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

Material Profile: Titanium Alloy Ti-6Al-4V (Grade 23 ELI) for Direct Metal Laser Sintering

SLS Engineering Material Technical Report Series

Compiled from manufacturer technical datasheets and peer-reviewed literature

Abstract—Ti-6Al-4V (Grade 5 standard / Grade 23 'ELI' — Extra Low Interstitial) is the workhorse α+β titanium alloy and the dominant titanium powder for laser powder-bed fusion. It combines a specific strength (UTS / density) approximately twice that of stainless steel, exceptional corrosion resistance in chloride and biological environments, and certified biocompatibility for permanent orthopaedic implants (ASTM F3001 specifies Ti-6Al-4V ELI for AM medical use). DMLS-built Ti6Al4V achieves as-built UTS ≈ 1 200 MPa and yield ≈ 1 050 MPa due to the rapid-solidification α' martensitic microstructure — substantially exceeding wrought Ti-64 (UTS ~ 950 MPa). Subsequent stress-relief (650–800 °C) decomposes the metastable α' to α + β, reducing UTS to ~ 950 MPa but raising elongation from 4 % to 10 % — typically required for biomedical and aerospace certification. ELI grade limits oxygen ≤ 0.13 wt% and iron ≤ 0.25 wt%, improving fracture toughness and notch sensitivity at the cost of slightly lower yield strength.

Index Terms—additive manufacturing, DMLS, SLM, Ti6Al4V, titanium alloy, Grade 23, ELI, biomedical, aerospace, ASTM F3001.

I.  MATERIAL IDENTIFICATION

This section establishes the canonical names and commercial designations under which the material is supplied.

A.  Designation

Trade names: EOS Titanium Ti64 (Grade 5) and Ti64 ELI (Grade 23); 3D Systems LaserForm Ti Gr5 / Gr23; SLM Solutions Ti Gr5 / Gr23; Renishaw Ti6Al4V ELI. The wrought / cast equivalent is ASTM B348 Grade 5 (standard interstitials) or Grade 23 (low interstitials). For AM specifically, ASTM F3001 is the dominant certification standard.

B.  Full Chemical Name

Two-phase (α + β) titanium alloy with aluminium and vanadium additions. Composition for Grade 23 ELI (wt%): Al 5.5–6.5, V 3.5–4.5, Fe ≤ 0.25, O ≤ 0.13, N ≤ 0.03, C ≤ 0.08, H ≤ 0.012, Y ≤ 0.005, Ti — balance. Aluminium is an α-stabiliser, vanadium a β-stabiliser; the eutectoid microstructure gives the alloy its characteristic α+β duplex morphology.

C.  Aliases and Alternative Designations

II.  COMPOSITION AND MOLECULAR STRUCTURE

A.  Empirical Chemical Formula

Ti(balance) — Al(5.5–6.5%) — V(3.5–4.5%) — minor interstitials O, N, C, H, Fe. Phases: hexagonal-close-packed α-Ti (matrix), body-centred-cubic β-Ti (intergranular), and rapidly-solidified α' martensite (dominant in as-built DMLS state).

Fig. 1.  Repeating unit / structural schematic of the polymer matrix.

Fig. 2.  Schematic of the single-phase polymer (no reinforcement).

B.  Composition Breakdown

TABLE I
 COMPOSITIONAL BREAKDOWN OF TI6AL4V GRADE 23 ELI (EOS TITANIUM TI64 ELI) (TYPICAL / PER SUPPLIER DATASHEET)

III.  MECHANICAL PROPERTIES — XY BUILD DIRECTION (HORIZONTAL)

In the XY orientation the tensile load is applied parallel to the powder-bed plane (in-plane). For polymer SLS this is typically the stronger orientation due to better neck formation between particles within a single layer; for metal DMLS/SLM, columnar β / α-grain growth perpendicular to the build direction also yields different anisotropy that is partially relieved by post-build heat treatment (e.g. stress-relief, HIP).

TABLE II
 MECHANICAL PROPERTIES — XY ORIENTATION (TI6AL4V GRADE 23 ELI (EOS TITANIUM TI64 ELI))

IV.  MECHANICAL PROPERTIES — Z BUILD DIRECTION (VERTICAL)

In the Z orientation the tensile load is applied perpendicular to the powder layers; failure occurs across inter-layer fusion bonds. For polymer SLS the Z properties are typically 70–90 % of XY; for metal LPBF (laser powder-bed fusion) processes Z elongation is often higher due to the columnar grain structure but UTS / yield can be slightly lower in the as-built state. Heat treatment (anneal, HIP) reduces the anisotropy substantially.

TABLE III
 MECHANICAL PROPERTIES — Z ORIENTATION (TI6AL4V GRADE 23 ELI (EOS TITANIUM TI64 ELI))

Ti6Al4V DMLS has an unusual anisotropy pattern: Z-direction UTS and elongation are slightly higher than XY because columnar prior-β grains grow parallel to the build direction, aligning with the load axis in Z-direction tensile testing. Heat treatment at 800 °C for 2 h decomposes the α' martensite to a fine α+β lamellar structure, raising elongation, slightly reducing UTS, and homogenising properties to near-isotropy. Hot Isostatic Pressing (HIP) at 920 °C / 100 MPa / 2 h is mandatory for fatigue-critical aerospace and biomedical applications — eliminates residual microporosity and dramatically improves fatigue life.

V.  RECOMMENDED PROCESS PARAMETERS

Values summarised below give consensus operating windows from public datasheets (EOS, 3D Systems, BASF Forward AM, SLM Solutions). Specific machines and parameter sets may differ within ±10 %; the supplier's verified parameter sheet always supersedes this table.

TABLE IV
 RECOMMENDED LASER POWDER-BED-FUSION PROCESS PARAMETERS FOR TI6AL4V GRADE 23 ELI (EOS TITANIUM TI64 ELI)

VI.  GLASS TRANSITION TEMPERATURE (TG)

Reported / typical Tg: Not applicable (metallic alloy).

Metallic alloys do not exhibit a glass transition. The α → β transus for Ti-6Al-4V is ~995 °C — above this temperature the HCP α phase fully transforms to BCC β. Continuous service temperature (oxidation-limited) is approximately 350 °C; mechanical-property-limited (creep) is ~ 400 °C.

VII.  HEAT DEFLECTION TEMPERATURE (HDT)

Heat deflection temperature is the temperature at which a standard bar deflects 0.25 mm under a specified flexural load (ASTM D648 / ISO 75).

TABLE V
 HEAT DEFLECTION TEMPERATURE OF TI6AL4V GRADE 23 ELI (EOS TITANIUM TI64 ELI) UNDER STANDARD TEST LOADS

VIII.  DISTINGUISHING CHARACTERISTICS AND STANDARDS

A.  Specific strength — twice steel

UTS / density of Ti-6Al-4V is approximately 270 MPa·cm³/g, vs ~85 for 316L stainless steel. This makes Ti-6Al-4V the alloy of choice for mass-critical aerospace, sport (cycling, racing) and orthopaedic-implant applications. The 113 GPa modulus is also closer to cortical bone (~20 GPa) than 316L (~190 GPa), reducing implant stress-shielding.

B.  Biocompatibility & ASTM F3001 certification

Ti-6Al-4V ELI Grade 23 is the only AM titanium alloy with a dedicated AM-specific medical-implant standard, ASTM F3001. The alloy passes ISO 10993 cytotoxicity, sensitisation, and intracutaneous reactivity, and is approved by FDA for permanent orthopaedic implants (acetabular cups, spinal cages, dental implants) when produced to F3001 with HIP and validated machining.

C.  Excellent corrosion resistance

Spontaneously forms a passive 2–5 nm TiO₂ surface oxide that is exceptionally stable in chloride (seawater, body fluids, sweat), oxidising acid, and most reducing media. Pitting and crevice corrosion resistance both exceed 316L by an order of magnitude — the principal reason for use in marine and biomedical applications.

D.  Anisotropy & heat-treatment dependence

As-built Ti-6Al-4V has high yield (~ 1 050 MPa) due to α' martensite, but limited elongation (~7 %). Stress relief at 650–800 °C decomposes α' to α+β, dropping UTS by ~10 % but doubling elongation. HIP further reduces porosity-driven fatigue scatter. Selecting the post-process route is essential — 'as-built' Ti-6Al-4V should never be used for fatigue-critical or impact-loaded parts.

E.  Oxygen sensitivity — strict argon control

Ti getters oxygen aggressively at temperatures above ~400 °C; build-chamber O₂ must be held below 100 ppm to avoid surface and through-thickness oxide pickup. Powder must be stored under inert gas, and recycled powder oxygen content must be monitored — typically rejecting powder once O₂ exceeds 0.20 wt% in ELI grade.

IX.  REPRESENTATIVE APPLICATIONS

Ti6Al4V Grade 23 ELI (EOS Titanium Ti64 ELI) is typically deployed in the following applications:

1)  Patient-specific orthopaedic implants: Acetabular cups, spinal cages, cranial plates, and custom tumour-resection implants — the prototypical AM application, leveraging F3001-certified Ti-64 ELI for permanent body contact.

2)  Dental implants and surgical guides: Personalised dental implants with surface lattice for osseointegration; sterilizable cutting guides.

3)  Aerospace structural brackets and frames: Mass-optimised brackets and engine-pylon fittings — typical 30–60 % mass reduction vs machined Ti billet at equivalent stiffness.

4)  Aircraft engine components: Static engine parts (compressor brackets, fuel-system fittings, heat-shield supports) — Ti-64 service limit (~350 °C) restricts to cold sections; hot sections use Ni-base superalloys (Inconel 718, 625).

5)  Motorsport and high-performance bicycle components: Lightweight handlebars, custom suspension uprights, and titanium racing bicycle frames — lattice-stiffened structures impossible to machine.

X.  REFERENCES

[1]  EOS GmbH, “EOS Titanium Ti64 ELI — Material data sheet,” EOS Metal Solutions, 2024.

[2]  ASTM International, “F3001-14: Standard Specification for Additive Manufacturing Titanium-6 Aluminum-4 Vanadium ELI (Extra Low Interstitial) with Powder Bed Fusion,” 2014.

[3]  Z. A. Mierzejewska, “Effect of Laser Energy Density, Internal Porosity and Heat Treatment on Mechanical Behavior of Biomedical Ti6Al4V Alloy Obtained with DMLS Technology,” Materials, vol. 12, no. 14, p. 2331, 2019. [Online]. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6678663/

[4]  M. Vrancken et al., “Mechanical Properties and Microstructure of DMLS Ti6Al4V Alloy Dedicated to Biomedical Applications,” Materials, vol. 12, no. 1, p. 176, 2019. [Online]. Available: https://www.mdpi.com/1996-1944/12/1/176

[5]  I. Yadroitsev and I. Smurov, “Tensile properties and microstructure of direct metal laser-sintered TI6AL4V (ELI) Alloy,” ResearchGate, 2016.

[6]  J. P. Choi et al., “A state-of-the-art direct metal laser sintering of Ti6Al4V and AlSi10Mg alloys,” Optik, vol. 248, 168162, 2021. [Online]. Available: https://www.sciencedirect.com/science/article/abs/pii/S0030399221004540

[7]  ISO 6892-1:2019, “Metallic materials — Tensile testing — Part 1: Method of test at room temperature,” ISO, 2019.

[8]  ASTM E8/E8M-22, “Standard Test Methods for Tension Testing of Metallic Materials,” ASTM International, 2022.

[9]  ASTM F3001-14, “Standard Specification for Additive Manufacturing Titanium-6 Aluminum-4 Vanadium ELI (Extra Low Interstitial) with Powder Bed Fusion,” ASTM International, 2014.

[10]  ASTM F3122-14, “Standard Guide for Evaluating Mechanical Properties of Metal Materials Made via Additive Manufacturing Processes,” ASTM International, 2014.

[11]  ASTM F3055-14a, “Standard Specification for Additive Manufacturing Nickel Alloy (UNS N07718) with Powder Bed Fusion,” ASTM International, 2014.

[12]  ASTM B348/B348M-19, “Standard Specification for Titanium and Titanium Alloy Bars and Billets,” ASTM International, 2019.

[13]  ISO 5832-3:2016, “Implants for surgery — Metallic materials — Part 3: Wrought titanium 6-aluminium 4-vanadium alloy,” ISO, 2016.

(Image Source : Forgelabs)