Ablation of materials subjected to laser radiation and high-speed gas flows

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Abstract
This paper presents results of investigations of the steady‐state ablation that takes place when materials are irradiated by high‐intensity laser radiation in high‐speed gas flows. Materials investigated were stainless steels 304 and 310, carbon steel 1020, titanium 6Al‐4V alloy, commercially pure titanium, and a glass fiber reinforced polyester. Four gases were used: air, a mixture of 40% oxygen and 60% nitrogen, argon, and nitrogen. Target samples were subjected to continuous‐wave irradiation by a carbon‐dioxide laser, and to tangential subsonic gas flows at a static pressure of 1 atm. The quantities measured included the ablation rates and surface temperatures. Analysis of the data for the metals yields values for the surface absorptances at 10.6 μm and values for the net contribution to the heat input provided by combustion and cooling. Information is also provided on the mechanism of melt removal and on the surface oxidation processes. For the nonmetal, the enthalpy required for ablation was obtained. These results, which are applicable to the upstream regions of irradiated areas, may be used to predict ablation characteristics for the gas‐assisted laser cutting of plates, and the production of large holes in plates.