电弧离子镀沉积Cr2AlC涂层的形成机理与抗高温腐蚀性能研究

As one of the MAX phases, Cr2AlC exhibits unique merits of both metals and ceramics, especially excellent high temperature corrosion resistance, has a great potential for applications as high temperature structural material and high temperature protective coating. In this project, a dense and single-phase crystalline Cr2AlC coating will be prepared from a single target of phase-pure Cr2AlC bulk and not phase-pure Cr2AlC bulk with addition of rare earth elements by cathodic arc ion plating at room temperature and subsequent annealing treatment. The formation mechanism and microstructure of crystalline Cr2AlC coating, and the effect of the deposition parameters and subsequent heat treatment conditions will be investigated systemically. The optimization of the processing conditions can be obtained. The high temperature oxidation and hot corrosion behavior of Cr2AlC coating will be investigated in detail to characterize the oxidation kinetics, the phase compositions, microstructure and adhesion of the oxide scales, and the phase transformation of the Cr2AlC coating. The mechanism of oxide scale growth and the degradation of the oxidation resistance of coating will be further understood. Especially, the process of dissolution of initial Al2O3 scale and formation of Cr2O3-enriched layer during hot corrosion will be explored. This research will provide the technical support for developing a high-efficiency and large-scale deposition method of MAX phases coatings and a novel high temperature protective coating.

三元层状化合物Cr2AlC综合了金属和陶瓷的性能特点，具有优良的抗氧化和热腐蚀性能，作为高温防护涂层极具应用潜力。提出采用纯Cr2AlC化合物单靶及添加稀土的非单相Cr2AlC热压块体作为靶材，室温下利用电弧离子镀在高温合金上沉积非晶涂层，继而通过后续热处理获得晶态Cr2AlC涂层的方法。研究沉积参数和后续热处理条件对涂层相和微观结构的影响，明确Cr2AlC涂层扩散反应形成机制，获得制备单相Cr2AlC涂层的优化工艺。研究Cr2AlC涂层高温氧化和热腐蚀性能，明确涂层初期选择性氧化行为和长时间氧化动力学规律，探讨氧化膜生长机制与界面结合机理，考察热腐蚀过程中Al2O3层溶解和完整富Cr2O3层形成的微观过程。本研究可为发展一种高效沉积MAX相涂层技术以及具有优异抗高温腐蚀性能的Cr2AlC高温防护涂层新体系奠定基础。

利用原位热压液/固相反应法制备了高纯、高密度的Cr2AlC块体靶材，采用二步法（电弧离子镀室温沉积非晶涂层+后续退火处理）成功制备了Cr2AlC涂层，确定了单靶电弧离子镀沉积Cr2AlC涂层的优化工艺。Cr-Al-C涂层中存在较多的C缺位，在620oC退火20h后转变为以Cr2AlC为主相同时含有AlCr2和少量Cr7C3的晶态涂层，涂层中原子尺度的界面结合有利于元素的快速扩散，使得Cr2AlC的形成温度远低于块体材料；Cr2AlC涂层在900-1100oC空气中的氧化动力学遵循抛物线规律，可发生选择性氧化生成连续、致密的保护性Al2O3氧化层，因此具有优异的抗高温氧化性能。Al2O3的生成与Cr2AlC的晶格结构和成键特性有关，涂层中Al的持续消耗会导致Cr-C相的生成。表面涂覆Na2SO4盐膜的Cr2AlC涂层在900oC和1000oC空气中具有良好的抗热腐蚀性能，原因是Cr2O3的碱性熔融反应降低了熔盐的碱度，从而有利于Al2O3膜的稳定存在；合成了(Cr2/3Ti1/3)3AlC2（312相）和(Cr5/8Ti3/8)4AlC3（413相）两种新型Ti-Cr-Al-C系的四元MAX陶瓷新相，分析了合成过程中的反应机制，提出了反应路径，确定了它们的晶体结构；创新性地改变靶材的结构形式，即通过低温（1000oC以下）热压烧结Cr粉、Al粉和石墨粉制备成非Cr2AlC化合物靶（仅形成Cr、Al和C之间的单相和双相复合化合物），然后采取“二步法”制备了Cr2AlC涂层，该方法发展了MAX相陶瓷涂层的低温高效制备技术，极大地拓展了MAX相涂层的制备方法及应用范围。尝试采用磁控溅射技术，利用低温高效制备技术制备了Cr2AlC晶态涂层，系统考察了靶材的成分、结构以及物理性能与涂层性能之间的关联性。研究结果对深入认识三元层状化合物Cr2AlC的形成机制，拓展Cr2AlC涂层的制备技术并促进其应用具有重要的指导意义。