The application of high-entropy alloys (HEA) in surface technology has great potential due to the high corrosion and wear resistance. A further improvement can be achieved by applying thermochemical treatments. Powder-pack boriding enables the formation of a protective precipitation layer. This process has already been applied for cast HEAs causing the formation of a diffusion-enriched surface layer and a distinct increase in wear resistance. In the current investigations, the alloy CrFeCoNi with a single-phase face-centred cubic (fcc) structure is considered. An efficient application can be achieved by limiting the material usage of HEAs to the surface. Therefore, the high-velocity-oxygen-fuel (HVOF) thermal spray process is applied. Boriding was conducted with an adapted powder-pack routine. Furthermore, borided bulk HEAs were considered as a reference. The influence of the production route and boriding treatment on the microstructure, phase formation, and properties was investigated in detail. For the coating and the cast HEA, a precipitation layer is formed. Hence, the hardness and wear resistance are significantly increased. The current study proves the suitability of the investigated process combination.

中文翻译：

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HVOF喷涂单相高熵合金CrFeCoNi的沉淀硬化

高熵合金（HEA）在表面技术中的应用由于其高耐腐蚀性和耐磨性而具有巨大的潜力。通过应用热化学处理可以实现进一步的改进。粉末包装的硼化使得能够形成保护性沉淀层。该方法已经应用于铸造HEA，其导致形成富集扩散的表面层并显着提高耐磨性。在目前的研究中，考虑了具有单相面心立方（fcc）结构的CrFeCoNi合金。通过将HEA的材料用量限制在表面上可以实现有效的应用。因此，应用了高速氧气燃料（HVOF）热喷涂工艺。用适合的粉末包装程序进行硼化。此外，硼化的散装HEA被视为参考。详细研究了生产路线和硼化处理对显微组织，相形成和性能的影响。对于涂层和流延的HEA，形成沉淀层。因此，硬度和耐磨性显着提高。当前的研究证明了所研究过程组合的适用性。