Haynes25 Alloy

Haynes25 (also designated as L-605 in domestic standards) is a high-performance cobalt-chromium-nickel (Co-Cr-Ni) based solid solution strengthened wrought superalloy, specifically engineered for medium-to-ultra-high temperature service scenarios demanding excellent thermal stability, oxidation resistance, and formability. Unlike Fe-Ni-Co based Kovar alloys (4J series, optimized for hermetic sealing), Haynes25 achieves strengthening primarily through the synergistic solid solution effect of chromium (Cr) and tungsten (W) — without relying on precipitation phases — and takes cobalt as the matrix element to enhance high-temperature ductility and thermal fatigue resistance. This alloy excels in continuous high-temperature environments ranging from 650℃ to 1095℃, making it a preferred material for components exposed to cyclic thermal stress, high-temperature gas erosion, and moderate corrosion.

Notably, Haynes25 forms a dense, adherent Cr₂O₃ protective oxide film at high temperatures, providing superior resistance to atmospheric oxidation, sulfur-containing flue gas, and weak acidic media. Its exceptional hot workability and weldability allow for manufacturing of complex-shaped components (e.g., honeycomb heat shields, welded exhaust manifolds), and it is widely used in aerospace propulsion systems, industrial heating equipment, and high-temperature mechanical components. The following is a comprehensive breakdown of its chemical composition, physical properties, mechanical properties, and application products.

1. Chemical Composition (Mass Fraction, %)

2. Physical Properties

2.1 Basic Physical Parameters

• Density: Approximately 9.13g/cm³ at room temperature (25℃), higher than Fe-Ni-Co based 4J36 (8.10g/cm³) due to high cobalt and tungsten content, but its exceptional high-temperature performance offsets weight concerns for critical components (e.g., aerospace exhaust parts), where reliability takes priority over weight.
• Melting Temperature Range: 1371-1432℃ (liquidus: ~1432℃; solidus: ~1371℃). The narrow and stable melting range ensures uniform solidification during casting and consistent deformation during hot working, reducing internal defects (e.g., segregation, shrinkage porosity) and improving structural integrity for welded components.
• Thermal Expansion Coefficient (CTE):

◦ 20-100℃: ~12.7×10⁻⁶/℃

◦ 20-600℃: ~14.4×10⁻⁶/℃

◦ 20-1000℃: ~16.1×10⁻⁶/℃

◦ 20-1095℃: ~16.8×10⁻⁶/℃

The gradual CTE increase minimizes thermal stress during frequent temperature fluctuations (e.g., aerospace engine start-stop, industrial furnace load adjustment), reducing thermal fatigue cracking risk by 45-55% compared to conventional Fe-Cr-Ni alloys (e.g., 310S stainless steel).

• Thermal Conductivity (λ):

◦ 100℃: ~14.2W/(m·K)

◦ 500℃: ~17.6W/(m·K)

◦ 1000℃: ~20.9W/(m·K)

◦ 1095℃: ~22.8W/(m·K)

The temperature-dependent conductivity improvement promotes efficient heat dissipation in high-temperature components, avoiding localized overheating (a major cause of material softening and creep acceleration) and extending part service life by 30-35% compared to similar cobalt-based alloys.

• Electrical Resistivity (ρ):

◦ Room temperature (25℃): 145-155×10⁻⁸Ω·m

◦ 1000℃: 200-210×10⁻⁸Ω·m

High resistivity reduces eddy current losses in high-temperature electromagnetic components (e.g., heating elements), making it suitable for high-frequency heating applications.

2.2 Magnetic Properties

Haynes25 is not optimized for magnetic performance, but its magnetic characteristics are relevant for magnetically sensitive applications:

• Magnetic Permeability (μ): ~1.010-1.018μ₀ (at H=800A/m, room temperature) — weakly magnetic at ambient temperature;
• Magnetic Property Variation with Temperature: Magnetic permeability gradually decreases with increasing temperature, becoming nearly non-magnetic (μ≈1.002-1.003μ₀) in the service temperature range (650-1095℃);
• Coercivity (Hc): ~160-240A/m (room temperature) — significantly higher than soft magnetic alloys (e.g., 1J50), ensuring it does not act as a magnetic core and avoids interfering with internal components.

3. Mechanical Properties (After Standard Heat Treatment: 1177-1232℃ solid solution for 1h, air cooling)

Key Notes:

• Exceptional Room-temperature Ductility: Elongation (δ₅ ≥25%) and high reduction of area (ψ ≥35%) ensure excellent formability, allowing the alloy to be processed into ultra-thin sheets (minimum thickness ≥0.1mm), honeycomb structures, and complex welded assemblies — a key advantage over less ductile high-temperature alloys;
• Stable High-temperature Strength: At 800℃ (a typical service temperature for industrial heating equipment), the creep rupture strength (≥300MPa) is 15-20% higher than that of 310S stainless steel, ensuring long-term structural stability under continuous high-temperature load;
• Reliable Ultra-high-temperature Performance: Even at 1095℃ (near its upper service limit), the retained elongation (≥15%) and tensile strength (≥340MPa) prevent brittle fracture during emergency shutdowns, making it suitable for components with extreme thermal cycling (e.g., aerospace exhaust nozzles);
• Low Room-temperature Hardness: Hardness (HRC 30-35) simplifies machining and forming processes, reducing production costs for complex-shaped components compared to harder precipitation-hardening alloys.

4. High-temperature Oxidation & Corrosion Resistance (Core Performance)

Key Notes:

• Dense Protective Oxide Film: The Cr₂O₃ film formed at high temperatures is tightly bonded to the matrix, resisting spallation during thermal cycling and providing long-term oxidation protection;
• Excellent Sulfur Corrosion Resistance: Suitable for industrial environments with sulfur-containing flue gas (e.g., coal-fired power plants, chemical furnaces), outperforming nickel-based alloys like Inconel 600 in sulfur-rich atmospheres.

5. Application Products & Industry Scenarios

5.1 Aerospace & Defense Field

As a core material for medium-to-high temperature components in aerospace and defense systems, Haynes25 is used for:

• Aerospace Exhaust Systems: Exhaust manifolds, tailpipes, and flame holders in aero-engines (operating temperature: 650-950℃), resisting high-temperature exhaust gas erosion and thermal fatigue; the alloy’s weldability allows for integration with titanium or nickel-based engine components;
• Thermal Protection Structures: Honeycomb heat shields and leading edge panels for aircraft wings and reentry vehicles, resisting 800-1000℃ aerodynamic heating; its high ductility enables forming of complex curved shapes to fit aerodynamic profiles;
• Rocket Propulsion Components: Thrust chamber liners and injector manifolds in solid rocket motors, withstanding 950-1095℃ combustion gas and thermal shock; its creep resistance reduces deformation by 35-45% compared to conventional Co-Cr alloys.

5.2 Industrial Heating & Furnace Field

In medium-to-ultra-high temperature industrial furnaces (operating temperature: 650-1050℃) for metallurgy, ceramics, and materials processing, Haynes25 is applied to:

• Furnace Liners & Muffle Tanks: Inner liners of carburizing furnaces and annealing furnaces, resisting high-temperature air oxidation and carbon diffusion; compared to 310S stainless steel, it extends service life by 70-80% and reduces maintenance costs by 50-60%;
• Heating Element Assemblies: Support brackets, terminal blocks, and protective sleeves for resistance heating elements (e.g., Kanthal, Nichrome), withstanding 800-1000℃ radiant heat and mechanical vibration;
• High-temperature Conveyors: Mesh belts and roller chains for continuous heat treatment lines (e.g., stainless steel annealing), resisting 650-850℃ high-temperature wear and thermal fatigue; the alloy’s ductility allows for easy repair of damaged conveyor sections.

5.3 Mechanical & Automotive Field

In high-temperature mechanical components and specialized automotive applications, Haynes25 is used for:

• High-performance Automotive Exhaust Parts: Exhaust headers and turbocharger casings for racing cars and heavy-duty diesel engines, resisting 700-900℃ exhaust gas corrosion and thermal cycling; its formability enables the design of complex, high-efficiency exhaust geometries;
• High-temperature Bearings & Seals: Bearings, bushings, and mechanical seals for industrial pumps and turbines operating at 650-800℃, resisting wear and corrosion in high-temperature lubricating oil environments;
• Valve Components: High-temperature valves and valve stems in power plant steam systems (operating temperature: 650-750℃), withstanding high-pressure steam erosion and thermal fatigue.
• Metallurgical Industry: High-temperature sample holders and crucibles for vacuum arc melting (VAM) of superalloys, resisting 1000-1095℃ molten alloy erosion and ensuring metal purity;
• Material Testing Equipment: Fixtures and sample frames for high-temperature tensile testing (650-1095℃) and thermal fatigue testing, providing stable support for long-term tests (up to 3,000 hours) and ensuring accurate data acquisition;
• Welding Consumables: Welding wires and electrodes for joining cobalt-based superalloys (e.g., Haynes25 itself, Haynes 188), ensuring weld joint strength and corrosion resistance matching the base metal.
• Hot Working: Forging temperature range: 1177-1260℃; initial forging temperature should not exceed 1260℃ to avoid grain coarsening, and final forging temperature should not be lower than 1038℃ to prevent work hardening; hot rolling is recommended for sheet production, with a reduction ratio of 30-40% per pass;
• Cold Working: Cold rolling, drawing, or stamping can be performed at room temperature, with total deformation up to 50-60% (for sheet materials); intermediate annealing (1149-1177℃, 30-60min, air cooling) is recommended after every 20-25% deformation to restore ductility;
• Welding: Highly weldable via TIG welding, MIG welding, electron beam welding, and resistance welding. Welding filler metal recommended: Co-Cr-Ni-W alloy (matching Haynes25 composition); preheating temperature: 150-250℃ (optional for thin sheets ≤3mm); post-weld heat treatment: 1177-1232℃ solid solution for 1h, air cooling, to eliminate welding stress and restore corrosion resistance;
• Machining: Machining is best performed in the solution-treated (soft) state (HRC 30-35) using high-speed steel or carbide tools; cutting fluids are recommended to reduce tool wear and avoid workpiece overheating; finish machining can be done after final forming to achieve precision dimensions (tolerance ±0.01mm).

5.4 Metallurgical & Materials Testing Field

6. Processing & Welding Recommendations

This comprehensive performance and application profile makes Haynes25 a versatile, cost-effective superalloy for medium-to-ultra-high temperature manufacturing, perfectly balancing high-temperature strength, oxidation resistance, ductility, and processability for complex-shaped components in aerospace, industrial heating, and mechanical engineering fields.