Research On The Energy Coupling Characteristic Of 45# Steel To Laser

The energy coupling coefficient is of great importance in the research of the laser-matter interaction.The energy coupling coefficient of 45#steel increased remarkably and fluctuated periodically with the increase of temperature.The interference effect is considered as the main reason of the periodic fluctuation of energy coupling coefficient The paper will further study the energy coupling characteristics of45#steel to the laser by the combination of experiment,theory and numerical simulation to reveal the energy coupling coefficient changes in the physical mechanism The main work and achievements are as follows:?1?Based on the Fresnel formula and Drude theory of ideal metal,the change law of absorptivity with temperature of ideal metallic material was analyzed and the main reason of energy coupling coefficient changing with temperature was introduced.The stratified oxidation mechanism was analyzed from kinetic viewpoint.The physical model of the oxide layer thickness growth on the surface of 45#steel was established.The influence of the oxide film on the energy coupling coefficient was analyzed based on the beam interference effect caused by the oxide film.?2?The change characteristic of energy coupling coefficient of 45#steel sample during heating was researched.The energy coupling coefficient measurement system based on the integrating sphere method set up previously was improved to eliminate the influence of the thermal radiation caused by the temperature rise of the integrating sphere for laser power monitoring.The change characteristic of energy coupling coefficient at 915nm and 532nm of the 45#steel sample under electronic heating was measured.The thickness and composition of the oxide layer on the surface of the heated sample were measured with the use of scanning electron microscope and energy dispersive spectrometer.The results showed that the interference effect and absorption effect of the oxide film on the laser led to the significant decrease of the reflectivity and the periodic fluctuations with the increase of the temperature.The change amplitude and change period were larger with longer laser wavelength.More maximal and minimal appeared on the reflectivity curves with faster heating rate and higher temperature.Within the temperature range investigated in the paper?the highest temperature of back surface of the sample was 605??,the temperature had great influence on the increase of oxide layer thickness.The oxide layer thickness would grow faster in higher temperature.When the thickness of oxide layer increased to a certain extent,the growth rate would slow down obviously and the thickness of the oxide layer tended to be stable,which agreed with the tendency of the reflectivity changing with time.?3?Based on the established growth model of 45#steel surface oxide thickness and the multi-beam interference model of the oxide film,combined with the measurement results of the oxide film thickness by scanning electron microscopy,the influence of the surface oxide layer structure of 45#steel sample to energy coupling coefficient was researched.The numerical simulation results show that the Fe₂O₃ oxide film mainly induces the periodic fluctuation of the reflectivity curve.The Fe₃O₄ oxide film has the interference effect and the absorption effect on the 915nm laser beam simultaneously,and the absorption effect is obviously stronger than that of the Fe₂O₃ oxide film.For the oxide film with the structure of Fe₂O₃-Fe₃O₄-FeO,only Fe₂O₃-Fe₃O₄ oxide film has an effect on the reflectivity of the 915nm laser when the thickness of the oxide film of Fe₃O₄ reaches 500nm.The oxide thickness growth model established on the surface of the pure iron can rightly describe the change of 45#steel Oxide film thickness with heating time.