• Low modulus compatible with bone elasticity
• Good strain recovery
• Excellent biocompatibility

The alloy has excellent flexibility and low modulus and can be used in either cast or wrought condition. The devices made of Flexium™ can be fabricated by casting, cold working and/or machining, and can be readily joined to other Ti components and coated to finish.

Metallurgical Properties
Flexium™ is a single-phase titanium alloy of body-center-cubic (bcc) ß structure after ß solution treatment and subsequent rapid cooling. The alloy possesses a critical ß stability such that when deformed crystalline phase change (martensitic transformation) or twining occurs giving rise to unique superelatic properties. The key properties of the alloy are listed in Table 1 in comparison to those of Ti-64 alloy.

Property	Flexium™	Ti-64
Nominal Composition	Ti-9.8Mo-4Nb-2V-3Al	Ti-6Al-4V
Metallurgical Microstructure	ß	+ß
Density	0.173 lb/in3 (4.8 g/cm3)	0.160 lb/in3 (4.4 g/cm3)
Melting Point	1,700°C	1,650°C
Transus	850°C	980°C
Annealing Temperature	870°C-900°C	700°C -785°C
Young’s Modulus	7-10 x 106 psi (50-70 GPa)	16.5 x 106 psi (113.8 GPa)
Plateau Stresses	60-80 Ksi (450 - 600 Mpa)	N/A
Yield strength	60-80 Ksi (450 – 600 Mpa)	128 Ksi (880 Mpa)
Ultimate Tensile Strength	110 – 130 Ksi (750 - 900 Mpa)	138 Ksi (950 Mpa)
Recoverable Strain	3 – 3.5%	0.5%
Tensile Elongation	15-20%	14%
Reduction of Area	40-45%	36%
Hardness (Vickers Scale)	300Hv	350Hv

Effects of Cold Work
Young’s Modulus
Young’s modulus of the alloy decreases with increasing amount of cold work. It drops from ~10 Msi for the betatized material to ~7 Msi after cold-working with reductions greater than 30% (Figure 1).

Tensile Strength (UTS)
The UTS is around 120 Ksi for materials in the fully betatized condition. With a small amount of precipitate, the UTS can be elevated to higher than 150 Ksi. Cold working further increases the tensile strength as shown in Figure 2 to ~170 Ksi after a 50% reduction. The data suggests a weak work hardening effect.

Superelasticity
Betatized materials exhibit pseudoelasticity (Figure 3). In contrast, the alloy after cold working exhibits linear superelasticity. A strain as high as 3% maybe recoverable in cold-worked materials. Examples of tensile stress-strain curves tested to 2% and 4% elongations of wires with a 19.4% cold-work reduction are shown in Figure 4. Ductility however decreases significantly when the cold work exceeds 25% reduction.

Effects of Heat Treatments
Brief aging of betatized materials for less than 30 minutes at 350 – 500°C generally improves pseudoelastic strain recovery. Avoid prolong aging at these temperatures as it leads to precipitation and embrittles the alloy. precipitation at 500-800°C also degrades elasticity. High temperature heat treatments and brazing must be carried out in either vacuum or inert gas atmosphere to avoid oxygen contamination and the formation of case. Significant case may degrade the flexibility and eventually embrittles the material.

Machining Characteristics
The machining characteristics for Flexium™ are generally similar to those for Ti-64. The alloy can be milled or turned using similar feed rates and cutting fluids for Ti-64 alloys with high speed steel tools. Longer tool life and better surface finish can be achieved with carbide tools. Milling and turning chips are typically stringy. Flexium? is slightly easier to drill or to grind when compared to Ti-64 alloys which tend to create bright sparks and wear out the wheel quickly. Flexium™ galls less, creates less heat and wears out the tools much less than does Ti-64 during these operations.

Corrosion Properties:
The corrosion resistance of Flexium™ is excellent. The key parameters are listed in Table 2 in comparison with those of Ti-64. A typical potentiodynamic polarization curve of annealed Flexium™ is shown in Figure 5. Cold-worked alloys exhibit similar corrosion characteristics.

Figure 5. Cyclic polarization curves for mechanically polished Flexium™.

Biocompatibility:
The alloy is biocompatibile and exhibits no toxicity as demonstrated by the test results in Table 3.