# Process Optimization and Wear Performance of Plasma-Cladding Fe5 Coatings on Rotary Tillage Blades
## 3 Results and Discussion
### Process Optimization of Plasma Cladding
#### 3.1.2 Optimization Results  
The experiment was a multi-factorial experiment with four factors and three levels. The level ranges of the factors to be optimized were determined based on the results of preliminary single-factor experiments, resulting in a total of 27 groups. Each group underwent three abrasive wear tests using a wet sand rubber wheel, and the average values of the results were recorded, as shown in the table below. The wear test results reveal significant differences in wear resistance among different groups, with the maximum difference reaching 56.97 mg. The results also exhibit certain characteristic patterns. Subsequently, further significance analysis of the data was conducted, and the interactive effects between different factors were discussed. The experimental results were processed using Design-Expert 13, resulting in a mathematical regression model for wear quality, shown in Equation (1):  
\[ \begin{array}{l}Y=18.43+5.4A-1.79B-14.53C-10.53D+4.01 AB-8.26 AC+4.36 AD-5.12 BC-8 BD-1.94 CD+0.9417A^{2}\\ +5.69B^{2}+6.43C^{2}+13.76D^{2}\end{array}  \tag{1}\]  
According to the analysis of variance (ANOVA) table for the regression model, the coating current, powder feeding rate, and coating distance have significant effects on the wear volume. The \(p\)-value of the model is less than 0.01, indicating that the model is highly significant, while the lack-of-fit term is not significant. Therefore, this model can be used for parameter optimization in plasma-cladding coating processes. The influence of each factor on the wear volume is ranked as follows: powder feeding rate > coating distance > coating current > coating speed. The response surfaces of the cladding current, cladding speed, cladding distance, and powder feeding rate were obtained based on the experimental results. As shown in Figure 2, there is a significant interaction between the powder feeding rate and cladding current. When performing plasma cladding with Fe5 alloy powder, with a constant cladding current, an increase in powder feeding rate leads to more powder being melted by the plasma arc, resulting in a denser coating and better wear resistance. When the powder feeding rate is constant, the wear amount increases with the increase in cladding current. This is because a higher current generates more heat, melting a larger volume of the substrate, which leads to the dilution of the coating and a decrease in wear resistance. There is also a significant interaction between the cladding distance and cladding speed. The wear volume exhibits a U-shaped pattern as the cladding distance changes. When the cladding distance is too small, i.e., when the nozzle of the welding gun is too close to the workpiece, if the cladding speed is too fast, some of the powder may not be adequately heated by the plasma arc flame before it comes into contact with the workpiece surface, leading to scattering upon impact and poor coating quality with high wear volume. If the cladding speed is too slow, it can cause excessive heating of the substrate, increasing the tendency for cracking in the coating. As the cladding distance gradually increases, more powder participates in the cladding process, resulting in a denser coating and a gradual decrease in wear volume. However, when the cladding distance continues to increase beyond the thermal influence zone of the current arc flame, the powder cannot be sufficiently melted and accurately deposited on the workpiece surface, causing the wear volume to rise again. The optimal combination of process parameters is a cladding current of 144 A, a cladding speed of 23 mm/s, a powder feeding rate of 23 g/min, and a cladding distance of 12 mm. The wear performance of the cladding layer with the optimal parameters was evaluated using a wet sand rubber wheel wear test. The predicted wear value was 7.68901 mg, while the measured values were 8.06 mg, 7.71 mg, and 7.93 mg, with an error less than 5%, indicating the reliability of the model.