# Process Optimization and Wear Performance of Plasma-Cladding Fe5 Coatings on Rotary Tillage Blades
## 3 Results and Discussion
### Structure and Properties of Fe5 Coatings Under Optimized Conditions  
#### 3.2.1 Microstructure of Fe5 Coatings  
Figure 3 presents the SEM microstructure of the plasma cladding layer, revealing no apparent porosity, cracks, or other impurities and indicating a clean interface. A distinct transition zone exists between the cladding layer and the substrate, which is attributed to elemental diffusion, resulting in a robust metallurgical bond. The SEM image shows that the cladding layer primarily consists of a light gray matrix phase and a dark gray hard phase. The hard phase exhibits various morphologies, which are mainly categorized into three types: needle-like T, hexagonal Q, and cellular S structures in triangular regions. Throughout the cladding layer, the growth direction of the hard phase is predominantly vertical or inclined upwards, providing support to the cladding layer and effectively resisting surface wear [27]. The size of the hard phase within the cladding layer varies; it is larger at the bottom, finer in the middle, and increasing again at the top. This variation is a result of the rapid heating and cooling characteristics of the plasma-cladding process, which influence the crystallization of the hard phase [28]. Figure 4 presents the X-ray diffraction (XRD) pattern of the cladding layer, revealing that the primary phases consist of \(\alpha\)-Fe, Cr\({}_{7}\)C\({}_{3}\), Cr\({}_{2}\)Fe\({}_{14}\)C, and Cr-Ni-Fe-C solid solutions. In the XRD pattern, the higher the relative peak intensity of a particular phase, the greater its content [29]. It can be observed that Cr\({}_{7}\)C\({}_{3}\) is the predominant hard phase in this cladding layer, with the highest proportion. Table 6 presents an energy spectrum analysis of the points in Figure 5. The analysis reveals that the elemental compositions of points a, b, and c are nearly identical, indicating that they belong to the same class of material. The atomic ratio of Cr to C is greater than 2.3, suggesting the presence of not only the Cr\({}_{7}\)C\({}_{3}\) phase but also, based on the XRD results, a minor amount of the iron-chromium compound Cr\({}_{2}\)Fe\({}_{14}\)C. Despite having the same chemical composition, the shapes of these points vary due to the poor directional growth of the hard  
Figure 2: Three-dimensional response surface; (**a**) response surface plot of the powder feed rate and cladding current; (**b**) response surface plot of cladding distance and cladding speed. Different colors represent varying degrees of wear, indicating the severity of wear, with red denoting the most severe wear and purple representing the least severe. The lines of different colors below indicate projections of various levels of wear. phase. Observations from different angles reveal different cross-sections, and the significant differences in shape are attributed to variations in crystallization methods [30; 31]. Cr\(\gamma\)C\({}_{3}\), presenting in strip and block forms, exhibits stable and superior mechanical properties, with its Vickers hardness reaching as high as HV1500-2100. Additionally, it possesses excellent wear resistance and other advantages [32; 33]. Point d is in the gray zone, where the Fe content is the highest, but the Cr content is low. There are trace amounts of Si and Ni, but no C is present. In conjunction with the XRD results, it can be determined that the primary phase is \(\alpha\)-Fe, with minor amounts of Si and Ni existing in the form of solid solutions within the cladding layer. Point e represents the white block-like region surrounding the hard phase. It exhibits the highest content of Fe and a low content of Cr, with the presence of C as well. Based on the XRD pattern, it can be inferred that the primary constituents are \(\alpha\)-Fe and Cr-Ni-Fe-C solid solutions. Additionally, there is a very small amount of carbides present; however,