Droplet-Plasma Interactions in Suspension Plasma Spray (SPS) and in Solution Precursor Plasmas Spray (SPPS)

热喷涂工艺是一种使部件免受恶劣环境影响的使能技术，可显著提高部件的性能。由于材料科学的快速进步、添加剂制造和3D打印的发展以及气候变化带来的日益严重的环境挑战等因素的综合作用。 在许多工业部门，与磨损、侵蚀、腐蚀和热效率相关的问题极大地增加了制造、维护和运营成本，防护涂层和相关表面技术是战略发展路线图中不可或缺的一部分。例如，2013年，美国全国腐蚀工程师协会估计，仅在美国，腐蚀、磨损和其他材料劣化的成本就超过276亿美元。通过沉积更好的防护涂层，可以大幅降低这种巨大的成本。 悬浮液和溶液前驱体等离子喷涂(SPS和SPPS)是两种新兴的非常有前途的涂层技术，已经产生了非常高质量的涂层，这是拟议研究的主题。 在溶液等离子喷涂(SPS)过程中，将微粉悬浮在液体中，并将其喷射到高温等离子喷嘴中。通过将粉末悬浮在液体中，避免了将细粉送入热等离子体的正常进料问题。 在溶液前驱体等离子喷涂(SPPS)中，前驱体是通过将盐溶解在液体中并将其喷射到等离子喷嘴中而形成的。当液体蒸发时，液滴变得过饱和，导致细小颗粒的成核，这些颗粒将被熔化并沉积在衬底上。 与传统的(粉末)热喷涂相比，SPS和SPPS涂层显示出了相当大的优势。这些工艺沉积的涂层的颗粒尺寸从几十纳米到几微米不等。研究表明，精细结构涂层具有较好的力学性能、热性能和化学性能。然而，与传统的粉末喷涂工艺相比，SPPS和SPPS要复杂得多，还需要更多的研究来更好地了解这两种工艺的细节。特别是，SPS和SPPS液滴如何与等离子体相互作用是理解这些过程的基础。 这项为期5年的研究计划提出了两个精确的数学/计算模型，用于研究单个SPS和SPPS液滴与热等离子体在受控条件下的相互作用。这些模型将通过在新开发的射频感应耦合等离子体炬(RF-ICP)中引入单个液滴来验证。利用粒子图像测速仪(PIV)，将监测液滴的轨迹，生成的粒子将被收集在离火炬出口不同距离的衬底上进行分析和表征。

Thermal spray coating process is an enabling technology which is employed to protect components from harsh environments and significantly enhances the performance of these components. Due to a combination of factors, such as rapid progress in materials science, development of additive manufacturing and 3D printing, as well as the increasing environmental challenges being brought on by climate change. Protective coatings and the related surface technologies are an indispensable part of strategic development roadmaps in many industrial sectors in which problems linked to wear, erosion, corrosion and thermal efficiency significantly increase manufacturing, maintenance and operating costs. As an example, in 2013, the US National Association of Corrosion Engineers estimated that the cost of corrosion, wear and other materials deterioration in the US alone exceeded $US 276 B. Such massive costs can be substantially reduced through deposition of better protective coatings. Suspension and solution precursor plasma spraying (SPS and SPPS), which is the subject of the proposed study, are two new emerging and very promising coating technologies that have produced very high-quality coatings. In the solution plasma spray (SPS) process, fine powders are suspended in a liquid and are sprayed into a high temperature plasma jet. By suspending the powder in a liquid, normal feeding problems associated with feeding fine powders into a thermal plasma are avoided. In the solution precursor plasma spray (SPPS), a precursor is formulated by dissolving salts in a liquid and spraying them into a plasma jet. As the liquid evaporates, the droplets become supersaturated, resulting in the nucleation of fine particles that will be melted and deposited onto a substrate. SPS and SPPS coatings have shown considerable advantages over the traditional (powder) thermal spray coatings. These processes deposit coatings with a particle size ranging from a few tens of nanometers to just a few micrometers. It has been shown that finely structured coatings have better mechanical, thermal and chemical properties. However, compared to the traditional powder spray coating process, SPPS and SPPS are far more complicated and much research is needed to better understand the details of these two processes. In particular, how do SPS and SPPS droplets interact with plasma is fundamental to understanding of these processes. This 5-year research program proposes the development of two accurate mathematical/computational models of the interaction of a single SPS and SPPS droplet with a thermal plasma under controlled conditions. The models will be validated by introduction of single droplets into a newly developed radio frequency inductively coupled plasma torch (RF-ICP). Employing particle image velocimetry (PIV), the droplet's trajectory will be monitored, the generated particles will be collected on a substrate at different distances from the torch exit for analysis and characterization.