Ti-6Al-4V ELI (Grade 23)
Introduction to Ti-6Al-4V ELI (Grade 23)
Ti-6Al-4V ELI (Grade 23) is the Extra-Low Interstitial (ELI) version of the widely used Ti-6Al-4V alloy, offering enhanced ductility, superior fracture toughness, and excellent biocompatibility. These characteristics make it ideal for critical medical implants, aerospace fasteners, and cryogenic components requiring exceptional purity and fatigue resistance.
Grade 23 is best manufactured using precision CNC machining services as a high-performance titanium alloy. Tight-tolerance CNC machined titanium parts from Ti-6Al-4V ELI are commonly used in high-stakes applications like surgical implants, engine mounts, and deep-sea hardware where material integrity is non-negotiable.
Chemical, Physical, and Mechanical Properties of Ti-6Al-4V ELI (Grade 23)
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Titanium (Ti) | Balance | Base element with corrosion resistance |
Aluminum (Al) | 5.5–6.5 | Alpha stabilizer, improves strength and thermal performance |
Vanadium (V) | 3.5–4.5 | Beta stabilizer, enhances strength and ductility |
Oxygen (O) | ≤0.13 | Reduced content improves ductility and fracture toughness |
Iron (Fe) | ≤0.25 | Residual element |
Carbon (C) | ≤0.08 | Controlled to maintain weldability |
Nitrogen (N) | ≤0.05 | Reduced to minimize embrittlement |
Hydrogen (H) | ≤0.0125 | Extra-low for biocompatibility and corrosion control |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 4.43 g/cm³ | ASTM B311 |
Melting Range | 1604–1660°C | ASTM E1268 |
Thermal Conductivity | 6.7 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.65 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 8.8 µm/m·°C | ASTM E228 |
Specific Heat Capacity | 560 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 114 GPa | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 825–900 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 795–860 MPa | ASTM E8/E8M |
Elongation | ≥15% | ASTM E8/E8M |
Hardness | 280–320 HB | ASTM E10 |
Fracture Toughness | >75 MPa√m | ASTM E399 |
Fatigue Resistance | Excellent | ASTM E466 |
Key Characteristics of Ti-6Al-4V ELI (Grade 23)
High Biocompatibility: Low oxygen and hydrogen levels make Grade 23 suitable for medical implants with strict ISO 10993 and ASTM F136 compliance.
Excellent Fracture Toughness: Improved toughness at cryogenic temperatures and under dynamic loads ensures reliability in critical aerospace and surgical applications.
Corrosion and Oxidation Resistance: Offers resistance to chlorides, saline, and bodily fluids, with stable oxide layer formation.
Weldability and Machinability: Easily welded with inert shielding; machinable to tight tolerances with proper tooling and cooling.
CNC Machining Challenges and Solutions for Grade 23 Titanium
Machining Challenges
Heat Generation and Low Conductivity: Similar to other titanium alloys, Ti-6Al-4V ELI accumulates heat in the cutting zone, accelerating tool wear.
Elastic Recovery: With a modulus of 114 GPa, spring back during finishing can affect dimensional precision in thin sections.
Galling and Notching: Galling can occur on cutting edges during dry machining or under insufficient cooling.
Surface Finish Requirements: Medical and aerospace parts often require Ra < 0.4 µm, demanding optimized cutting and post-processing.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Fine-grain carbide or coated carbide | Ensures edge retention and thermal resistance |
Coating | AlTiN or TiCN (≥3 µm) | Reduces adhesion and tool oxidation |
Geometry | Sharp edge, positive rake | Minimizes cutting forces and heat buildup |
Cutting Speed | 20–45 m/min | Controls thermal stress |
Feed Rate | 0.10–0.20 mm/rev | Ensures stable chip formation |
Coolant | Water-based emulsion ≥100 bar | Enhances cooling and surface integrity |
Ti-6Al-4V ELI (Grade 23) Cutting Parameters (ISO 3685 Compliance)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 20–30 | 0.15–0.20 | 2.0–3.0 | 80–100 (Through-tool) |
Finishing | 40–50 | 0.05–0.10 | 0.2–0.5 | 100–150 |
Surface Treatment for Grade 23 Titanium Parts
Hot Isostatic Pressing (HIP) improves fatigue resistance and eliminates internal porosity, vital for biomedical and flight hardware.
Heat Treatment includes stress relief and aging at ~700°C to enhance mechanical consistency and dimensional stability.
Superalloy Welding ensures high-integrity welds for surgical tools or aerospace housings using inert gas shielding.
Thermal Barrier Coating (TBC) offers protection in turbine and engine mounts where thermal cycling is extreme.
CNC Machining supports ±0.01 mm tolerances for implants and engine fittings requiring dimensional precision.
Electrical Discharge Machining (EDM) creates complex micro features without inducing mechanical stress.
Deep Hole Drilling enables the drilling of precision bores with Ra ≤1.6 µm and L/D > 30:1 in orthopedic implants or aerospace actuators.
Material Testing includes tensile testing, microstructure evaluation, and ultrasonic flaw detection in accordance with ASTM F136 and AMS 4930.
Material Testing and Analysis
Grade 23 undergoes rigorous validation, including tensile tests, fracture toughness evaluation, SEM inspection, corrosion testing, and ultrasonic flaw detection to meet aerospace and medical certification standards.
Industry Applications of Ti-6Al-4V ELI (Grade 23)
Medical Devices: Surgical implants, bone screws, and dental frameworks requiring superior fatigue and biocompatibility.
Aerospace: Jet engine brackets, structural fasteners, and cryogenic fuel systems.
Power Generation: Corrosion-resistant high-pressure components in turbines and piping.
Industrial Equipment: Components for cleanroom systems, chemical reactors, and marine environments.
FAQs
What makes Ti-6Al-4V ELI (Grade 23) suitable for medical implants and surgical instruments?
How does Grade 23 differ from standard Ti-6Al-4V in terms of purity and mechanical performance?
What surface treatments improve corrosion resistance for Ti-6Al-4V ELI?
How tight are the tolerances achievable in CNC machining of Grade 23 titanium?
In what conditions is HIP used for Ti-6Al-4V ELI parts?
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