Ti-6Al-7Nb

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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]

Contents

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]

PropertyMinimum ValueMaximum ValueUnit
Density4.514.53g/cm3
Hardness27002900Mpa
Melting point18001860K
Specific heat540560J/kg*K
Elastic limit895905MPa
Energy content7501250MJ/kg
Latent heat of fusion360370kJ/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 900-1400o 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

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


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]

Related Research Articles

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Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.

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References

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  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.
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  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.
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  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.
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  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.
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  16. Disegi, John (November 2008). Implant Materials (PDF) (2nd ed.). Synthes. Archived from the original (PDF) on 11 December 2015.
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Further reading