Ti-6Al-7Nb

Ti-6Al-7Nb (UNS designation R56700) is an alpha-beta titanium alloy first synthesized in 1977 containing 6% aluminum and 7% niobium. It features high strength and has similar properties as the cytotoxic vanadium 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 with aluminium) and regular body-centred phase β (stabilised with niobium). The alloy is characterized by added advantageous mechanical properties, it has higher corrosion resistance and biotolerance in relation to Ti-6Al-4V alloys.^[2][3][4]

Physical properties

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]

Property	Minimum Value	Maximum Value	Unit
Density	4.51	4.53	g/cm^3
Hardness	2700	2900	Mpa
Melting point	1800	1860	K
Specific heat	540	560	J/kg*K
Elastic limit	895	905	MPa
Energy content	750	1250	MJ/kg
Latent heat of fusion	360	370	kJ/kg

^[7]

As shown in the above table, alloying is one of the effective methods to improve the mechanical properties and since Niobium belongs to the same group of Vanadium in the periodic table it is of course acts as α –β stabilizing elements (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]

Production

Ti-6Al-7Nb is produced by powder metallurgy methods. The most common methods are hot pressing, metal injection mouldering and blending and pressing. In the production of Ti-6Al-7Nb, usually a sintering temperature between 900-1400^o 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

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 of ductility, 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]

Applications

• 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]
• Dental application^[15]

Biocompatibility

Ti-6Al-7Nb has a high biocompatibility. The oxides from Ti-6Al-7Nb is saturated in the body and are not transported in 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]

Specification

Designations for Ti-6Al-7Nb in other naming conventions include:^[17]

• UNS: R56700
• ASTM Standard: F1295
• ISO Standard: ISO 5832-11

References

1. Fellah, Mamoun; Labaïz, Mohamed; Assala, Omar; Dekhil, Leila; Taleb, Ahlem; Rezag, Hadda; Iost, Alain (21 July 2014). "Tribological behavior of Ti-6Al-4V and Ti-6Al-7Nb Alloys for Total Hip Prosthesis". Advances in Tribology. 2014: 1–13. doi:10.1155/2014/451387. hdl:10985/9566.
2. 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.
3. 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. CiteSeerX 10.1.1.472.7717. doi:10.1016/j.mser.2004.11.001.
4. 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.
5. 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.
6. Ajeel, Sami Abualnoun; Alzubaydi, Thair L.; Swadi, Abdulsalam K. (2007). "Influence of Heat Treatment Conditions on Microstructure of Ti- 6Al-7Nb Alloy As Used Surgical Implant Materials". Engineering and Technology Journal. 25 (Suppl 3): 431–442. doi:10.30684/etj.25.3.15. S2CID 55885379.
7. "Properties: Titanium Alloys - Ti6Al7Nb Properties and Applications".
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. PMID 15348689. S2CID 13241089.
9. 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. S2CID 137360703.
10. Oliveira, V.; Chaves, R. R.; Bertazzoli, R.; Caram, R. (December 1998). "Preparation and characterization of Ti-Al-Nb alloys for orthopedic implants". Brazilian Journal of Chemical Engineering. 15 (4): 326–333. doi:10.1590/S0104-66321998000400002. S2CID 94310566.
11. 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.
12. 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.
13. 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.
14. Elias, C. N.; Lima, J. H. C.; Valiev, R.; Meyers, M. A. (1 March 2008). "Biomedical applications of titanium and its alloys". JOM. 60 (3): 46–49. Bibcode:2008JOM....60c..46E. doi:10.1007/s11837-008-0031-1. S2CID 12056136.
15. 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. PMID 15348689. S2CID 13241089.
16. Disegi, John (November 2008). (PDF) (2nd ed.). Synthes. Archived from the original (PDF) on 11 December 2015.
17. Milne, Ian; Ritchie, R. O.; Karihaloo, B. L. (25 July 2003). Standardized titanium and titanium alloys. Elsevier. p. 163. ISBN 9780080490731. in Sumita, M.; Hanawa, T.; Ohnishi, I.; Yoneyama, T. (2003). "Failure Processes in Biometallic Materials". Comprehensive Structural Integrity. pp. 131–167. doi:10.1016/B0-08-043749-4/09143-6. ISBN 978-0-08-043749-1.

Further reading

• Kazek-Kęsik, Alicja; Kalemba-Rec, Izabela; Simka, Wojciech (2019). "Anodization of a Medical-Grade Ti-6Al-7Nb Alloy in a Ca(H2PO2)2-Hydroxyapatite Suspension". Materials. 12 (18): 3002. Bibcode:2019Mate...12.3002K. doi:10.3390/ma12183002. PMC 6766300. PMID 31527501.
• 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. PMID 12527293.
• 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. PMID 30074223. S2CID 49365946.
• 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. PMID 29507440.
• 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. PMID 16770546. S2CID 8548688.
• Pennekamp, Peter H.; Gessmann, Jan; Diedrich, Oliver; Burian, Björn; Wimmer, Markus A.; Frauchiger, Vinzenz M.; Kraft, Clayton N. (March 2006). "Short-term microvascular response of striated muscle to cp-Ti, Ti-6Al-4V, and Ti-6Al-7Nb". Journal of Orthopaedic Research. 24 (3): 531–540. doi:10.1002/jor.20066. PMID 16463365. S2CID 39224569.
• 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. PMID 16078208.
• Duarte, Laís T.; Bolfarini, Claudemiro; Biaggio, Sonia R.; Rocha-Filho, Romeu C.; Nascente, Pedro A. P. (1 August 2014). "Growth of aluminum-free porous oxide layers on titanium and its alloys Ti-6Al-4V and Ti-6Al-7Nb by micro-arc oxidation". Materials Science and Engineering: C. 41: 343–348. doi:10.1016/j.msec.2014.04.068. PMID 24907769.
• 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. PMID 10208405.
• 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. PMID 23349101.