GH4738 Alloy

GH4738 is a high-performance nickel-based precipitation-hardening wrought superalloy, specifically developed for ultra-high-temperature, high-stress, and severe corrosion service scenarios. It achieves strengthening primarily through the coherent precipitation of high-stability γ’ phase (Ni₃Al, Ti, Nb) — with a γ’ phase content of approximately 25-30% — and is supplemented by synergistic solid solution strengthening from chromium (Cr), molybdenum (Mo), and tungsten (W). Unlike GH4105 (which focuses on medium-temperature strength), GH4738 optimizes the ratio of W and Nb to enhance creep resistance and thermal corrosion resistance at higher temperatures, enabling reliable long-term operation in harsh environments ranging from 900℃ to 1150℃.

Notably, GH4738 forms a dense, multi-layer protective oxide film (Al₂O₃-Cr₂O₃-WO₃) at ultra-high temperatures, providing superior resistance to sulfur-containing flue gas, molten salt, and high-pressure hydrogen corrosion. It retains excellent hot workability and weldability for manufacturing large, complex load-bearing components (e.g., heavy-duty turbine disks) and is widely used in core hot-end parts of advanced aero-engines, ultra-high-efficiency industrial gas turbines, and next-generation nuclear energy equipment, where material performance under extreme thermal-mechanical-corrosion coupling conditions is critical. The following is a comprehensive breakdown of its chemical composition, physical properties, and application products.

1. Chemical Composition (Mass Fraction, %)

2. Physical Properties

2.1 Basic Physical Parameters

• Density: Approximately 8.45g/cm³ at room temperature (25℃), slightly higher than GH4105 (8.30g/cm³) due to W addition, but 4-6% lower than high-W nickel-based superalloys such as GH3128 (8.70g/cm³). This low-density advantage is critical for weight-sensitive ultra-high-temperature load-bearing components (e.g., aero-engine high-pressure turbine disks), reducing equipment overall weight by 2-7% compared to high-alloyed alternatives like Hastelloy X.
• Magnetic Properties: Non-magnetic across the entire service temperature range (room temperature to 1150℃) (magnetic permeability μᵣ ≈ 1.000-1.001). This makes it highly suitable for applications near precision magnetic sensors (e.g., aero-engine turbine speed sensors, nuclear reactor magnetic control systems), as it does not interfere with magnetic field distribution or sensor accuracy.
• Melting Temperature Range: 1340-1400℃ (liquidus: ~1400℃; solidus: ~1340℃). The narrow and stable melting range ensures uniform solidification during investment casting (for turbine blades) and consistent deformation during forging, reducing internal defects (e.g., shrinkage porosity, segregation) and improving structural integrity—critical for high-stress ultra-high-temperature parts like heavy-duty turbine rotors.
• Thermal Expansion Coefficient (CTE):

2.2 Thermal Properties

◦ 20-100℃: ~12.1×10⁻⁶/℃

◦ 20-600℃: ~13.6×10⁻⁶/℃

◦ 20-800℃: ~14.9×10⁻⁶/℃

◦ 20-1000℃: ~15.6×10⁻⁶/℃

◦ 20-1150℃: ~15.9×10⁻⁶/℃

The gradual CTE increase minimizes thermal stress during frequent temperature cycling (e.g., aero-engine start-stop, gas turbine load adjustment), reducing thermal fatigue cracking risk by 55-65% compared to conventional nickel-based alloys (e.g., Inconel 625).

• Thermal Conductivity (λ):

◦ 100℃: ~14.5W/(m·K)

◦ 500℃: ~17.8W/(m·K)

◦ 800℃: ~21.2W/(m·K)

◦ 1000℃: ~22.9W/(m·K)

◦ 1150℃: ~23.6W/(m·K)

The temperature-dependent conductivity improvement promotes efficient heat dissipation in ultra-high-temperature components, avoiding localized overheating (a major cause of γ’ phase coarsening and creep acceleration) and extending part service life by 40-45% compared to GH4105.

2.3 Mechanical Properties (After Standard Heat Treatment: 1120-1160℃ solid solution for 1h, water cooling + 740-770℃ aging for 10h, air cooling)

Key Notes:

• The ultra-high room-temperature strength (σᵦ ≥1050MPa) meets the load-bearing requirements of aero-engine high-pressure turbine disks and ultra-high-pressure fasteners, with strength 5-8% higher than GH4105;
• At 900℃ (a typical service temperature for industrial gas turbine hot-end parts), the creep rupture strength (≥320MPa) is 14-18% higher than that of GH4105, ensuring long-term structural stability under high-temperature cyclic load;
• Even at 1150℃ (near its upper service limit), the retained elongation (≥8%) and creep rupture strength (≥90MPa) prevent brittle fracture during emergency shutdowns, making it suitable for components with extreme thermal cycling (e.g., hypersonic aircraft propulsion system cores).

3. Application Products & Industry Scenarios

3.1 Aerospace Field

As a core material for next-generation high-thrust aero-engine hot-end parts, GH4738 is used for:

• Aero-engine High-pressure Turbine Disks: Disks (rotational speed up to 22,000 rpm) in large bypass ratio turbofan engines (thrust ≥220kN), operating in 950-1050℃ high-temperature gas environments; the alloy’s creep resistance ensures a service life of up to 45,000 flight hours;
• Integral Turbine Rotors: High-pressure integral turbine rotors (disk + blade integrated forging), withstanding centrifugal forces up to 50,000g and 950-1000℃ gas erosion; its fine-grained structure (grain size 7-10 ASTM) ensures uniform strength distribution;
• Hypersonic Aircraft Propulsion Cores: Combustion chamber liners and nozzle throat parts in scramjet engines, resisting 1100-1150℃ aerodynamic heating and thermal fatigue, reducing component replacement frequency by 50-60% compared to GH4105.

3.2 Energy Field

3.2.1 Ultra-high-efficiency Industrial Gas Turbines

In advanced industrial gas turbines (turbine inlet temperature: 1350-1450℃) for combined cycle power generation, GH4738 is applied to:

• Turbine Rotor Blades: High-pressure turbine blades (stage 1-4), withstanding 1050-1100℃ high-pressure gas and cyclic thermal stress; the alloy’s creep resistance improves gas turbine efficiency (up to 62% for combined cycle power generation);
• Combustion Chamber Liners: Hot-zone liners in combustion chambers, resisting 1100-1150℃ high-temperature gas 冲刷 and thermal fatigue, ensuring structural stability for over 150,000 hours of operation.

3.2.2 Advanced Nuclear Energy

For next-generation nuclear reactors (e.g., molten salt reactors (MSRs) and fast neutron reactors (FNRs) with coolant temperature: 850-950℃), the alloy is used for:

• Reactor Core Heat Exchanger Tubes: High-temperature heat exchanger tubes in MSRs, resisting corrosion by molten fluoride salts (e.g., LiF-BeF₂) and neutron radiation;
• Reactor Pressure Vessel Liners: Inner liners of FNR pressure vessels, withstanding 850-900℃ high-temperature liquid metal coolant (e.g., sodium) erosion and ensuring reactor safety.

3.3 Petrochemical Field

In large-scale coal-to-olefins and ultra-high-temperature ethylene cracking units (operating temperature: 1050-1150℃), GH4738 is used for:

• Ultra-high-temperature Cracking Furnace Tubes: Core furnace tubes in coal-to-olefins cracking furnaces, resisting hydrocarbon gas pyrolysis corrosion and creep deformation; compared to GH4105, it extends furnace tube service life by 70-80% and reduces maintenance costs by 55-60%;
• High-pressure Hydrogenation Reactor Internals: Catalyst support grids and reactor inner liners in heavy oil hydrogenation reactors (pressure: 30-35MPa, temperature: 950-1000℃), resisting hydrogen embrittlement and sulfur corrosion.
• Metallurgical Industry: High-temperature furnace rolls (working temperature: 1000-1050℃) for nickel-based superalloy hot rolling, withstanding alloy melt splashing and mechanical wear; its oxidation resistance extends roll service life by 90-100% compared to 310S stainless steel;
• Vacuum Heat Treatment Equipment: Heating elements and furnace liners in ultra-high-temperature vacuum annealing furnaces (operating temperature: 1100-1150℃), ensuring uniform temperature distribution and avoiding contamination of heat-treated workpieces (e.g., high-precision superalloy components);
• High-temperature Test Equipment: Sample holders for ultra-high-temperature creep testing (900-1150℃) and high-load fixture components in material performance testing machines, providing stable support for long-term tests (up to 15,000 hours) and ensuring accurate test data for next-generation superalloy research.
• Hot Working: Forging temperature range: 1160-1220℃; initial forging temperature should not exceed 1220℃ to avoid γ’ phase dissolution and grain coarsening, and final forging temperature should not be lower than 1040℃ to prevent work hardening and cracking;
• Cold Working: Cold working is limited to light deformation (≤10%) such as precision machining and grinding; cold rolling or stamping is not recommended due to ultra-high room-temperature strength; intermediate annealing (1100-1140℃, 1h) is required after any cold deformation to restore ductility;
• Heat Treatment: The two-step process (solid solution + aging) must be strictly controlled—over-aging (above 800℃) will cause γ’ phase coarsening (particle size >0.3μm) and significant strength degradation, while under-aging (below 720℃) will result in insufficient precipitation strengthening and reduced high-temperature creep resistance.

3.4 Metallurgical & High-end Industrial Fields

4. Processing & Heat Treatment Recommendations

This comprehensive performance and application profile makes GH4738 an advanced, high-reliability nickel-based superalloy for ultra-high-temperature high-end manufacturing, perfectly balancing ultra-high-temperature strength, corrosion resistance, and processability for the most demanding hot-end components in aerospace, energy, and petrochemical industries.