The Interaction Between Metallic Glass And Nano-second Pulsed Laser: Mechanisms And Processing

Due to the long-range disorder structures,metallic glass(MG)has many unique properties,such as high strength,high hardness,large elastic-strain limit,wear resistance and corrosion resistance and excellent soft magnetic properties of the Fe-based MGs.Being a rapidly developing new materials,MG is applied on the aerospace,military defense,bio-medicines,electronics,sports and jewelries fields.On the other hand,laser is an advanced technology widely used in many fields,including medicals,automotive,aerospace and scientific research.In the past decades,laser technology has been widely applied in oxide glass,ceramics,titanium and aluminum alloy,stainless steel and other materials.And there are also many laser applications in MGs,including laser welding,laser coating,laser cladding,laser surface treatment and laser additive manufacturing.However,there is few studies on the interaction between MG and laser,it is urgent to study systematically the interdisciplinary between glassy physics and laser physics.Therefore,it is important to clarify the interaction mechanism between MG and laser for both application and theory.In this thesis,the interaction between laser and MG was studied,and new ways for laser processing on MGs were developed.As an important laser mode,pulsed laser is suitable for the laser processing of MG,because its pulsed duration is so short that crystallization can be avoided.The first part of this thesis reports nanosecond(ns)pulsed laser welding in MG ribbons and the mechanism.After laser welding,complex3D structures are formed,including bracelets and Mobius rings.By optimizing the focus distance and laser power factor,the fracture strength of welded joint between MG ribbons can reach 70%-90%of the as-spun MG ribbon.A processing phase diagram is constructed to help understand the mechanism of interaction between MGs and laser,and the mechanism for laser processing on crystallization and vitrification of MGs.Via analyzing welded MG ribbons of different thicknesses,an optimal volume density parameter of the laser power(10⁴-10⁵ W mm^–3)was found.The second part of this thesis focus on the self-forming via self-buckling in Fe₇₈Si₉B₁₃ MG ribbon under ns-pulsed laser processing.The function structures of Mimosa-like or windmill-like structures are realized on MG by laser-induced self-buckling,enabling shape changes under external force or field.The curvature of the buckling can be controlled by the laser processing parameters.The magnetic domain distribution of the Fe-based MG ribbons around the laser lines are observed by the magneto-optical Kerr microscope,the results indicate the existence of periodic tensile and compressive stresses perpendicular or parallel to the laser lines.The phenomenon of laser-induced self-buckling can be explained by the principle of energy minimization.In the third part of this thesis,the surface of Zr-based MG is colorized by ns-pulsed laser processing.The color is induced by surface plasmon resonance mechanism,which is due to the formation of nano-porous microstructure on the surface of MG thin-film.By tuning the focus distance,scanning times,laser-line spacing,power factor,repetition frequency,scanning speed,the colors can be controlled.The microstructure,reflectivity,reflectance spectrum,structural stability,corrosion resistance and hydrophobicity of the laser-colorized MG were also systematically characterized.The experimental results show that the surface plasmonic color produced by laser treatment of MG is a brilliantly mixed color.This structural color has many advantages of high resolution,good stability,corrosion resistance,oxidation resistance,good hydrophobicity,large coloring area,no pollution,no angle dependence,fast processing speed and low cost.Compared with the ns-pulsed laser oxidation color of the crystalline alloy,the plasmonic structure color of the MG has more kinds of color,higher stability,higher resolution and stronger controllability.The research of this thesis provides a theoretical guidance for the laser processing of metallic glass.