Mar-M 247 Superalloy Single Crystal Casting Turbine Rotors
Introduction
Turbine rotors are subjected to the most demanding operational conditions in gas turbines—combining high centrifugal forces, extreme thermal loads, and prolonged exposure to oxidation and creep. To meet these requirements, advanced nickel-based superalloys like Mar-M 247 are used for their outstanding high-temperature mechanical properties. When produced using single crystal casting, Mar-M 247 turbine rotors achieve grain boundary-free structures, offering superior creep resistance, fatigue strength, and thermal stability under continuous operation above 1000°C.
Neway AeroTech provides vacuum investment casting of single crystal Mar-M 247 components using spiral grain selectors and precise directional solidification control. Our castings support aerospace propulsion, power generation, and defense systems where dimensional integrity and fatigue resistance are mission-critical.
Core Technology of Single Crystal Casting for Mar-M 247 Rotors
Wax Pattern Fabrication Wax models are created with ±0.05 mm accuracy to replicate rotor hub geometry, blade attachments, and cooling slot details.
Shell Mold Construction Refractory ceramic molds are built up to 10 mm thick, supporting the thermal and mechanical demands of large rotor castings.
Grain Selector Integration Spiral selectors initiate controlled [001] grain growth from the rotor hub outward, eliminating all grain boundary weaknesses.
Vacuum Induction Melting Mar-M 247 is melted under vacuum (≤10⁻³ Pa) at 1450–1480°C, preserving alloy chemistry and preventing gas inclusions.
Directional Solidification Process The mold is withdrawn at 2–4 mm/min under a precisely controlled thermal gradient to produce single crystal structures throughout the rotor diameter.
Shell Removal and Cleaning Shells are removed with high-pressure blasting and chemical leaching to retain edge integrity and surface quality.
Hot Isostatic Pressing (HIP) HIP at 1180°C and 150 MPa removes shrinkage porosity and improves fatigue life in high-stress regions.
Heat Treatment and Final Machining A solution and aging cycle stabilizes the γ′ phase. Final dimensions are achieved using CNC machining and EDM.
Mar-M 247 Material Properties in Single Crystal Rotor Applications
Max Operating Temperature: 1150°C
Tensile Strength: ≥1100 MPa at room temperature
Creep Rupture Strength: ≥220 MPa at 980°C for 1000 hours
Gamma Prime Content: ~65–70%
Oxidation Resistance: Excellent in continuous hot gas environments
Microstructure: [001] oriented single crystal with <2° deviation
Case Study: Mar-M 247 Single Crystal Rotor for Heavy-Duty Gas Turbine
Project Background
Neway AeroTech was contracted to produce a single crystal Mar-M 247 rotor for an industrial gas turbine used in continuous base-load power generation. The component required zero porosity, tight dimensional tolerances, and verified single crystal grain orientation to operate above 1050°C under 24/7 load conditions.
Application Examples
Aeroengine Core Rotors (e.g., HPT stages): Rotating blades and disks exposed to cyclic stress and thermal gradients.
Power Generation Rotors: Turbine wheels used in Frame-class industrial gas turbines requiring high creep strength and oxidation resistance.
Marine Propulsion Turbines: Rotors subject to salt-laden, high-temperature gas streams with rapid start-stop cycles.
Manufacturing Solution for Mar-M 247 Single Crystal Turbine Rotors
CFD-Informed Mold Design Casting system designs, including chill plates and selector orientation, are validated through CFD simulation to minimize turbulence and promote directional solidification.
Vacuum Casting Execution Vacuum investment casting is performed with precise thermal zone control to maintain grain orientation and eliminate stray grains.
Post-Casting HIP and Heat Treatment HIP removes internal porosity. Heat treatment promotes uniform γ′ distribution, maximizing thermal fatigue strength.
Final Machining and Inspection Critical surfaces are finished by CNC and EDM. Inspection includes CMM, X-ray, and EBSD analysis.
Key Challenges in Rotor Casting
Maintaining single crystal growth through large-diameter rotor hubs
Preventing hot tearing at cooling slot transitions and blade roots
Avoiding recrystallization in low-mass or high-thermal gradient areas
Controlling dimensional distortion during HIP and heat treatment
Results and Verification
[001] grain orientation confirmed via EBSD with <2° deviation across entire rotor
0% porosity confirmed post-HIP through ultrasonic and X-ray testing
Creep rupture performance exceeded 220 MPa at 980°C
Dimensional precision within ±0.03 mm at critical blade root interfaces
100% pass rate in mechanical and NDT acceptance tests
FAQs
Why is Mar-M 247 ideal for single crystal turbine rotor applications?
What are the benefits of single crystal over equiaxed rotor castings?
How is [001] grain orientation maintained across large rotor diameters?
What industries use Mar-M 247 single crystal rotors?
What inspections ensure the structural integrity of turbine rotors?
