Diffusion Bonding of Ti-6Al-4V Sheet with Ti-6Al-4V Foam for Biomedical Implant Applications
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RODUCTION
HUNDREDS of thousands of biomedical devices are implanted into patients each year and, with an increasingly active population, patients are receiving orthopedic implants at younger ages. Implant osseointegration (the ability of the implant to form a lasting bond with the body cells and tissues) must be improved to avoid implant loosening and subsequent removal, especially for uncemented implants.[1] Currently, there are many areas of research focusing on improving osseointegration in biomedical implant devices. Common techniques include mechanical surface treatments, chemical surface treatments, physical deposition of material onto the surface, and the attachment of porous coatings by a variety of processes.[1–5] Recently, a new technique was developed to create Ti-6Al-4V foams[6] by entrapping argon gas during the high-pressure densification of a powder preform, and subsequently expanding the gas within the solid, creeping Ti-6Al-4V in vacuum.[6–10] This method allows for tailored porosity and pore size. These titanium alloy foams can be used in the aerospace industry as lightweight structural panels consisting of a porous core with two fully BRITTANY HAMILTON, Research Assistant, and DANIEL LEWIS, Associate Professor, are with the Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180. Contact e-mail: [email protected] SCOTT OPPENHEIMER, formerly Research Assistant with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL, is now Materials Scientist with the General Electric Corporation, Niskayuna, NY. DAVID C. DUNAND, James N. and Margie M. Krebs Professor of Materials Science and Engineering, is with the Department of Materials Science and Engineering Northwestern University. This paper is based on a thesis submitted by B. Hamilton to the Graduate Office of Rensselaer Polytechnic Institute in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering. Manuscript submitted August 2, 2012. Article published online October 8, 2013. 1554—VOLUME 44B, DECEMBER 2013
dense face sheets. Ti-6Al-4V has become the preferred metallic material for orthopedic devices due to its high strength, low density, and biocompatibility.[11,12] For biomedical applications, Ti-6Al-4V foams further provide a reduction in stiffness important to reduce stress shielding, and an open porosity allowing for osseointegration. The aim of this study is to demonstrate that direct bonding of a Ti-6Al-4V foam (produced in a prior step in a controlled manner) onto bulk Ti-6Al-4V is an alternative to existing implant surface treatments.[13–16] A series of specimens with embedded metallic foam were fabricated by diffusion bonding in a thermo-mechanical simulator. Mechanical testing and microscopy characterization were performed to determine bond quality. The structural integrity and fracture surfaces of the metallic foam were also evaluated.
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EXPERIMENTAL
A. Materials The materials used in this diffusion bonding s
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