Research On The Formation Mechanism And Characteristics Of Micro/Nano-Structures On Zr-Based Metallic Glass Surface Induced By Nanosecond Laser

Due to their unique long-range disordered atomic structure,metallic glasses(MGs)exhibit excellent mechanical,physical and chemical properties,which makes them promising candidates for a wide range of applications in high-tech fields such as aerospace technology,micro/nano-optics,biomedicine,as well as high value-added products such as intelligent electronic products and sports equipment.Based on preserving the essential characteristics of MGs,the construction of surface micro/nano-structures can endow them some novel surface properties.Nanosecond laser micro/nano-processing is an effective approach for preparing micro/nano-structures on the surface of materials.In view of the problems of unclear understanding of the interaction process and mechanism between nanosecond laser and MG,few types of prepared micro/nano-structures,and difficulty in fabrication of regularly ordered micro/nano-structures,this paper systematically investigated the evolution of surface micro/nano-structures of a typical Zr-based MG(Vitreloy 1)when subjected to nanosecond laser irradiation,and discovered some new phenomena such as transformation between microconcave and micro-convex on the MG surface induced by nanosecond laser irradiation,and accordingly,the processes and physical mechanisms of these new phenomena were investigated and elucidated.Further,a method for the creation of micro/nano-structures on the MG surface based on nanosecond laser spot and line irradiation has been developed,and the manipulation of surface wettability,optical and mechanical properties was achieved.The main contents of this paper are listed as follows:(1)The evolution of micro/nano-structure on the Zr-based MG surface induced by singlespot multi-pulse nanosecond laser irradiation was studied.Through single-variable experiment,the influence of laser irradiation parameters on the surface morphology of MG was explored,and a new phenomenon of transformation between micro-concave and micro-convex on the MG surface induced by nanosecond laser spot irradiation was found.Further,the dependence of micro-concave and micro-convex on the peak laser power intensity,number of laser pulses,laser repetition frequency and other parameters was established through experiments.(2)The physical process and mechanism of concave-convex transformation on the MG surface induced by nanosecond laser were investigated.Through the contrast experiment of laser irradiation in different gas atmospheres and on samples with different crystallinity,the relationship between the concave-convex transformation and the environmental atmosphere,as well as the sample crystallinity was revealed.The temporal evolution of surface temperature of MG during laser irradiation has been investigated via the finite element method.Through high temperature wettability tests,the wettability behavior of MG melts at high temperatures was obtained,and the evolution of surface tension of MG melts with the temperature was analyzed.Based on the above research results and the evolution of surface micro/nanostructures with the laser irradiation parameters,the physical process and mechanism of concave-convex transformation on the MG surface induced by nanosecond laser spot irradiation has been elucidated by integrating the recoil pressure and the Marangoni effect.(3)A method for the construction of micro/nano-structures on the MG surface based on nanosecond laser irradiation has been developed,and the manipulation of surface wettability,optical and mechanical properties was achieved.Taking the single-point micro-convex as the basic unit,the flexible creation of micro/nano-structures(including micro-convex array structure,the English abbreviation "JLU" pattern of Jilin University,etc.)on the MG surface was achieved through patterned design and laser path control.The construction of the microconvex array structure not only changed the diffraction characteristics of the MG surfaces,but also resulted in a significant reduction in their reflectance.The results of wettability tests showed that the introduction of micro-convex array structure enhanced the hydrophilicity of the MG surface,and the surface superhydrophobicity could be achieved after modification with fluoroalkylsilane,with the contact angle up to 155.1°.The surface morphology,chemical composition,and mechanical properties of micro-convexes obtained under different gas atmospheres(high-purity argon,high-purity nitrogen,air)were compared and analyzed,and the influence of the gas atmosphere on the microscopic properties of micro-convex was elucidated.(4)The formation and evolution of micro/nano-structures on the MG surface induced by nanosecond laser line irradiation were investigated.The effects of laser irradiation parameters on the surface morphology of MG have been studied,and the experimental results indicated that under some specific laser irradiation parameters,highly homogeneous laser-induced periodic surface structure(LIPSS)could be formed on the MG surface,and meanwhile,the transformation of LIPSS and periodic nano-dot structure could be achieved by adjusting the laser irradiation parameters.Combined with phase analysis and the influence of sample crystallinity and surface pretreatment state on the formation and evolution of LIPSS,the formation process and physical mechanism of LIPSS were explained.A novel method for the construction of micro-nano composite structure on the MG surface by two-step nanosecond laser irradiation was proposed by fusing micron-scale micro-convex structure and nano-scale LIPSS patterns.In summary,this paper systematically investigated the interaction processes and mechanisms between nanosecond laser and Zr-based MG through nanosecond laser spot and line irradiation,and found two new phenomena,namely the concave-convex transformation on the Zr-based MG surface induced by nanosecond laser spot irradiation and the formation of highly homogeneous LIPSS induced by nanosecond laser line irradiation.Accordingly,the underlying physical mechanisms of these two phenomena were explained.On this basis,the construction method of micro/nano-structures on the MG surface based on the nanosecond laser spot and line irradiation has been developed,and the manipulation of surface wettability,optical properties and mechanical properties was achieved.The above results would not only enhance the knowledge and understanding of the interaction process and mechanism between nanosecond laser and MG,but also provided new ideas for the creation and functional applications of micro/nano-structures on the surface of MG materials.