Experimental Determination of Impurity and Interdiffusion Coefficients in Seven Ti and Zr Binary Systems Using Diffusion
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THE number of hip and knee arthroplasties in the United States has surged over the past decade and is projected to increase to 3.5 million procedures a year by 2030.[1] The rising demand signifies the importance of structural biomaterials in clinical applications, especially for bone replacement and fastening surgeries. In recent years, Ti alloys have been widely used as implants due to their low elastic moduli, outstanding biocompatibility, and good corrosion resistance in comparison with stainless steels and Cobalt-based alloys.[2–4] Ti alloys exhibit a phase transformation between the low temperature a (hcp) phase and the high temperature b (bcc) phase. Compared to a and a + b type Ti alloys, b type Ti alloys are more attractive for biomedical implant applications due to their lower elastic moduli.[4] With additional advantages like high strengthening effect and non-toxicity, alloying elements Mo, Nb, Ta, and Zr have been frequently added in recent years.[5–7] The b type Ti alloys with additions of these elements can
ZHANGQI CHEN and JI-CHENG ZHAO are with the Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210. Contact e-mail: [email protected] ZI-KUI LIU is with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. Manuscript submitted December 5, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
achieve low elastic modulus such as Ti-24Nb-4Zr-7.9Sn (33 GPa[7]) and Ti-35Nb-Ta-Zr (61 GPa[8]), which is getting close to match that of bones (~ 10 to 30 GPa). The elastic modulus mismatch between the bio-implants and bones often leads to ‘‘stress shielding’’ which is one of the key mechanisms of implant failure.[9] It is thus highly desirable to engineer the elastic modulus of biocompatible Ti alloys to match that of bones. This study is part of a project funded by the DMREF (Designing Materials to Revolutionize and Engineer our Future) program of the U.S. National Science Foundation to establish a knowledge base of thermodynamics, kinetics, and elastic properties of the Ti-Mo-Nb-Ta-Zr system for the accelerated development of Ti alloys for biomedical implant applications.[10–12] Diffusion multiples integrate several diffusion couples and diffusion triples into high-throughput samples.[13–15] High temperature diffusion annealing creates wide composition ranges for the associated binary and ternary systems from which composition-dependent material properties can be obtained.[16–20] In this study, three Ti-Mo-Nb-Ta-Zr diffusion multiples were made and heat treated at 800 C, 1000 C, and 1200 C from which large amounts of phase equilibria, kinetics, and composition-dependent property information will be obtained. This article reports the impurity and interdiffusion coefficients of seven Ti- and Zr-containing binary systems. It is noted that even though our study is intended for the biomedical Ti alloy development. The diffusion coefficients of the Ti-Mo-Nb-Ta-Zr system are also valuable parameters for the design of structural T
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