Functional Surfaces via Electrical Discharge Methods

电火花加工（EDM）是一种在坚硬材料中实现复杂特征的优良工艺。电火花加工利用反复放电从工件上去除材料。每次放电形成一个等离子通道，导致从电火花加工机器的电极（“工具”）和工件上去除少量材料。优化了机器参数和火花条件，因此在典型条件下，与每次放电相比，从工件上去除的材料更多。当等离子体电弧撞击时，局部区域被迅速加热并从大块中解放出来。这些“碎片”通常被所谓的冲洗机制从火花间隙中抽离。火花间隙是在一个令人难以置信的暴风雨的地方，因此很难理解。然而，这种行为的知识对于提高我们对工业应用的ED技术的理解至关重要。结果表明，在正确的物理条件下，这些放电产生的碎片可以用于涂覆涂层并构建低纵横比表面结构。这为高价值的制造商提供了一个有趣的机会，他们经常负责加工精度特征，然后应用精密涂层，或者修复高价值部件的磨损区域。然而，这一过程的物理学尚未完全理解，仍然需要从基本原理显著推进这项技术。该项目将从一个新的、多学科的角度探索这项技术，包括实验和建模活动。研究人员将向社区展示对碎片动态放电涂层技术的深刻理解，并将利用这些新知识创建复杂的多层涂层，这些涂层将在航空航天，生物医学和工具制造行业中得到应用。在这些行业经营的公司依靠其产品相对于竞争对手的技术优势而蓬勃发展。例如，所有这些产品都需要先进的摩擦学性能以及其他复杂的表面特性。有一系列表面改性技术可供制造商使用，如激光熔覆、冷/等离子喷涂、PVD等，这些技术在过去20年中发展迅速。然而，这些都没有直接集成到一个也可以去除材料的过程中。所有这些涂层技术的快速采用都源于对工艺力学、材料科学和应用优化的深刻理解。在这些涂层技术的所有高价值应用中，表面完整性至关重要，因为由于腐蚀，疲劳或高温效应而发生的故障来自表面或近表面。增强表面完整性是表面处理的核心原理，尽管涂层也经常用于美学目的。近年来，随着现代机器制造商声称已经开发出能够实现所谓“近零”重铸层的工艺，电火花加工本身已经有了显著的发展。这是对电火花加工引起的表面损伤所进行的广泛研究的回应，已知电火花加工会引起有害的拉伸应力。然而，目前还没有针对这一问题的固体解决方案，这意味着目前对电火花加工表层的信心很低。然而，固结涂料的应用可能能够解决这一问题，并将在本项目中进行研究。在同一过程中去除材料和涂覆涂层的能力具有显著的优势。因此，使用ED涂层方法在提高产品性能方面具有很大的潜力，而且通过节省工艺效率来提高高价值制造。

Electrical discharge machining (EDM) is an excellent process of realising complex features in tough materials. EDM makes use of repeated electrical discharges to remove material from a workpiece. Each discharge constitutes a plasma channel which results in removal of a small amount of material from both the EDM machine's electrode ('the tool') and the work piece. Machine parameters and spark conditions are optimised such that under typical conditions more material is removed from the work piece when compared to the tool per discharge. When the plasma arc strikes a localised region is rapidly heated and liberated from the bulk. This 'debris' is then normally evacuated from the spark gap by the so called flushing mechanism. The spark gap is in an incredibly tempestuous place and hence very difficult to understand. However, knowledge of this behaviour is crucial to advancing our understanding of ED techniques for industrial applications.It has been shown that under the correct physical conditions in the spark gap the debris created by these discharges can be used to apply a coating and build low aspect ratio surface structures. This presents an interesting opportunity to high value manufacturers who are often tasked with machining precision features and then applying precision coatings or, perhaps, repairing worn regions in high value components. However, the physics of this process is not yet fully understood and there remains a requirement to advance this technology significantly from fundamental principles.This project will explore the technology from a new, multidisciplinary perspective which will incorporate both experimental and modelling activities. The investigators will present a solid understanding of the debris dynamics electrical discharge coating techniques to the community and will use this new knowledge to create complex multi-layer coatings which will have applications in the aerospace, biomedical and tool making industries. Companies operating in these industries thrive on the technological advantage their products possess over competitors. For example all of these products require advanced tribological properties amongst other complex surface characteristics. There is an array of surface modification techniques available to manufactures such as laser cladding, cold/plasma spray, PVD amongst others which have developed rapidly in the last 20 years. However, none of these have been directly integrated into a process which can also remove material. The rapid adoption of all of these coating techniques has been borne out of a solid understanding of the process mechanics, materials science and optimisation for application. In all of the high value applications for these coating techniques surface integrity is critical since failures which occur as a result of corrosion, fatigue or high temperature effects emanate from the surface or near surface. Enhancing surface integrity is the core rationale for surface treatment although coatings are also often applied for aesthetic purposes also.EDM itself has developed significantly in recent years with modern machine makers claiming to have developed processes capable of the so called 'near zero' recast layer. This is in response to the extensive studies which have been undertaken on the surface damage that results from EDM and is known to induce deleterious tensile stresses. However, no solid solution to this has been developed which means the confidence in EDM surface layers is currently low. However, the application of consolidated coatings may be able to tackle this problem and will be investigated in this project. The ability to remove material and apply a coating within the same process presents significant advantages. Therefore the use of ED coating methods has great potential to enhance high value manufacturing in terms of enhanced product performance but also through process efficiency savings.