TECHNOLOGICAL FEATURES OF PERIODIC MICROSTRUCTURE FORMATION OF THE «FISH-SCALE» TYPE ON THE SURFACE OF 12Х18Н10Т STAINLESS STEEL BY NANOSECOND LASER IRRADIATION

The paper presents a scientific substantiation of the technological aspects of forming periodic microstructures of the "fish scale" type on the surface of AISI 321 stainless steel using nanosecond laser irradiation. The study establishes the fundamental interactions between laser radiation and the material, develops a mathematical model of heating, phase transitions, ablation, and surface relief formation, and experimentally validates the results. From an engineering perspective, the controlled formation of periodic microstructures on metal surfaces enables the modification of their operational properties, including increased wear resistance, reduced friction coefficient, enhanced adhesion characteristics, and improved corrosion resistance. This opens up broad prospects for applying laser microtexturing in aerospace, automotive, medical, and energy engineering industries, where surface microrelief optimization can significantly enhance component functionality and durability. The study thoroughly examines the interaction of nanosecond laser radiation with metal surfaces, considering key physical processes such as heating, phase transitions, ablation, and surface roughness formation. A theoretical model of the process is developed based on heat conduction equations, phase transition kinetics, and ablation mechanisms. The model incorporates the laser system Minimarker 2 parameters and the material properties of AISI 321 stainless steel, including density, heat capacity, thermal conductivity, melting and boiling temperatures, absorption coefficient, and specific latent heat of fusion and vaporization. A numerical simulation of heat transfer, phase transitions, and material ablation under laser irradiation is conducted using the finite element method (FEM) and finite difference method (FDM). The model accurately predicts temperature distribution, crater formation, and microstructure evolution in response to laser pulses. The results confirm that with increasing pulse energy, the ablation depth also increases, which is supported by three-dimensional visualizations of craters and temperature fields. Experimental validation of the numerical model uses a nanosecond Minimarker 2 laser to texture the surface of AISI 321 stainless steel. Optical microscopy with a ZEISS AXIO digital microscope is employed to analyze the resulting microstructures. The experimental findings align closely with the numerical predictions, demonstrating that laser-induced periodic microstructures exhibit consistent geometry and high reproducibility. The study also highlights the impact of scan line spacing on the clarity and uniformity of the microstructures. The KEYENCE VHX 7100 digital microscope performs a detailed surface roughness analysis. The roughness profile reveals a periodic, nearly Gaussian distribution, with minor asymmetries attributed to local thermal effects and material reorganization. The results confirm that the developed numerical model accurately describes the heating, phase transitions, and ablation processes in AISI 321 stainless steel under nanosecond laser pulses. The combination of numerical modeling and experimental verification provides a reliable framework for optimizing laser processing parameters to achieve controlled microstructure formation, which is crucial for advancing surface engineering technologies in high-performance industrial applications.