## 2 Implementation Details  
There has been a revolution, particularly in aircraft/aerospace industries, in relation to the manufacturing and development of highly precise components of aircraft with superior strength, toughness, and corrosion resistance properties. AISI 52100 steel is a high-carbon chromium alloy steel used widely in aircraft bearings and in automobile applications such as shafts, heavy-duty gear, pinions, gudgeon pins, ball screws, camshafts, gauges, CV joints, etc., because of their certain properties like a higher hardness value, superior load capacity to thermal shock, and high wear resistance effects. However, due to its high strength and toughness, AISI 52100 alloy steel is very complex to cut. Therefore, for the machinability improvement of this material, a cylindrical shape of AISI 52100 steel rod, with dimensions of length and diameter of 150 mm and 50 mm, respectively, was chosen for machinability investigation. Initially, the selected rod specimens were heated uniformly to the hardening temperature, 850 \({}^{\circ}\)C, and held at 850 \({}^{\circ}\)C for 30 min. Then, each set of specimens were quenched immediately in an oil chamber for an oil bath for 4 h. After quenching, the specimens were taken out from the oil chamber and cleaned properly for the process of tempering. Then, the quenched specimens again heated up to 250 \({}^{\circ}\)C slowly and held at that temperature for 30 min (soaking time). Then, let the material cool slowly in the air to develop the desired levels of hardness and toughness (55 \(\pm\) 1) HRC [25]. The hard turning operation was performed using a Jyoti DX 200-4A-CNC lathe machine tool. This machine tool has a power rating of 7.5 kW and a variable spindle speed range of 50 to 4000 r/min. In the present study, the finishing operation involved the utilization of a WIDIA carbide insert coated with a single-layer PVD (AlTiN) coating, specifically the CNMG120408 MS-WS10 PT grade. Additionally, a PCLNR 2525M12 tool holder was employed. The hard turning experiment involved the selection of four cutting parameters, namely cutting speed (70, 140, 210, and 280 m/min), feed (0.05, 0.1, 0.15, and 0.2 mm/rev), depth of cut (0.1, 0.2, 0.3, and 0.4 mm), and lubricant flow rate (20, 30, 40 and 50 mL/hr). The current experiment follows the Taguchi-based L\({}_{16}\) OA design of experiment. Various output responses, including flank wear, cutting temperature, cutting power, surface roughness, cutting sound, and chip morphology, were observed and analyzed for each experiment. The analysis of tool wear and chip images was conducted using an Olympus STM 6 optical microscope manufactured by Olympus Corporation, Shinjuku, Tokyo, Japan. The surface finishing of a machined cylindrical surface was achieved by utilizing the Surftest SV-2100 surface measuring instrument manufactured by Mitutoyo Corporation, Sakado, Takatsu-ku, Kawasaki, Kanagawa, Japan. The three-phase multi-function bidirectional power cum energy meter, specifically the EMT34 model, was employed for power measurement purposes. The T540 professional thermal camera by FLIR was employed to examine the temperature degradation that occurs during machining in the cutting zone. Noise emission during the turning process is recorded by a sound level meter manufactured by Fluke (Model-Fluke 945) (Everett, WA, USA). The advanced analysis of tool wear and chip morphology was conducted using the ZEISS Gemini SEM 450 (Jena, German)scanning electron microscope, and the resulting reports were analyzed using the EDS or EDAX software. The study commenced by procuring commercially accessible ZnO nanoparticles (supplied by AD-Nano Technologies Pvt Ltd., Shimoga, Karnataka, India) with a size range of 30-50 nm. The details of EDS test of ZnO powder are displayed in Figure 1. From this analysis, it is ensured that the powder contains element Zn and O with % weight of 98.1% and 1.9%, respectively.