Ti-6Al-7Nb (UNS designationR56700) is an alpha-betatitanium alloy first synthesized in 1977 containing 6%aluminum and 7%niobium. It features high strength and has similar properties as the cytotoxicvanadium containing alloy Ti-6Al-4V. Ti-6Al-7Nb is used as a material for hip prostheses.[1]
Ti―6Al―7Nb is one of the titanium alloys that built of hexagonal α phase (stabilised withaluminium) and regular body-centred phase β (stabilised withniobium). The alloy is characterized by added advantageous mechanical properties, it has higher corrosion resistance and biotolerance in relation toTi-6Al-4V alloys.[2][3][4]
The physical properties of the alloy are mostly dependent on the morphology and the fractions volume of the phases presence from the parameters obtained from the manufacturing process.[5][6][7]
As shown in the above table, alloying is one effective method to improve mechanical properties, and since Niobium belongs to the same group as Vanadium in theperiodic table, it also acts as α β-stabilizing element (similar to Ti-6Al-4V alloy); however, the strength of Nb alloy is little less than that of Ti-6Al-4V .The main difference between Ti-6Al-4V and Ti-6Al-7Nb is related to different factors such as solid-solution strengthening, the structure-refining strengthening provided by the refined two-phase structure, and the difference in the microstructure between the two alloys.[8]
Ti-6Al-7Nb is produced bypowder metallurgy methods. The most common methods are hot pressing,metal injection mouldering and blending and pressing. In the production of Ti-6Al-7Nb, usually asintering temperature between 900 and 1400o C is used. Altering the sintering temperature gives the Ti-6Al-7Nb different properties such as different porosity and microstructure. It also gives a different composition between alpha, beta and alpha+beta phases. In the recent years Ti-6Al-7Nb alloys could also be made by different 3D-printer technique such as SLM and EBM.[9][10]
Heat treatment of titanium is demonstrated to have significant influences on reducing the residual stresses, improving the mechanical properties (i.e. tensile strength or fatigue strength by solution treatment and ageing). Moreover, heat treatment provides an ideal combination ofductility, machinability and structural stability due to the differences in microstructure and cooling rates between α and β phases.[11]
The cooling rate have an impact of the morphology . When the cooling rate is reduced for example from air cool to slow cooling, the morphology of the transformed α increases in thickness and length and is contained within fewer, larger α colonies.[12] The α colony size is the most important microstructural properties due to its influences the fatigue properties and deformation mechanics of β processed α+ β alloys.[13]
Implant devices replacing such as : failed hard tissue, artificial hip joints, artificial knee joints, bone plates, screws for fracture fixation, cardiac valve prostheses, pacemakers, and artificial hearts.[14]
Ti-6Al-7Nb has a highbiocompatibility. The oxides from Ti-6Al-7Nb are saturated in the body and are not transportedin vivo or are a bioburden. The alloy will not create adverse tissue tolerance reactions and creates fewer giant cell nuclei. Ti-6Al-7Nb also shows a high compatibility to ingrowth to the human body.[16]
^Chlebus, Edward; Kuźnicka, Bogumiła; Kurzynowski, Tomasz; Dybała, Bogdan (1 May 2011). "Microstructure and mechanical behaviour of Ti―6Al―7Nb alloy produced by selective laser melting".Materials Characterization.62 (5):488–495.doi:10.1016/j.matchar.2011.03.006.
^Liu, Xuanyong; Chu, Paul K.; Ding, Chuanxian (24 December 2004). "Surface modification of titanium, titanium alloys, and related materials for biomedical applications".Materials Science and Engineering: R: Reports.47 (3):49–121.CiteSeerX10.1.1.472.7717.doi:10.1016/j.mser.2004.11.001.
^López, M. F; Gutiérrez, A; Jiménez, J. A (15 February 2002). "In vitro corrosion behaviour of titanium alloys without vanadium".Electrochimica Acta.47 (9):1359–1364.doi:10.1016/S0013-4686(01)00860-X.
^Lütjering, G. (15 March 1998). "Influence of processing on microstructure and mechanical properties of (α+β) titanium alloys".Materials Science and Engineering: A.243 (1):32–45.doi:10.1016/S0921-5093(97)00778-8.
^Kobayashi, E.; Wang, T.J.; Doi, H.; Yoneyama, T.; Hamanaka, H. (1998). "Mechanical properties and corrosion resistance of Ti–6Al–7Nb alloy dental castings".Journal of Materials Science: Materials in Medicine.9 (10):567–574.doi:10.1023/A:1008909408948.PMID15348689.S2CID13241089.
^Bolzoni, Leandro; Hari Babu, N.; Ruiz-Navas, Elisa Maria; Gordo, Elena (2013). "Comparison of Microstructure and Properties of Ti-6Al-7Nb Alloy Processed by Different Powder Metallurgy Routes".Key Engineering Materials.551:161–179.doi:10.4028/www.scientific.net/KEM.551.161.hdl:10016/20805.S2CID137360703.
^Sercombe, Tim; Jones, Noel; Day, Rob; Kop, Alan (26 September 2008). "Heat treatment of Ti-6Al-7Nb components produced by selective laser melting".Rapid Prototyping Journal.14 (5):300–304.doi:10.1108/13552540810907974.
^Sercombe, Tim; Jones, Noel; Day, Rob; Kop, Alan (26 September 2008). "Heat treatment of Ti-6Al-7Nb components produced by selective laser melting".Rapid Prototyping Journal.14 (5):300–304.doi:10.1108/13552540810907974.
^Lütjering, G. (15 March 1998). "Influence of processing on microstructure and mechanical properties of (α+β) titanium alloys".Materials Science and Engineering: A.243 (1):32–45.doi:10.1016/S0921-5093(97)00778-8.
^Kobayashi, E.; Wang, T.J.; Doi, H.; Yoneyama, T.; Hamanaka, H. (1 October 1998). "Mechanical properties and corrosion resistance of Ti–6Al–7Nb alloy dental castings".Journal of Materials Science: Materials in Medicine.9 (10):567–574.doi:10.1023/A:1008909408948.PMID15348689.S2CID13241089.
^Disegi, John (November 2008).Implant Materials(PDF) (2nd ed.). Synthes. Archived fromthe original(PDF) on 11 December 2015.
Iijima, D; Yoneyama, T; Doi, H; Hamanaka, H; Kurosaki, N (April 2003). "Wear properties of Ti and Ti–6Al–7Nb castings for dental prostheses".Biomaterials.24 (8):1519–1524.doi:10.1016/s0142-9612(02)00533-1.PMID12527293.
Hamad, Thekra I.; Fatalla, Abdalbseet A.; Waheed, Amer Subhi; Azzawi, Zena G. M.; Cao, Ying-guang; Song, Ke (1 June 2018). "Biomechanical Evaluation of Nano-Zirconia Coatings on Ti-6Al-7Nb Implant Screws in Rabbit Tibias".Current Medical Science.38 (3):530–537.doi:10.1007/s11596-018-1911-4.PMID30074223.S2CID49365946.
Kajzer, Anita; Grzeszczuk, Ola; Kajzer, Wojciech; Nowińska, Katarzyna; Kaczmarek, Marcin; Tarnowski, Michał; Wierzchoń, Tadeusz (2017). "Properties of Ti6Al7Nb titanium alloy nitrocarburized under glow discharge conditions".Acta of Bioengineering and Biomechanics.19 (4):181–188.doi:10.5277/ABB-00892-2017-03.PMID29507440.
Osathanon, Thanaphum; Bespinyowong, Kritchai; Arksornnukit, Mansuang; Takahashi, Hidekazu; Pavasant, Prasit (1 July 2006). "Ti-6Al-7Nb promotes cell spreading and fibronectin and osteopontin synthesis in osteoblast-like cells".Journal of Materials Science: Materials in Medicine.17 (7):619–625.doi:10.1007/s10856-006-9224-8.PMID16770546.S2CID8548688.
Kraft, Clayton N.; Burian, Björn; Diedrich, Oliver; Gessmann, Jan; Wimmer, Markus A.; Pennekamp, Peter H. (1 October 2005). "Microvascular response of striated muscle to common arthroplasty-alloys: A comparativein vivo study with CoCrMo, Ti-6Al-4V, and Ti-6Al-7Nb".Journal of Biomedical Materials Research Part A.75A (1):31–40.doi:10.1002/jbm.a.30407.PMID16078208.
Khan, M.A.; Williams, R.L.; Williams, D.F. (April 1999). "The corrosion behaviour of Ti–6Al–4V, Ti–6Al–7Nb and Ti–13Nb–13Zr in protein solutions".Biomaterials.20 (7):631–637.doi:10.1016/s0142-9612(98)00217-8.PMID10208405.
Challa, V. S. A.; Mali, S.; Misra, R. D. K. (July 2013). "Reduced toxicity and superior cellular response of preosteoblasts to Ti-6Al-7Nb alloy and comparison with Ti-6Al-4V".Journal of Biomedical Materials Research Part A.101A (7):2083–2089.doi:10.1002/jbm.a.34492.PMID23349101.
