LASER PROCESSING OF MULTILAYER COATINGS ON METAL

10.25712/ASTU.1811-1416.2026.02.013

Abstract

The constructed model of laser processing of metals with picosecond pulses makes it possible to determine the dependence of temperature and pressure in the irradiated layer on the pulse energy, light frequency, beam diameter and heat capacity of the metal. Simple dependence of temperature and pressure on these parameters in adiabatic isochoric process of layer heating is obtained, which follows from equality of real and imaginary parts of refraction index for metals. The calculated dependencies of the processing capacity and ablation parameters on the process parameters are consistent with the known experimental data. The pressure in the layer is proportional to the temperature and volumetric heat capacity with a proportionality coefficient equal to the Gruneisen co-coefficient and amounts to tens of GPa at a temperature of about 10,000 K. This dependence follows from the consideration of the adiabatic isochoric process of heating the layer, since other processes (expansion, heat dissipation, evaporation, ablation), except for heating the layer, do not have time to develop picosecond pulse. The pulse energy is mainly spent on heating the ion lattice and increasing elastic energy due to the interaction of phonons with heated electrons, since the electron energy relaxation time of the order of 10^-14 s is significantly less than the pulse duration of 10^-12 s, and the heat capacity of the electron gas is significantly less than the heat capacity of the crystal lattice. If the heating temperature (less than 9000 K) does not exceed the critical phase transition to the gas (fluid) phase, then for a time of about 10^-10 s after the end of the pulse due to the internal tensile pressure, solid or liquid microparticles are torn off by the elastic spring mechanism. If the temperature exceeds the critical one, then the destruction of the layer occurs by splashing a jet of partially ionized gas (plasma) with a degree of ionization of several percent, observed in the form of a glow. If the treatment is in air, then the glow is possible due to the combustion of microparticles. Performance increases with increasing pulse energy, beam diameter and decreasing heat capacity and is independent of pulse duration. Copper is processed faster than iron. Light frequency has little effect on performance within the limits considered.