Ti-3Al-2. 5V (Grade 12)

Ti-3Al-2.5V (Grade 12) is a corrosion-resistant titanium alloy optimized for weldability, moderate strength, and CNC machinability in marine, power, and chemical processing environments.

Introduction to Ti-3Al-2.5V (Grade 12)

Ti-3Al-2.5V, commonly called Grade 12 titanium, is a titanium alloy with a near-alpha microstructure strengthened by small additions of aluminum and vanadium. It offers a superior combination of moderate strength, high weldability, excellent corrosion resistance, and enhanced formability, especially in hot and marine environments.

Due to its strength and outstanding corrosion resistance—particularly in acidic, chloride, and oxidizing environments—Ti-3Al-2.5V is widely used for industrial piping systems, heat exchangers, and marine components. Manufacturers rely on CNC machining services and advanced processes to produce high-quality CNC machined titanium parts from Grade 12 with tight tolerances for long-term field performance.

Chemical, Physical, and Mechanical Properties of Ti-3Al-2.5V (Grade 12)

Chemical Composition (Typical)

Element	Composition Range (wt.%)	Key Role
Titanium (Ti)	Balance	Base element, excellent corrosion resistance
Aluminum (Al)	2.5–3.5	Alpha stabilizer, increases strength and ductility
Vanadium (V)	1.5–2.5	Beta stabilizer, improves hardenability and fatigue resistance
Oxygen (O)	≤0.25	Interstitial strengthener
Iron (Fe)	≤0.30	Residual element
Hydrogen (H)	≤0.015	Controlled to prevent embrittlement

Physical Properties

Property	Value (Typical)	Test Standard/Condition
Density	4.48 g/cm³	ASTM B311
Melting Range	1600–1650°C	ASTM E1268
Thermal Conductivity	7.2 W/m·K at 100°C	ASTM E1225
Electrical Resistivity	1.65 µΩ·m at 20°C	ASTM B193
Thermal Expansion	8.5 µm/m·°C	ASTM E228
Specific Heat Capacity	570 J/kg·K at 20°C	ASTM E1269
Elastic Modulus	110 GPa	ASTM E111

Mechanical Properties (Annealed Condition)

Property	Value (Typical)	Test Standard
Tensile Strength	620–725 MPa	ASTM E8/E8M
Yield Strength (0.2%)	500–620 MPa	ASTM E8/E8M
Elongation	≥18%	ASTM E8/E8M
Hardness	230–270 HB	ASTM E10
Creep Resistance	Moderate	ASTM E139
Fatigue Resistance	Good	ASTM E466

Key Characteristics of Ti-3Al-2.5V (Grade 12)

High Corrosion Resistance: Outstanding performance in oxidizing and mildly reducing environments, especially chlorides, nitric acid, and seawater.
Excellent Weldability and Ductility: Grade 12 welds cleanly without post-weld cracking and retains ductility, making it ideal for tanks, pipes, and marine structures.
Thermal Stability and Oxidation Resistance: Suitable for continuous use up to 400°C with strong surface oxide stability.
Good Cold and Hot Workability: Superior formability makes Grade 12 practical for heat exchangers, flanges, and fittings that require bending or deep drawing.

CNC Machining Challenges and Solutions for Grade 12 Titanium

Machining Challenges

Galling Tendency: Like other titanium alloys, Grade 12 sticks to tools, especially at elevated temperatures, affecting surface finish and precision.
Heat Accumulation: With moderate thermal conductivity (7.2 W/m·K), the alloy generates high local heat at the tool-workpiece interface, reducing tool life.
Springback and Low Modulus: The elastic modulus of 110 GPa causes noticeable springback in thin-walled parts, impacting finishing accuracy.
Tool Wear: Though not as hard as Grade 5 or 7, Grade 12’s work hardening behavior can degrade uncoated cutting tools rapidly under poor cooling conditions.

Optimized Machining Strategies

Tool Selection

Parameter	Recommendation	Rationale
Tool Material	Uncoated carbide or CBN	Maintains sharp edge and high heat resistance
Coating	TiAlN or TiSiN (3–5 µm PVD)	Helps prevent chip welding and galling
Geometry	Positive rake, honed edges	Reduces heat and cutting pressure
Cutting Speed	20–50 m/min	Prevents overheating and excessive tool wear
Feed Rate	0.10–0.25 mm/rev	Promotes chip evacuation and surface finish
Coolant	Water-soluble emulsion, ≥100 bar	Ensures temperature control and chip flushing

Ti-3Al-2.5V (Grade 12) 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 Grade 12 Titanium Parts

Hot Isostatic Pressing (HIP) is applied to critical parts to eliminate internal voids and increase fatigue and corrosion resistance.

Heat Treatment involves annealing at 700–760°C to improve ductility and dimensional stability in formed or welded parts.

Superalloy Welding enables robust welded joints for pressure vessels and chemical piping systems using matching filler wire.

Thermal Barrier Coating (TBC) offers added protection in heat exchanger and seawater systems where oxidation and scale formation are concerns.

CNC Machining supports tight-tolerance production of valves, pump parts, and tank nozzles with precision down to ±0.01 mm.

Electrical discharge machining (EDM) is effective in making micro holes and fine internal features without mechanical stress.

Deep Hole Drilling enables drilling to L/D > 30:1 with bore straightness under 0.3 mm/m and Ra ≤ 1.6 µm in chemical system assemblies.

Material Testing includes intergranular corrosion testing, tensile validation, SEM microstructural inspection, and ultrasonic flaw detection.

Material Testing and Analysis

Grade 12 titanium parts are tested for corrosion resistance (ASTM G28), mechanical strength (ASTM E8), and weld integrity through non-destructive testing (NDT) methods to meet industry and client specifications.

Industry Applications of Ti-3Al-2.5V (Grade 12)

Power Generation: Used in heat exchangers, pressure vessels, and steam condensers for its corrosion resistance and thermal stability.
Marine: Ideal for piping systems and structural elements in seawater or brine service conditions.
Chemical Processing: Resists attack in chlorinated and acidic media, including hypochlorite and nitric acid environments.
Defense: Grade 12 tubing and cladding used for ship systems and propulsion components requiring corrosion endurance.
Industrial Equipment: Used in fittings, tanks, and pressure system parts exposed to aggressive process media.