Microstructure and Corrosion Behavior of (CoCrFeNi)95Nb₅ High-Entropy Alloy Coating Fabricated by Plasma Spraying

Wenrui Wang; Wu Qi; Lu Xie; Xiao Yang; Jiangtao Li; Yong Zhang

doi:10.3390/ma12050694

Microstructure and Corrosion Behavior of (CoCrFeNi)₉₅Nb₅ High-Entropy Alloy Coating Fabricated by Plasma Spraying

Materials (Basel). 2019 Feb 27;12(5):694. doi: 10.3390/ma12050694.

Authors

Wenrui Wang^{1

2}, Wu Qi^{3

4}, Lu Xie^{5

6}, Xiao Yang^{7

8}, Jiangtao Li^{9

10}, Yong Zhang¹¹

Affiliations

¹ School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China. gmbitwrw@ustb.edu.cn.
² Key Laboratory of Fluid Interaction with Material, Ministry of Education, Beijing 100083, China. gmbitwrw@ustb.edu.cn.
³ School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China. wu.qi@xs.ustb.edu.cn.
⁴ Key Laboratory of Fluid Interaction with Material, Ministry of Education, Beijing 100083, China. wu.qi@xs.ustb.edu.cn.
⁵ School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China. xielu@ustb.edu.cn.
⁶ Key Laboratory of Fluid Interaction with Material, Ministry of Education, Beijing 100083, China. xielu@ustb.edu.cn.
⁷ Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China. yangxiao@mail.ipc.ac.cn.
⁸ Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China. yangxiao@mail.ipc.ac.cn.
⁹ Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China. lijiangtao@mail.ipc.ac.cn.
¹⁰ Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China. lijiangtao@mail.ipc.ac.cn.
¹¹ State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China. drzhangy@ustb.edu.cn.

Abstract

In this paper, the (CoCrFeNi)₉₅Nb₅ high-entropy alloy (HEA) coating with a thickness of 500 μm on Q235 steel substrate was fabricated by plasma spraying. The microscopic results showed that a new Laves phase is formed in the (CoCrFeNi)₉₅Nb₅ HEA coating compared to the HEA powder, and elemental segregation occurs between the dendrites and the interdendrites of the coating, while the interdendritic phase enriches with the Cr and Nb. The phase composition change and elemental segregation behavior were mainly due to the faster cooling rate of the plasma spraying technique. At the junction of the coating and the substrate, the HEA coating bonded well to the substrate; in addition, the width of transition zone was merely 2 μm. The microhardness of the (CoCrFeNi)₉₅Nb₅ HEA coating was 321 HV0.5, which is significantly higher than that of the substrate. In terms of corrosion resistance, the (CoCrFeNi)₉₅Nb₅ HEA coating has good corrosion resistance in NaCl solution. Although the corrosion form was pitting corrosion, the pitting potential of the (CoCrFeNi)₉₅Nb₅ HEA coating was significantly higher than that of other coatings, which was mainly because of the dense passivation film formed by Cr and Nb on the surface of the coating. Once the passivation film was destroyed by Cl^-, the selective corrosion occurred on the surface of the (CoCrFeNi)₉₅Nb₅ HEA coating. In summary, the (CoCrFeNi)₉₅Nb₅ HEA coating prepared by plasma spraying technology can significantly improve the corrosion resistance and mechanical properties of the Q235 steel substrate.

Keywords: corrosion resistance; high-entropy alloy coating; microstructure; plasma spray.

Abstract

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