Comprehensive analysis of shielding gas flow rate effects on geometric optimization, microstructural evolution, and gas porosity formation in single-pass laser cladding of IN625 on René 125 turbine blade

This study critically evaluates the mechanistic interplay of argon shielding gas flow rate (20–31 L/min) on geometric characteristics, microstructure, and gas porosity during laser directed energy deposition(LDED) of IN625 (Inconel 625) superalloy onto a Rene 125 superalloy substrate. Microstructural analysis was performed via SEM, cross-sectional geometric measurements, and secondary dendrite arm spacing (SDAS) quantification. Results revealed that elevating the gas flow rate from 20 to 26 L/min systematically reduced single-pass width from 1450 to 1207 µm, whereas further increments to 31 L/min induced a rebound to 1332 µm due to amplified melt pool instability. Concurrently, single-pass height attained a maximum of 354 µm at 26 L/min before diminishing as powder scattering intensified. A thermally calibrated model incorporating spatially resolved correction factors was subsequently developed to predict cooling kinetics. The developed thermal model captures the region-dependent cooling behavior, while the hybrid porosity model successfully predicts the dominant porosity mechanisms in good agreement with experimental results. Furthermore, a hybrid porosity prediction model was formulated by integrating three dominant mechanisms (gas entrapment, oxidation-induced void formation, and base porosity propagation) thereby establishing a quantitative linkage between shielding gas dynamics and defect generation.