声场作用下等离子喷涂涂层的组织演变及性能控制

Plasma spray was widely used for depositing coatings for its advantages, e.g. almost all kinds of materials could be sprayed, little heat affected on workpieces, high deposition efficiency, constituent and thickness could be controlled accurately, not be affected by matrix and shape of substrates, and so on. The performances of coatings were affected by the wetting and solidification process of molten droplets on substrate, during the spraying process. The effects of sound fields, such as sound pressure, acoustic streaming, mechanical effect and thermal effect, could promote wetting property of materials and affect solidification process. In this project, sound fields will be loading on stainless steel or Ni-based superalloy substrates during the plasma spray process of Ni-Al or Al2O3 coatings. The influence and mechanism of the sound fields on the microstructure, phase composition, crystallite size and distribution, roughness and bonding mode of interface of the particle coatings will be studied. And then, the evolution and mechanism of the sound fields on the microstructure of surface and cross section, phase composition and distribution, porosity and distribution, bonding stress, oxidation and corrosion resistance of the coatings will be studied. After that, the relations between evolution of microstructure and coating performance will be studied, and the prototypes of plasma spraying coatings controlled by sound fields will be proposed.

等离子喷涂技术凭借其可喷涂材料范围广、对工件热影响小、沉积效率高、成分和厚度精确可控、不受基体面积和形状因素影响等特点被广泛应用于涂层制备。喷涂过程中，熔滴在基体表面的润湿和凝固过程将影响涂层的组织及性能，而声场通过声压、声流效应、机械效应及热效应等作用能够促进材料润湿并影响凝固过程。本课题将声场作用于涂层等离子喷涂过程，在不同条件声场作用的不锈钢或镍基高温合金基体上沉积Ni-Al或Al2O3涂层，考察声场对等离子喷涂单层颗粒层的铺展形貌、相组成、晶粒尺寸及分布、表面粗糙度、界面结合方式的影响规律和作用机制；在此基础上，考察不同声场条件和不同等离子喷涂工艺下，涂层的表、截面组织形貌、相组成及其分布、孔隙率及其分布、与基体间结合强度的演变规律，以及涂层抗氧化、耐腐蚀等性能的演变规律及声场作用机制；在综合分析涂层组织演变与性能之间关系的基础上，提出利用声场控制涂层等离子喷涂过程的技术原型。

等离子喷涂技术凭借其可喷涂材料范围广、对工件热影响小、沉积效率高、成分和厚度精确可控、不受基体面积和形状因素影响等特点被广泛应用于材料的表面防护。涂层沉积过程中，熔滴在基体和已凝固熔滴表面的润湿、在已凝固熔滴间隙间的填充及凝固共同构成影响等离子喷涂涂层组织及性能的基本物理过程。声场通过其声压、声流效应、机械效应及热效应等作用能够促进材料润湿和流动并影响凝固过程。本项目通过研究声场作用下单层颗粒层和涂层的等离子喷涂沉积过程，探索了声场对等离子喷涂涂层组织及性能的影响规律和作用机制。研究结果表明，将声场作用于单层颗粒层的等离子喷涂过程，单层颗粒层在基体表面的铺展被有效促进。同时，声场的作用效果随其频率和基体对熔滴润湿性能的增强而显著增强。涂层沉积过程中加载声场，其组织变得致密，与基体间的结合强度显著提升；同时，涂层内部的残余应力降低、耐磨性能提高。声场的作用效果与其频率和喷涂工艺有关，增大频率能够有效提升涂层的综合性能；通过调控喷涂工艺而提升熔滴温度亦能有效提升声场的作用效果。通过合理调控声场频率和喷涂工艺，涂层的孔隙率可降低70%以上，同时涂层与基体的结合强度可提高75%以上。声场通过影响涂层等离子喷涂沉积过程的基本物理过程实现对涂层组织及性能的有效调控。因此，该手段适用于多种材料的等离子喷涂的组织及性能调控；同时，其他与等离子喷涂基本物理过程相近的热喷涂亦可通过该手段实现对涂层组织及性能的调控。