Grade 5 (Ti-6Al-4V) and Grade 23 (Ti-6Al-4V ELI) share the same base composition of 6% aluminum and 4% vanadium. The critical difference lies in interstitial element control — Grade 23 limits oxygen to 0.13% max versus Grade 5’s 0.20% max, along with tighter caps on nitrogen and hydrogen. This chemistry change produces meaningfully different mechanical behavior: Grade 23 delivers significantly higher elongation and fracture toughness (75–90 MPa√m vs 55–75 MPa√m), with comparable tensile and yield strength in annealed conditions. For medical implants governed by ASTM F136, Grade 23 is mandatory. For general aerospace and industrial structural work, Grade 5 remains the default — and the more cost-effective choice.
What Does ELI Actually Stand For — And Why Should You Care?
ELI stands for Extra Low Interstitials. It is not a separate alloy — it is a higher-purity production variant of the same Ti-6Al-4V chemistry. The “extra low” designation refers specifically to the interstitial elements: oxygen, nitrogen, carbon, and hydrogen. These are small atoms that sit in the gaps (interstices) of the titanium crystal lattice, and they have an outsized effect on how the metal behaves under stress.
In my experience working with procurement specs, the most common misunderstanding is that ELI is a “different alloy.” It is not. If you sent both Grade 5 and Grade 23 to a spectrometer and only measured aluminum, vanadium, and titanium, you would see nearly identical results. The difference shows up in the impurity limits — and those limits are what make Grade 23 the mandated choice for implantable medical devices.
The reason interstitials matter so much is metallurgical. Oxygen and nitrogen are strong alpha-phase stabilizers. They raise the alpha-to-beta transition temperature and produce a notable hardening effect on the titanium lattice. More oxygen means higher tensile strength, but also means less ability to deform before fracture. In a static load-bearing bracket on an aircraft, that trade-off favors Grade 5. In a spinal rod that flexes millions of times over a patient’s lifetime, it favors Grade 23.
Grade 5 vs Grade 23: Side-by-Side at a Glance
The following table compares the two grades across every metric that matters for engineering selection. Values are drawn from ASTM B348 specifications, Carpenter Technology datasheets, and MakeItFrom.com material databases. Where ranges are given, they represent the spread across multiple certified sources.
Chemical Composition Limits (Maximum Weight %)
| Elemento | Grado 5 (Ti-6Al-4V) | Grado 23 (Ti-6Al-4V ELI) | Perché è importante |
|---|---|---|---|
| Alluminio (Al) | 5.5–6.75% | 5.5–6.75% | Alpha stabilizer; identical range |
| Vanadio (V) | 3.5–4.5% | 3.5–4.5% | Beta stabilizer; identical range |
| Ossigeno (O) | ≤ 0,20% | ≤ 0,13% | Primary differentiator — drives strength vs. ductility trade-off |
| Azoto (N) | ≤ 0,05% | ≤ 0,03% | Alpha stabilizer; affects toughness and weldability |
| Ferro (Fe) | ≤ 0,40% | ≤ 0,25% | Beta stabilizer; affects microstructure homogeneity |
| Carbonio (C) | ≤ 0,08% | ≤ 0,08% | Identical limit |
| Idrogeno (H) | ≤ 0,015% | ≤ 0,0125% | Affects embrittlement risk |
| Titanio (Ti) | Balance (~88%) | Balance (~89%) | Higher Ti balance due to lower impurities |
Proprietà meccaniche (condizione di ricottura)
| Proprietà | Grado 5 (Ti-6Al-4V) | Grado 23 (Ti-6Al-4V ELI) | Δ Difference |
|---|---|---|---|
| Ultimate Tensile Strength (UTS) | Min 895 MPa; Typical 950–1000 MPa | Min 860 MPa; Typical 860–930 MPa | Grade 5 slightly higher |
| Resistenza allo snervamento (offset 0,2%) | Min 828 MPa; Typical ~880 MPa | Min 795 MPa; Typical ~795–830 MPa | Grade 5 slightly higher |
| Allungamento a rottura | Min 10%; Typical 14–18% | Min 10%; Typical 14–16% | Grade 23 comparable to slightly better |
| Reduction in Area | Min 20–25%; Typical ~36% | Min 25%; Typical 30–40% | Grade 23 higher ductility |
| Fracture Toughness (K_IC) | 55–75 MPa√m | 75–90 MPa√m | Grade 23 is ~30% higher |
| Resistenza alla fatica (10⁷ cicli) | ~510 MPa | ~500 MPa | Comparable |
| Modulo elastico | 114 GPa | 113 GPa | Virtually identical |
| Durezza | 34–36 HRC | 30–35 HRC | Negligible difference |
Proprietà fisiche e termiche
| Proprietà | Grado 5 | Grado 23 |
|---|---|---|
| Densità | 4,43 g/cm³ | 4,43 g/cm³ |
| Melting Range | 1604–1660°C | 1604–1660°C |
| Conduttività termica | 6.8 W/m·K | 7.1 W/m·K |
| Max Service Temperature | ~350°C | ~350°C |
The takeaway in one sentence: Grade 5 gives you higher static strength; Grade 23 gives you dramatically better damage tolerance — the ability to resist crack growth and survive cyclic loading without catastrophic failure.
The ASTM Standards Maze: B348, F136, and F1472
One of the most confusing aspects of specifying titanium alloy is that multiple ASTM standards cover the same base chemistry. This is not redundant — each standard governs a different product form or end-use application.
ASTM B348 covers titanium alloy bar and billet for general purposes. Both Grade 5 and Grade 23 are defined here with their respective chemical and mechanical requirements. This is the “general supply chain” standard — what you encounter most often when ordering mill products.
ASTM F136 is the implant-grade standard for wrought Ti-6Al-4V ELI for surgical implant applications. This standard references Grade 23 chemistry and specifies tighter mechanical property windows tailored to medical requirements. If your product is an implant or surgical instrument, F136 is the standard that matters — and it mandates ELI chemistry. Grade 5 does not qualify under F136.
ASTM F1472 covers Ti-6Al-4V for surgical implant applications, but references the standard (non-ELI) Grade 5 composition. In practice, F136 (ELI) dominates the implant market because of its superior fatigue and fracture resistance.
Here is the practical decision rule: If your application requires ASTM F136 compliance, you must use Grade 23. There is no substitution path. If your application calls for general structural titanium (aerospace brackets, industrial components, race car parts), ASTM B348 Grade 5 is the standard — and it is the more economical choice.
| Standard | Covers | Grades Included | Applicazione tipica |
|---|---|---|---|
| ASTM B348 | Bar and billet (general) | Grade 5, Grade 23 | General engineering supply |
| ASTM F136 | Wrought surgical implant | Grade 23 (ELI) only | Medical implants, surgical instruments |
| ASTM F1472 | Wrought surgical implant | Grade 5 only | Less common for implants |
| ASTM B863 | Welding wire | Grade 5, Grade 23 | Welding consumables |
Mechanical Properties Deep Dive: Where Each Grade Wins
Strength: Grade 5’s Advantage
In annealed condition, both grades show comparable tensile and yield strengths — Grade 5 is only marginally higher. However, Grade 5 can be heat-treated to higher strength levels (UTS up to 1000+ MPa) more readily than Grade 23, because the higher oxygen content promotes a stronger alpha phase. In a static load scenario — a bracket holding a sensor, a structural frame member, a flange connection — this strength advantage lets you design thinner, lighter parts.
However, the gap is narrower than many engineers assume. Grade 23’s yield strength of 795 MPa (minimum per ASTM F136) is still impressively high, and for most structural applications, it exceeds design requirements by a wide margin. The strength difference only becomes a constraint in applications pushing the material to its limits.
Ductility and Toughness: Grade 23’s Advantage
This is where Grade 23 separates itself. With elongation of 14–16% (vs 14–18% for Grade 5 in typical annealed condition — the ranges overlap more than many sources suggest) and a fracture toughness of 75–90 MPa√m (vs 55–75 MPa√m), Grade 23 is more resistant to crack initiation and propagation.
In my assessment of real-world failure modes, fracture toughness is the property that separates inconvenient damage from catastrophic failure. A Grade 5 part with a small surface crack may tolerate it up to a critical size, then fail suddenly. A Grade 23 part tolerates a larger crack before reaching that critical point — giving inspectors more time to catch it and engineers more margin for error.
For cyclic loading environments — anything that experiences repeated stress cycles, from spinal fixation rods to landing gear bushings to vibrating industrial equipment — this toughness advantage directly translates to longer service life.
Fatigue: Closer Than You Think
Fatigue strength at 10⁷ cycles shows both grades performing similarly — approximately 500 MPa for Grade 23 and 510 MPa for Grade 5 in unnotched testing. The headline fatigue strength number favors Grade 5 slightly, but the more relevant metric for structural integrity is the fatigue crack growth rate — how quickly a crack extends once it has initiated.
Carpenter Technology data and published research consistently show Grade 23 ELI has a slower fatigue crack propagation rate, meaning once a crack does start, it grows more slowly. For damage-tolerant design philosophies — which govern most aerospace and implant applications — this is the metric that matters, not the initiation strength.
Medical Implants: Why ELI Is Non-Negotiable
For any device implanted in the human body — joint replacements, spinal instrumentation, dental implants, bone screws, pacemaker casings — Grade 23 (Ti-6Al-4V ELI) is the industry standard material, and in most cases, the regulatory requirement.
The reasons go beyond “better numbers on a spec sheet.”
Regulatory compliance. ASTM F136, the governing standard for wrought Ti-6Al-4V surgical implants, explicitly specifies ELI chemistry. A Grade 5 part with higher oxygen content does not meet F136 requirements. Submitting a 510(k) premarket notification to the FDA with Grade 5 material for an implant application would fail the material specification review.
Biocompatibility. While both grades show good biocompatibility, the lower interstitial content in Grade 23 produces a cleaner, more homogeneous surface oxide layer (TiO₂). The ELI chemistry is the industry standard for implant applications precisely because it meets the stricter requirements of ASTM F136 and has been validated across decades of clinical use in hip replacements, spinal implants, and dental applications.
Fatigue in the body. A hip implant femoral stem experiences approximately 1–2 million load cycles per year. A spinal rod in an active patient flexes with every movement. The human body is an extraordinarily demanding fatigue environment. Grade 23’s superior fracture toughness and slower crack growth rate directly address this challenge.
Revision surgery margin. When an implant must be revised or removed, the surrounding bone and tissue are compromised. Grade 23’s higher ductility means the implant can be more easily extracted without fracturing, and its tolerance for pre-existing micro-damage is higher.
I have seen procurement teams attempt to substitute Grade 5 for Grade 23 on implant components to reduce material cost by 20–30%. In every case I am aware of, this substitution has been rejected at the quality review stage. The regulatory and performance case for ELI in implants is simply too strong.
Engineering Applications Beyond Medical
Aerospace Structural Components
Grade 5 dominates general aerospace structural applications — bulkheads, wing fittings, engine mounts, landing gear components. Over 70% of all titanium alloy melted globally is some form of Ti-6Al-4V, and the majority of that is standard Grade 5.
Grade 23 appears in fracture-critical airframe structures — components where failure would be catastrophic and where inspection intervals must accommodate crack growth between checks. Think landing gear beams, wing carry-through structures, and engine fan blades. The extra toughness buys time in the inspection cycle.
Motorsport and High-Performance Automotive
In race car suspension components, chassis members, and drivetrain parts, Grade 5 is the default choice. The strength advantage matters more than the toughness advantage in these applications because parts are designed for shorter service lives with more frequent replacement.
That said, I have seen Grade 23 specified for roll cage joints and crash-structure components where energy absorption through deformation matters more than peak strength.
Fabbricazione additiva
The AM landscape is creating new nuances in the Grade 5 vs Grade 23 discussion. For powder bed fusion (PBF-LB, formerly SLM), Grade 23 ELI powder is increasingly preferred because:
- Lower oxygen content in the starting powder translates to lower oxygen in the finished part
- AM parts inherently have higher residual porosity than wrought, making fracture toughness more critical
- The slower solidification rates in AM produce different microstructures where the toughness advantage of ELI is preserved
For directed energy deposition (DED/WAAM), both grades are used. Published research (Mashigo et al., SAIMM 2021) found that WAAM-produced Grade 5 walls showed greater strength and hardness but lower ductility than Grade 23 walls — consistent with wrought behavior, confirming that the interstitial effect persists regardless of manufacturing method.
Cost Considerations: What the ELI Premium Really Looks Like
Grade 23 ELI carries a premium over Grade 5, typically in the range of 15–40% depending on product form, order volume, and supplier. For bar stock in common sizes, expect roughly 20–40% more. For certified medical-grade bar to ASTM F136 — with full material traceability, mill test reports, and lot-level documentation — the total cost premium can be higher due to the additional testing and certification overhead.
The cost premium reflects two factors. First, the tighter chemistry control during melting and refining requires additional processing steps and higher rejection rates. Second, medical-grade material carries the overhead of full material traceability, certified test reports (mill certificates), and lot-level quality documentation.
Is the premium justified? It depends entirely on the application:
| Applicazione | Grade 5 Cost-Efficiency | Grade 23 Justification |
|---|---|---|
| General aerospace structure | ✅ Grade 5 wins | No — standard strength is sufficient |
| Fracture-critical airframe | — | ✅ ELI mandatory per design spec |
| Medical implant | — | ✅ ELI required by ASTM F136/FDA |
| Racing component | ✅ Grade 5 wins | Only for crash structures |
| AM prototype (PBF-LB) | Consider Grade 23 | ✅ Better results in finished parts |
| Industrial equipment | ✅ Grade 5 wins | No — cost penalty without benefit |
Decision Framework: Which Grade Should You Specify?
Rather than a blanket recommendation, here is a decision tree based on the application requirements:
Step 1: Is the part implanted in the human body or a surgical instrument? → If YES: Grade 23 (ELI) — mandated by ASTM F136. No alternative. → If NO: Proceed to Step 2.
Step 2: Is the part fracture-critical (failure = safety incident)? → If YES: Strongly consider Grade 23 for the fracture toughness margin. → If NO: Proceed to Step 3.
Step 3: Is the part subject to significant cyclic loading (>10⁶ cycles)? → If YES: Evaluate whether Grade 5’s fatigue strength meets design requirements with adequate safety factor. If the margin is tight, Grade 23’s crack growth resistance provides insurance. → If NO: Proceed to Step 4.
Step 4: Is the design strength-limited (operating near yield)? → If YES: Grade 5 may be the better choice for its 3–8% strength advantage. → If NO: Grade 5 is the cost-effective default.
Step 5: Is the part made by additive manufacturing (PBF-LB)? → If YES: Consider Grade 23 ELI powder for better finished-part properties. → If NO: Grade 5 for general engineering.
Welding, Machining, and Heat Treatment Differences
Practically speaking, Grade 5 and Grade 23 behave very similarly during manufacturing. Both are fully heat treatable in section sizes up to approximately 15mm and can be solution treated and aged (STA) to enhance strength. Both respond well to conventional machining with proper tooling and parameters.
The differences are subtle but real:
Welding. Grade 23’s lower nitrogen content produces better weldability. Nitrogen increases the risk of weld porosity and embrittlement. For critical welded structures, ELI filler wire (ASTM B863 Grade 23) is preferred even when welding Grade 5 base material. In aerospace welding specifications, ELI consumables are often mandatory regardless of the base grade.
Heat treatment response. The lower oxygen content in Grade 23 means slightly different phase transformation behavior during heat treatment. The alpha-beta transition temperature shifts, and the resulting microstructure after STA may differ. For most applications, the standard heat treatment cycles work for both grades, but if you are optimizing for specific properties (e.g., maximizing fatigue life in an AM part), grade-specific heat treatment development is worthwhile.
Machining. No meaningful difference in practice. Both grades require the same tooling, speeds, and feeds. The slightly higher strength of Grade 5 may marginally increase tool wear, but this is within normal process variation.
Common Mistakes Engineers Make
Mistake 1: Assuming “higher strength = better.” Grade 5’s strength advantage exists mainly in heat-treated conditions. In annealed condition, both grades show comparable tensile and yield strengths. Specifying Grade 5 “because it is stronger” ignores the toughness trade-off and may result in a part that fails more catastrophically.
Mistake 2: Confusing ASTM B348 with ASTM F136. A B348 Grade 5 bar and an F136 Grade 23 bar look identical. They are not interchangeable for implant applications. Always verify which standard your design specification actually calls for.
Mistake 3: Treating ELI as a marketing label. Some suppliers market “ELI” quality without full F136 certification. If your application requires implant-grade material, insist on ASTM F136 certification with full material test reports — not just “ELI composition.”
Mistake 4: Ignoring oxygen content in AM powders. If you are specifying titanium powder for 3D printing, the oxygen content of the starting powder directly affects the finished part properties. Grade 5 powder with 0.20% oxygen will not produce Grade 23 properties in the finished part, regardless of the printing parameters.
Mistake 5: Overlooking cost at the system level. The material premium for Grade 23 is often small relative to the total cost of a finished implant (machining, surface treatment, sterilization, regulatory compliance, packaging). In my experience, the material cost difference is typically 2–5% of the total device cost — far less than the regulatory cost of getting a material substitution approved.
People Also Ask: Quick Answers
What is the difference between Ti-6Al-4V Grade 5 and Grade 23?
Grade 23 (ELI) has lower maximum limits for oxygen (0.13% vs 0.20%), nitrogen (0.03% vs 0.05%), and hydrogen (0.0125% vs 0.015%). This produces significantly higher fracture toughness (75–90 vs 55–75 MPa√m) and comparable ductility, with similar tensile strength in annealed condition.
Is Grade 23 titanium the same as implant-grade titanium?
Yes, Grade 23 (Ti-6Al-4V ELI) is the standard implant-grade titanium alloy when specified to ASTM F136. It is the most widely used medical implant-grade titanium alloy globally.
What does ELI stand for in titanium?
ELI stands for Extra Low Interstitials — referring to reduced oxygen, nitrogen, carbon, and hydrogen content compared to the standard alloy grade.
Is Grade 23 titanium better than Grade 5?
Neither is universally “better.” Grade 23 has superior ductility, fracture toughness, and biocompatibility. Grade 5 has higher tensile strength and lower cost. The right choice depends on the application.
Can Grade 23 be substituted for Grade 5?
Yes, Grade 23 can substitute for Grade 5 in most applications (it meets or exceeds Grade 5 mechanical requirements except for the modest strength difference). However, substituting Grade 5 for Grade 23 is not acceptable in implant applications governed by ASTM F136.
Why is Ti-6Al-4V ELI used instead of standard Grade 5?
For applications requiring superior damage tolerance (fracture toughness, fatigue crack growth resistance) or regulatory compliance with ASTM F136 for medical implants.
What is the price difference between Grade 5 and Grade 23?
Grade 23 typically costs 15–40% more than Grade 5 for commercial bar stock, depending on product form, order volume, and certification requirements. Certified medical-grade F136 material carries additional premium due to testing and traceability requirements.
Summary: An Engineer’s Perspective
After years of working with titanium alloy specifications across aerospace, medical, and industrial applications, the Grade 5 vs Grade 23 decision is one I see mishandled more often than it should be — usually because engineers default to Grade 5 “because it is stronger” without fully understanding the toughness trade-off.
Here is my bottom line:
Grade 5 is the workhorse. It is the right default for 80% of titanium structural applications. It is stronger, it is cheaper, and it is what your supplier has in stock. Do not switch away from it without a technical reason.
Grade 23 is the specialist. It exists for three specific reasons: medical implant compliance (ASTM F136), fracture-critical structural applications, and environments where damage tolerance matters more than peak strength. When you need it, you really need it — and there is no workaround.
The oxygen content is the entire story. If you remember nothing else from this article, remember this: 0.13% vs 0.20% oxygen is the line between these two grades. Everything else flows from that single chemistry specification.
If you are at the point of placing a material order and still uncertain which grade fits your application, I would strongly recommend consulting your material supplier’s technical team with your specific design requirements. The cost of that conversation is zero; the cost of specifying the wrong grade can be measured in rejected parts, failed certifications, or — in the worst case — field failures.
