Grade 23 titanium (Ti-6Al-4V ELI) is a very pure form of Ti-6Al-4V that is made to be tougher, more flexible, and more resistant to fatigue. Its very low interstitial content makes it more reliable and resistant to corrosion, which makes it perfect for biomedical, aerospace, marine, and cryogenic uses. This article looks at the microstructure, processing, and performance of Grade 23 titanium to explain why it is used in important, high-precision engineering systems.
Introduction
What Is Grade 23 Titanium ?
Grade 23 titanium (Ti-6Al-4V ELI, UNS R56401) is a high-performance α–β alloy that comes from Grade 5. It has less oxygen, carbon, nitrogen, and hydrogen than other grades. This improvement makes the material tougher, more flexible, and better able to withstand fatigue, especially when it is loaded in cycles or at very low temperatures.
Grade 23 has a tensile strength of about 860–900 MPa and is very biocompatible and resistant to corrosion. It is widely used in medical implants, aerospace parts, and precision-engineered parts. It is one of the most reliable titanium alloys for important uses because its stable TiO₂ passive film and ability to keep its strength at very high and low temperatures.
Key Differentiators from Standard Grade 5
| Property | Grade 5 (Ti-6Al-4V) | Grade 23 (Ti-6Al-4V ELI) | Remarks |
| Oxygen content | ≤ 0.20% | ≤ 0.13% | Lower O improves fracture toughness and fatigue resistance |
| Yield strength | ~880 MPa | ~860 MPa | Slight trade-off in strength for higher ductility |
| Elongation | 10–12% | 14–15% | Better plastic deformation tolerance |
| Fracture toughness (K_IC) | ~55 MPa√m | >75 MPa√m | Critical for fatigue- and impact-prone environments |
From a materials design point of view, getting rid of interstitials makes the lattice less distorted and less likely to break, which makes the microstructure more uniform. This means that Grade 23 is the best alloy to use when biointegration, surface finish, or failure tolerance are more important than small increases in strength.
For engineers, this means that they can trust parts that are critical to fatigue more; for procurement managers, it means that parts will fail less often and last longer in environments with changing stress or corrosion.
Common Application Fields
Grade 23 Titanium is engineered for mission-critical applications where structural reliability and human safety are non-negotiable:
- Aerospace & Cryogenic Systems – turbine blades, cryogenic pressure vessels, and high-cycle fatigue components benefit from its toughness and crack resistance at low temperatures.
- Medical & Biomedical Devices – orthopedic implants, dental screws, and surgical instruments leverage its biocompatibility (ISO 5832-3 compliant) and excellent osseointegration.
- Marine & Chemical Processing Equipment – pump housings, valves, and fasteners in seawater or chloride-rich environments where both strength and corrosion resistance are vital.
- Additive Manufacturing (3D Printing) – Ti-6Al-4V ELI powder is widely used in DMLS and EBM processes, enabling lightweight, custom geometries while retaining full mechanical integrity.
In essence, Grade 23 (Ti-6Al-4V ELI) represents the refined evolution of titanium engineering — maintaining the robust mechanical foundation of Grade 5 while optimizing microstructural purity and long-term reliability for the most demanding medical, aerospace, and marine systems.
Chemical Composition and Material Standards
Typical Composition (wt.%)
| Element | Al | V | Fe | O | C | N | H | Ti |
| Range | 5.5–6.75 | 3.5–4.5 | ≤0.25 | ≤0.13 | ≤0.08 | ≤0.05 | ≤0.0125 | Balance |
Grade 23 titanium maintains the same Al–V ratio as Grade 5, ensuring a balanced α+β dual-phase structure, but its significantly reduced interstitial content—especially oxygen and hydrogen—yields enhanced ductility, fatigue resistance, and fracture toughness. The lower impurity levels improve grain boundary cohesion, limiting microvoid formation under cyclic stress and enhancing resistance to hydrogen embrittlement and cold cracking.
Applicable Standards
- ASTM F136 – Medical implant-grade Ti-6Al-4V ELI
- ASTM B348 / AMS 4930 – Bars and forgings for aerospace and industrial use
- ISO 5832-3 – Biocompatibility compliance for surgical implants
- UNS R56401 – Unified Numbering System designation
Available forms: bar, plate, sheet, wire, tube, forgings, and AM-grade powder (for DMLS/EBM additive manufacturing). The alloy is typically supplied in mill-annealed or solution-treated and aged (STA) conditions, depending on strength and ductility requirements. STA condition achieves tensile strength up to 930 MPa while retaining excellent elongation (~14%).
Alpha-Beta Alloy System
Grade 23 is part of the α–β titanium alloy family, combining the benefits of both crystal structures:
- α-phase (hexagonal close-packed) → contributes corrosion resistance, thermal stability, and creep strength.
- β-phase (body-centered cubic) → provides formability, toughness, and hardenability.
The ELI-grade purity (Extra-Low Interstitials) strengthens the α/β phase interface, reducing the risk of microcrack propagation and fatigue initiation. This refined microstructure is particularly beneficial in fatigue-critical and biomedical environments, where both mechanical resilience and microstructural cleanliness are essential.
Microstructure and Mechanical Behavior
Microstructural Features
Grade 23 Titanium (Ti-6Al-4V ELI) exhibits a refined α + β dual-phase microstructure, optimized through controlled processing and low interstitial levels. The alloy typically contains 70–80% α phase distributed in a lamellar or bimodal morphology, with β phase forming between α colonies to enhance ductility and stress redistribution. The α grain size, generally 10–15 µm in the annealed condition, is tightly controlled to balance yield strength, ductility, and fatigue resistance.
The low oxygen content (≤ 0.13%) significantly reduces α-case embrittlement and improves crack-tip plasticity, allowing higher resistance to fatigue-crack propagation under cyclic stress. This clean microstructure—with minimal inclusions and homogeneous α/β interface bonding—is key to the alloy's exceptional fracture toughness and biomedical reliability.
Typical Mechanical Properties (Annealed Condition)
| Property | Typical Value |
| Density | 4.43 g/cm³ |
| Ultimate Tensile Strength (UTS) | 860 – 930 MPa |
| Yield Strength (0.2%) | 795 – 860 MPa |
| Elongation | 14 – 15 % |
| Elastic Modulus | 113 GPa |
| Hardness | ~ 32 HRC |
| Fatigue Strength (10⁷ cycles) | ~ 500 MPa |
Compared with standard Grade 5, Grade 23 provides a 10–15% increase in ductility and 20–30% higher fracture toughness, while maintaining nearly the same tensile strength. This makes it a superior choice where damage tolerance and cyclic durability are vital—such as medical implants, turbine fasteners, and aerospace joints.
Fracture and Fatigue Performance
The Extra-Low Interstitial (ELI) purity markedly improves fracture toughness (> 75 MPa√m) and reduces susceptibility to microcrack initiation. Under cyclic or corrosive service conditions, Ti-6Al-4V ELI demonstrates outstanding resistance to fatigue-crack growth, especially in environments where standard Grade 5 may show micro-notch sensitivity.
This enhanced performance stems from:
- Clean grain boundaries → minimize microvoid coalescence during cyclic loading.
- Uniform α/β interface bonding → stable crack-tip stress distribution.
- Reduced hydrogen and oxygen → elimination of brittle α-case formation.
As a result, Grade 23 is the material of choice for rotating, pressurized, or biomedical load-bearing components, ensuring long-term structural reliability and patient safety across demanding applications.
Processing, Machining, and Welding Guidelines
Machining Recommendations (Titanium Grade 23 Machining)
Grade 23 Titanium (Ti-6Al-4V ELI) maintains the same machining behavior as standard Grade 5 but is slightly more forgiving due to its higher ductility and lower interstitial content. However, its low thermal conductivity (~6.7 W/m·K) and high chemical reactivity with tool materials make it challenging to machine efficiently.
Machinability Index: ≈ 25–30% of AISI 4340 steel.
Recommended CNC Machining Parameters:
| Operation | Cutting Speed (m/min) | Feed (mm/rev) | Tool Type | Notes |
| Turning / Milling | 25–45 | 0.05–0.10 | Sharp carbide or TiAlN-coated tools | Avoid tool rubbing & built-up edge |
| Drilling | 10–25 | 0.03–0.10 | Solid carbide / PCD | Step drilling to reduce heat |
| Tapping | ≤15 | — | Spiral-flute TiN taps | Use high-lubricity oil |
| Surface Finish | — | — | Polished inserts | Maintain Ra < 0.8 µm for fatigue-critical parts |
Key machining practices:
- Always use flood or high-pressure coolant (water-based emulsion) to dissipate heat.
- Avoid dwell or tool rubbing — localized heating can cause work hardening and micro-cracking.
- After heavy machining, perform stress-relief annealing (600 °C / 1 h) to restore dimensional stability.
Forming, Forging, and Heat Treatment
Grade 23 retains good formability and forgeability for both aerospace and biomedical fabrication, provided proper temperature control is maintained.
- Hot working: 850–950 °C; avoid overheating to prevent grain coarsening.
- Cold working: feasible for thin-wall tubing, sheet, and wire—ensure intermediate annealing to prevent cracking.
- Annealing: 700–750 °C for 1 hour in an inert or vacuum environment to optimize ductility.
- Stress relief: 600 °C / 1 hour post-machining or forming effectively reduces residual stress while maintaining strength.
This controlled thermal treatment refines the α+β microstructure, enhancing both fatigue resistance and fracture toughness critical for cyclic or pressurized systems.
Welding and Additive Manufacturing
| Method | Recommendation |
| TIG / MIG | Use high-purity argon (99.999%) or helium shielding; ensure full back-purge coverage to prevent oxidation and embrittlement. |
| EBW / Laser Welding | Preferred for precision or thin-wall assemblies; produces clean fusion zones with minimal heat-affected distortion. |
| Additive Manufacturing (AM / 3D Printing) | Use low-oxygen Ti-6Al-4V ELI powder (≤0.13% O₂); apply post-build anneal (700 °C / 2 h) to restore ductility and reduce residual stress. |
| Post-weld Heat Treatment | 650–700 °C / 1 h improves joint toughness and relieves stress without altering base microstructure. |
Engineering insight: Grade 23's superior weldability and stable α+β balance make it highly suitable for complex medical implants, aerospace tubing, and thin-walled 3D printed structures, where precision and metallurgical integrity are critical. The ELI purity ensures minimal microstructural contamination, preserving long-term reliability in both static and fatigue-loaded applications.
Corrosion and Environmental Resistance
Surface Passivation Behavior
Grade 23 Titanium (Ti-6Al-4V ELI) exhibits exceptional corrosion resistance derived from its stable and self-healing TiO₂ passive film, which spontaneously forms upon exposure to air, water, or physiological fluids. This oxide layer—typically 3–6 nm thick—acts as a highly protective, adherent barrier that prevents further oxidation or ion diffusion. The ELI-level purity (reduced O, N, H) enhances the continuity and uniformity of this film, improving both electrochemical stability and resistance to chloride-induced breakdown. This makes Grade 23 one of the most reliable materials for long-term biomedical implants and marine applications, where exposure to saline or corrosive environments is unavoidable.
Key properties of the passive layer include:
- Low dissolution rate (<10⁻⁹ g/cm²·s) in saline and oxidizing media.
- Rapid reformation (<1 second) after mechanical damage or wear.
- Excellent bioinertness, ensuring no cytotoxic ion release in body fluids.
Environmental Stability
| Environment | Resistance | Remarks |
| Seawater | ★★★★★ | Immune to crevice and pitting corrosion up to 80 °C; superior to stainless steels and Ni-based alloys. |
| Body fluids | ★★★★★ | Completely biocompatible; forms a stable TiO₂ layer preventing metal ion leaching. |
| Oxidizing acids | ★★★★☆ | Excellent in nitric acid; not suitable for HF or concentrated HCl exposure. |
| Alkalis | ★★★★☆ | Stable against NaOH/KOH; surface oxidation may slightly increase at elevated temperatures. |
| Cryogenic conditions | ★★★★★ | Maintains toughness and ductility down to −196 °C; used in cryogenic pressure vessels. |
These characteristics enable Grade 23 to perform reliably across extreme environments—ranging from subzero aerospace systems to implant-grade biomedical conditions—without losing mechanical integrity or surface passivity.
Surface Enhancement Techniques
To further optimize corrosion, fatigue, and biocompatibility, a range of surface modification techniques are applied to Ti-6Al-4V ELI:
- Anodizing: Enhances corrosion resistance, aesthetic color control (for implants), and improves oxide layer thickness (~100 nm).
- Electropolishing: Produces mirror-like finishes with Ra < 0.2 µm, minimizing bacterial adhesion and stress concentrators — critical for medical implants and aerospace seals.
- PVD / DLC Coatings: Applied for wear-intensive or fatigue-loaded parts, providing additional protection against fretting, abrasion, and fatigue–corrosion coupling in cyclic load environments.
Collectively, these treatments ensure surface stability, biocompatibility, and long-term corrosion reliability, making Grade 23 a premier material for implantable devices, offshore systems, and cryogenic applications alike.
Comparative Analysis — Grade 23 vs Grade 5 Titanium
Mechanical and Physical Comparison
Grade 23 Titanium (Ti-6Al-4V ELI) can be viewed as the "refined" variant of Grade 5 Titanium, maintaining nearly identical mechanical performance while offering superior ductility, fracture toughness, and biocompatibility due to its lower interstitial content (O, N, C, H). These differences make Grade 23 ideal for critical or fatigue-sensitive applications, especially in biomedical and cryogenic environments.
| Parameter | Grade 5 (Ti-6Al-4V) | Grade 23 (ELI) | Impact / Engineering Implication |
| Oxygen (wt%) | ≤ 0.20 | ≤ 0.13 | Reduced oxygen enhances ductility & toughness |
| Yield Strength (MPa) | 880 | 820–860 | Slightly lower; still suitable for high-strength use |
| Elongation (%) | 10–12 | 14–15 | Greater formability & impact resistance |
| Fracture Toughness | ~55 MPa√m | >75 MPa√m | Superior crack resistance under fatigue loads |
| Fatigue Strength (10⁷ cycles) | 510 MPa | 500 MPa | Nearly equivalent in cyclic endurance |
| Biocompatibility | Good | Excellent | Ideal for medical implants and surgical tools |
Engineering Insight: The enhanced toughness and purity of Grade 23 make it far more forgiving during machining, welding, and additive manufacturing, where contamination or microdefects could compromise performance. Its microstructural uniformity also reduces the risk of stress-corrosion cracking and hydrogen embrittlement in marine and biomedical applications.
Design and Application Decision Matrix
When selecting between Grade 5 and Grade 23, designers should align alloy choice with the specific performance and reliability requirements of their systems:
Choose Grade 23 Titanium (ELI) for:
- Biomedical and Implant Applications: orthopedic, dental, spinal, or cardiovascular implants due to superior biocompatibility and fatigue resistance.
- Cryogenic and Fatigue-Critical Components: structural parts operating under high cycle loads or low temperatures.
- Thin-Wall or Welded Assemblies: aerospace tubing, marine piping, and precision structures requiring clean welds and ductile joints.
- Additive Manufacturing or Small-Batch Precision Parts: its refined chemistry improves layer bonding and reduces residual stress cracking.
Choose Grade 5 Titanium for:
- High-Load Structural Components: aerospace brackets, fasteners, engine parts, and automotive drivetrain elements requiring maximum static strength.
- Cost-Sensitive Industrial Uses: where extreme toughness or biocompatibility is not critical.
Lifecycle Cost and Reliability
| Metric | Grade 5 Titanium | Grade 23 Titanium (ELI) |
| Processing Cost | Moderate | Slightly higher (due to stricter purity control) |
| Maintenance / Replacement | Moderate | Lower — reduced fatigue failures and corrosion issues |
| Expected Service Life | 20–25 years | 30+ years (marine or biomedical use) |
| Lifecycle Cost Efficiency | 1 | ~1.25× better overall LCC performance |
Summary: While Grade 23 carries a slightly higher initial material cost, its superior fracture toughness, fatigue life, and chemical stability substantially lower the total cost of ownership (TCO) over long service intervals. For engineers and procurement specialists, this means fewer replacements, enhanced safety margins, and greater long-term reliability — especially in mission-critical aerospace or medical environments.
Engineering Applications and Case Studies
Medical and Biomedical
Grade 23 Titanium (Ti-6Al-4V ELI) is the benchmark material for high-performance medical and dental applications. Its extra-low interstitial (ELI) composition provides the ideal balance of biocompatibility, fatigue strength, and corrosion resistance, making it suitable for both temporary and permanent implants.
Typical applications include:
- Orthopedic implants: hip and knee joints, bone plates, spinal fixation rods, and trauma screws.
- Dental components: abutments, implants, and precision screws with tight-tolerance threads.
- Surgical tools: forceps, scalpels, retractors, and minimally invasive instruments.
Engineering benefits:
- Non-toxic and non-allergenic — chemically inert in contact with bone and soft tissue.
- Non-magnetic — compatible with MRI and CT imaging systems.
- Corrosion-free in body fluids — stable in saline, blood plasma, and interstitial fluids due to its protective TiO₂ passive film.
For biomedical design engineers, Grade 23 offers superior fatigue resistance (≈500 MPa @ 10⁷ cycles) and fracture toughness (>75 MPa√m), ensuring long-term implant reliability under cyclic loading, especially in orthopedic prostheses that endure millions of stress cycles annually.
Aerospace and Cryogenic Systems
In aerospace and cryogenic applications, Grade 23 Titanium is preferred when fracture toughness and low-temperature ductility are paramount. Its refined α+β structure maintains mechanical stability and resists embrittlement even at cryogenic temperatures down to −253 °C.
Key applications:
- Cryogenic storage tanks and pressure vessels for rocket propellants (LH₂, LOX).
- Aerospace engine housings, hydraulic fittings, and precision tubing.
- Thin-walled structures in launch vehicles or satellite propulsion systems.
Advantages:
- Maintains >90% of room-temperature strength at −200 °C.
- Exceptional stress-corrosion and hydrogen embrittlement resistance.
- Compatible with TIG, EBW, and laser welding, ensuring defect-free cryogenic joints.
This combination of toughness, corrosion immunity, and lightweight structure makes Grade 23 an ideal alternative to stainless steels and nickel superalloys in low-temperature aerospace systems.
Marine and Offshore Structures
Grade 23 Titanium demonstrates outstanding long-term durability in seawater and chloride-rich environments, where other metals like stainless steel or bronze often suffer pitting or crevice corrosion. Its self-healing TiO₂ film provides continuous protection, even under cyclic mechanical loading or micro-scratches.
Typical marine uses:
- Offshore oil & gas valves, pumps, and connectors.
- Desalination plant piping, heat exchangers, and condenser tubes.
- Submersible frames, control housings, and underwater robotics components.
Performance insights:
- Resists biofouling and galvanic corrosion — compatible with mixed-metal systems.
- Fatigue strength retention >90% after prolonged saltwater exposure.
- Service life exceeds 30 years with minimal maintenance in offshore conditions.
By combining Grade 5–level strength with Grade 2–level corrosion immunity, Grade 23 has become the preferred titanium alloy for mission-critical marine and medical components, ensuring reliability where material failure is not an option.
Design, Manufacturing, and Quality Considerations
Design for Manufacturability (DFM)
When designing components from Grade 23 Titanium (Ti-6Al-4V ELI), engineers must carefully balance mechanical performance, fatigue reliability, and manufacturability. The alloy's high strength and moderate elasticity require specific geometry and process control to prevent localized stress and distortion.
Key DFM Guidelines:
- Avoid sharp corners — adopt fillet radii ≥ 2 mm to minimize stress concentration and crack initiation during cyclic loading.
- Surface finish control — for fatigue-critical or biomedical parts, maintain Ra ≤ 0.8 µm (preferably ≤ 0.4 µm) through electropolishing or fine grinding to enhance fatigue life and corrosion resistance.
- Wall thickness uniformity — ensures even stress distribution and predictable deformation during hot or cold forming.
- Minimize welded joints — use monolithic designs whenever possible; if welding is necessary, apply post-weld annealing (650–700 °C) to restore α+β balance and relieve residual stress.
- Dimensional control for implants — CNC finishing tolerance ±0.005 mm is typical to meet medical-grade fit and surface requirements.
These guidelines are crucial for applications such as orthopedic implants, cryogenic tanks, and pressure housings, where dimensional stability and fatigue resistance directly affect product lifespan and safety certification.
Quality Control and Inspection
Due to its application in high-reliability and regulated industries (aerospace, medical, defense), Grade 23 Titanium demands comprehensive quality assurance throughout the manufacturing workflow.
Inspection and Certification Standards:
- Non-Destructive Testing (NDT):
- Ultrasonic Testing (UT) — detects internal porosity or inclusions.
- Dye Penetrant Testing (PT) — identifies surface microcracks after machining or welding.
- Microhardness Mapping — ensures uniform heat treatment response.
- Material Traceability: Each batch must conform to ASTM F136 / AMS 4930 / ISO 13485 requirements with full heat number tracking and mechanical certification (UTS, YS, elongation, hardness).
- Surface Integrity Validation (Implant Use):
- Surface roughness (Ra) verified via profilometry.
- Residual contamination control (per ISO 10993-18).
- Passivation and corrosion resistance testing (ASTM F86).
High-precision measurement tools—CMM, optical interferometry, and SEM analysis—are recommended for critical dimensions and surface cleanliness verification.
Sustainability and Recyclability
Grade 23 Titanium supports closed-loop manufacturing and green engineering principles due to its fully recyclable and inert nature.
Key sustainability advantages:
- 100% recyclability — remelting does not alter mechanical or chemical properties, ensuring circular material use.
- Minimal environmental impact — no toxic leaching or degradation products, even in long-term medical or marine service.
- Extended lifecycle — long service life (>30 years) reduces total material consumption and maintenance emissions.
- Compliance — meets RoHS, REACH, and ISO 14001 environmental management standards.
These factors make Ti-6Al-4V ELI an ideal choice for sustainable, high-reliability manufacturing, providing engineers and procurement teams with both technical performance and environmental responsibility in one material system.
Summary
Grade 23 titanium (Ti-6Al-4V ELI) is a very pure, very low-interstitial version of Ti-6Al-4V. It has an excellent balance of strength, ductility, fracture toughness, and resistance to fatigue. It has a tensile strength of 860–930 MPa and an elongation of about 15%, so it works well in cyclic, cryogenic, or corrosive conditions. Because it is biocompatible, resistant to corrosion, and doesn't react with other materials, it is the best material for medical implants, aerospace parts, and marine systems where safety and durability are very important.
Machining is hard, but precise CNC control, optimized tooling, and post-weld annealing make sure that the quality and dimensions stay the same. Grade 23 meets the standards set by ASTM F136 and ISO 13485. It has a long service life, can be recycled, and has low maintenance costs, making it a sustainable and high-value choice for important engineering applications that need reliability, performance, and biocompatibility.
FAQ
Q1: What is Grade 23 Titanium?
A: Grade 23 is Ti-6Al-4V ELI (Extra-Low Interstitial) — a titanium alloy with reduced oxygen, carbon, nitrogen, and hydrogen levels. This purity enhancement improves toughness, ductility, and fatigue resistance, making it ideal for high-reliability applications.
Q2: How is it different from Grade 5 Titanium?
A: Compared to Grade 5, Grade 23 has lower interstitial content, resulting in higher fracture toughness, improved ductility, and better biocompatibility. While slightly lower in strength, it performs better in fatigue-critical or medical uses.
Q3: Is Grade 23 suitable for marine environments?
A: Yes. It provides excellent resistance to seawater and chloride corrosion, maintaining integrity even in long-term offshore or submerged conditions.
Q4: Can Grade 23 be machined easily?
A: It is moderately machinable — use sharp carbide or TiAlN-coated tools, low cutting speeds (25–45 m/min), and ample cooling to prevent galling. It machines slightly easier than standard Grade 5.
Q5: Is it safe for implants and medical tools?
A: Absolutely. Grade 23 conforms to ASTM F136 and ISO 5832-3 standards for surgical implants. It's biocompatible, non-toxic, non-magnetic, and inert in body fluids.
Q6: What surface finishes are recommended for implants?
A: Electropolished or anodized finishes are preferred. Achieving Ra < 0.2 µm ensures optimal tissue integration, reduced bacterial adhesion, and enhanced corrosion resistance for long-term biomedical use.
About the Author: Gavin Xia
This article was written by engineers from the RAPID PROTOS team. Gavin Xia is a professional engineer and technical expert with 20 years of experience in rapid prototyping, metal parts, and plastic parts manufacturing.
