## 1 Introduction  
As modern industrial demands continue to grow, the performance of traditional alloys is approaching its limits and is unable to meet the need for higher material properties. The concept of HEAs has emerged as a novel material that is gaining significant attention in research. Unlike traditional alloys, HEAs possess a uniform structural composition, which leads to an enhanced microstructure and superior properties. The different elemental compositions of HEAs result in various characteristics, enabling a broader range of industrial applications. For example, high radiation resistance and corrosion-resistant coatings of HEAs can be applied in nuclear fuel and high-pressure vessels. Their high-temperature stability, hardness, and wear resistance make HEAs ideal for use in the power generation and aerospace industries, and other high-temperature environments such as nuclear reactors, liquid rocket engine nozzles, heat exchanger tubes, aerospace propulsion systems, gas turbines, X-ray generating rotating anodes, turbine blades, and even armor applications. Compared to the traditionally used titanium alloys, HEAs demonstrate superior performance. To adapt HEAs for various industrial fields, different combinations of elements have been developed, each with distinct mechanical properties. For instance, the CoCrFeNiMn HEA is particularly suitable for low-temperature applications, such as liquefied gas storage, as it maintains excellent mechanical properties at temperatures as low as \(-196\)\({}^{\circ}\)C. With a 75% increase in strength and a 35% increase in elongation, this alloy becomes stronger and tougher, making it suitable for applications like cryogenic storage tanks and natural gas storage. FeCoNiCrMn is a type of HEA characterized by high strength, hardness, and excellent corrosion resistance. It is composed of multiple elements in equal molar ratios, where chromium and nickel contribute to its superior corrosion resistance, cobalt and iron provide mechanical strength, and manganese gives ductility and toughness enhancements. These elements form a complex multi-phase microstructure, allowing the material to maintain stable performance even in high-temperature and harsh environments. Due to the interactions between the elements and the effects of varying elemental ratios, the alloy's high hardness and strength increase the cutting forces during machining processes, leading to accelerated cutting tool wear. Additionally, the presence of multiple phases can cause interface disruption during the cutting process, resulting in machining defects such as surface quality and dimensional accuracy reductions. The interaction and matching properties of different elements in HEAs with cutting tools are not the same during the cutting process. Under the actions of cutting loading, the alloy may experience defects such as internal cracking, surface spalling, and material deformation. [PERSON] et al. [1] investigated the machinability of CoCrFeMnNi HEA and CoCrNi medium-entropy alloy (MEA). Ultrasonic-assisted milling (USAM) was performed in dry conditions using a physical vapor deposition (PVD) AlSiTiN-coated tungsten carbide end mill using different milling process parameters for these alloy materials. The effects of varying cutting speed, spindle speed, and feed rate on cutting force, tool wear, and surface roughness were examined. It was found that when machining CoCrFeMnNi HEA, the cutting force could be reduced to 35 N by decreasing the feed rate and increasing the cutting speed. The cutting force was further reduced by 2 N through ultrasonic-assisted milling, and surface integrity was improved, leading to a reduction in tensile residual stresses and defect density near the machined surface. Additionally, the size of the subsurface deformation-affected zone was reduced by USAM. Furthermore, the lowest surface roughness was achieved at a cutting speed of 50-70 m/min. When machining CoCrNi MEA, severe tool wear was observed during the experiment, resulting in a significant increase in cutting force.