Research On The Femtosecond Laser Fabrication Technology Of Surface Functional Micro Structures On Alloys

Owing to the excellent physical and chemical properties,alloys have been widely employed in the industrial fields,for instance,aeronautic s and astronautics,mechanical manufacturing,instruments and apparatus,etc.Except for the macroscopic outline structure,surface functional micro structures are also discovered to have significant impact on the working performance of components.Electro discharge machining ? ion beam machining and long/short pulse laser machining are commomly employed to fabricate these micro structures.However,nonnegligible problems exist during their application.While femtosecond laser has become an important tool for mircomachining in recent decades.Comparing with other fabrication technologies,femtosecond laser is charaterized by the ultrashort pulse duration and ultrahigh peak power density,which endows it with the capacity of high machining precision,excellent machining quality,high level of machining controllability and universality in machining materials.This work focuses on the research of femtosecond laser fabrication technology of typical surface functional micro structures on alloys,namely surface micro-nano composite structure(SMNCS),surface micro texture(SMT)and micro hole.First,the dynamic energy coupling model describing the interaction between femtosecond laser and alloy is established referring to the classical Drude free electron gas theory and other theoretical bases.An approximate treatment method is proposed to deal with the initial thermodynamic parameters of alloy.The evolutions of transient surface optical and thermodynamic properties as well as ablation profile of K24 superalloy(K24)? GCr15 bearing steel(GCr15)and YT15 cemented carbide(YT15)are investigated.To validate the accuracy of established model,femtosecond laser single-point multi pulses ablation and scribing experiments are carried out.Secondly,the formation mechanism of micro-sized stripes on metal surface irradiated by femtosecond laser is explored.Femtosecond laser processing system is built and the alloy's response characteristic to multi laser pulses is analyzed.The evolution mechanism of SMNCS morphology is investigated through numerical simulation and ablation experiments.Referring to the surface wetting theory,the influence of variation of femtosecond laser intensities on the SMNCS morphology and its wetting property is further studied.Thirdly,the femtosecond laser fabrication technologies of SMT on alloy with different morphologies are digged through processing experiments.Unidirectional rotating friction tests are carried out on GCr15 with SMT arrays.Referring to the established flow field model for friction pair and surface oleophilic analysis,the influence of SMT morphology on the friction property of GCr15 surface is analyzed.Cylindrical turning experiments are also conducted using YT15 cutting tool with micro groove arrays on the rake face.Considering the established orthogonal cutting model and surface hydrophilic anaylysis,the impact of micro groove morphology on the cutting property of YT15 cutting tool is then analyzed.Besides,the alternation of micro hole morphologies on the surface of K24 using different laser scanning modes is analyzed.The appropriate scanning modes for micro holes with different diameters and depth-to-diameter ratios are discovered.On the basis of Fokker-Planck equation and other theoretical bases,the evolution model of free electron density within water irradiated by single femtosecond laser pulse is put forward.The influence of position of laser focal plane on femtosecond laser drilling ability underwater is compared and analyzed through numerical simulations and ablation experiments.Single-factor optimized experiments as well as orthogonal experiments are proceeded to investigate the influencing mechanism of femtosecond laser processing parameters on micro hole morphology.The fabrication of micro holes in high quality and efficiency is realized after the optimization of processing parameters.The microscopic morphology of the inner wall of micro hole is analyzed,and the influence of which on its potential application is also explored.