Cobalt plating is a high-performance electroplated or electroless metallic coating known for its exceptional hardness, wear resistance, high-temperature stability, corrosion resistance, and magnetic characteristics. It is widely used as an environmentally compliant alternative to hard chromium plating.
What Is Cobalt Plating?
Cobalt plating is the deposition of a thin, adherent cobalt metal layer onto a substrate such as steel, copper, brass, stainless steel, or nickel alloys using:
• Electroplating
• Electroless (chemical) plating
• Alloy plating (Co–P, Co–Ni, Co–W, Co–Mo)
Typical coating thickness ranges from 2 to 50 µm.
Chemical Composition
| Type | Composition |
|---|---|
| Pure Cobalt Plating | ≥ 99.0% Co |
| Co–P | Co 85–95%, P 5–15% |
| Co–Ni | Co 40–70%, Ni balance |
| Co–W | Co 70–90%, W 5–20% |
| Co–Mo | Co 75–90%, Mo 5–15% |
Key Mechanical Properties
| Property | Typical Range |
|---|---|
| Hardness (as-plated) | 450 – 700 HV |
| Hardness (heat-treated) | 800 – 1200 HV |
| Tensile Strength | 900 – 1400 MPa |
| Wear Resistance | Excellent |
| Fatigue Resistance | Very high |
| Adhesion Strength | Excellent |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.9 g/cm³ |
| Melting Point | 1495 °C |
| Thermal Conductivity | 70 – 100 W/m·K |
| Electrical Resistivity | ~0.06 µΩ·m |
| Magnetic Behavior | Ferromagnetic |
| Coefficient of Friction | 0.2 – 0.4 |
Strengthening & Metallurgical Behavior
• Fine grain structure (Hall–Petch strengthening)
• Solid-solution strengthening in alloy coatings
• Precipitation hardening (Co–P, Co–W systems)
• Residual compressive stresses improve fatigue life
• Maintains hardness up to 600–700 °C
Corrosion & Environmental Resistance
Cobalt plating provides excellent resistance to oxidation, alkaline environments, and high-temperature corrosion. It offers superior performance to chromium plating under thermal cycling and resists hydrogen embrittlement.
Processing & Post-Treatment
• Surface degreasing and activation
• Electroplating or electroless deposition
• Heat treatment for hardness enhancement
• Grinding, polishing, or lapping if required
Applications
Aerospace
Landing gear, actuators, turbine wear parts
Automotive
Piston rings, fuel systems, transmission shafts
Oil & Gas
Valve seats, pump components, drilling tools
Industrial & Medical
Molds, dies, surgical instruments, printing rollers
Advantages
✔ Hard chromium replacement
✔ Exceptional hardness and wear resistance
✔ High-temperature stability
✔ Uniform coating on complex geometries
✔ Environmentally compliant
Limitations
❌ Higher cost than nickel plating
❌ Controlled chemistry required
❌ Brittle if improperly heat treated
Why Choose Cobalt Plating?
Choose cobalt plating when components face severe wear, elevated temperatures, chromium restrictions, or demand long service life with minimal maintenance.