开沟器铲尖表面等离子熔覆Mo2FeB2涂层制备及其磨损性能

为了解决开沟器铲尖耕作过程中耐磨性差、易失效的问题，利用等离子熔覆技术在开沟器铲尖表面制备Mo₂FeB₂金属陶瓷涂层，并对其微观组织结构、物相组成、显微硬度以及耐磨性能进行研究。通过正交试验得到熔覆层制备的最优工艺参数组合为：熔覆电流80 A，熔覆距离10 mm，熔覆速度20 cm/min，并以此来制备耐磨熔覆层。结果表明，熔覆层与基体呈现良好冶金结合，其组织主要由方形、蝶状、十字镖形、树形以及不规则长条状的硬质相、网状共晶组织和铁基粘结相组成，其主要物相组成为Mo₂FeB₂、M₃B₂(M: Mo, Fe, Cr)、(Cr, Fe)₇C₃、MoB、CrB、Fe₂B以及Fe-Cr固溶体。熔覆层的平均显微硬度为9618 MPa，为开沟器铲尖基体的2.79倍。相同工况下的磨损试验表明熔覆层的平均磨损量（19.20 mg）和平均摩擦系数（0.294）与基体相比分别降低了52.9%和42.4%；不同载荷下的磨损试验表明，随着载荷的增加，熔覆层与基体的摩擦系数呈现逐渐减小的趋势，但熔覆层的整体摩擦系数均低于基体，且其磨损形貌较基体轻微。土槽试验结果表明，熔覆层开沟器铲尖的平均磨损量（4.60 g）比常规开沟器铲尖（15.54 g）降低了70.4%；田间试验结果表明，在实际土壤环境中，开沟器铲尖熔覆层的平均磨损量（34.34 g）仅为常规开沟器铲尖（79.06 g）的43.4%，通过对比磨损形貌发现，熔覆层的存在可以有效抵御土壤磨损，使开沟器铲尖在经过长时间的磨损后能最大程度的保持原貌，从而使其表现出优异的耐磨性能。该研究结果可为提高农机触土部件的耐磨性提供理论参考和可行技术方案。

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 9618 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.