Research On Forming Mechanism And Properties Of Micro-scale Controllable Surface Morphology By Laser Shock Processing

Laser shock processing is an emerging technique which uses high-pressure plasma shock wave induced by laser pulse to realize material strengthening and forming.It has some advantages such as target with ultra-high strain rate,suitable for the manufacturing of micro-parts,large processing flexibility,and high efficiency.Currently,the preparation of controllable surface morphologies with high-performance is a research focus,and the controllable surface morphologies of metals at a micron scale has been widely used in the fields of MEMS,micro sensors,micro actuators,printed circuit boards,micro reactors,and hot padding dies.In this work,from the research purpose,this technique would be improved and perfected properly,so as to complete the forming of profile-free copper foil with high-performance,3D metal micro-structure with high-temperature stability,and thermally controllable surface morphology.Furthermore,through the experiment and numerical simulation,the effects of various processing parameters on the forming quality of metal foil were studied;the micro forming process of micro-structures and the comprehensive properties of controllable surface morphologies were discussed;and the corresponding plastic deformation mechanism,strengthening mechanism,phase transformation process,and various stability mechanisms were revealed.Firstly,the theory of laser shock processing was systematically discussed,including the processing principle,the adjustment of process parameter,the interaction between laser and material,the strain rate effect,and the deformation mechanism of metal material,which laid a perfect theoretical foundation for the subsequent simulation analysis and experimental research.Then,the experimental bedstands of laser shock processing with high-pulse energy and low-pulse energy were built,respectively.Meanwhile,for the theoretical model of laser shock processing,a numerical simulation method suitable for this model was proposed,and the simulation model was established by ABAQUS.In addition,varieties of performance characterization methods and measurement equipments were selected.Secondly,the laser shock flattening(LSF)was proposed to manufacture the profile-free copper foil with high-performance.The results showed that the copper foil had the better flattening effect at the power density of 3.1 GW/cm~2 and the overlap rate of 25%.At this time,its surface roughness(Sa)decreased by 67.0%from52.1 nm to 17.2 nm.Subsequently,the residual internal stress of flattened copper foil was analyzed by ABAQUS,the microstructures and micro-defects of copper foil before and after flattening were observed using transmission electron microscopy,and the flattened mechanism and deformation mechanism were revealed.Furthermore,the test results showed that the LSF technique had a good strengthening effect on annealed copper foil;therefore,the corresponding strengthening mechanism of LSF was discussed.Then,the temperature-assisted laser shock imprinting(TALSI)was used to obtain large-area 3D micro-structures on metal surface,which improved the forming quality and high-temperature stability of micro-structures successfully.By measuring the forming height,surface roughness,and surface oxidation degree of micro-structures at different conditions,and monitoring their load–displacement curves,the effects of imprinting times and stress annealing on warm laser shock imprinting(WLSI)were explored.Meanwhile,the distribution of residual stress and transient deformation process induced by WLSI were simulated by ABAQUS,the micro forming process of WLSI was analyzed,and the influence of imprinting temperature on the forming effect and comprehensive properties was revealed.Subsequently,the high-temperature recovery experiments were carried out at different temperatures to study the high-temperature stability of micro-structures.The results showed that compared with the LSI at room temperature,the WLSI could effectively improve the high-temperature stability of the plastic deformation and mechanical properties of micro-structures.Finally,the laser shock imprinting(LSI)was used to induce the two-way shape memory effect(TWSME)of shape memory alloy(SMA)at the micron scale;meanwhile,the precision forming of NiTi SMA Plate was achieved.By monitoring the strain recovery of the formed part as well as bending workpiece during the thermal cycle and the theoretical calculations of the LSI induced TWSME,the mechanism of TWSME of NiTi SMA induced by LSI was discussed.Moreover,the effects of LSI on the phase transition temperatures,phase transition process,and mechanical properties of formed parts were studied,and the thermal cycle stability test was carried out to reveal the strengthening mechanism of the LSI technique and the stability mechanism of the TWSME of formed parts.There are 92 figures,14 tables,and 152 references in this paper.