Microstructure and mechanical properties of electron beam weld joints of a Zr 41 Ti 14 Cu 12 Ni 10 Be 23 bulk metallic g
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S. Bysakh Defense Metallurgical Research Laboratory, Hyderabad 500058, India
Y. Kawamura and M. Yamasaki Department of Materials Science and Engineering, Shock Wave and Condensed Matter Research Center, Kumamoto University, Kumamoto 860-8555, Japan
U. Ramamurty and K. Chattopadhyaya) Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India (Received 14 September 2006; accepted 10 October 2006)
The electron beam welding technique was used to join Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) to crystalline pure Zr. Compositional, microstructural, and mechanical property variations across the welded interface were evaluated. It is shown that a crystalline layer develops close to the welding interface. Transmission electron microscopy of this layer indicates the crystalline phase to be tetragonal with lattice parameters close to that reported for Zr2Ni. However, the composition of this phase is different as it contains other alloying additions. The interface layer close to the bulk metallic glass side contains nanocrystalline Zr2Cu phase embedded in the glassy matrix. Nanoindentation experiments indicate that the hardness of the crystalline layer, although less than the bulk metallic glass, is more than the Zr itself. Commensurately, tensile tests indicate that the failure of the welded samples occurs at the Zr side rather than at the weld joint.
I. INTRODUCTION
Bulk metallic glasses (BMGs) are candidate materials in many structural applications because of their attractive mechanical properties such as high strength and stiffness. Further, they possess good workability and formability above the glass transition temperature, Tg.1 However, components made of BMGs must be joined with other metallic structural components in many structural application scenarios. Welding is by far the most popular joining technique in industrial practice. Kawamura and coworkers2–4 have demonstrated the success of several welding processes, namely, friction, spark, pulse current, and electron beam welding (EBW) in joining BMGs with other crystalline metallic materials. Other techniques such as the use of Ni/Al multilayer foils capable of producing a self-propagating exothermic reaction have also been used for welding of amorphous alloys with other metals.5 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0046 J. Mater. Res., Vol. 22, No. 2, Feb 2007
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One of the BMGs that has a good potential for structural engineering applications is Zr41Ti14Cu12Ni10Be23 (Vit1).1 This BMG exhibits an excellent glass forming ability (GFA) and can be processed for various sizes and shapes by simple casting processes at low cooling rates. However, available sample thickness and size continue to be limiting parameters for structural applications. Therefore, joining with other structural elements is an alternate possibility for overcoming these limitations. The scientific issues associated with welding of the
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