Microstructure, Mechanical Properties, and Electrochemical Behavior of Ti-Nb-Fe Alloys Applied as Biomaterials
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A major issue in the development of devices applied in load-bearing orthopedic functions is the need for materials that merge high mechanical strength, high biocompatibility, high corrosion resistance, and especially low elastic modulus.[1] Low elastic modulus materials are required to avoid the phenomenon known as bone stress-shielding, which is caused by a mismatch between the rigidity of the implant material and that of implanted bone.[2] It is well known that the bone architecture adjusts according to the load applied,[3] and bone stress-shielding can therefore cause bone loss and, occasionally, bone fracture.[4] Metastable b Ti alloys subjected to specific processing routes present features that make them suitable metallic materials for the manufacture of orthopedic devices, particularly Ti alloys containing Nb.[5] In addition to E´DER SO´CRATES NAJAR LOPES, Assistant Professor, CAMILO AUGUSTO FERNANDES SALVADOR, DENIS RENATO ANDRADE, and KAIO NIITSU CAMPO, Ph.D. Students, and RUBENS CARAM, Full Professor, are with the School of Mechanical Engineering, University of Campinas, Rua Mendeleiev, 200, Campinas, SP 13083-860, Brazil. Contact e-mail: caram@fem. unicamp.br ALESSANDRA CREMASCO, Assistant Professor, is with the School of Applied Sciences, University of Campinas, Rua Pedro Zaccaria, 1300, Limeira, SP 13484-350, Brazil. Manuscript submitted June 9, 2015. Article published online March 10, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
high biocompatibility and corrosion resistance, depending on composition and phase transformation pathways, Ti-Nb alloys subjected to aging heat treatment show a very low elastic modulus combined with reasonable mechanical strength. The addition of Fe to Ti-Nb alloys changes the b phase stability and hence the balance between the stable phases. Dobromyslov and Elkin suggested that the addition of Fe to Ti alloys causes a significant reduction in the martensite start temperature (Ms), which may lead to the presence of the b phase at room temperature.[6] Lin et al., based on the valence electron structure parameters, suggested that the addition of alloying elements such as Al, Sn, Fe, Mn, and Cr causes suppression of the orthorhombic martensite (a¢¢) transformation[7] that is expected in Ti-Nb systems with high Nb content. Lin et al. showed that the addition of 1 wt pct Fe to Ti-7.5Mo-xFe alloys was enough to retain a full b structure after casting in graphite molds.[8] This addition also resulted in a reasonable increase in hardness due to the precipitation of the x phase. The x phase was still present in alloys with 2 and 3 pct Fe, but as the Fe content increased, the ‘‘z’’ lattice parameter of the x phase structure decreased towards that of a less stable x phase.[8] Previous studies on the Ti-Nb-Fe system reported that the Fe acts as an efficient b stabilizer alloying element. Hsu et al. verified that 5 wt pct Fe content in as-cast Ti-5Nb-xFe alloys produced a fully b phase
VOLUME 47A, JUNE 2016—3213
structure, although alloys with Fe content between 2 and 4 wt pct
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