## 4 Results and Discussion
With the increase in radial depth of cut, the contact area between the tool and workpiece is increased accordingly, leading to higher cutting loading and frictional heat, both of which contribute to intensify the tool wear. In Figure 23, it can be observed that as the radial depth of cut is increased from 0.3 to 0.7 mm, the flank wear marks on the tool surface become more prominent as indicated by the red boxes in Figure 23d,g,h, particularly in the materials with x = 0.1 and x = 1.0. These flank wear marks reflect the different wear behaviors of the tool under high-stress and high-temperature conditions. With the higher hardness and strength properties in the case of the x = 1.0 material, the cutting tool is prone to fracture due to the high loading impact at the beginning of tool-workpiece engagement. On the other hand, with the higher ductility and plasticity of the x = 0.1 material, the chips may not be removed completely from the workpiece material, resulting in a built-up edge on the tool surface, which generates excessive friction and heat accumulation, ultimately causing cutting edge chipping. As the spindle speed is increased, the higher speeds enhance cutting efficiency and surface quality while frictional heat and tool wear may also be deduced. Figure 24 shows the comparison of cutting tool wear using the process parameter combinations of the L\({}_{9}\) orthogonal array in the second phase experiment for different elemental compositions. It can be observed that with increasing spindle speed, there are two distinct phenomena in cutting tool wear. For softer materials such as x = 0.1, high spindle speeds may lead to severe wear marks on the tool surface, as the heat accumulation at high speeds accelerates tool wear and damage as indicated by the red boxes in Figure 23g. However, for harder materials such as x = 1.0, at an appropriately high spindle speed tool wear may be reduced because the increase in spindle speed may decrease the feed per tooth for a constant feed rate, and thereby the cutting loading and tool wear are reduced. Figure 5:9 Cont. Figure 25 shows the machined surface morphology of HEAs with different elemental ratios (x = 0.1 and x = 1.0) using different cutting parameter combinations of the L\({}_{9}\) orthogonal array in the second phase experiment. As the x value is increased, the hardness and strength of the material increase accordingly, resulting in reductions in surface deformation and related waviness structure, and more uniform cutting traces and better surface quality are thus obtained. This is because higher x value alloys such as x = 1.0 possess a greater resistance to deformation during the machining processes, leading to less surface damage, while lower x value materials such as x = 0.1 or x = 0.5 are more prone to deformation, resulting in poorer surface quality. In terms of milling process parameters, feed rate, radial depth of cut, and spindle speed significantly influence the surface morphology of HEAs. As the feed rate and radial depth of cut are increased, surface quality typically decreases, especially for low x value materials as shown in Figure 25b,c,g, in which intense surface deformation areas or locations where secondary cutting occurred caused by chip scratching on the machined surface are indicated by red boxes. Increasing the spindle speed may have a positive effect on surface quality, but excessively high speeds may also lead to adverse effects. To achieve optimal surface quality, it is necessary to optimize the cutting parameters based on the specific material characteristics and machining performance requirements. Figure 6:0 Cutting tool wear using the process parameter combinations of the L\({}_{9}\) orthogonal array in the second phase experiment. (**a**) x = 0.1, Set 1. (**b**) x = 1.0, Set 1. (**c**) x = 0.1, Set 3. (**d**) x = 1.0, Set 3. (**e**) x = 0.1, Set 6. (**f**) x = 1.0, Set 6. (**g**) x = 0.1, Set 7. (**h**) x = 1.0, Set 7. (**i**) x = 0.1, Set 8. (**j**) x = 1.0, Set 8.