Ti-6Al-4V ELI (Grade 23) Titanium

Quick Answer

What is Ti-6Al-4V ELI (Grade 23) titanium?
Grade 23 (Ti-6Al-4V ELI — Extra Low Interstitial) is a higher-purity version of Grade 5 with reduced oxygen, iron, carbon, nitrogen, and hydrogen content. The lower interstitial element levels improve fracture toughness, fatigue resistance, and notch sensitivity at the cost of a minor reduction in absolute strength. Grade 23 is the standard material for surgical implant applications (ASTM F136) and is also specified for cryogenic aerospace components where enhanced toughness is critical.

Chemical Composition

Element	Weight %
Titanium (Ti)	balance
Aluminium (Al)	5.50–6.50
Vanadium (V)	3.50–4.50
Iron (Fe)	≤ 0.25
Oxygen (O)	≤ 0.13
Carbon (C)	≤ 0.08
Nitrogen (N)	≤ 0.05
Hydrogen (H)	≤ 0.012
Yttrium (Y)	≤ 0.005

Note: Reduced oxygen (≤ 0.13% vs ≤ 0.20% in Grade 5) is the primary distinction giving ELI its enhanced fracture toughness.

Mechanical Properties

Property	Value
Density	4.43 g/cm³
Tensile Strength	860 MPa (min)
Yield Strength (0.2% offset)	795 MPa (min)
Elongation	15%
Reduction of Area	35%
Hardness	34 HRC
Modulus of Elasticity	114 GPa
Max Service Temperature	400°C
Fracture Toughness (K₁c)	75 MPa√m (vs 55 MPa√m for Grade 5)
Fatigue Endurance Limit	480 MPa (10⁷ cycles)

Machinability

Grade 23 machines similarly to Grade 5 but with slightly lower cutting forces due to its reduced oxygen and iron content. The improved ductility can produce longer, stringier chips, requiring careful chip management. Tool life is comparable to Grade 5 under identical parameters.

Recommended Cutting Parameters

Operation	Speed (SFM)	Feed (IPT)	DOC
Rough Milling	150–250	0.004–0.008	0.100–0.200
Finish Milling	200–300	0.003–0.005	0.010–0.050
Turning	200–350	0.005–0.012	0.050–0.150
Drilling	50–120	0.002–0.006	—

Key considerations:

• Chip control is more important than for Grade 5; use chip breakers where possible
• Medical-grade surface finishes (Ra ≤ 0.4 µm) require dedicated finishing passes with wiper inserts
• Low-speed finishing (200–250 SFM) with small DOC (0.010–0.020 in) produces the best surface integrity
• Avoid chlorinated cutting fluids — residuals can cause corrosion in implant applications
• Cleanliness protocols for medical manufacturing (ISO 13485) add process overhead

Typical Applications

• Medical: Orthopaedic implants (hip stems, acetabular cups, knee components, trauma plates, spinal fixation), dental implants and abutments, surgical instruments requiring high fatigue life
• Aerospace (Cryogenic): Liquid hydrogen and oxygen tankage, cryogenic valve components, pressure vessels for space vehicles
• Semiconductor: Ultra-high vacuum (UHV) chamber components where outgassing limits are critical
• Research: Superconducting magnet containment structures, cryostat components

Related Standards

• ASTM F136 — Wrought Ti-6Al-4V ELI Alloy for Surgical Implant Applications (primary standard)
• ASTM B348 — Titanium and Titanium Alloy Bars and Billets
• ASTM B265 — Titanium and Titanium Alloy Strip, Sheet, and Plate
• ISO 5832-3 — Implants for Surgery — Ti-6Al-4V Wrought Alloy
• AMS 4930 — Titanium Alloy Sheet, Strip, and Plate (ELI, aerospace spec)

Related Processes

• 5-Axis CNC Machining — Essential for complex implant geometries (hip stems, spinal cages)
• CNC Turning — High-volume production of cylindrical implant components and dental abutments
• Wire EDM — Used for precision cutting of implant blanks and prototype runs
• Additive Manufacturing (DMLS) — Increasingly adopted for custom patient-specific implants
• Electropolishing — Produces mirror finishes (Ra < 0.2 µm) for implant bearing surfaces
• Passivation — Nitric acid passivation per ASTM F86 enhances the protective oxide layer