Ti6Al7Nb (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. Ti6Al7Nb is used as a material for hip protheses. Ti6Al7Nb 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.
Ti-6Al-7Nb is a dedicated high strength titanium alloy with excellent biocompatibility for surgical implants.
Ti-6Al-7Nb alloy is double or triple vacuum melted to provide an ingot composition that is very uniform and homogeneous. The ingot is hot pressed, and finished into round and flat bar products using conventional titanium alloy processing methods.
Physical properties of Ti6Al7Nb
- Usual state: solid
- Colour: silver-white
- Melting point: 1720°C
- Molar volume: 10.64.10-6m3/mol
- Density: 4,507 g/cm3
- Electrical conductivity: 2.34.106S/m
- Thermal conductivity: 21.9W/(m•K)
- Coefficient of thermal expansion: 8.5.10-6/°C
Chemical composition of Ti6Al7Nb (%, max.)
| Weight % | Al | Nb | Ta | Fe | O | C | N | H | Ti |
|---|---|---|---|---|---|---|---|---|---|
| Titanium 6Al-7nb | 5.5-6.6 | 6.5-7.5 | 0.50 max | 0.25 max | 0.20 max | 0.08 max | 0.05 max | 0.009 max | Bal |
Production
Ti6Al7Nb is produced by powder metallurgy methods. The most common methods are hot pressing, metal injection mouldering and blending and pressing. In the production of Ti6Al7Nb a sintering temperature between 900-1400o C usually are used. Altering the sintering temperature gives the Ti6Al7Nb 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 Ti6Al7Nb alloys could also be made by different 3D-printer technique such as SLM and EBM.
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.
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.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.
Available forms
- Ingot
- Forging
- Rod and bar
- Plate and sheet
- Wire
- Custom-made
Characteristic
- Good formability and cutting.
- Alloy can be easily welded in the annealed condition.
- Dense and stable passive layers that form
Specification
- UNS: R56700
- ASTM Standard: F1295
- ISO Standard: ISO 5832-11
Applications of Ti6Al7Nb
- 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
- Dental application
- Aircraft materials
Titanium Ti6Al7Nb was developed for use in the medical and surgical device applications although its properties are nearly identical to Ti6Al4V however Niobium has been substituted for Vanadium as the beta stabilizing agent giving improved biocompatability. Ti6Al7Nb is widely used in the medical device industry.
Biocompatibility
Ti6Al7Nb has a high biocompatibility. The oxides from Ti6Al7Nb 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 nucleis. Ti6Al7Nb also shows a high compatibility to ingrowth to the human body.
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