Ti-5Al-5V-5Mo-3Cr (Ti5553)

Ti-5Al-5V-5Mo-3Cr (Ti5553) is a high-strength near-beta titanium alloy tailored for CNC machining in aerospace and defense systems requiring exceptional strength, fatigue, and thermal performance.

Introduction to Ti-5Al-5V-5Mo-3Cr (Ti5553)

Ti-5Al-5V-5Mo-3Cr, widely known as Ti5553, is a high-strength near-beta titanium alloy developed for aerospace, defense, and structural applications requiring exceptional mechanical performance. It is known for its excellent strength-to-weight ratio, high fatigue resistance, and deep hardenability, making it ideal for components under extreme loading conditions.

Due to its hardness and metallurgical complexity, Ti5553 is best processed using advanced CNC machining services. High-precision CNC machined titanium parts made from Ti5553 must meet tight dimensional tolerances and stringent surface finish requirements, especially for use in aircraft structural elements, landing gear, and military systems.

Chemical, Physical, and Mechanical Properties of Ti-5Al-5V-5Mo-3Cr (Ti5553)

Chemical Composition (Typical)

Element	Composition Range (wt.%)	Key Role
Titanium (Ti)	Balance	Provides corrosion resistance and base strength
Aluminum (Al)	4.5–5.5	Alpha stabilizer, increases high-temperature strength
Vanadium (V)	4.5–5.5	Beta stabilizer, improves fatigue and toughness
Molybdenum (Mo)	4.5–5.5	Enhances creep resistance and hardenability
Chromium (Cr)	2.5–3.5	Contributes to phase stability and corrosion resistance
Zirconium (Zr)	≤0.3	Increases creep and fatigue resistance
Oxygen (O)	≤0.15	Strengthens alloy, affects ductility
Iron (Fe)	≤0.25	Residual element
Hydrogen (H)	≤0.015	Controlled to prevent embrittlement

Physical Properties

Property	Value (Typical)	Test Standard/Condition
Density	4.78 g/cm³	ASTM B311
Melting Range	1600–1650°C	ASTM E1268
Thermal Conductivity	6.8 W/m·K at 100°C	ASTM E1225
Electrical Resistivity	1.70 µΩ·m at 20°C	ASTM B193
Thermal Expansion	8.6 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	1100–1350 MPa	ASTM E8/E8M
Yield Strength (0.2%)	1030–1250 MPa	ASTM E8/E8M
Elongation	≥8%	ASTM E8/E8M
Hardness	340–390 HB	ASTM E10
Creep Resistance	Excellent	ASTM E139
Fatigue Resistance	High	ASTM E466

Key Characteristics of Ti-5Al-5V-5Mo-3Cr (Ti5553)

Ultra-High Strength: With yield strengths exceeding 1200 MPa, Ti5553 rivals steel in performance while offering nearly half the density.
Beta Phase Dominance: Its near-beta microstructure provides excellent hardenability and good thermal processability, ideal for forged or thick-section components.
Superior Fracture Toughness: Performs well in high-cycle fatigue environments, critical for aerospace fasteners and structural links.
Thermal Stability and Weldability: Although welding is challenging due to beta content, it can be achieved with proper filler and post-weld heat treatment.

CNC Machining Challenges and Solutions for Ti5553

Machining Challenges

High Strength and Work Hardening: Ti5553 rapidly works and hardens, leading to increased cutting forces and surface distortion if not machined with optimized tools.
Low Thermal Conductivity: Generates heat at the tool-workpiece interface, accelerating tool wear and risking dimensional drift.
Tool Adhesion and Notching: The alloy’s beta phase promotes galling and notch wear, especially on tool edges during turning and drilling.
Tight Tolerance Control: Springback and elastic recovery (~115 GPa modulus) require compensation in the final finishing stages.

Optimized Machining Strategies

Tool Selection

Parameter	Recommendation	Rationale
Tool Material	Fine-grain carbide or CBN	Ensures durability under high cutting stress
Coating	AlTiN or TiSiN (≥4 µm)	Provides thermal and abrasive protection
Geometry	Positive rake, edge honed	Minimizes cutting pressure and edge wear
Cutting Speed	20–50 m/min	Reduces thermal buildup
Feed Rate	0.10–0.25 mm/rev	Ensures clean chip formation
Coolant	High-pressure emulsion ≥100 bar	Prevents tool overheating and chip welding

Ti-5Al-5V-5Mo-3Cr (Ti5553) 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	45–60	0.05–0.10	0.2–0.5	100–150

Surface Treatment for Ti5553 Titanium Parts

Hot Isostatic Pressing (HIP) increases fatigue resistance and structural soundness, ideal for landing gear and linkage systems.

Heat Treatment involves treating the solution at ~830–870°C and aging at 480–600°C for strength optimization.

Superalloy Welding requires a beta-compatible filler and post-weld stress relief to prevent alpha cases or brittleness.

Thermal Barrier Coating (TBC) protects components in high-temperature thrust and propulsion environments.

CNC Machining ensures ±0.01 mm tolerances on parts like control arms and high-load structural brackets.

Electrical Discharge Machining (EDM) suits complex internal profiles and fine features.

Deep Hole Drilling delivers straightness <0.3 mm/m with Ra ≤1.6 µm in thick or structural aerospace assemblies.

Material Testing includes SEM, hardness mapping, creep analysis, and ultrasonic inspection to ensure aerospace-grade compliance.

Material Testing and Analysis

Ti5553 is evaluated through high-temperature tensile testing, microstructural phase validation, creep resistance testing, and ultrasonic NDT, following AMS and ASTM standards.

Industry Applications of Ti-5Al-5V-5Mo-3Cr (Ti5553)

Aerospace: Used in bulkheads, landing gear beams, and structural members requiring ultra-high strength.
Defense: Applied in armor frames, missile components, and blast-resistant structures.
Power Generation: Ideal for compressor casings and turbine components exposed to cyclical loads.
Industrial Equipment: High-stress mechanical couplings and load-bearing assemblies in automation and robotics.