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Titanium Alloy

Ti-6Al-4V · Grade 5 · 880 MPa Yield · 4.43 g/cm³ · Zero Corrosion · Biocompatible

Ti-6Al-4V (Grade 5) is the most widely used titanium alloy — responsible for 50% of all titanium production. Its dual-phase α+β microstructure delivers an extraordinary strength-to-weight ratio: stronger than most steels at 57% of their density. The native TiO₂ passivation layer renders it immune to seawater, hydrochloric acid, and human body fluids simultaneously.

880 MPa
Yield Strength
4.43 g/cm³
Density
200 GPa
equiv. STS
316°C
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Ti-6Al-4V: A PhD-Level Tour

10 interactive modules — HCP crystal, dual-phase microstructure, corrosion immunity, fatigue, biocompatibility, and beyond.

Hexagonal Close-Packed (HCP) Structure
Pure titanium below 882°C adopts the α-phase: hexagonal close-packed (HCP). Each Ti atom has 12 nearest neighbours. The c/a ratio (1.587) is below ideal (1.633), creating slight anisotropy in slip systems that directly affects texture-dependent mechanical properties.
Crystal structure (α)HCP (P6₃/mmc)
Lattice a2.951 Å
Lattice c4.684 Å
c/a ratio1.587 (sub-ideal)
β transus temp995°C (Ti-6Al-4V)
Primary slip system⟨11̄20⟩{0001} basal
Coordination number12

The sub-ideal c/a ratio means prismatic slip planes ⟨11̄20⟩{101̄0} are easier to activate than ideal HCP metals. This gives Ti greater ductility than expected for HCP — critical for formability in aerospace manufacturing.

B Ti c = 4.684 Å a=2.951Å c/a = 1.587 ideal HCP = 1.633
Dual α+β Microstructure
Ti-6Al-4V contains 6 wt% Al (α-stabiliser, raises β transus) and 4 wt% V (β-stabiliser, lowers β transus). Below ~995°C, both α (HCP) and β (BCC) phases coexist. This dual-phase matrix provides simultaneously high strength (β) and ductility (α). Heat treatment controls the α/β volume fraction and morphology (equiaxed, lamellar, bimodal).
α phase fraction~90 vol% (STA)
β phase fraction~10 vol% (STA)
α crystalHCP · Al-rich
β crystalBCC · V-rich
β transus995 ± 15°C
Orientation relationshipBurgers: {110}β ∥ {0001}α

Bimodal microstructure (equiaxed primary α + lamellar transformed β) achieves the best combination of fatigue strength and fracture toughness. It is the standard for aerospace structural components like turbine blades, airframe brackets, and landing gear.

BIMODAL MICROSTRUCTURE (SEM MODEL) α α α β β β α phase (HCP, Al-rich ~90%) β phase (BCC, V-rich ~10%)
TiO₂ Passivation: Instantaneous & Permanent
Titanium reacts with oxygen in microseconds to form a dense, adherent TiO₂ layer (2–7 nm). Unlike iron oxide (rust), TiO₂ is thermodynamically stable in most environments, prevents further oxidation at all temperatures up to 500°C, and self-repairs when scratched in air or water.
OxideTiO₂ (rutile/anatase)
Thickness2–7 nm
Formation time<1 ms in air
Seawater corrosion rate0.00 mm/yr
HCl (20%) corrosion rate~0.01 mm/yr
H₂SO₄ (10%) corrosion~0.03 mm/yr
Pitting potential>10 V vs SCE

Titanium's outstanding corrosion resistance in chloride environments (seawater, body fluids, bleach) surpasses even 316L stainless steel. This makes it irreplaceable for offshore oil platforms, desalination plants, and medical implants that must last 30+ years inside the human body.

Ti BULK TiO₂ passivation (2–7 nm) O₂ O₂ Cl⁻ ⟵ ALL IONS REPELLED ⟶ O₂, Cl⁻, H₂O ENVIRONMENT Fe₂O₃ (rust): porous, non-adherent, grows without limit TiO₂: dense, adherent, self-limiting at 2–7 nm
Specific Strength: The Aerospace Metric
Specific strength (strength/density) determines material efficiency in weight-critical structures. Ti-6Al-4V achieves 200 kN·m/kg — surpassing all aluminium alloys and most steels, while being 57% the density of steel.
ASHBY CHART: SPECIFIC STRENGTH vs DENSITY 250 200 160 120 80 40 0 Spec. Strength (kN·m/kg) 1 2 4 6 8 10 Density (g/cm³) CFRP 240 Ti-64 200 Al 7075 175 Mar. Steel 240 316L SS 65 IN718 130 ★ Best strength/weight metal
200 kN·m/kg
Specific Strength
57%
of Steel Density
880 MPa
Yield Strength
114 GPa
Young's Modulus
Fatigue Strength & S-N Curve
Ti-6Al-4V exhibits an endurance limit of ~500 MPa at 10⁷ cycles — 57% of its UTS. Unlike aluminium which has no true fatigue limit, titanium alloys reach a stress below which fatigue does not occur. Surface treatment (shot peening, laser shock) further improves fatigue life by introducing compressive residual stresses.
UTS950 MPa
Fatigue limit (10⁷ cycles)~500 MPa
σ_f / UTS ratio0.53–0.58
Crack growth rate da/dN~10⁻⁸ m/cycle
Paris law exponent m3–5
Fracture toughness KIc75 MPa·m½

Shot peening introduces residual compressive stress of −400 to −600 MPa on the surface, effectively preventing crack initiation. In turbine blades, this extends maintenance intervals from 1000 to 5000 flight cycles.

S-N WÖHLER CURVE 950 800 650 500 350 0 Stress (MPa) 10³ 10⁴ 10⁵ 10⁶ 10⁷ Cycles to Failure (N) ~500 MPa Endurance Limit Al (no limit)
Phase Diagram & Thermal Processing
The binary Ti-V and Ti-Al phase diagrams together explain Ti-6Al-4V's thermal behaviour. Al raises the β transus (α-stabiliser), while V lowers it (β-stabiliser). Solution treatment above the β transus produces a fully β microstructure; cooling rate then controls the final α morphology.
β Single Phase Region (BCC) α + β Two-Phase Region β transus ~995°C 1100°C 995°C 800°C 500°C Sub-β anneal → equiaxed α+β Solution treat + quench RT Age 500°C/4h → lamellar α+β TREATMENT OUTCOMES Sub-β anneal: σ_y = 880 MPa KIc = 75 MPa·m½ ε_f = 14% (ductile) STA (solution+age): σ_y = 1100 MPa KIc = 55 MPa·m½ ε_f = 8% (harder) Beta anneal: σ_y = 840 MPa KIc = 88 MPa·m½ ε_f = 15% (toughest) ↑ Trade-off: strength vs toughness
Biocompatibility & Osseointegration
Ti-6Al-4V ELI (Extra Low Interstitial) is the gold standard for orthopedic and dental implants. The TiO₂ surface promotes direct bone bonding (osseointegration) without cement. Implants achieve >95% osseointegration at 12 weeks. Zero cytotoxicity — ISO 10993 certified.
ISO standardISO 5832-3 (ELI grade)
CytotoxicityZero (ISO 10993)
Osseointegration rate>95% at 12 wks
Elastic modulus114 GPa (vs bone 10–30)
Stress shieldingModerate (ELI grade)
Corrosion in PBS~0 µg/cm²·yr
ApplicationsHips, knees, spine, dental

The biggest challenge is the elastic modulus mismatch with bone (114 vs 20 GPa), causing "stress shielding" and bone resorption. Next-generation porous Ti-6Al-4V lattices printed by AM reduce effective modulus to 10–30 GPa — perfectly matching bone.

TiO₂ Osseointegration in progress New bone tissue bonds to TiO₂ surface No cement required · 30+ year lifespan Cortical bone Cortical bone Ti-6Al-4V ELI implant
Machinability Challenges & Solutions
Titanium's low thermal conductivity (7 W/m·K) concentrates cutting heat at the tool tip, causing rapid tool wear. Its high chemical reactivity with WC-Co tools causes built-up edge (BUE). Machinability rating: 20–40% of 316L steel. Solutions include cryogenic machining (LN₂), sharp carbide + TiAlN coating, low cutting speeds.
Thermal cond.7.2 W/m·K
vs Steel thermal cond.50 W/m·K (7× better)
Machinability rating20–40 (Al=100)
Cutting speed (WC)30–60 m/min
Depth of cut0.5–2 mm
Feed rate0.05–0.2 mm/rev
CoolantHigh-pressure flood / LN₂
Key Machining Strategies

✔ Sharp edges only — rake angle 5–15°, avoid built-up edge

✔ Cryogenic LN₂ cooling — 3× tool life vs dry machining

✔ PCD tools for high-volume runs (>10,000 parts)

✔ High-pressure coolant (70–100 bar) direct to cutting zone

✔ Vibration-assisted machining reduces cutting force 30%

✔ Near-net-shape AM minimises material removal (<10% vs 90% in billet machining)

Additive Manufacturing: LPBF & EBM
Ti-6Al-4V is the #1 metal for additive manufacturing. Laser Powder Bed Fusion (LPBF, 60–80 µm layers) produces dense parts (99.8%) with columnar β grains. Electron Beam Melting (EBM, 50–100°C preheat) yields better ductility through in-situ annealing. Buy-to-fly ratio drops from 20:1 to 1.2:1 for complex aerospace brackets.
LPBF density>99.8%
Layer thickness30–60 µm (LPBF)
σ_UTS (LPBF)1250 MPa (as-built)
Ductility (LPBF)6–8% (vs 14% wrought)
EBM temperature700–800°C (preheat)
Surface roughnessRa 4–20 µm (as-built)
Buy-to-fly ratio1.2:1 (vs 20:1 billet)
LPBF LAYER-BY-LAYER DEPOSITION Ti-6Al-4V powder bed Galvo scanner ↔ recoater Argon atmosphere · O₂ < 100 ppm Build volume: 250×250×300 mm typical Laser: 200–400 W IPG Ytterbium fiber Layer time: 30–60 µm in 30–90 s
Ti-6Al-4V vs Competitor Aerospace Alloys
Comprehensive comparison across density, strength, temperature, cost, and machinability against aluminium 7075-T6, Inconel 718, and maraging steel 350.
Property Ti-6Al-4V ★ Al 7075-T6 Inconel 718 Mar. Steel 350 316L SS
Density (g/cm³) 4.43 2.81 8.19 8.0 8.0
Yield Strength (MPa) 880 503 1036 2400 290
Spec. Strength (kN·m/kg) 200 179 127 300 36
Max Temp. (°C) 316 120 650 200 870
Corrosion (seawater) Excellent Fair Excellent Poor Good
Machinability (%) 30 100 10 30 50
Biocompatible Yes ✔ Partial No No Partial

Ti-6Al-4V is the only metal simultaneously competitive in aerospace (specific strength), marine (corrosion), biomedical (biocompatibility), and chemical processing (inertness). No single competing alloy covers all four domains — making titanium the universal premium structural metal.

Titanium Alloy for Your Application

Neo Materials supplies Ti-6Al-4V Grade 5 and ELI Grade 23 as bar, sheet, tube, forging, and additive manufacturing powder. Custom heat treatment and surface finishing available.

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