Inconel 738LC Superalloy Directional Casting Turbine Wheel
Introduction
Inconel 738 equiaxed crystal casting is an advanced solution for producing gas turbine wheels with outstanding mechanical strength, oxidation resistance, and thermal fatigue durability. At Neway AeroTech, we cast Inconel 738 gas turbine wheels for use in power generation, aerospace auxiliary turbines, and energy systems. These components perform reliably under continuous operation at temperatures up to 980°C, with excellent creep and fatigue performance over long service hours.
Equiaxed casting enables complex geometry, consistent grain structure, and cost-effective production of large turbine wheels used in industrial and aviation environments.
Core Technology of Inconel 738 Equiaxed Casting
Wax Pattern and Assembly: High-precision wax models of the turbine wheel are injection-molded and assembled with ±0.05 mm dimensional repeatability.
Ceramic Shell Mold Creation: Multi-layer ceramic shells (8–10 coatings) are applied to form high-strength molds for vacuum investment casting.
Vacuum Melting and Pouring: Inconel 738 alloy is melted in a vacuum furnace and poured at ~1500°C to minimize oxidation and porosity.
Controlled Equiaxed Solidification: Cooling is managed to promote uniform equiaxed grain formation, typically ASTM grain size 3–6.
Post-Casting Heat Treatment: Solution and aging heat treatment refine the microstructure and improve mechanical and thermal properties.
Precision CNC Machining: Machining of bore, fir-tree root, and bolt circles conducted with ±0.02 mm accuracy using CNC machining.
Optional Coatings: Thermal Barrier Coatings (TBC) applied for extended oxidation and thermal shock resistance.
Material Characteristics of Inconel 738 for Turbine Wheels
Property | Value |
|---|---|
Max Operating Temperature | 980°C |
Ultimate Tensile Strength | 1130–1250 MPa |
Yield Strength | ≥850 MPa |
Creep Resistance | Excellent at high temperatures |
Oxidation Resistance | Superior in combustion gas environments |
Grain Size (Equiaxed) | ASTM 3–6 |
Dimensional Tolerance | ±0.02 mm (machined surfaces) |
Case Study: Inconel 738 Turbine Wheel for Heavy-Duty Industrial Gas Turbine
Project Background
A power generation OEM required a robust turbine wheel for a 30–50 MW industrial gas turbine with a service life target of 30,000 hours at 950°C. Inconel 738 was selected for its balance of castability, mechanical strength, and oxidation resistance.
Typical Applications of Inconel 738 Equiaxed Turbine Wheels
GE Frame 6B Second-Stage Turbine Wheel: Equiaxed Inconel 738 wheels used for stationary base-load operations at 900–950°C in industrial power plants.
Solar Mars 100 Gas Turbine Wheel: Compact turbine module operating at high thermal cycles in offshore power and gas compression platforms.
Rolls-Royce 501-K Series APU Wheel: Aerospace auxiliary power unit turbine wheels exposed to cyclic thermal stress with long-hour performance at elevated temperatures.
Mitsubishi M501J Turbine Wheel (Backup Component): Used in mid-duty and emergency turbine modules requiring high oxidation resistance and dimensional stability.
Siemens SGT-400 Power Turbine Wheel: Industrial-class turbine using Inconel 738 wheels for reliable, corrosion-resistant performance in high-temperature energy systems.
Manufacturing Process
Wax Injection and Pattern Assembly: Molded wax patterns precisely replicate blade root forms and hub geometry. Assembled into clusters for casting.
Shell Molding: Ceramic shell built up to 10 mm thick, providing strength during high-temperature casting.
Vacuum Casting: Inconel 738 melted and cast in a vacuum (<10⁻² torr) to eliminate porosity and control alloy segregation.
Solidification and Cooling: Cooling rate controlled to ensure equiaxed grain structure and minimize hot tearing and shrinkage defects.
Shell Removal and Cleaning: Shell material removed using high-pressure water jet and blasting, followed by acid cleaning.
Heat Treatment: Solution heat treatment at ~1120°C and aging at 845–870°C improves γ′ phase formation and high-temperature performance.
CNC Machining: All critical surfaces—bore, bolt holes, blade root interface—machined with ±0.02 mm precision.
NDT and Inspection: X-ray inspection and CMM used to verify internal and dimensional quality.
Results and Verification
Mechanical Properties: Final UTS >1150 MPa; YS >850 MPa at 900°C; suitable for long-term high-load operation.
Fatigue Life: Exceeded 25,000 cycles under thermal and mechanical fatigue testing at 950°C.
Creep Resistance: <0.5% deformation over 1000 hours at 950°C under design stress.
Oxidation Resistance: Passed cyclic oxidation test (1000 hours at 980°C) with no scale flaking or degradation.
Dimensional Control: Machined turbine wheels verified within ±0.02 mm tolerance via CMM.
FAQs
Why is Inconel 738 suitable for equiaxed turbine wheels?
How does equiaxed casting compare to directional solidification for gas turbine discs?
Can Inconel 738 turbine wheels be coated with TBC for additional protection?
What is the typical service life of an Inconel 738 turbine wheel?
What testing is used to ensure mechanical and thermal integrity of cast turbine wheels?
