MAR-M-247 is a superalloy used in aerospace applications. Melting point: 1,315 °C. Tensile strength: 965 MPa.
Deep inside a rocket engine, a fan-like wheel spins in gas hot enough to melt most metals. MAR-M-247 is one of the special alloys engineers trust to spin there without softening, stretching, or burning away.
Quick facts
- Type: a nickel-based “superalloy” — a metal designed to keep its strength when it is glowing red-hot. It is vacuum-melted and cast, and can be made as ordinary metal (lots of tiny crystal grains, called polycrystalline), directionally solidified (grains lined up in one direction), or as a single crystal (one continuous grain).
- Created by: Danesi and Lund at Martin Metals / Martin Marietta Corporation in the early 1970s. The “MAR-M” in the name is the maker’s designation; “247” identifies this specific recipe.
- Main ingredients (by weight, the rest nickel): about 10% cobalt, 10% tungsten, 8.25% chromium, 5.5% aluminum, 3% tantalum, 1.5% hafnium, 1.0% titanium, 0.7% molybdenum, plus small amounts of carbon, zirconium, and boron.
- Heat tolerance: stays strong at temperatures approaching 1000 °C (about 1830 °F).
- Density: roughly 8.5 g/cm³ — a little heavier than steel. (The closely related lighter variant DS CM247LC is about 7.8 g/cm³.)
What it is and how it works
A turbine — a wheel of angled blades — spins extremely fast inside searing gas. Ordinary metals would soften, slowly stretch out of shape (a problem engineers call “creep”), or oxidize, meaning they react with oxygen and crumble away like rust on fast-forward. MAR-M-247 resists all three at once.
The secret is its microstructure, the metal’s internal architecture. About 62% of the alloy is made of tiny, neatly ordered particles called gamma-prime [Ni₃(Al,Ti)] sitting inside a nickel background. Think of them as countless microscopic rivets that pin the metal in place so it holds its shape even when nearly molten-hot. Heavy “refractory” atoms — tantalum, tungsten, and molybdenum, elements with very high melting points — dissolve into the metal and slow the atomic shuffling that causes creep. Chromium and aluminum grow a thin protective oxide skin that fends off oxidation and corrosion. Small additions of boron, carbon, zirconium, and hafnium reinforce the boundaries between the metal’s grains, so a part won’t crack along those seams.
The alloy can also be cast so that all its grains line up in one direction, or grown as a single crystal with no internal boundaries at all. Removing those weak crossways boundaries dramatically improves how long a blade lasts under heat, stress, and vibration — exactly the punishment a rocket turbopump blade endures.
Why it matters
In a rocket engine, turbopumps are the high-speed pumps that force propellant into the combustion chamber at enormous pressure. Their turbine blades sit in some of the hottest, most heavily stressed conditions anywhere in the vehicle, and a single blade failure can destroy the engine. MAR-M-247’s mix of high-temperature strength, creep resistance, ease of casting, and oxidation resistance made it a leading candidate and test material for advanced turbopump turbine blades.
It also helped shape modern engines far beyond rockets. As an early directionally solidified superalloy, it became the parent of widely used descendants — including CM247LC for directional solidification and the CMSX family of single-crystal alloys — so its chemistry underpins much of today’s jet-engine and gas-turbine technology.
Where it is used and notable examples
- Space Shuttle Main Engine (SSME): single-crystal alloys derived from MAR-M-247, along with other single-crystal superalloys, were cast and tested for high-pressure turbopump turbine blades, including high-cycle-fatigue testing and full-scale SSME test firings.
- Advanced liquid rocket engines: evaluated to meet the safety and durability demands of next-generation turbopump turbine blades.
- Aircraft and industrial gas turbines: directionally solidified MAR-M-247 blades and vanes have been produced in volume for hot-section parts, such as Garrett gas turbines.
- Turbocharger wheels: turbine rotors that run at around 980 °C.
Trade-offs and details
The same boron, carbon, zirconium, and hafnium that strengthen grain boundaries also lower the alloy’s melting point, limiting how hot it can be heat-treated. Single-crystal versions have no grain boundaries to protect, so those elements can be removed — allowing much higher-temperature treatment and as much as a roughly tenfold gain in how long the part survives under steady stress. When directionally solidified or grown as a single crystal, the alloy is anisotropic, meaning its strength depends on crystal direction, so castings must be carefully aligned. Tiny carbide inclusions formed during casting can start fatigue cracks, the material is hard to machine, and it is increasingly being explored for 3D printing methods, though cracking during printing remains a known challenge.
Ni 59%, Cr 8.25%, Co 10%, W 10%, Al 5.5%, Ti 1%, Ta 3%, Hf 1.5%, Mo 0.7%
| DENSITY | 9 kg/m³ |
| TENSILE STRENGTH | 965 MPa |
| YIELD STRENGTH | 815 MPa |
| STRENGTH-TO-WEIGHT | 113130.1 kN·m/kg |
| MELTING POINT | 1,315 °C |
| MAX SERVICE TEMPERATURE | 1,050 °C |
| THERMAL CONDUCTIVITY | 10.5 W/m·K |
| THERMAL EXPANSION | 12.0 µm/m·K |
| CATEGORY | Superalloy |
| DESIGNATIONS | AMS 5757 |
| MANUFACTURER | Martin Marietta (now Lockheed Martin) |
| DENSITY | 9 kg/m³ |
| TENSILE STRENGTH | 965 MPa |
| YIELD STRENGTH | 815 MPa |
| MELTING POINT | 1,315 °C |
| MAX SERVICE TEMP | 1,050 °C |
| THERMAL CONDUCTIVITY | 10.5 W/m·K |
| THERMAL EXPANSION | 12.0 µm/m·K |
| CORROSION RESISTANCE | Good |
| WELDABILITY | Poor |
| MACHINABILITY | Poor |
| COST RATING | Very High |
