Deformation Behavior Of Metallic-glass Wires And Enhancement Of Plasticity By Electrochemical Deposition

Metallic glass wires usually experience catastrophic fracture without plastic deformation.The fracture mechanism of metallic glass wires are governed by the initiation and propagation of shear bands.The catastrophic fracture of high brittle nature MG wires without any warning indicates that MG fibers are less reliable.Therefore,understanding of relationship between metallic glass wire's deformation and shear bands is vital to engineering applications.Tensile deformation behavior,strength reliability,and enhancement of plasticity of metallic glass wires by electrodeposition of Cu,Ni and Cu/Ni bilayer onto Cu₅₀Zr₅₀,Ni₅₆Nb₄₄ and Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass wires were studied at room temperature.The amorphous structure of metallic glass wires were tested via X-ray diffractometer?XRD?and differential scanning calorimetery?DSC?.Fracture surface morphology was determined by SEM.Typical vein-like pattern and round core can be observed on the fracture surface of metallic glass wires.The second approach which was applied in this study was the extrusion process also known as cold-drawing to homogenize the surface quality of as-cast metallic glass wires.The third approach was to electrodeposits soft ductile metal?Cu?and hard metal?Ni?onto the surface of metallic glass wires to enhance their plasticity.Cu layer was electrodeposited on the surface of Pd₄₀Cu₃₀Ni₁₀P₂₀ by using electrochemical deposition techniques.The 4th approach was the electrochemical deposition of Cu/Ni bilayer onto Ni₅₆Nb₆₆ metallic glass wires via electrochemical deposition technique and test of their plasticity,which are very important to understand elastic and plastic deformation behavior of metallic glass wires.Metallic glass wires have fascinated much research attention due to their excellent mechanical properties.Understanding of their atomic structure and mechanical properties especially at micron and sub-micron sizes at room temperature is still challengeable,poor deformability at room temperature hinders their commerce,and engineering applications.Many research group have developed many approaches to enhance the plasticity of metallic glass wires,such as foreword of crystalline phases,the attainment of a high value of possion,s ratio and metal and metal alloys electrochemical deposition onto the surface of metallic glass wires.Most of the researchers focused on enhancement of compressive plasticity of metallic glasses by Cu,Ni and Cu/Ni bilayer electroplating at the size of 1mm and above.On the other hand the effect of metals and metal alloys electrodeposition and a tensile investigation on the fundamental mechanism for the improvement of tensile plasticity have yet to be undertaken.In the current research work the effect of Cu,Ni and Cu/Ni-bilayer electrodeposition onto the surface of small size metallic glass wires with precisely control volume fractions of metals coating were further analyzed.Our experimental results exposed that as-cast Cu₅₀Zr₅₀,Ni₅₆Nb₄₄ and Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass wires fractured catastrophically without plastic deformation;however Cu,Ni and Cu/Ni bilayer electrodeposition onto the surface of metallic glass wires have a significant effect on the enhancement in tensile plasticity of coated metallic glass wires.However a Thick Cu,Ni and Cu/Ni-electrodeposited bilayer has exhibited significant enhancement in plasticity as compared to un-electrodeposited metallic glass wires,demonstrating that the Cu,Ni and Cu/Ni bilayer-electrodeposition is an effectual way for enhancement of plasticity in metallic glass wires.In the present work,Cu,Ni and Cu/Ni bilayer electrodeposition with precisely control volume fractions of metals coating was applied onto the above mentioned metallic glass wires.In the Cu/Ni bilayer electrodeposition,the inner soft Cu-layer act as a good crack barrier zone to captivate the elastic deformation energy released by metallic glass wires during tension test,while the outer Ni-layer assisted in intensification the statistical imprisonment.Thick bilayer Cu/Ni-electrodeposited Ni₅₆Nb₄₄ metallic glass wires with higher R values,R=65%to R=95%,were observed to exhibit remarkable improvement in tensile plasticity?5.8%for R=95%Cu/Ni bilayer-coating?at room temperature at the constant strain rat of 1x10^-4 s^-1.The finding of this work shows the way to improved perceptive and also put down an excellent underpinning for further optimizing this unique technique for tensile plasticity enhancement of metallic glass wires.Cu,Ni and Cu/Ni bilayer electrochemical deposition successfully block the rapid propagation of primary shear bands and promote the initiation of secondary shear bands.This can caused improvement in plasticity of metallic glass wires.The major finding of this work gives a new perspective of enhancement in tensile plasticity of metallic glass wires by electrochemical deposition.However it is necessary to improve procedures and parameter to gets better electrochemical deposition results.The reliability of the mechanical characteristics is needed to be characterized,which is very important for the potential application of metallic glass wires in the field of structural materials.Till now the deformation behavior especially tensile fracture strength,tensile stress,young modulus,yielding behavior and plastic deformation of Cu₅₀Zr₅₀ and Ni₅₆Nb₄₄ and Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass wires have not been sufficiently investigated.In the present study the yielding behavior,fracture strength reliability and improvement in tensile plasticity of metallic glass wires by electrochemical deposition of metals is analyzed.The objective is to provide a fundamental basis for the evaluation of service reliability of metallic glass wires.