**3.1 The processing**

152 Recent Advances in Arthroplasty

Also, V can cause potential citotoxicity and adverse tissue reactions (Steinemann, 1980), and

Briefly, a biocompatible titanium base alloy suitable for bone implant should meet at least




Consequently, the recent trend in research and development of titanium for biomedical applications is to develop alloys composed of non-toxic and non-allergenic elements with excellent mechanical properties (low modulus-high strength) and workability (Niinomi, 1999). The first generation of design orthopaedic alloys try to replace the V and Al alloys with other

Subsequent developments in orthopaedic Ti-base alloys have been motivated by the requirement of low elastic modulus. The stiffness of titanium and its alloys is still largely greater than that of cortical bone, although it is less than that of Co-Cr type alloys and stainless steels used for biomedical applications. This difference of rigidity produced the stress-shielding phenomenon. Stress shielding occurs because of the mismatch between the stiffness of the bone, which has a Young modulus of 7–25 GPa (Currey, 1998), and that of the

Various methods of solving this problem have been considered, including changing the size and shape of the stem to reduce the differences in the structural stiffness of the implant and the surrounding bone and changing the implant material from steel to commercially pure

Metastable -Ti alloys were developed for this purpose, with low elastic modulus. In Table 4 it could be observed some old and new Ti-base alloys develop specifically for biomedical

Low modulus alloys are nowadays desired because the moduli of alloys are required to be much more similar to that of bone. These new alloys have an elastic modulus ranging 55-85 GPa, so it could be minimized the stress shielding phenomena because it is more proximally

> 11. **Ti-15Mo** (low modulus) 12. Ti-16Nb-10Hf (low modulus) 13. Ti-15Mo-5Zr-3Al (low modulus)

10. **Ti-12Mo-6Zr-2Fe** (ASTM F1813- low modulus)

14. Ti-15Mo-2.8Nb-0.2Si-0.26O (low modulus)

15. Ti-35Nb-7Zr-5Ta (low modulus) 16. Ti-29Nb-13Ta-4.6Zr (low modulus)

to the bone modulus. However, they are still greater than that of cortical bone.

Table 4. Ti alloys developed for biomedical applications (in bold) and for other uses

Al ions from the alloy might cause long-term Alzheimer diseases (Rao et al., 1996).

aluminium, should be used only in minimum, acceptable amounts

modulus, high strength and good smooth and notched fatigue strength

non toxic components such as Nb, Fe and Mo (for the V) and Ta, Hf and Zr (for the Al).

the following requirements (Mehta, 2008):



titanium or Ti alloys with low modulus (Sarmiento et al., 1979).

completely

metal implant stem.

purpose (Guilemot et al., 2004).

1. Titanium CP (ASTM F 67) 2. Ti-6Al-4V ELI (ASTM F 136) 3. Ti-6Al-4V (ASTM F 1108) 4. **Ti-6Al-7Nb** (ASTM F 1295) 5. Ti-5Al-2.5Fe (ISO 5832) 6. Ti-5Al-3Mo-4Zr 7. Ti-15Sn-4Nb-2Ta-0.2Pd 8. Ti-15Zr-4Nb-2Ta-0.2Pd 9. **Ti-13Nb-13Zr** (low modulus) A great problem of these new alloys is its fabrication processes because most beta titanium alloys contain considerable amounts of refractory elements with high melting temperatures. This results in heavily weight, difficult melting and solidification processing, low plastic deformability and high materials costs.

The various refractory materials employed in casting are attacked by titanium with such severity that sounds castings, possessing good mechanical properties are difficult to obtain. So, conventional methods are not practical with titanium.

The molten metal and the hot casting are susceptible to atmospheric contamination. Because Ti is very reactive with oxygen and other atmospheric gases, the melting and casting processes implies high temperature fusion and casting under vacuum or protective neutral atmospheres. Another casting problem is the maintenance of good flow over severe changes of dimensions or direction within the mold.

Powder metallurgy (P/M) is an alternative method of fabrication in which metal powders are utilized by compacting and sintering to form useful products. This method is employed primarily to produce simple shapes with good dimensional stability, to form shapes with material of extremely high melting temperatures and to produce parts not feasible by other means.

Production of cast titanium today takes 16 times more energy per tonne than the production of steel. Instead of conventional melting, milling and machining, P/M techniques implies powders that remain in solid form during the entire procedure. This saves a tremendous amount of processing energy with a reduction of over 50% (Mehta, 2008).
