Cobalt alloys are high-performance engineering materials designed to operate under extreme wear, high temperature, corrosive, and high-stress environments. They are renowned for exceptional hot hardness, wear resistance, oxidation resistance, corrosion resistance, and biocompatibility.
What Are Cobalt Alloys?
Cobalt alloys are metallic systems where cobalt is the primary base element, alloyed with chromium, tungsten, molybdenum, nickel, and carbon to enhance strength, wear, and environmental resistance.
Major families include:
• Cobalt–Chromium (Co–Cr)
• Cobalt–Chromium–Tungsten (Co–Cr–W)
• Cobalt–Nickel–Chromium
• Cobalt-based superalloys
• Hardfacing cobalt alloys (Stellite® type)
Typical Chemical Composition
| Element | Typical wt% |
|---|---|
| Cobalt (Co) | Balance (50 – 65) |
| Chromium (Cr) | 25 – 32 |
| Tungsten (W) | 4 – 14 |
| Carbon (C) | 0.8 – 2.5 |
| Nickel / Iron | ≤ 3 |
| Silicon, Manganese | Trace |
Key Mechanical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 750 – 1400 MPa |
| Yield Strength | 450 – 1000 MPa |
| Hardness | 35 – 60 HRC |
| Hot Hardness | Up to 800 – 900 °C |
| Fatigue Resistance | Excellent |
| Wear Resistance | Outstanding |
| Creep Resistance | Very high |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.3 – 9.2 g/cm³ |
| Melting Range | 1250 – 1450 °C |
| Thermal Conductivity | 14 – 25 W/m·K |
| Electrical Resistivity | 0.6 – 0.9 µΩ·m |
| Magnetic Behavior | Non-magnetic to weakly magnetic |
| Oxidation Resistance | Excellent |
Strengthening & Metallurgical Behavior
• Solid-solution strengthening (Cr, W, Mo)
• Carbide strengthening (Cr₇C₃, WC)
• Stress-induced FCC ↔ HCP phase transformation
• Grain refinement and work hardening
• Stable microstructure at elevated temperatures
Key Characteristics
✔ Exceptional wear & galling resistance
✔ Retains hardness at red-hot temperatures
✔ Superior corrosion resistance in acids & seawater
✔ High resistance to erosion and cavitation
✔ Biocompatible (medical grades)
Refining & Processing
• Vacuum Induction Melting (VIM)
• Vacuum Arc Remelting (VAR)
• Electroslag Remelting (ESR)
• Investment casting, forging, powder metallurgy
• Additive manufacturing & hardfacing
Available Forms
Ingots
Cast components
Bars & rods
Sheets & plates
Powders (AM & thermal spray)
Wires, electrodes, overlays
Applications
Aerospace
Turbine parts, bearings, hot-section components
Medical
Orthopedic implants, dental prosthetics, surgical tools
Oil & Gas
Valve seats, downhole tools, wear sleeves
Industrial & Power
Cutting tools, extrusion dies, pumps, turbine components
Advantages
✔ Superior hot hardness
✔ Exceptional wear resistance
✔ Excellent corrosion & oxidation resistance
✔ Outstanding fatigue & creep performance
✔ Long service life in severe environments
Limitations
❌ High material cost
❌ Difficult machining
❌ Higher density than aluminum or titanium
❌ Strategic material with supply risk
Why Choose Cobalt Alloys?
Choose cobalt alloys when extreme temperature capability, wear resistance, corrosion resistance, and long-term dimensional stability are critical.