Abstract

The evolution of element distribution during laser cladding involves two dynamic behaviors, i.e., liquid molten pool flow and FeCoCrNi high-entropy alloy (HEA) coatings solidification. However, it is quite difficult to characterize element distribution during the flow of the liquid molten pool rigorously. The current investigation conducted the optical microscopy, scanning electron microscopy, X-ray diffraction analysis and energy dispersive spectrometer to study the dilution, phase composition, microstructure of the FeCoCrNi coatings. The flow field was simulated to uncover the dynamic change mechanism of the molten pool and explain the experimental results. The results indicated that the coating is substantially composed of FCC and BCC solid solution with a typical dendrite microstructure. Gray Laves phase-(Ni, Co)₂Ti and a small number of white dot particles, Fe–Cr phase, are dispersed in the inter-dendritic region. The HEA atoms (Fe, Co, Cr, Ni) gradually aggregate from the center to the side at the coating boundary region, while the Ti atom is the opposite. The Marangoni flow inflection point at the molten pool boundary will cause HEA atoms to aggregate. On the contrary, Ti atom enters the molten pool from the bottom with the heat buoyance flow and then migrates to the boundary along with the Marangoni flow. Therefore, the content of Ti in the coating boundary decreases. The Marangoni flow, heat buoyance flow, and recoil pressure flow are interwoven in the middle region of the coating, resulting in a more uniform element distribution than the boundary region.

Graphic Abstract

中文翻译：

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激光熔覆Ti-6Al-4V表面FeCoCrNi高熵合金涂层元素非均匀分布的分析

摘要

激光熔覆过程中元素分布的演变涉及两个动态行为，即液态熔池流动和FeCoCrNi高熵合金（HEA）涂层凝固。然而，在液体熔池的流动过程中严格地表征元素分布是非常困难的。当前的研究进行了光学显微镜，扫描电子显微镜，X射线衍射分析和能量色散光谱仪，以研究FeCoCrNi涂层的稀释度，相组成和微观结构。模拟流场以揭示熔池的动态变化机理并解释实验结果。结果表明该涂层基本上由具有典型枝晶微结构的FCC和BCC固溶体组成。格雷Laves相-（Ni，Co）₂Ti和少量的白色点状颗粒Fe–Cr相分散在树突间区域。HEA原子（Fe，Co，Cr，Ni）在涂层边界区域从中心到侧面逐渐聚集，而Ti原子相反。熔池边界处的Marangoni流拐点将导致HEA原子聚集。相反，Ti原子随着热浮力流从底部进入熔池，然后与Marangoni流一起迁移到边界。因此，涂层边界中的Ti含量降低。Marangoni流，热浮力流和反冲压力流交织在涂层的中间区域，与边界区域相比，元素分布更加均匀。

图形摘要