Incoloy 903 Alloy
Low Thermal Expansion, High-Strength Nickel-Iron-Cobalt Alloy
Supplied by Huaxiao-Alloy – Your Trusted Global Alloy Partner
Incoloy® 903 Alloy is a precipitation-hardenable nickel-iron-cobalt alloy engineered for applications that demand very low thermal expansion, high strength, and excellent dimensional stability over a wide temperature range. It is especially valued where tight tolerances must be maintained during thermal cycling, making it a preferred material in aerospace, precision engineering, and high-performance mechanical systems.
Huaxiao-Alloy supplies Incoloy 903 Alloy in all product forms, strictly compliant with international standards, supporting aerospace manufacturers, energy equipment suppliers, and high-end engineering projects worldwide.
1. Incoloy 903 Alloy Overview
Incoloy 903 is designed to bridge the gap between Invar-type low-expansion alloys and high-strength nickel alloys. By combining nickel, iron, and cobalt with controlled additions of niobium, titanium, and aluminum, the alloy achieves:
Exceptionally low coefficient of thermal expansion (CTE)
High tensile and yield strength after aging
Excellent resistance to stress relaxation
Good fatigue and creep resistance
These characteristics make Incoloy 903 ideal for precision components exposed to temperature variation, where dimensional accuracy is mission-critical.
2. Chemical Composition (%)
| Element | Content (%) |
|---|---|
| Nickel (Ni) | 36.0 – 38.0 |
| Iron (Fe) | Balance |
| Cobalt (Co) | 14.0 – 16.0 |
| Chromium (Cr) | ≤ 0.50 |
| Niobium (Nb) | 2.4 – 2.8 |
| Titanium (Ti) | 0.6 – 1.0 |
| Aluminum (Al) | 0.3 – 0.7 |
| Carbon (C) | ≤ 0.03 |
| Manganese (Mn) | ≤ 0.50 |
| Silicon (Si) | ≤ 0.50 |
| Sulfur (S) | ≤ 0.015 |
Design Principle:
The Ni-Fe-Co matrix provides low thermal expansion, while Nb-Ti-Al precipitation delivers high mechanical strength after aging.
3. Mechanical Properties
Solution Annealed + Aged (Typical)
| Property | Value |
|---|---|
| Tensile Strength | ≥ 1200 MPa |
| Yield Strength (0.2%) | ≥ 850 MPa |
| Elongation | ≥ 12% |
| Hardness | 36 – 42 HRC |
| Fatigue Strength | Excellent |
| Stress Relaxation Resistance | Outstanding |
Properties may vary depending on section size and heat-treatment condition.
4. Physical Properties
| Property | Value |
|---|---|
| Density | 8.15 g/cm³ |
| Melting Range | 1360 – 1420°C |
| Coefficient of Thermal Expansion (20–300°C) | ~7.5 μm/m·K |
| Elastic Modulus | 195 GPa |
| Electrical Resistivity | 1.15 μΩ·m |
📌 Key Advantage:
The thermal expansion of Incoloy 903 is significantly lower than conventional nickel alloys, ensuring dimensional stability under thermal cycling.
5. Key Features & Advantages
📐 Extremely Low Thermal Expansion
Ideal for components where dimensional accuracy is critical.
💪 High Strength After Aging
Precipitation hardening provides exceptional yield and tensile strength.
🔁 Excellent Fatigue & Stress Relaxation Resistance
Performs reliably in cyclic loading and long-term service.
🔧 Good Fabricability
Can be machined and welded in solution-annealed condition, then aged for strength.
6. Available Product Forms (Huaxiao-Alloy Supply)
Huaxiao-Alloy offers Incoloy 903 Alloy in full range of forms:
Tubular Products
Seamless tubes
Precision mechanical tubing
Flat Products
Sheets
Plates
Strips
Long Products
Round bars
Square / flat bars
Forged bars
Wire & wire rod
Custom Components
Aerospace fasteners
Precision shafts
Instrumentation parts
Machined structural components
7. Standards & Equivalent Grades
| Standard | Designation |
|---|---|
| UNS | N19903 |
| ASTM | B637 |
| AMS | AMS 5708 / AMS 5710 |
| ASME | SB-637 |
| EN / DIN | Equivalent available upon request |
📄 Certification: EN 10204 3.1 / 3.2, full traceability available
8. Corrosion Resistance
Incoloy 903 is not designed as a corrosion-resistant alloy like Inconel or Incoloy Cr-rich grades. However, it offers:
Good resistance to atmospheric corrosion
Stable performance in controlled industrial environments
Excellent oxidation resistance at moderate temperatures
For aggressive corrosion environments, material selection support is recommended.
9. Typical Applications
Aerospace & Aviation
Engine casings
Structural rings
Precision fasteners
Control system components
Energy & Power Systems
Gas turbine components
Generator structural parts
Precision Engineering
Dimension-critical shafts
Instrumentation housings
Thermal cycling components
Defense & Advanced Manufacturing
High-performance mechanical assemblies
Fatigue-critical structural elements
10. Heat Treatment & Fabrication
Heat Treatment
Solution annealing: ~980°C, air cool
Aging: 720–760°C for precipitation hardening
Machining
Best performed in solution-annealed condition
Carbide tooling recommended
Welding
GTAW / GMAW suitable
Weld in solution-annealed condition
Post-weld aging restores strength
11. Quality Control & Inspection
Huaxiao-Alloy ensures:
Chemical analysis & mechanical testing
Heat-treatment verification
Ultrasonic & surface inspection
Dimensional inspection
PMI testing
Full mill test certificates
12. Why Choose Huaxiao-Alloy for Incoloy 903?
✔ Direct access to certified mills
✔ Aerospace-grade quality control
✔ Custom heat treatment available
✔ Precision machining support
✔ Export-standard packaging
✔ Competitive pricing & reliable delivery
📍 Production & Stock: Wuxi · Foshan · Shanghai Baoshan
🌍 Global Supply: North America · Europe · Middle East · Asia-Pacific
For dimension-critical components requiring low thermal expansion and high strength.
Incoloy 903 offers much higher strength while maintaining low thermal expansion.
Moderate corrosion resistance; not intended for highly aggressive environments.
Yes, AMS-certified supply is available on request.
Yes, aging heat treatment is required to achieve full strength.
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