Study On Experiment And Mechanism Of Laser Surface Texture Underwater

Surface morphology has a significant effect on the surface properties of the materials.Therefore,surface texture technology emerged.Laser surface machining is an important surface texture technology.In the past,most researchers studied laser surface texture technology in the air.When laser-matter interaction occurs in the liquid environment,the liquid confinement,liquid cooling,and laser-induced cavitation processes will exert an important influence on the process and effect of laser-matter interaction.At present,there are few related researches.In the present study,the texture experiment on 304 stainless steel surface was carried out by nanosecond pulse laser in water environment.The influence of parameters and formation mechanism on the surface morphology of 304 stainless steel were studied systematically.The main research contents and conclusions are as follows:(1)The experiment of nanosecond laser surface texture underwater was carried out.The microhole structure with transverse dimension less than 2 ?m was obtained on the surface.The main results were as follows.The transverse dimension of microhole increased by increasing the pulse width.With the reduction of scanning speed,the number of microholes in the surface increased.The decrease of scanning speed and the increase of laser fluence resulted in deepening microholes.The surface structure became smoother with the increase of laser fluence.With the increase of scanning times,the number and depth of microholes increased.When the ultra-thin metal foil was used as the target material,the through-hole structure with large area distribution can be successfully prepared by the method of underwater surface texture.(2)The formation mechanism of surface texture morphology underwater was studied by EDS analysis,metallographic analysis and high-speed camera monitoring.The conclusions were as follows.Bubbles were induced by rised surface temperature due to the laser action on the material surface.Water jet produced when bubble collapsed.Then,water jet had an impact on target surface removal material,which was the direct reason of microhole formation.The increase of pulse width led to the increase of the diameter of the bubble,which resulted in the increase of microhole size.With the decrease of scanning speed,the distribution density of the bubble increased gradually,which resulted in increasing the number of microholes.Increasing laser fluence could increase the number of bubbles.The increase of scanning times could increase the number of bubbles in the fixed area and finally achieve the preparation of large area group microholes texture.Sufficient number of bubbles were essential for the generation of group microholes.The number of microholes on the surface existed saturation state.When the number of microholes reached the saturation state,the increase of the number of bubbles didn't continue to increase the number of microholes.However,the depth of microholes increased because of multiple erosion of water jet.The diameter of the bubble was an important influencing factor on the surface morphology in saturated state.(3)The influence of surface microstructure on the erosion process of water jet was investigated through experiments.The results were presented as follows.The surface microstructure would cause the tendency movement in the process of bubble pulsation.When the microstructure existed in the maximum diameter range of the bubble oscillation process,it would induce the surface position of the water jet erosion.By utilizing this characteristic,it is promising to realize the inducted localized machining of water jet.