Microstructures and Properties of High Strength and Toughness Fe-Based Coatings Fabricated by Plasma Arc Deposition

Currently, surface coatings on agricultural machinery are crucial for extending service life. However, achieving coating strength and toughness remains a challenge. In this paper, two types of high-hardness iron-based coatings, referred as S1 and S2, were prepared by modulating the Mo/V ratio in the Fe-C-V-Mo-B system, and their microstructural evolution and property changes were investigated. The results show that the S1 coating primarily consist of martensitic matrix, spherical VC, blocky Mo₂B, and a small amount of skeleton-like Mo₂B. In contrast, the S2 coating consist of martensitic matrix, petal-like VC, and skeleton-like Mo₂B. Compared with S1, the VC volume fraction in S2 increases by 6.5%, and the Mo₂B volume fraction increases by 16.3%. The average microhardness of S1 and S2 coatings are 737 HV_0.5 and 954 HV_0.5, respectively, indicating that the S2 coating exhibits a 22.7% higher microhardness compared with S1. The average friction coefficients of S1 and S2 coatings are 0.434 and 0.398, respectively. Furthermore, the wear loss of S2 coating is approximately half that of S1. The fracture toughness of S1 and S2 coatings are 51.9 MPa·m^1/2 and 51.7MPa·m^1/2, respectively. Fracture analysis reveals that the skeleton-like eutectic structure in S2 can deflect cracks generated by impact, increase the length of propagation path, and improve the toughness of coating. It allows S2 coating to achieve high hardness and wear resistance, while maintaining toughness comparable to S1 coating. This study provides a theoretical basis for the design and development of iron-based coatings with high hardness, high abrasion resistance, and impact resistance for agricultural machinery.