synchronously. The thickness is 1 mm and the wave absorption The peak reflectance of the wave-absorbing coating with a volume fraction of 28% is -2.01 dB, which is 73.3% lower than that at room temperature, and the wave-absorbing performance is greatly reduced.

Key Words： Temperature-resistant absorbing material; nanocrystalline FeCo powder; micro-morphology; electromagnetic properties; thermal stability

目 录

摘 要 I

Abstract II

第1章 绪论 1