Influence of the melt thermal conductivity on temperature fields in aluminum oxide upon heating by concentrated laser radiation

Abstract

The influence of the melt thermal conductivity Λ_m on the formation of temperature fields upon heating and melting of a plane aluminum oxide layer by CO₂ laser radiation with a flux density q from 200 to 3000 W/cm² is investigated using a rigorous model of transient combined radiative and conductive energy transfer. The maximum heating time is 100 s. Parameter Λ_m varies from 1.5 to 3 W/(m K). Absorption coefficient k_l for the laser radiation is assumed to be 1000 cm^–1. The formation of a two-phase region,which exists for a short time, has been observed in the initial melting stage at a depth less than the penetration depth of the heating laser radiation. Maxima of the heated-surface temperature and melt thickness (not coinciding in time) are found at q < 600 W/cm². The melt thickness and its value at the maximum depend only slightly on q, while parameter Λ_m significantly affects the melt thickness at the maximum and during the entire heating process. It is shown that similar temperature profiles are established in the solid phase at different Λ_m values while approaching the quasi-steady state due to large values of the melt absorption coefficient in the wavelength range that is most energetically important for radiative transfer. The melt thermal conductivity affects only slightly the temperature of the “cold” surface that is opposite the melt.