Ti-6Al-4V ELI Alloy(ASTM F136)
Ti-6Al-4V ELI Alloy(ASTM F136) has good mechanical properties, but exhibits a possibly toxic effect from released vanadium and aluminum. For this reason, vanadium- and aluminum-free Ti-based alloys have been proposed for biomedical applications.
The selection of materials for medical devices is based on mechanical properties, chemical composition, and biocompatibility. Technical Standard ASTM F-136/ISO 5832-3 covers the mechanical properties and chemical composition requirements for Ti Grade 23 (Ti6Al4V ELI alloy, extra low interstitial) to be used in the manufacture of surgical implants.
Ti6Al4V ELI alloy has good mechanical properties, but exhibits a possibly toxic effect from released vanadium and aluminum. For this reason, vanadium- and aluminum-free Ti-based alloys have been proposed for biomedical applications.
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Chemical Composition
|
ASTM F136 |
|
| Composition |
ASTM F136 |
| Nitrogen | 0.05 max |
| Carbon | 0.08 max |
| Hydrogen | 0.012 max* |
| Iron | 0.25 max |
| Oxygen | 0.13 max |
| Aluminum | 5.50 - 6.50 |
| Vanadium | 3.50 - 4.50 |
| Titanium | Balance |
|
*Material 0.813 mm [0.032 in] and under may have hydrogen content up to 0.0150%. |
|
Physical Properties
|
Metric |
English |
|
| Density | 4.43 g/cm³ | 0.160 lbs/in³ |
| Modulus of elasticity | 105 GPa | 15.2 Mpsi |
| Electrical resistivity | 1750 µohms*mm | 68.9 µohms*in |
| Thermal conductivity | 0.865 W/(m*°C) |
6.0 BTU*in/(hr*ft²*F) |
| Coefficient of thermal expansion | 8.64 µm/(m*°C) | 4.8 µin/(in*°F) |
*Values calculated at 22 °C [72 °F].
Mechanical Properties
| Size |
Ultimate tensile strength (mis.) |
Yield strength* (min.) | 4D elongation** (min.) % |
| < 4.75 mm [< 0.187 in] |
860 MPa [125 ksi] | 795 MPa [115 ksi] | 10 |
| 4.75 mm - 6.35 mm [0.187 in - 0.0250 in] |
860 MPa [125 ksi] | 795 MPa [115 ksi] | 10 |
|
* 2% offset |
|||
Ti 6Al-4V ELI is an alpha-beta alloy containing 6% aluminum, 4% vanadium, and extra-low interstitials (ELI). Interstitial elements such as iron and oxygen are tightly controlled during the melt process in order to improve the ductility and fracture toughness.
Currently, dental implant manufacturers use commercially pure titanium (Ti G2 and Ti G4) and Ti–6Al–4V alloy (Ti G5) with a surface treatment in order to optimize the contact between bone cells and the device. This interaction between bone cells and dental implant surfaces is called osseointegration.
However, Ti G2 and Ti G4 are not used in medical applications that involve high stresses, such as orthopedic prostheses and narrow dental implants.
For orthopedic applications, Cr–Co, stainless steel, and Ti G5 (Ti–6Al–4V alloy) are the preferred choices due to their high mechanical resistance. These alloys ensure load transmission to bone tissues over a long time, which is necessary when damaged hard tissues are replaced by prostheses.
Application
Grade 23 Ti 6Al 4V ELI alloy is used in the following areas:
- Surgical implants
- Aircraft components
- Structural components
- In a variety of saltwater applications
- In high-pressure cryogenic vessels down to -320°C
- In applications requiring excellent fracture toughness and fatigue strength.
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