复杂环境纳米吸波涂层瞬态相演化机理研究

The preparation of hexagonal ferrite coating through thermal spraying can solve absorbing coating adhesion and low abrasion scratch problem. However, the hexagonal phase crystallized slowly, there is no enough time in process of condensation crystallization in thermal spray high quenching temperature, it is difficult to form hexagonal phase, the phase transformation process is extremely complex, involving thermodynamics and the dynamics of multiple physical and chemical processes, there is no related research about the mechanism at home and abroad, it is helpful to clarify the mechanism for preparation of high performance absorbing coating, and benefitting of theoretical basis for material control.. This project intends to use polyethylene as protection phase to avoid excessive melting of ferrite, nano-ferrite / polyethylene composite coatings is prepared by plasma spraying, a series of mechanism is studied on thermodynamics and kinetics of hexagonal phase transformation to reveal evolution mechanism of ferrite phase suddenly cooling at high temperature in complex environment, which is useful to solve hexagonal ferrite coating preparation; this research also clarify the interface effect, including heterogeneous formation of polyethylene and ferrite phase interfacial compatibility, internal defects and stress concentration to reveal the interface scientific problems of composite coating; the influence of electromagnetic properties and microwave absorbing properties for micro/ nano crystalline interface effect on the composite coatings and small size effect were studied, the establishment of nano composite coating absorbing mechanism model will provide a theoretical basis for the development of high performance absorbing coating.

热喷涂制备磁铅石铁氧体涂层可解决传统涂覆型吸波涂层附着力低、擦伤划伤问题，但由于磁铅石相结晶缓慢，在热喷涂高温骤冷过程中没有足够时间冷凝结晶，难形成磁铅石相，相转变过程极为复杂，涉及热力学、动力学等多个物理化学过程，相关机理国内外尚没有研究，理清该机理有助于制备高性能吸波涂层，为材料控形和控性提供理论依据。. 本项目拟采用聚乙烯作为保护相，避免铁氧体过度熔融，通过等离子喷涂制备纳米铁氧体/聚乙烯复合涂层，重点开展磁铅石铁氧体涉及相变的一系列热力学、动力学研究，揭示铁氧体在高温骤冷复杂环境中的相演化机理，解决磁铅石铁氧体涂层制备问题；阐明聚乙烯与铁氧体构成的异质相的界面效应、界面相容性、内部缺陷和应力集中，揭示复合涂层的界面科学问题；研究微晶/纳米晶在复合涂层中的界面效应和小尺寸效应对电磁性能和吸波性能的影响规律，建立纳米复合涂层吸波机理模型，为发展高性能吸波涂层提供理论基础。

热喷涂制备吸波涂层是近年出现的新工艺，涂层具有结合强度高，适应性强等特点。采用等离子喷涂制备磁铅石铁氧体时，铁氧体受热熔融首先快速形成尖晶石相，而形成磁铅石相是一个高温缓慢过程。由于等离子喷涂是快速冷却过程，涂层中难以形成磁铅石相，需要对涂层进行高温热处理得到磁铅石相。本项目研究目的是采用等离子喷涂直接制备含有磁铅石相结构的铁氧体涂层。技术路线是在磁铅石铁氧体中引入聚乙烯，采用聚乙烯保护铁氧体，使其不能全部受热熔融，在涂层中保留磁铅石相结构。采用喷雾干燥造粒工艺制备了铁氧体与聚乙烯质量比为1.6:1、9:1和15:1的复合粉体材料。采用等离子喷涂制备了三种配比的铁氧体/聚乙烯复合涂层。研究了复合涂层的微观组织形貌和相结构。质量比为1.6:1的铁氧体/聚乙烯复合涂层，聚乙烯为连续相，铁氧体为分散相，涂层中的块状分散颗粒是铁氧体，磁铅石相含量为76%，尖晶石相含量为24%。质量比为9:1的铁氧体/聚乙烯复合涂层，涂层致密区为铁氧体，缺陷和孔隙部位为聚乙烯，磁铅石相含量为48%，尖晶石相含量为52%。质量比为15:1的铁氧体/聚乙烯复合涂层，熔融较好的致密区域主要是铁氧体，孔隙和缺陷部位主要是聚乙烯，磁铅石相含量为45%，尖晶石相含量为55%。通过拉曼光谱测定铁氧体四面体和八面体中Fe-O振动峰，也表明涂层中同时存在尖晶石结构和磁铅石结构。研究了铁氧体/聚乙烯复合材料的电磁性能和吸波性能，复合材料以磁损耗为主吸收电磁波，自然共振是磁损耗主要机制。研究结果表明：随聚乙烯含量增加，复合涂层中的磁铅石相含量提高，复合材料的饱和磁化强度下降，矫顽力增加。复合材料受热熔融，聚乙烯黏着在涂层表面，不利于连续喷涂成型，并增加喷涂成本。综合考虑涂层成型性和喷涂成本，质量比为9:1的铁氧体/聚乙烯复合涂层性能相对较好。本项目意义是通过等离子喷涂直接制备含有磁铅石相结构的铁氧体涂层，有望省去高温热处理工艺，降低涂层制备成本。