Overview

Titanium is a high-strength, low-density, corrosion-resistant light metal with the highest strength-to-weight ratio of any common engineering metal. Commercially pure (CP) Grade 2 is the most widely used titanium grade, offering excellent corrosion resistance to seawater, chlorides, and oxidizing acids, with good formability and weldability.

ρ = 4510 kg/m³ — roughly half the density of steel (7850 kg/m³) but with comparable strength at ~60% of the weight

Mechanical Properties (Grade 2 CP)

Property	Value
Density	4,510 kg/m³ (0.163 lb/in³)
Young's Modulus	107 GPa (half that of steel — 200 GPa)
Yield Strength	275 MPa (40,000 psi)
Ultimate Tensile	345 MPa (50,000 psi)
Elongation	20%
Hardness	120-200 BHN
Fatigue Limit	160 MPa
Melting Point	1668°C (higher than steel)

Grade 2 vs Grade 5 (Ti-6Al-4V)

Grade 5 (Ti-6Al-4V) is the most common titanium alloy — 900 MPa yield, but less ductile and harder to form. Grade 2 (CP) is preferred for chemical process equipment, heat exchangers, and marine applications where corrosion resistance and formability matter more than maximum strength.

Thermal Properties

Property	Value
Thermal Conductivity (20°C)	22 W/m·K (low — good insulator relative to steels)
Specific Heat	520 J/kg·K
Coefficient of Thermal Expansion	8.6 × 10⁻⁶ /°C (lower than steel)
Maximum Service Temperature	~600°C (oxidation limits)

Corrosion Resistance

Titanium's exceptional corrosion resistance comes from a self-healing TiO₂ passive film that forms instantly in oxygen-containing environments:

Seawater: essentially immune (negligible corrosion rates even after decades)
Chlorides: resistant to seawater, brines, bleach, wet chlorine gas
Oxidizing acids: excellent in nitric, chromic acids
Neutral/alkaline solutions: excellent
Weldable without loss of corrosion resistance (in inert atmosphere)

Titanium is attacked by:

Reducing acids (hydrochloric, sulfuric without oxidizers)
Hydrofluoric acid (aggressive attack, used for etching)
Hot concentrated caustic (above ~80°C)
Dry chlorine gas (without water, can ignite)

Applications

Aerospace: Aircraft structural components, engine parts, fasteners, landing gear (Grade 5 alloy)
Chemical processing: Heat exchangers, reactors, piping, valves, pumps for chloride service
Marine: Ship hulls, propeller shafts, seawater piping, offshore platform components
Medical: Implants (hip, knee, dental), surgical instruments (biocompatible, MRI safe)
Desalination: Evaporators, brine heaters, condenser tubing
Pulp & paper: Bleach plant equipment
Automotive: High-performance exhaust, valves, connecting rods (Grade 5)
Sporting goods: Bicycle frames, golf clubs, tennis rackets (Grade 9)

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Fabrication Notes

Welding: Readily weldable by GTAW (TIG), GMAW, PAW in pure argon atmosphere; requires trailing shield to protect hot metal from air
Machining: Lower modulus means more deflection; requires sharp tools, high feed rates, rigid setups
Forming: Grade 2 can be cold formed; springback is significant due to low modulus
Cost: Expensive (typically $20-50/kg vs $1-2/kg for steel), but justified by performance in demanding service

Titanium Fire Risk

Titanium can ignite and burn in high-oxygen environments (enriched air, LOX, pure oxygen at elevated pressure). Never use titanium in oxygen service above specific pressure-velocity thresholds without testing.

Summary

Titanium Grade 2 (density 4510 kg/m³) delivers steel-like strength at half the weight with near-immunity to seawater and chloride corrosion. It is the material of choice for aerospace (high strength-to-weight), chemical processing (chloride service), and marine applications despite its high cost. Its passivating TiO₂ film makes it one of the most corrosion-resistant engineering metals available.

Titanium (Grade 2 CP)