Cobalt-Based Superalloys: Grades, Properties & Selection Guide

Cobalt-based superalloys are engineered to execute beyond the molecular dynamics of nickel-based alloys at elevated temperatures through carbide and summation reinforcement. The attainment of such properties in these alloys as hot corrosion resistance, thermal fatigue resistance, and wear resistance can only be possible through solidification. Therefore, they should be chosen for stationary gas turbine vanes, articles for implants in medicine, and extreme wear conditions; nevertheless, the consideration of such alloys by many engineers is limited because of the more common use of such metals as nickel and titanium rather than cobalt.

When David Chen, who works as a materials engineer at a marine gas turbine firm in Singapore, recommended Inconel 718 for the construction of the stationary vanes within the new auxiliary power unit, it went down as reasonable. Inconel was very familiar, widely researched, and available. However, after 18 months, the vanes had suffered a massive case of sulfidation attack. The levels of sulfur in the fuel were higher than what had been catered for. High temperatures caused corrosion to the point it was beyond gamma prime strengthening. The new specification had to be Haynes 188 cobalt base alloys with nearly 22% chromium content. The cobalt vanes completed the same inspection after 25,000 hours without any degradation detected. Cobalt was far from being a rare component. It was about finding the perfect material for the conditions.

Throughout this manual, cobalt-based superalloys and their advantages over other options, such as nickel or titanium, grades for different uses, their sourcing, including guarantees and tracking authorization, will be discussed.

Key Takeaways

• Cobalt-based superalloys rely on carbide precipitation and solid solution strengthening, with newer gamma-prime (γ’) variants emerging for advanced turbine applications.
• Stellite alloys dominate wear-resistant applications. Haynes 188 and L-605 excel in high-temperature oxidation environments. MP35N delivers ultra-high strength for medical implants and aerospace fasteners.
• Cobalt alloys offer superior hot corrosion resistance and thermal fatigue resistance compared to nickel-based superalloys, but generally lower creep resistance under high stress.
• Medical grades (ASTM F562 for MP35N) and aerospace grades (AMS 5844 for MP35N) are not interchangeable — certification and traceability requirements differ.
• Cobalt alloy pricing typically ranges from 45to45to120 per kilogram depending on grade, form, and certification level.

What Are Cobalt-Based Superalloys?

Composition and Alloying Elements

Cobalt-Based Superalloys are a type of enhanced metal matrix, which is mainly cobalt mixed with nickel, chromium, tungsten, molybdenum, carbon, and some other elements. The percentage of chromium usually varies within 20 to 30 wt %. This forms Cr2O3 that acts as an oxide scale, which is anti-oxidizing and prevents hot corrosion. Tungsten and molybdenum enhance the solidification and strengthen the alloys at elevated temperatures. It forms carbide phases, hardening the solid solution of chromium and tungsten, and in abrasion-resistant grades, usually around 0.5 to 3.5 % of Carbon is present. Nickel is also often included to change or promote ductile behavior by retaining a face-centered cubic crystal lattice.

The exact balance of these elements determines whether the alloy prioritizes wear resistance, oxidation resistance, or ultra-high strength. For a broader overview of the specialty metals family, see our titanium alloys complete guide.

Strengthening Mechanisms

Cobalt-Based Superalloys, as opposed to their nickel-based counterparts, do not depend on the strengthening mechanism of gamma prime (γ′) precipitates, but on three very different approaches. The first approach involves the precipitation of carbides like M7C3 and M23C6 at the grain boundaries, termed as a creep-resistant mechanism. The second approach, solid solution strengthening, is the most common method used, in which high-melting-point elements are dissolved in the other metals, such as cobalt. The final approach is grain boundary strengthening, which is achieved through the controlled distribution of the carbides.

In 2006, scientists were once again able to find a way to strengthen cobalt superalloys with the addition of Co3(Al, W) due to gamma prime. This phase. Over the years, these advances have led to the elimination of tungsten to make Co3(Al,Mo,Nb) in the year 2015 and Co3(Ta,V) in the year 2017. These particular W-free versions are lower in weight and are progressively being considered for use in aeroplanes, especially for turbines, given the significance of weight.

How They Differ from Nickel-Based Superalloys

Cobalt additionally possesses a greater melting point than nickel at 1,495 degrees Celsius, roughly, and 1,455 degrees Celsius, respectively. This means that mechanical properties are easier to maintain at elevated temperatures. Cobalt-based superalloys else are more resistant to hot corrosion, including thermal-structural deformation under high temperature exposure in electrolytes infused with sulphur or vanadium ions.

But in general, above 800 degrees Celsius, the creep resistance of nickel-based superalloys in high stresses outperforms that of cobalt-based superalloys. In the case of sustained loading, gamma-prime strengthening in nickel is more efficient than carbide strengthening in cobalt. Accordingly, it is necessary to take into account what type of destruction will prevail: corrosion, abrasive, creeping failure or fatigue.

Contact our metallurgical engineers to determine whether cobalt or nickel is optimal for your operating environment.

Common Grades of Cobalt-Based Superalloys

Stellite Alloys (Co-Cr-W)

Stellite forged core line of cobalt-based material grades originated from the Haynes Stellite Company. Today, however, the technology is maintained by Kennametal. Differentiated high chromium and tungsten concentrations characterize the same alloys, while the amount of carbon varies according to specifications.

Outside of the boxed set, Stellite 1 techniques, around 2.5% carbon and nearly 30% chromium (margins are excluded) go into the alloy composite. High strain and wear strength make it suitable for regions with intense wear, such as valve seats, bearings, and pump parts. One sort is named Stellite 6, used by many customers, with about 1% of carbon and 28% of chromium. Wear resistance, in this case, is attained within reasonable limits of ductility to withstand thermal shock. On the scale of strong materials – Stellite, there belongs the grade Stellite 12 being considerably harder than Stellite 6, particularly, working on the license valves and abrasive materials. On the other hand, a decrease in the level of carbon and ductility in Stellite 21 has put it into the category of applications such as a prosthesis or dental filling.

Haynes Alloys (Co-Ni-Cr-W)

Haynes International manufactures cobalt superalloys that are particularly resistant to oxidation even at elevated temperatures. Alloy Haynes 188 consists of 22% chromium, 22% nickel, and includes a 14% volume of tungsten. The alloy does not lose its strength properties even at 1,100°C in an oxygen-rich environment. In addition, Haynes 188 is specified for parts of combustor liners, afterburners, and industrial furnaces.

The material findings state that the Haynes L-605 variable is also denoted as HS 25, which contains competitive strength, corrosion-resistance, and formability. Its applications include fasteners in the aerospace industry, implants in the medical sector, as well as industrial heaters and cooking equipment. This variety, named Haynes 150, allows the equipment to deal with chemical processing, enhancing sulfur-containing atmospheres due to sulfuring.

Multiphase Alloys (MP35N and MP159)

MP35N is an alloy consisting of cobalt, nickel, chromium, and molybdenum in the nominal composition of thirty five percent of cobalt, 35 percent of nickel, 20 percent of chromium, and 10 percent of molybdenum. The alloy can be work hardened, strengthened by solid solution, and hardened further by aging, such that its ultimate tensile strength reaches up to 2,070 MPa. The MP35N is safe for human implantation, it is non-magnetic, and most importantly, it does not corrode. MP35N is exemplified in orthopedic bone screws, cardiovascular leads, and fasteners in the aerospace industry.

The MP159, on the other hand, resembles the MP35N through its basic elements but has some extra alloying elements which increases its strength retention capabilities even at temperatures of 540 degrees. Application areas of the alloy include bolts that require strength at room temperature or tolerates some heat.

Grade Selection by Application

While going through a procurement procedure in Rotterdam, a team ordered Stellite 6 weld rods for use in valve hardfacing during a refinery turnaround. But the supplier offered a less expensive, generic cobalt-chromium alloy for 32 per kilogram. It is worth mentioning that the cost of genuine Kennametal- Stellite 6 approved rods is much higher, at 55 per kg. The prospect gave the project manager all the other information, so they resorted to the cheaper material and managed to keep the budget in control. Six months post-commissioning, severe damage was observed on the valves. The cladding was cracking and scaling off. A detailed analysis established that the amount of carbides inside the coating was 50% of the required amount for Stellite 6. In the end, the general 20,000 savings from one would result in new 180,000 costs in 6 months of unscheduled shutdown and repairs. Stellite 6 could have been used for up to ten years.

Key Properties of Cobalt-Based Superalloys

High-Temperature Performance

Cobalt-Based Superalloys, Can Withstand General Strength and Resist Oxidation At High-Temperature Where Many Materials Would Deform. Haynes 188 Survive Cycles as High as 1100 Degrees in Oxidizing Media. The Presence of Chromium Generates the Protective Layer Cr2203 Whenever it is Damaged. This is Particularly Important for the Parts of Combustion Engines and Industrial Furnaces, Where the Ceramic Coating Could Crack Due to Thermal Loads.

Wear Resistance

Cobalt-Based Superalloys are considered benchmark materials for both abrasive and adhesive wear resistance. Even under ASTM G65 abrasion tests, Stellite grade 6 only loses between 20 to 40 milligram materials, while AISI 300 series stainless steel loses between 100 and 200 milligrams. Hard carbide phases of the cobalt matrix effectively deter abrasives from penetrating the material’s surface. The phenomenon of work hardening is also involved: Stellite 6 cast originally at 40 HRC is able to undergo a work hardening process into more than 50 HRC in the event of repeated impact or sliding contact.

Corrosion Resistance

Cobalt alloys excel in hot corrosion environments, particularly those containing sulfur, vanadium, or chlorides. The high chromium content provides resistance to sulfidation attack. MP35N demonstrates exceptional resistance to chloride stress corrosion cracking, matching or exceeding that of Hastelloy C-276 in many environments. For a detailed comparison of corrosion-resistant materials, see our guide on titanium vs stainless steel.

Mechanical Properties

The mechanical properties differ for each grade and condition. In case of Haynes 188 in solution-treated condition, the tensile strength of around 965 MPa can be achieved with elongation of 45 percent. MP35N under cold work and age conditions can reach 2,070 MPa tensile strength with 10 – percent elongation. Thus, it is easy to see that with higher strength, the Artists will face lower ductility. It implies matching the properties of the material with the type of load expected for a given application.

Applications by Industry

Aerospace and Defense

Cobalt-based superalloys serve in gas turbine stationary vanes, combustion chambers, and afterburner components where hot corrosion resistance outweighs the need for maximum creep strength. Haynes 188 sheet is used for combustor liners in both commercial and military engines. MP35N wire and bar are specified for aerospace fasteners requiring ultra-high strength and corrosion immunity. For components where titanium plate is the better option, see our guide on aerospace titanium plate.

Medical Devices

A major cobalt alloy in implants is MP35N. In order to be considered surgical implant materials, only those that are ASTM F562 compliant, biocompatible, and possess qualified machinability are considered MP35N. MPs35N is used in all orthopaedic bone screws, spinal rods, cardiac leads, and dental implants. Stellite 21 and cast Co-Cr-Mo are the target ASTM F1537 alloys used for ACL/THR exudates, specifically due to the polymeric bearing components.

There is a difference in certification requirements for both the medical and aerospace grade MP35N. As per ASTM F562, certain types of biocompatibility testing are required to be performed per ISO 10993. AMS 5844 presents the criteria for mechanical properties and traceability of the material for flight hardware. Chemically, there is not much difference in the composition of the materials, but the paperwork, testing, and quality assurance systems differ. The usage of aerospace-certified MP35N in implant fabrication may result in FDA rejection.

A newly launched Boston-based healthcare technology firm unveiled its latest spinal implant device in 2024 and chose to use MP35N for the rods simply due to its mechanical properties. The detailed AMS 5844 specification was of the aviation variant, which it had from a supplier who was present all the while. When they submitted for the FDA clearance in advance, the specification was spotted by a reviewer. They dealt with facilities for such R&D or other facilities, especially specialized labs in certain areas, within a reasonable timeframe, and in the end managed to gain filing of a 510(k) approval nine months later than expected. The material was vital. The documented text was faulty.

Oil and Gas and Chemical Processing

Stellite coatings offer critical protection to valve seats, gates, and trim in aggressive and sour gas applications operating at elevated temperatures, extending the life of such components. This is because these coatings have improved wear performance, which makes them suitable for use in situations where abrasive particles would destroy more “delicate” stainless steel or nickel alloy in a few short months. Haynes 150 alloy also finds application for the furnace tubes and fixtures used in wet chemical processes that promote sulfidation.

Industrial Wear Components

Cobalt-based superalloys called stellites may be applied to machine elements used as cutting inserts, saws, erosion shields for steam turbines, pump plunger tips, and waring surfaces of bearings. Cast Stellite parts may also be manufactured as nearly shape symmetric components, hence reducing the machining operations of hardened surfaces. Welded cobalt alloy surfaces are used to improve the surfaces of existing steel components.

Cobalt-Based vs Nickel-Based Superalloys

When to Choose Cobalt

Cobalt-based superalloys are used whenever wear due to dry abrasion, hot corrosion, or thermal cycling are the predominant failure mechanism. Examples may include marine gas turbines operated with sulfur fuels as a traditional use of cobalt. High wear applications such as valve hardfacing, pump sleeves and bearings usually employ Stellite alloys. In cases that necessitate both very high strength and biocompatibility for medical implants, MP35N will work well.

Cobalt alloys are also some of the easily weldable alloys, unlike many hardenable nickel alloy systems. Alloys such as L-605 and Haynes 188 can be welded by ordinary gas tungsten arc welding with much less difficulty cracking in comparison to Inconel 718 or Rene 41.

When Nickel Wins

Cobalt-Based Superalloys are still the preferred option for components subjected to rotation, while creep resistance is crucial. Blades, disks, and high-pressure compressor sections are all faced with prolonged centrifugal loads at temperatures of up to 800 and sometimes more than 800 degrees. The gamma prime phase of nickel permits a much better creep capability under the above-mentioned conditions.

In addition, one has to keep in mind that nickel-type alloys are usually cheaper and more common, including supply in large sizes and complicated shapes. In many cases, a cheaper option such as Inconel 718 or Waspaloy would suffice.

Side-by-Side Comparison

Procurement and Quality Assurance

Material Specifications to Demand

Every cobalt alloy grade has governing specifications that buyers must reference in their purchase orders:

• Stellite castings: AMS 5387, AMS 5389, or proprietary Kennametal specifications
• Haynes 188 sheet: AMS 5608
• Haynes 188 wire: AMS 5772
• Haynes L-605 sheet: AMS 5537
• Haynes L-605 bar: AMS 5759
• MP35N aerospace: AMS 5844 (wire, bar, strip)
• MP35N medical: ASTM F562 (implant grade)

Documentation Requirements

Mill Test Reports are required, containing heat number, chemical composition, and mechanical properties for the complete documentation package. Standards compliance is confirmed with a Conformance Certificate. Biocompatibility testing under ISO 10993 is required for medical grades. Records of the heat treatment detailing solution temperature, holding time, and cooling rate must be kept.

Supplier Qualification

Pre-order conditions are that the supplier meets the minimum requirements for ISO 9001 certification. AS9100 is needed for aerospace applications. ISO 13485 is required for medical device applications. It is paramount to note that end-to-end traceability from raw material to the produced product is required, especially when dealing with cobalt alloys in which supply chain and conflict minerals come to play and complicate matters.

Cost and Lead Time Trends

Cobalt-Based Superalloys madeacias discounts for short lead order durations are rare. Normal business environments do not allow lead acceptance times, which are one of the constant factors in any industry. Demand, however, dictates the rise and fall of these two aspects’ statistics. It is not uncommon for one facet to seize whilst the other skyrockets in value with the increase in competition fabricants. It also provides a good opportunity for superlinear promotional stock build-up campaigns on Cobalt-Based Superalloys with excessive pallets & containerships.

Stellite coatings manufacturing and weld-inserted tungsten welding rod are valued at approximately 45 berclareons per kg for steel grades, raising their monetary value to approximately 100 berclareons per kg in high-end welding. Hayness 188 plates and sheets are priced at an average price of 80 and 120 per kg, respectively. As for MP35N wire and bar, the prices are 90, 90 to 150 based on the certification level, diameter and the order quantity. Medical materials such as this have a 20% to 30% increase in price for the cannas grade materials due to more frequent testing and tracing requirements.

Frequently Asked Questions

What is the principal distinction between cobalt and nickel superalloys?

Cobalt-Based Superalloys are particularly effective in preventing hot corrosion, thermal fatigue, and wear. In contrast, nickel-based super alloys are effective because they undergo very little creep under pressure a such high temperatures. The answer is simply to which failure mode will be more prominent in the application of selection.

Can you explain why MP35N gets used for implantable medical devices?

MP35N integrates very high strength of around 2070 MPa with excellent corrosion resistance and a compatibility that is human-friendly. It is compliant with ASTM F562, specified medical grade materials for implants, and eliminates the problem of chloride SCC in body fluids.

Is it possible to weld cobalt alloys?

Of course. Solid solution Cobalt alloys, such as Haynes 188 and L-605, are conveniently welded by gas tungsten arc welding process using cobalt filler rods. Stellites which are rich in carbides are best manufactured as either casting processes or overlay welding as opposed to processes which involve wrought metal forming.

How is Stellite applied?

Wear-resistant elements like valve seats, pump casing sleeves, cutting tools, and hardfacing overlays are some components that are obtained from the use of stellite alloys. Stellite 6 provides a useful combination of resistance to abrasion and some amount of ductility.

Are cobalt alloys more costly?

Cobalt-based superalloy costs more compared to stainless steels and most nickel-based alloys. Per kg, Stellite could be 45to45to75. For Haynes 188, the weight pot is 80to80to120 per kg. 90to90to150 per kg can be spared for MP35N. But the additional cost is compensated for by the improved service time in harsh conditions.

What is the maximum temperature that cobalt alloys can work in?

Haynes 188 can work at 1,100 degrees Celsius inside oxidizing atmospheres for a long time. One can bear 1,200 degrees Celsius for a while. For temperatures above this point, it might be necessary to use ceramics or refractory materials.

Conclusion

Cobalt-Based Superalloys are a classic example of the infill of some blank spaces that occur in the range of materials. They are superior to nickel alloys when it comes to hot corrosion and subsequent emergency wear. They are far better than titanium in terms of holding out for higher temperature oxidation. They are also the only metal family that offers an inherently compatible biological structure as well as multiple ranges of mechanical strength. However, these benefits only come in when the right specification is prescribed, approved, and ordered.

That is not a fortunate accident that some engineers and procurement managers perform well where cobalt alloys are concerned. The failure mechanism: Stellite for wear, Haynes for oxidation, MP35N for strength and biocompatibility, is channeled in the grade. Those standards are then expressly elaborated in the purchase order. Supplier certifications are checked beforehand. All shipments are accompanied by appropriate accompanying records and provenance requests.

If your project requires cobalt-based superalloys, whether for gas turbine hardware, medical implants, or severe wear components, our metallurgical team is available to recommend the optimal grade, confirm specification compliance, and deliver certified material with complete documentation. Contact an expert or request a quote today.