等离子物理气相沉积AlCoCrFeNi高熵合金涂层机理与性能研究

High-entropy alloys has become potential advanced materials in application due to its excellent performance. However, common fabrication method of high-entropy alloys in present, vacuum arc melting and casting method, was suitable for the block material, which resulted in limiting production size and higher production cost. So the development and application of high-entropy alloys was restricted in engineering. While high-entropy alloys coatings not only avoided the above problems, also excellent performance was the same as that for block high-entropy alloys. This project aimed at the existing potential applications and the problems about preparation of high-entropy alloys, we proposed a new methods on plasma spray-physical vapor deposition(PS-PVD) to fabricate high-entropy alloys coatings in this project, which first heated AlCoCrFeNi high-entropy alloys powders with mixing metal powder by high temperature plasma jet, and then excellent performance AlCoCrFeNi high-entropy alloys coatings was deposited by the control of sedimentary particles with different states about gas phase, liquid phase, solid phase and multiphase under the condition of ultra low pressure. In this study, interaction influence between plasma jet and the multiphase with gas phase, liquid phase, solid phase and multiphase of flying particles was studied for high-entropy alloys powders, and then deposition behavior patterns on gas phase, liquid phase, solid phase and multiphase for flying particles of high-entropy alloys in plasma jet including morphology and composition of sediment is investigated systematically. On this basis, the effect law on deposition behavior of flying particles on microstructure and properties of high-entropy alloys coatings is mainly studied, which revealed deposition mechanism of high-entropy alloys coatings by PS-PVD. Finally we tried to put forward the control of theory and methods on the microstructure and properties for high performance high-entropy alloys coatings, which are expected to provide a guideline for fabricating high-performance high-entropy alloys coatings.

高熵合金因其优异性能而成为应用潜力巨大的材料。目前高熵合金常用制备方法—真空熔炼法只适应块体材料，且存在制备尺寸受限、生产成本高等缺点，严重制约其应用。而高熵合金涂层能避免上述弊端，同样具有优异性能。本项目针对高熵合金应用潜力及制备存在的问题，提出等离子物理气相沉积（PS-PVD）制备高熵合金涂层的新方法，即在超低压条件下，利用等离子射流加热AlCoCrFeNi高熵合金粉末形成气液固多相颗粒，通过调控多相颗粒沉积状态制备出高性能AlCoCrFeNi高熵合金涂层。本项目通过研究气液固多相高熵合金飞行颗粒与射流相互作用的规律，探究多相高熵合金飞行颗粒凝固过程及沉积行为，实现PS-PVD工艺优化；重点研究多相高熵合金飞行颗粒沉积行为对涂层组织与性能的影响规律，阐明PS-PVD沉积高熵合金涂层机理，提出高性能高熵合金涂层的结构与性能调控理论和方法，为PS-PVD制备高熵合金提供理论基础。

高熵合金具有许多优异的性能并有潜力成为新型的涂层材料。等离子喷涂-物理气相沉积（Plasma spray-physical vapor deposition, PS-PVD）是一种新型热喷涂技术，已成功用于热障涂层、透氧过滤涂层、核反应堆壁涂层等功能涂层的制备，并有望进一步拓展其应用领域，能制备出更高性能的涂层。. 本项目采用PS-PVD技术在不同参数条件下制备了等摩尔比AlCoCrFeNi高熵合金涂层，采用抛光的316L不锈钢基板收集了不同参数沉积的高熵合金颗粒，研究了高熵合金粉末沉积行为与喷涂工艺参数之间关系，优化喷涂工艺参数，探究喷涂电流和喷涂距离等PS-PVD工艺参数对涂层组织结构和性能的影响，揭示高熵合金涂层沉积机理。. 研究结果表明：AlCoCrFeNi高熵合金粉末的物相为BCC相和B2相，其平均颗粒直径为22.567 μm，平均晶粒尺寸为36.52 nm。采用PS-PVD制备的高熵合金涂层由BCC相、B2相和FCC相组成；AlCoCrFeNi高熵合金粉末颗粒在喷涂沉积的过程中经历了加热熔化、飞行雾化以及碰撞沉积三个阶段，其沉积到316L不锈钢基板表面后呈现的形貌主要为圆盘状和向日葵状，并且其边缘外围出现了较多的“触角”状形貌，表明其具有明显的液相沉积特点；喷涂距离为475 mm时，随着喷涂电流的增大，高熵合金涂层的结合强度先提高后降低，表面显微硬度先减小后增大，磨损率呈现先增大后减小的趋势。当喷涂电流为1800 A时，涂层的结合强度随着喷涂距离的增大而提高，表面硬度则先减小后增大，磨损率则逐渐下降。当喷涂电流为1800 A、喷涂距离为550 mm时，涂层的结合强度与表面硬度最高，分别为71.5 ± 2.1 MPa与526 ± 17 HV，并表现出良好的耐磨性能，其体积磨损率为(1.72 ± 0.14) × 10-4 mm3 / (N·m)。随着喷涂电流与喷涂距离的提高，高熵合金涂层的氧化总增重及其平均氧化速率均呈现出先下降后上升的趋势。综合来看，当喷涂电流为1800 A、喷涂距离为475 mm时，高熵合金涂层具有良好的综合性能。在该工艺参数下，涂层的平均沉积速率为14.25 ~ 15.58 μm / 次，涂层厚度为179 ± 8 μm，并具有较高的结合强度（49.5 ± 0.7 MPa）。该工艺制备的涂层表现出了良好的抗氧化