Microstructure and Properties of AlCoCrFeNiSi High-Entropy Alloy Coating on AISI 304 Stainless Steel by Laser Cladding Guozhong Zhang, Hao Liu, Xianhua Tian, Peijian Chen, Haifeng Yang, and Jingbin Hao (Submitted October 7, 2018; in revised form December 30, 2019) In this paper, to improve the hardness and wear resistance, AlCoCrFeNiSi HEA coatings were synthesized on AISI 304 stainless steel by laser cladding. The microstructure, chemical composition, constituent phases, microhardness, wear resistance and corrosion resistance of the coating were analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), x-ray diffraction (XRD), Vickers microhardness tester, pin-on-disk tribological tester and electrochemical workstation, respectively. The experimental re- sults showed that the coating possessed a single body-centered cubic (BCC) phase structure (Fe-Cr). Si element was dissolved into Fe-Cr solid solution, resulting in severe lattice distortion. The dislocation density of the coating was as high as 1.07 3 10 14 m 22 . Therefore, the microhardness (630.36 HV 0.3 ) of the HEA coating was significantly improved by the effect of solid solution strengthening and dislocation strength- ening. The coating exhibited excellent wear resistance, and abrasive wear was effectively avoided. The wear mechanism of the coating involved mainly oxidation wear and slight adhesion wear. The corrosion resis- tance of the coating was better than that of AISI 304 stainless steel in 3.5% NaCl solution. In conclusion, the AlCoCrFeNiSi HEA coating prepared by laser cladding can provide excellent wear protection to stainless steel at no expense to its own corrosion resistance. Keywords AlCoCrFeNiSi, high-entropy alloys, laser cladding, microstructure, strength mechanism, wear and corrosion 1. Introduction With the continuous development of the machinery industry, AISI 304 stainless steel with excellent corrosion resistance and toughness has been applied to automotive, ship and agricultural machinery industries. Unfortunately, AISI 304 stainless steel is prone to wear and deformation when it is employed in a harsh working environment because of its low hardness. Modifying the surface property with a protective coating on AISI 304 stainless steel is an effective way to solve this inherent problem. In recent years, efforts have been made to develop high- performance coatings to deal with the poor hardness and wear properties of AISI 304 stainless steel using laser cladding technology (Ref 1, 2). Laser-cladded coatings usually exhibit excellent metallurgical bonding between the coating and the substrate, which plays an important role in engineering applications. The performance of laser-cladded coating mainly depends on the cladding materials. In 2004, Ye et al. put forward a new concept of high-entropy alloy (HEA), which broke the traditional idea of alloy design. HEA is composed of 5 to 13 principal elements in equimolar or near-equimolar ratios (Ref 3). An important feature of HEA is that it consists of a simple solid solution phase rather than many complex inter- metallic phases (Ref 4). Due to the large atomic size difference, the solid solution phase suffers from severe lattice distortion, resulting in a remarkable increase in the hardness and strength of the HEA (Ref 5). For example, Al 3 CoCrFeNi alloy has a very high value of hardness of over 660 HV (Ref 6). HEAs strengthened by solid solution have better wear resistance than conventional alloys reinforced by hard particles with the same hardness, since three-body wear caused by falling off of the particles is avoided (Ref 7). Among the HEAs studied previously, AlCoCrFeNiCu HEA is a typical case. The research on AlCoCrCuFeNi HEA shows that its microstructure is characterized by the existence of Cu- rich phase (Ref 8, 9). To solve the problem of serious segregation of Cu, many elements were evaluated to replace Cu. Shivam et al. (Ref 10) used Mn element to replace Cu element in the AlCoCrFeNiCu system. The results showed that all the elements of the alloy were distributed uniformly. Zhu et al. (Ref 11) analyzed the effect of Mo content on the microstructure of AlCoCrFeNi HEA system and found that the elements of the alloy were distributed uniformly when Mo content was 0.1. Loebel et al. (Ref 12) synthesized AlCoCrFe- NiTi HEA coating. The distribution of elements in the coating was in accordance with the nominal content, and there was no obvious segregation phenomenon. Zhang et al. (Ref 13) investigated FeCoNiCrAl 2 Si HEA under laser-induced rapid solidification condition and found that micro-segregation existed in the coatings. Guozhong Zhang, Xianhua Tian, Haifeng Yang, and Jingbin Hao, School of Mechanical and Electrical Engineering, China University of Mining and Technology, Xuzhou, China; Hao Liu, School of Mechanical and Electrical Engineering, China University of Mining and Technology, Xuzhou, China; and Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining and Technology, Xuzhou, China; Peijian Chen, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, China. Contact e-mail: liuhao56@cumt.edu.cn. JMEPEG ÓASM International https://doi.org/10.1007/s11665-020-04586-3 1059-9495/$19.00 Journal of Materials Engineering and Performance