Ti-6Al-4V (Grade 5) vs Ti-6Al-4V ELI (Grade 23)
Ti-6Al-4V Grade 5 and its ELI variant Grade 23 share the same alpha-beta alloy base but differ in purity. Grade 5 is the standard high-strength workhorse titanium alloy used across aerospace and industry. Grade 23 (ELI, Extra-Low Interstitials) reduces oxygen and iron for superior fracture toughness and ductility, making it the medical-implant grade. The trade is slightly lower strength for better damage tolerance.
The verdict
Choose Grade 5 for general high-strength structural and aerospace parts where maximum strength and lower cost matter. Choose Grade 23 ELI for fracture-critical and medical-implant applications, where its lower interstitials deliver better fracture toughness, ductility, and biocompatibility despite slightly reduced strength.
Side-by-side data
| Property | Ti-6Al-4V (Grade 5) | Ti-6Al-4V ELI (Grade 23) |
|---|---|---|
| Category | Titanium | Titanium |
| Density (g/cm³) | 4.43 | 4.43 |
| Tensile strength (MPa) | 1000 | 860 |
| Yield strength (MPa) | 910 | 790 |
| Elongation (%) | 14 | 15 |
| Hardness | 36 HRC | 34 HRC |
| Max service temp (°C) | 400 | 400 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 6.7 | 7 |
| Typically used for | Aerospace & medical — best strength-to-weight | Medical implants & fracture-critical |
Which should you choose?
Choose Ti-6Al-4V Grade 5 when…
- You need maximum strength (~1000 MPa tensile, ~910 MPa yield) per the data
- The part is a general aerospace, automotive, or industrial structural component
- Best strength-to-weight ratio is the governing requirement
- The application is not fracture-critical or implant-grade
- Standard alpha-beta alloy availability and lower cost are advantages
- High corrosion resistance (rating 5.0) is needed alongside strength
Choose Ti-6Al-4V ELI Grade 23 when…
- The part is a medical implant or fracture-critical component
- Superior fracture toughness and damage tolerance are required
- Lower interstitials (oxygen, iron) improve ductility (~15% elongation)
- Biocompatibility for surgical and dental implants is essential
- Cryogenic or high-toughness service benefits from ELI purity
- You accept slightly lower strength (~860 MPa tensile) for toughness
Key differences that matter
- Both are the same alpha-beta Ti-6Al-4V alloy; ELI Grade 23 simply has reduced interstitials (lower oxygen and iron)
- Grade 5 is stronger (tensile ~1000 vs 860 MPa, yield ~910 vs 790 MPa); Grade 23 trades strength for toughness
- Grade 23 has higher elongation (~15% vs 14%) and notably better fracture toughness and damage tolerance
- Grade 23 ELI is the medical-implant standard thanks to biocompatibility and superior crack resistance
- Both share identical density (~4.43), maximum corrosion resistance (5.0), and the same difficult machinability (1.5)
- Grade 23 is also favored for cryogenic and fracture-critical aerospace parts where toughness governs
- Cost index is equal (5.0); selection turns on strength versus fracture toughness, not price
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What does ELI mean and why does it matter?
ELI stands for Extra-Low Interstitials, meaning reduced oxygen, nitrogen, carbon, and iron. Lowering these elements improves ductility and fracture toughness, so Grade 23 resists crack propagation better than standard Grade 5. That damage tolerance is critical for medical implants and fracture-critical parts, even though it slightly lowers strength.
Why is Grade 23 preferred for medical implants?
Grade 23 combines titanium's excellent biocompatibility and corrosion resistance with superior fracture toughness and ductility from its low interstitials. Implants must tolerate cyclic loading and resist crack growth over years in the body, so the ELI grade's damage tolerance, plus its clean chemistry, make it the standard for orthopedic and dental implants.
How much strength do I give up choosing Grade 23?
Modestly. In this data Grade 23 shows about 860 MPa tensile and 790 MPa yield versus Grade 5's roughly 1000 and 910 MPa, so you lose around 10 to 15% strength. In return you gain meaningfully better fracture toughness and ductility, a worthwhile trade for fracture-critical and implant applications.
Are they machined and finished the same way?
Essentially yes. Both share the same density, corrosion resistance, and a low machinability rating of 1.5, so both are slow and challenging to machine, requiring rigid setups, sharp tooling, flood coolant, and conservative speeds. The ELI grade's slightly higher ductility does not materially change machining practice between the two.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.