## 1 Introduction
Moreover, severe surface defects were found on the CoCrNi MEA, including breakouts at the surface and the initiation of high tensile residual stresses. [PERSON] et al. [2] investigated the machinability and surface integrity of CoCrFeNi MEA using USAM. A full-factorial experiment was designed to perform milling experiments at different cutting speeds and feed rates. A PVD AlSiTiN-coated tungsten carbide end mill was utilized in USAM experiments, and measurements of cutting force, surface morphology, surface roughness, and residual stresses were also carried out. It was found that under the conditions of low feed rate, high cutting speed, and the use of USAM, the cutting force was reduced. Tear/groove defects were observed on the workpiece surface in both conventional milling and USAM. Therefore, no significant effect of USAM or cutting speed on surface roughness was observed. A noticeable reduction in surface roughness was only found when the feed rate was decreased. Regarding residual stresses, higher tensile residual stresses were generated on the surface during conventional milling as the feed rate and cutting speed were increased. Compared to conventional milling, USAM exhibited lower tensile residual stresses at higher feed rates and cutting speeds. [PERSON] et al. [3] investigated the surface integrity of CoCrFeMnNi HEA under conventional milling and USAM conditions. A full-factorial experiment was designed to perform milling experiments at different cutting speeds and feed rates. USAM was conducted using a PVD TiAlSiN-coated tungsten carbide end mill, and measurements of cutting force, surface integrity, surface roughness, and residual stresses were carried out. It was found that as the feed rate decreased, the cutting force was reduced by 38%. When the cutting speed was increased from 40 to 110 m/min, a 28% reduction in cutting force was observed. Through USAM, the average cutting force was further reduced by 5%. Regarding surface integrity, a significant improvement in the surface integrity of CoCrFeMnNi HEA was observed with USAM compared to conventional milling. This was confirmed by a reduction in microdefects on the machined surface and a decrease in tensile residual stresses at or below the surface. [PERSON] et al. [4] conducted micro-milling experiments on FeCoNiCrAl\({}_{\mathrm{x}}\) HEMs using an ultra-precision milling machine to investigate the effects of different aluminum contents (x = 0.1, 0.5, 1) on tool wear, surface quality, and cutting force. First, the machining parameters and tool parameters were kept constant, and then experiments were carried out with varying aluminum content. Finally, the machining characteristics obtained with different aluminum contents were measured and observed. The results showed that the combined effects of adhesive wear, mechanical shock damage, abrasive wear, and oxidative wear were the main mechanisms of tool wear, while the influence of diffusive wear was relatively insignificant. As the aluminum content was increased, the cutting force became larger, leading to a higher cutting temperature and more severe tool wear. Specifically, when x = 1, tool wear was increased by approximately 53.2% compared to x = 0.1. Additionally, when the micro-milling distance reached 120 mm, surface roughness was decreased by about 20%. [PERSON] et al. [5] conducted an experimental study on the machining characteristics of FeCoNiCrAl\({}_{\mathrm{x}}\) HEA for micro-milling. First, FeCoNiCrAl\({}_{\mathrm{x}}\) HEA was prepared using vacuum arc melting, with the aluminum content (x = 0.1, 0.5, 1) modified to induce changes in hardness. Then, micro-milling experiments were performed by varying process parameters such as spindle speed, feed rate, and cutting depth. Finally, the microstructure was observed and measured using an electron microscope. The results showed that as the aluminum content was increased, the crystal structure transformed from FCC to FCC + BCC when x = 1.