Nickel–Copper alloys are a family of corrosion-resistant alloys containing primarily nickel (60–70%) and copper (20–35%), with minor additions of iron, manganese, or aluminum to enhance strength and corrosion control.
The most well-known Ni–Cu alloys are marketed under the Monel® name and are widely used in marine, chemical, oil & gas, and offshore applications due to their outstanding durability in aggressive environments.
Definition & Major Grades
| Alloy | UNS | Key Feature |
|---|---|---|
| Monel 400 | N04400 | General-purpose Ni–Cu alloy |
| Monel 401 | N04401 | Controlled carbon (electrical) |
| Monel 404 | N04404 | Low Curie temperature |
| Monel K-500 | N05500 | Precipitation-hardened |
| Monel R-405 | N04405 | Free-machining grade |
Chemical Composition – Monel 400
| Element | wt% |
|---|---|
| Nickel (Ni) | 63 – 70 |
| Copper (Cu) | 28 – 34 |
| Iron (Fe) | ≤ 2.5 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 0.5 |
| Carbon (C) | ≤ 0.3 |
| Sulfur (S) | ≤ 0.024 |
Chemical Composition – Monel K-500
| Element | wt% |
|---|---|
| Nickel | Balance |
| Copper | ~30 |
| Aluminum | 2.3 – 3.2 |
| Titanium | 0.35 – 0.85 |
| Iron | ≤ 2.0 |
Mechanical Properties
| Monel 400 (Annealed) | |
|---|---|
| Tensile Strength | 480 – 620 MPa |
| Yield Strength (0.2%) | 170 – 345 MPa |
| Elongation | 35 – 45% |
| Hardness | ~65 – 75 HRB |
| Impact Toughness | Excellent |
| Monel K-500 (Aged) | |
|---|---|
| Tensile Strength | 960 – 1100 MPa |
| Yield Strength | 690 – 760 MPa |
| Hardness | 30 – 40 HRC |
| Elongation | 20 – 25% |
Physical Properties
| Property | Value |
|---|---|
| Density | ~8.8 – 8.9 g/cm³ |
| Melting Range | 1300 – 1350 °C |
| Thermal Conductivity | ~22 W/m·K |
| Electrical Conductivity | ~3 – 4% IACS |
| Elastic Modulus | ~180 – 190 GPa |
| Magnetic Behavior | Non-magnetic (400) |
Corrosion Resistance
Nickel–Copper alloys offer exceptional resistance to seawater (static and flowing), hydrofluoric acid, alkalis, neutral salts, and brine environments. They are highly resistant to cavitation and erosion-corrosion.
Resistance is limited in strong oxidizing acids (such as nitric acid) and high-temperature sulfur environments.
Available Forms
Sheets & plates
Rods, bars & wire
Pipes & tubes
Forgings
Fasteners
Castings
Marine components
Applications
Marine & Offshore
Pump shafts, propeller shafts, valves, seawater piping
Chemical Processing
HF acid handling, alkali equipment, heat exchangers
Oil & Gas
Subsea components, corrosive service hardware
Power & Energy
Condensers, desalination plants
Advantages
✔ Exceptional corrosion resistance
✔ High strength without brittleness
✔ Excellent fatigue & impact resistance
✔ Long service life in seawater
✔ Good weldability
✔ Low maintenance
Limitations
❌ High material cost
❌ Limited resistance to oxidizing acids
❌ Machining difficulty in hardened condition
Why Choose Nickel–Copper Alloys?
Nickel–Copper alloys are selected when long-term corrosion resistance, mechanical reliability, and durability in marine or chemically aggressive environments are critical and maintenance access is limited.