Abstract Thick electrical discharge coatings, also known by the commercial name “MSCoating”, can be applied on complex shapes and cavities to repair components or act as protective coatings. A variant of the EDM process, it can be used to make coatings up to several mm thickness on electrically conductive substrates. In this paper, an insight into the microstructure and formation mechanism is made through the production of experimental coatings using sacrificial Stellite 31 electrodes on stainless steel substrates. The coatings comprised mostly of ‘splats’ of CoCr. In addition, a significant amount of directly deposited un-melted electrode material was present, along with regions of oxide splats and substantial porosity. Using single discharge analysis, individual deposits contained both melted and un-melted electrode material. Through analysis of the debris, it was found that electrode material either formed spherical particles through melting and resolidification within the discharge gap, or in the form of original unmelted electrode material. It is thought that the low peak pulse section of the current waveform results in increased melting and solidification of material within the discharge gap and on the workpiece. The high peak pulse section of the waveform results in increased mechanical pull-out from the electrode, a proportion of which attaches to the workpiece. The ratio between the peak pulses was found to affect the amount of energy per unit volume of coating material for re-melting. The process is then followed by several discharges preferentially located in the spark region resulting in coating consolidation and build-up through further deposition and re-melting of material. Clustering of discharges was found to be critical in coating formation, where such areas exhibited increased deposition of electrode material. Under the conditions used in the study, the threshold for electrode particle size was found to be between 45 and 70 μm, suggesting that powder diameter is fundamental to thick coating formation. The density of debris within the discharge gap, dependant on the Duty Factor, is thought to correlate with the rate of material deposition from electrode to substrate, where an ideal density of debris produces a large amount of uncontrolled and preferential sparking/arcing, enhancing depositon and attachment.

中文翻译：

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厚放电涂层的形成

摘要 厚的放电涂层，也被称为“MSCoating”，可应用于复杂的形状和腔体，以修复部件或作为保护涂层。作为 EDM 工艺的一种变体，它可用于在导电基材上制作厚度达几毫米的涂层。在本文中，通过在不锈钢基板上使用牺牲性司太立 31 电极生产实验涂层，深入了解了微观结构和形成机制。涂层主要由 CoCr 的“碎片”组成。此外，存在大量直接沉积的未熔化电极材料，以及氧化物碎片和大量孔隙的区域。使用单次放电分析，单个沉积物包含熔化的和未熔化的电极材料。通过对碎屑的分析，发现电极材料要么在放电间隙内通过熔化和再凝固形成球形颗粒，要么以原始未熔化的电极材料的形式存在。据认为，电流波形的低峰值脉冲部分会导致放电间隙内和工件上材料的熔化和凝固增加。波形的高峰值脉冲部分导致电极的机械拉出增加，其中一部分附着在工件上。发现峰值脉冲之间的比率影响用于重新熔化的每单位体积的涂层材料的能量量。然后在该过程之后进行多次放电，这些放电优先位于火花区，通过进一步沉积和重新熔化材料导致涂层固结和堆积。发现放电聚集对涂层形成至关重要，其中这些区域表现出电极材料沉积增加。在研究中使用的条件下，发现电极粒径的阈值在 45 到 70 μm 之间，这表明粉末直径是形成厚涂层的基础。放电间隙内的碎屑密度取决于占空系数，被认为与从电极到基板的材料沉积速率相关，其中理想的碎屑密度会产生大量不受控制的优先火花/电弧，从而增强沉积和附件。