Preparation and wear properties of plasma cladding Mo₂FeB₂ coating on the surface of the furrow opener tip

Here Mo₂FeB₂ cermet coating was prepared on the surface of the furrow opener tip using plasma cladding. The microstructure, phase composition, microhardness and wear resistance of the coating were investigated to improve the wear resistance and to address the susceptibility to failure in the tillage process. Firstly, cladding current, cladding speed, powder delivery rate and cladding distance were set as the experimental parameters. The optimal combination of process parameters was obtained using orthogonal test: cladding current 80 A, cladding distance 10 mm and cladding speed 20 cm/min. Subsequently, the wear-resistant cladding coatings was prepared under the optimal conditions. The microstructure and phase composition of the cladding coatings were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The results revealed that excellent metallurgical bonding was achieved between the cladding coatings and the substrate. The microstructure consisted of square, butterfly, cross darts, dendritic structures as well as irregular long strips of hard phase along with network eutectic microstructure and iron-based bonding phase. The phase composition included Mo₂FeB₂, M₃B₂(M: Mo, Fe, Cr), (Cr, Fe)₇C₃, MoB, CrB, Fe₂B and Fe-Cr solid solutions. The hardness and wear resistance of cladding coatings were characterized using microhardness tester and the reciprocating friction and wear tester. An outstanding decreasing trend in microhardness from the surface to the substrate was observed for the cladding coatings, indicating a smooth transition in stress between cladding coatings and the substrate. The average microhardness of the cladding coating reached 9 618 MPa, which was 2.79 times higher than that of the furrow opener tip. The wear test showed that the average wear amount (19.20 mg) and the average friction coefficient (0.294) of the cladding coating were reduced by 52.9% and 42.4%, respectively, compared with the substrate. Wear tests under various loads revealed that the friction coefficient between the cladding coating and the substrate gradually decreased with the increasing load, yet overall remained lower than that of the substrate. The wear morphology of the cladding coating under different loads was found to be lighter compared to the substrate. This was attributed to the presence of terterine borides with the high hardness, which acted as a wear-resistant skeleton, accompanying with the eutectic microstructure and bonding. The Mo₂FeB₂ cladding coating exhibited improved anti-plowing and anti-falling properties, leading to better wear resistance when compared with grade 45 steel substrate. The soil tank test was conducted using self-made friction and wear testing machine. The average wear of the tip of the coated layer was reduced by 70.4% (4.60 g), compared with the conventional tip (15.54 g). Field test demonstrated that the average wear amount (34.34 g) of the coated furrow opener tip was only 43.4% of that of the conventional one (79.06 g) in real soil conditions. The wear morphology revealed that the presence of the coating was effectively resisted the soil wear. The original appearance of furrow opener tip was maintained after a long time of wear, thus demonstrating the exceptional wear resistance. The results of this study can provide theoretical reference and feasible technical solutions for improving the wear resistance of agricultural machinery's soil-engaging parts.