The dominant titanium alloy — roughly 50% of all titanium produced worldwide. Ti-6Al-4V combines 896 MPa yield strength with biocompatibility, excellent corrosion resistance, and a strength-to-weight ratio that makes it structurally efficient where aluminum is too weak and steel is too heavy. Aerospace, medical implants, offshore, and motorsport are the primary consumers.
Titanium sits in a unique position in the materials spectrum: 45% lighter than steel, 65% stronger than aluminum, and more corrosion-resistant than either. Ti-6Al-4V (the "workhorse" grade) hits a sweet spot of strength, formability, and cost that no other titanium grade matches. Grade 2 pure titanium is more corrosion-resistant but too weak for structural use; the higher beta alloys (Grade 19, 23) have specialized applications but cost 2–3× more with marginal performance gains for most uses.
The main reason Ti-6Al-4V parts are expensive isn't the material cost (though at $25–40/kg it's 4× aluminum) — it's the machining difficulty. Titanium has low thermal conductivity (6.7 W/m·K vs. 167 for aluminum), so heat stays concentrated at the cutting edge, rapidly degrading carbide tooling. It chemically reacts with most tool materials at elevated temperatures. And it's stiff and springy, making thin walls prone to chatter. Expect Ti-6Al-4V parts to cost 3–5× the equivalent aluminum part, driven largely by cycle time and tooling consumption.
Before specifying Ti-6Al-4V, ask: is the weight savings worth 3–5× the cost vs. 7075 aluminum or 17-4 PH stainless? For aerospace primary structure and implants, yes. For brackets, enclosures, and general hardware, almost never. One common procurement win: identify legacy titanium parts whose original design rationale no longer applies (weight-critical became non-critical, or corrosion requirement softened) and value-engineer to aluminum or stainless.
| Element | Min % | Max % | Role |
|---|---|---|---|
| Titanium (Ti) | balance | Matrix | |
| Aluminum (Al) | 5.5 | 6.75 | Alpha stabilizer, strengthening |
| Vanadium (V) | 3.5 | 4.5 | Beta stabilizer, ductility |
| Iron (Fe) | — | 0.30 | Impurity, reduces ductility |
| Oxygen (O) | — | 0.20 | Controlled for strength (ELI = 0.13) |
| Carbon (C) | — | 0.08 | Impurity |
| Nitrogen (N) | — | 0.05 | Impurity |
| Hydrogen (H) | — | 0.0125 | Critical — hydrogen embrittlement |
For medical implants, specify Ti-6Al-4V ELI (Grade 23, ASTM F136) with tighter O, N, C, Fe limits and better fracture toughness.
| Property | Metric | Imperial | Test method |
|---|---|---|---|
| Ultimate tensile strength | 950 MPa min | 138,000 psi | ASTM E8 |
| Yield strength (0.2%) | 880 MPa min | 128,000 psi | ASTM E8 |
| Elongation at break | 14% min | 14% | ASTM E8 |
| Hardness | 334 HV / ~36 HRC | — | ASTM E384 |
| Modulus of elasticity | 114 GPa | 16.5×10⁶ psi | Half of steel — flex-prone |
| Density | 4.43 g/cm³ | 0.160 lb/in³ | — |
| Thermal conductivity | 6.7 W/m·K | — | Very low — heat stays at tool |
| Coefficient of thermal expansion | 8.6×10⁻⁶/K | — | Low — good for precision fits |
| Beta transus temperature | 995°C | 1823°F | Above this, phase change |
| Max service temperature | ~400°C | ~750°F | Sustained; creep above this |
| Biocompatibility | ISO 10993 compliant | Non-reactive with tissue | |
Titanium machining fundamentals: keep speeds down, feeds up, coolant heavy. Never let tools dwell or rub. Sharp cutting edges are mandatory — dull edges generate excess heat that destroys the tool and work-hardens the surface. Flood coolant (7% emulsion, high pressure 70+ bar through-spindle if possible).
| Operation | Surface speed (m/min) | Feed per tooth (mm) | Depth of cut | Tool |
|---|---|---|---|---|
| Face milling (rough) | 50–80 | 0.10–0.20 | 1.5–3 mm | Coated carbide, positive rake |
| Face milling (finish) | 60–90 | 0.08–0.12 | 0.2–0.4 mm | PVD-coated carbide or PCD |
| End milling (rough) | 40–70 | 0.05–0.12 | 0.5–1× dia | Solid carbide, variable helix, chip breakers |
| End milling (finish) | 50–90 | 0.03–0.08 | 0.1–0.3 mm | Fine-grain coated carbide, 4-flute |
| Drilling | 15–30 | 0.05–0.15/rev | — | Solid carbide, peck cycle, heavy coolant |
| Tapping | 3–6 | — | — | Cobalt spiral-flute, thread-form paste |
| Turning (rough) | 50–80 | 0.20–0.35/rev | 2–4 mm | Positive-rake carbide, chip breaker |
| Turning (finish) | 60–100 | 0.08–0.15/rev | 0.2–0.5 mm | Coated carbide or ceramic (limited) |
Engine fan blades, landing gear forgings, airframe fittings. Often forged then finish-machined. AMS 4928 / AMS 4911 specs.
Hip stems, knee components, bone plates, pedicle screws. Usually specified as Ti-6Al-4V ELI (Grade 23) per ASTM F136 for better fracture toughness.
Endosseous implants, abutments. Grade 4 or Grade 23 more common than standard Grade 5 for osseointegration surface treatments.
Subsea valves, heat exchangers, riser components. Ti's immunity to seawater crevice corrosion makes it cost-effective vs. super-duplex stainless in some applications.
F1 valve springs, connecting rods, wheel studs, suspension uprights. Weight reduction at stressed joints.
Reactor vessels, pump impellers handling chlorine, wet chlorine dioxide, nitric acid. Ti's uniform corrosion resistance in oxidizing chloride environments is unmatched.
| Grade | Composition | UTS | Primary use |
|---|---|---|---|
| Grade 1 | CP-Ti, 99.5%+ | 240 MPa | Chemical process liner, heat exchanger |
| Grade 2 | CP-Ti, 99.2%+ | 345 MPa | General industrial, offshore, weldable hardware |
| Grade 4 | CP-Ti, highest strength of unalloyed | 550 MPa | Surgical instruments, dental implants |
| Grade 5 (Ti-6Al-4V) | α-β alloy | 950 MPa | Aerospace structure, general implant grade |
| Grade 23 (Ti-6Al-4V ELI) | Low-interstitial Grade 5 | 860 MPa | Medical implants, cryogenic |
| Grade 19 (Ti-3Al-8V-6Cr-4Mo-4Zr) | β-alloy | 1240 MPa | Springs, high-strength fasteners |
Not primarily from material (though titanium is ~4× aluminum by weight, part weights are similar). The real cost driver is machine time: cutting speeds are 1/5–1/8 aluminum, tool life is shorter, and tolerances are usually tighter because the application demands them.
Titanium's low elastic modulus (half of steel) means thin walls flex more during machining and in service. If you need 0.5 mm walls, expect either significantly higher cost (multi-fixture strategy) or consider a 2024/7075 aluminum alternative.
Titanium absorbs hydrogen above 400°C, causing embrittlement. Avoid chlorinated solvents, some electroplating processes, and uncontrolled hot-acid cleaning. Post-machining contamination testing per ASTM E1447 is standard for aerospace parts.
Standard Grade 5 is acceptable for most aerospace uses, but medical implants require the extra-low interstitial variant (ASTM F136) for fracture toughness under cyclic loading. Costs ~10% more than Grade 5. Never substitute.
Fine titanium chips are pyrophoric. Our shop uses flood coolant (not air), collects chips in sealed containers, and never accumulates swarf near grinding operations. This is operationally routine but worth noting — cheap shops cutting dry titanium are a fire risk.
AS9100D documentation, AMS / ASTM-compliant material, passivation and electropolish for medical. Quote within 4 business hours.