Surface Topographical Analysis of Diametric and Kerf Behavior in Micro-Hole Piercing on Inconel 718 using AWJM

Precision piercing of nickel-based superalloys remains challenging because abrasive waterjet (AWJ) penetration can produce non-uniform entry-exit geometry and kerf taper, particularly in deep micro-hole applications. This study systematically investigates the formation, geometrical accuracy, and surface morphology of AWJ-pierced holes in 12-mm-thick Inconel 718 using silicon carbide (SiC) abrasives. The influence of key process parameters, namely abrasive mesh size (size Mesh ), abrasive jet pressure (Pr Jet ), stand-off distance (Dist stand-off ), and machining time (M Time ), was systematically examined through a full experimental design comprising 96 trials. Hole quality was evaluated from the top and bottom diameters and the resulting kerf angle using a calibrated video measuring system, while scanning electron microscopy was employed to elucidate the associated material-removal mechanisms. The results demonstrate that machining time is the dominant parameter governing kerf-angle formation, accounting for 79.632% of the total variation, followed by pressure with a 3.645% contribution; abrasive mesh size and stand-off distance exhibit comparatively minor effects within the investigated ranges. Kerf angle decreased from 0.91-1.60° at 40 s to 0.03-0.59° at 60 s, while a lowest measured kerf angle of 0.02° was achieved at 80 s. The optimum condition was identified as 120# SiC, 100 MPa jet pressure, 3 mm stand-off distance, and 80 s machining time, producing a near-cylindrical hole profile with top and bottom diameters of 1.83 and 1.82 mm, respectively. Repeatability assessment at the optimum condition yielded a standard deviation of 0.001° and a 95% confidence interval of ±0.0025°, indicating good experimental repeatability under the selected optimum condition. SEM observations indicate predominantly ductile erosion characterized by micro-cutting, ploughing, particle embedment, and localized plastic deformation, with possible localized brittle damage under high-energy impacts.