Cobalt-Chromium -Molybdenum (Co-Cr-Mo) alloys are a class of high-performance materials with cobalt (Co) as the base, alloyed with chromium (Cr) and molybdenum (Mo). These alloys exhibit exceptional corrosion resistance, wear resistance, biocompatibility, and high-temperature stability, making them widely used in medical implants (e.g., artificial joints, dental prosthetics), aerospace, petrochemicals, and industrial wear-resistant components.
This article systematically reviews the key grades, compositional characteristics, mechanical properties, heat treatment processes, and typical applications of Co-Cr-Mo alloys. A comparative analysis with Stellite alloys is also provided to assist engineers and researchers in material selection.
Classification and Grades of Co-Cr-Mo Alloys:
Co-Cr-Mo alloys can be categorized based on manufacturing process (cast/wrought), carbon content (high/low), and application (medical/industrial). Major grading systems include ASTM (American Society for Testing and Materials), ISO (International Organization for Standardization), and commercial grades (e.g., Vitallium).
2.1 ASTM Standard Grades
| Grade | Type | Composition (wt%) | Primary Applications |
|---|---|---|---|
| F75 | High-Carbon Cast | Co-28Cr-6Mo-0.3C (C≈0.25-0.35%) | Artificial joints, dental implants |
| F1537 | Low-Carbon Wrought | Co-28Cr-6Mo-0.15C (C≤0.15%) | Orthopedic implants (hip/knee) |
| F799 | Modified Wrought | Similar to F75, refined grain structure | High-load medical devices |
| F90 | Tungsten/Nickel-Containing | Co-20Cr-15W-10Ni (L605/HS-25) | Aircraft engine components |
| F562 | Ultra-High Strength | Co-35Ni-20Cr-10Mo (MP35N) | Cardiovascular stents, aerospace fasteners |
2.2 ISO Standard Grades:
ISO 5832-4: Equivalent to ASTM F75 (cast medical Co-Cr-Mo).
ISO 5832-6: Equivalent to ASTM F1537 (wrought low-carbon Co-Cr-Mo).
2.3 Commercial Grades
Vitallium: Classic cast Co-Cr-Mo alloy (≈F75), used in dentistry and joint replacements.
UMCo-50 (Haynes 25): High-temperature alloy with W and Ni, for turbine components.
3. Key Properties of Co-Cr-Mo Alloys
3.1 Mechanical Properties
3.2 Corrosion Resistance
Passive Film Protection: High chromium content (≥26%) forms a Cr<sub>2</sub>O<sub>3</sub> oxide layer, resistant to bodily fluids, salt spray, and chemicals.
Medical Low-Carbon Grades (e.g., F1537): Reduced carbide precipitation enhances corrosion resistance.
3.3 Biocompatibility
Certified under ISO 5832 and ASTM F75/F1537, with minimal nickel leaching risk (some grades require caution).
3.4 High-Temperature Performance
Molybdenum (Mo) and tungsten (W) improve thermal stability, e.g., HS-25 (L605) operates up to 1100°C.
4. Co-Cr-Mo Alloys vs. Stellite Alloys
| Property | Co-Cr-Mo Alloys (e.g., F75/F1537) | Stellite Alloys (e.g., Stellite 6) |
|---|---|---|
| Core Composition | Co-Cr-Mo (low carbon) | Co-Cr-W-C (high carbon, W-dominant) |
| Strengthening Mechanism | Mo solid-solution + minor carbides | W + high-carbon carbides (e.g., Cr<sub>23</sub>C<sub>6</sub>) |
| Wear Resistance | Moderate | Exceptional (HRC 40-50) |
| Corrosion Resistance | Excellent (medical-grade) | Good (high carbon may reduce resistance) |
| Primary Applications | Artificial joints, dentistry | Valve seats, drill bits, high-temperature tool coatings |
Key Differences:
Co-Cr-Mo Alloys: Focus on biocompatibility + corrosion resistance, ideal for long-term implants.
Stellite Alloys: Optimized for wear resistance + high-temperature performance, suited for industrial wear environments.
5. Typical Applications
5.1 Medical Field
Artificial Joints: F75 (cast), F1537 (wrought low-carbon).
Dental Prosthetics: Vitallium (cast crowns, bridges).
Cardiovascular Stents:MP35N (F562).
5.2 Industrial Field
Aerospace: HS-25 (L605) for engine blades. Petrochemicals:
Stellite 6 for valve sealing surfaces. High-Temperature Fasteners: UMCo-50 (Haynes 25).
6.Heat Treatment and Processing
Cast Alloys (F75): Typically undergo hot isostatic pressing (HIP) to reduce porosity.
Wrought Alloys (F1537): Strengthened via solution treatment + aging.
Stellite Alloys: Often applied as laser-clad or plasma-sprayed coatings for wear resistance.
Co-Cr-Mo alloys are the material of choice for medical implants due to their balanced properties, while Stellite alloys dominate in extreme wear and high-temperature environments. Future trends include:
3D Printing: Customized orthopedic implants (e.g., F75 powder bed fusion).
Surface Modification: Nanocoatings to enhance wear resistance (e.g., nitrided F1537 surfaces).
Low-Carbon & Nickel-Free Development: Reducing biological risks.
Optimal alloy selection requires balancing mechanical needs, corrosion environment, and cost. The comparative data provided herein serves as a practical guide for engineering applications.
Post time: Aug-25-2025