11Cr-3Al (TC11)
Introduction to 11Cr-3Al (TC11)
11Cr-3Al, designated as TC11, is a high-strength, high-temperature alpha-beta titanium alloy developed primarily for demanding aerospace and power generation applications. With excellent high-temperature mechanical properties, superior creep resistance, and stable oxidation behavior, TC11 is ideal for service environments up to 500°C.
The alloy's strength and favorable machinability in the annealed or solution-treated condition make it a strong candidate for CNC-machined titanium parts. When processed using advanced CNC machining services, TC11 components can achieve high precision, superior fatigue performance, and long-term thermal stability for aerospace structures, compressor disks, and engine cases.
Chemical, Physical, and Mechanical Properties of 11Cr-3Al (TC11)
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Titanium (Ti) | Balance | Corrosion-resistant base with structural stability |
Chromium (Cr) | 10.0–12.0 | Beta stabilizer, improves oxidation and creep resistance |
Aluminum (Al) | 2.5–3.5 | Alpha stabilizer, increases strength and oxidation resistance |
Molybdenum (Mo) | 0.8–1.5 | Enhances hardenability and creep strength |
Silicon (Si) | ≤0.30 | Improves oxidation resistance |
Iron (Fe) | ≤0.50 | Residual element |
Oxygen (O) | ≤0.15 | Strength enhancer, must be controlled for ductility |
Carbon (C) | ≤0.08 | Residual element |
Hydrogen (H) | ≤0.015 | Controlled to prevent embrittlement |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 4.57 g/cm³ | ASTM B311 |
Melting Range | 1620–1670°C | ASTM E1268 |
Thermal Conductivity | 6.3 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.67 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 8.5 µm/m·°C | ASTM E228 |
Specific Heat Capacity | 560 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 115 GPa | ASTM E111 |
Mechanical Properties (Solution Treated + Aged)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 950–1050 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 850–950 MPa | ASTM E8/E8M |
Elongation | ≥10% | ASTM E8/E8M |
Hardness | 300–340 HB | ASTM E10 |
Creep Resistance | Excellent up to 500°C | ASTM E139 |
Fatigue Resistance | High | ASTM E466 |
Key Characteristics of 11Cr-3Al (TC11)
High-Temperature Performance: Maintains tensile strength above 950 MPa and exceptional creep resistance in continuous service at 450–500°C.
Oxidation and Thermal Stability: Chromium and aluminum promote the formation of a dense, protective oxide film, limiting material degradation in turbine and exhaust environments.
Excellent Fatigue Resistance: Suitable for rotating or vibrating components exposed to cyclical thermal and mechanical stress.
Good Weldability and Structural Integrity: Allows reliable joining and consistent mechanical performance post-heat treatment.
CNC Machining Challenges and Solutions for TC11 Titanium
Machining Challenges
Thermal Accumulation: TC11 has relatively low thermal conductivity, causing tool edge overheating and reduced lifespan during continuous cutting.
Elastic Recovery and Work Hardening: High elastic modulus and strain-hardening tendencies complicate final pass accuracy and chip control.
Abrasive Oxide Formation: The formation of hard surface oxides during high-speed machining can increase cutting tool wear.
High Surface Quality Requirements: Demands fine finishes (Ra < 0.8 µm) for aerospace sealing surfaces and rotating parts.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Fine-grain carbide, coated inserts | High-temperature wear resistance |
Coating | AlTiN or TiSiN | Resists adhesion, improves oxidation resistance |
Geometry | Positive rake, 0.05 mm honed edge | Reduces cutting force and heat buildup |
Cutting Speed | 20–45 m/min | Prevents thermal damage and chip welding |
Feed Rate | 0.10–0.20 mm/rev | Balances tool pressure and finish quality |
Coolant | Through-tool emulsion ≥100 bar | Enhances flushing and temperature control |
11Cr-3Al (TC11) Cutting Parameters (ISO 3685 Compliance)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 20–30 | 0.15–0.20 | 2.0–3.0 | 80–100 (Through-tool) |
Finishing | 40–50 | 0.05–0.10 | 0.2–0.5 | 100–150 |
Surface Treatment for TC11 Titanium Parts
Hot Isostatic Pressing (HIP) improves fatigue and creep performance by eliminating porosity and enhancing density.
Heat Treatment involves solution annealing at 950–970°C and aging at 500–540°C for optimal creep strength.
Superalloy Welding enables structural assembly under argon shielding with post-weld stress relief for aerospace integrity.
Thermal Barrier Coating (TBC) protects TC11 parts operating in oxidizing and thermal cycling environments such as turbine cases.
CNC Machining ensures ±0.01 mm tolerance and low Ra surface for critical rotating components.
Electrical Discharge Machining (EDM) allows precise feature generation on hardened and thick-walled parts.
Deep Hole Drilling supports L/D >30:1 with Ra ≤1.6 µm in high-temperature cooling components.
Material Testing includes creep testing, phase analysis, SEM imaging, and ultrasonic NDT to ensure structural soundness.
Material Testing and Analysis
TC11 components are subjected to tensile and creep testing at elevated temperatures, microstructure characterization via SEM, and ultrasonic flaw detection based on GB, AMS, and aerospace standards.
Industry Applications of 11Cr-3Al (TC11)
Aerospace: Compressor disks, engine casings, and load-bearing structures exposed to high thermal cycles.
Power Generation: Used in turbine blades, transition ducts, and combustion chambers for high-temperature strength.
Industrial Equipment: Ideal for rotating shafts and high-load mechanical assemblies subjected to thermal fatigue.
Defense: Utilized in aerospace defense propulsion and structural frame components.
FAQs
What CNC machining techniques are recommended for achieving tight tolerances on TC11 titanium parts?
How does TC11 compare to Ti-6Al-4V in high-temperature performance and oxidation resistance?
What post-processing methods improve TC11’s creep resistance and fatigue life?
Which industries use TC11 for turbine and thermal structural components?
What dimensional stability can be maintained in deep-pocket machining of TC11 titanium?
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