1. CHARACTERISTICS AND HEAT TREATMENTS
1.1. TYPES OF ALLOYS
1.1.1. α alloys
1.1.1.1. Characteristics
1.1.1.1.1. Moderate strength
1.1.1.1.2. High corrosion resistance
1.1.1.1.3. Single phase or small quantities of β
1.1.1.1.4. Properties highly depend on composition
1.1.1.2. Types
1.1.1.2.1. CP titanium
1.1.1.2.2. α alloys
1.1.1.2.3. near-α alloys
1.1.1.3. Strengthening mechanisms
1.1.1.3.1. Solid solution strenghtening
1.1.1.3.2. Grain size strengthening
1.1.1.3.3. Texture strengthening
1.1.1.3.4. Precipitation hardening
1.1.1.4. Microstructure
1.1.1.4.1. Equiaxed grains
1.1.1.4.2. Martensitic α'
1.1.1.4.3. Widmanstatten plates
1.1.1.4.4. “Basket weave”
1.1.2. α + β alloys
1.1.2.1. Characteristics
1.1.2.1.1. Contain 10-50% β phase at Troom
1.1.2.1.2. Most common: Ti-6Al-4V
1.1.2.1.3. Good formability
1.1.2.2. Heat treatments: high variety of microstructures
1.1.2.2.1. Structures
1.1.2.2.2. Process
1.1.3. β alloys
1.1.3.1. Characteristics
1.1.3.1.1. No martensitic transformation upon fast cooling
1.1.3.1.2. High formability (BCC structure)
1.1.3.1.3. Excellent forgeability
1.1.3.1.4. High hardenability
1.1.3.1.5. High yield strength (up to 1200MPa)
1.1.3.1.6. Low % β alloy usage
1.1.3.1.7. High content of solute elements
1.1.3.2. Most common
1.1.3.2.1. Ti-10V-2Fe-3Al
2. APPLICATIONS
2.1. Most Popular Ti alloy: Ti-6Al-4V
3. HELICOPTERS
4. LANDING GEAR ASSEMBLY
5. ROTOR HEAD
6. PHASE TRANSFORMATIONS
6.1. BCC-β -> HCP-α
6.1.1. depending on the cooling rate and alloy composition
6.1.1.1. Martensitic transformation (diffusionless)
6.1.1.1.1. Hexagonal
6.1.1.1.2. Athermal ω phase
6.1.1.1.3. Orthorhombic
6.1.1.2. Nucleation and growth (diffusion controlled
6.1.1.2.1. when cooling β to α+β phase at low rate
6.1.1.2.2. Increasing cooling rate
6.1.2. 12 different hexagonal α structures