Ti-6Al-7Nb (UNS designation R56700) is an alpha-beta

titanium alloy Titanium alloys are alloys that contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness (even at extreme temperatures). They are light in weight, have extraordinary corrosion resista ...

first synthesized in 1977 containing 6%

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

and 7%

niobium Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...

. 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. Ti―6Al―7Nb is one of the titanium alloys that built of hexagonal α phase (stabilised with

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

) and regular body-centred phase β (stabilised with

). The alloy is characterized by added advantageous mechanical properties, it has higher corrosion resistance and biotolerance in relation to

Ti-6Al-4V Ti-6Al-4V (UNS designation R56400), also sometimes called TC4, Ti64, or ASTM Grade 5, is an alpha-beta titanium alloy with a high specific strength and excellent corrosion resistance. It is one of the most commonly used titanium alloys and is applie ...

alloys.

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. 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 The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...

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.

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.

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.

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. * Dental application * Aircraft materials

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 nucleis. Ti-6Al-7Nb also shows a high compatibility to ingrowth to the human body.

Specification

Designations for Ti-6Al-7Nb in other naming conventions include: in * UNS: R56700 * ASTM Standard: F1295 * ISO Standard: ISO 5832-11