Hot sections.
Superalloys.
Up to 1500°C+.
At elevated temperature, most materials lose strength, creep, oxidize, or distort. Material selection for high temperature requires specific knowledge — this guide maps temperature ranges to appropriate materials.
Material zones by temperature.
Continuous service temperature ranges. Above these, materials degrade rapidly or fail.
| Temperature range | Typical materials | Typical applications |
|---|---|---|
| Up to 100°C | Aluminum 6061, plastics | General use |
| 100-200°C | Aluminum 6061 (derated), plastics (PEEK, Ultem) | Automotive under-hood, appliances |
| 200-400°C | Carbon steels, standard stainless (304/316) | Boiler hardware, general industrial |
| 400-600°C | 316L, 321, 347 stainless | Steam systems, chemical reactors |
| 600-800°C | Inconel 718, Hastelloy X, 310 stainless | Jet engine hot section, industrial furnaces |
| 800-1000°C | Inconel 625, Hastelloy C-276, Rene alloys | Gas turbines, high-performance aerospace |
| 1000-1200°C | Haynes 230, Inconel 740H, Mo-TZM | Gas turbine hot zone, specialty furnaces |
| 1200-1500°C | Molybdenum TZM, tantalum | Refractory applications, rocket hot section |
| 1500-2000°C | Tungsten, carbon-carbon composites | Rocket throats, ion thruster components |
| 2000°C+ | Carbon-carbon, ceramic matrix composites | Specialty rocket nozzles, research hardware |
How materials fail at temperature.
Slow deformation
Material slowly stretches under sustained load at temperature. Governs design above ~30% of melting point (absolute scale). Inconel 718 designed for creep to 650°C; aluminum creeps above 150°C.
Material loss
Surface oxidizes, flakes away. Consumes material over time. Stainless oxidizes slowly to 900°C; carbon steel scales rapidly above 500°C. Requires oxidation-resistant alloy for extended high-temp service.
Yield drops
Yield strength decreases with temperature. 4140 yield: 655 MPa at 20°C, ~500 MPa at 300°C, ~300 MPa at 500°C. Design for temperature-appropriate derated strength.
Structural change
Some materials undergo phase transitions affecting properties. Austenitic stainless transforms above 800°C causing embrittlement. Age-hardened aluminum over-ages above 200°C.
Cyclic cracking
Repeated heating/cooling causes cracking from thermal expansion stress. Critical for aerospace parts that cycle through temperature. Requires thermal fatigue-resistant alloys.
Self-accelerating
Some failures self-accelerate — oxide layer flakes exposing fresh metal which oxidizes more. Molybdenum in oxygen above 500°C undergoes catastrophic thermal runaway.
Nickel-based superalloys.
Nickel superalloys dominate high-temperature structural applications from 600-1000°C.
Inconel grades
- • Inconel 718: precipitation-hardened, 650°C service, aerospace workhorse
- • Inconel 625: solid solution strengthened, 800°C, corrosion + temperature
- • Inconel X-750: age-hardened, 980°C short-term, moderate long-term
- • Inconel 600: oldest, 700°C, general service
- • Inconel 601: oxidation-resistant, 1200°C short-term, heater elements
Hastelloy & Haynes
- • Hastelloy X: 1150°C short-term, combustor liners
- • Hastelloy C-276: 800°C + severe corrosion, chemical plants
- • Haynes 230: 1150°C, gas turbine hot sections
- • Haynes 188: cobalt-based, 1100°C + oxidation, aerospace
- • Haynes 25: cobalt-based, 870°C long-term
Beyond superalloys.
For temperatures above ~1200°C, refractory metals take over.
1800°C vacuum
Molybdenum and TZM alloy for 1500-1800°C service in vacuum or inert atmosphere. Oxidizes catastrophically in air above 500°C — coatings required for air service.
2500°C+ vacuum
Tungsten for extreme temperature in vacuum. Jet engine/rocket applications. Brittle, difficult to machine — typically used as refractory coating or sintered assembly.
HCl + high-temp
Tantalum for corrosion + temperature. Essentially immune to chemical attack. Used in chemical processing, capacitor foil, specialty refractory.
1300°C with coating
Niobium alloys (C-103) for aerospace hot section. Requires oxidation-resistant coating above 500°C. Used in rocket engines, hypersonic aerospace.
Ultra high-temp
Rhenium and rhenium alloys (Re/Mo) for ultimate high-temp metal applications. Rocket engine thrust chambers, thermocouple wire. Very expensive.
2000°C+
Carbon fiber in carbon matrix. Used for rocket nozzle throats, hypersonic leading edges, brake discs. Strength increases with temperature up to ~2000°C.
FAQ
How much strength do materials lose with temperature?
Generally: materials lose 10-30% strength for every 100°C above room temperature. Specifically: 6061 aluminum loses 50% strength by 200°C. Mild steel loses 30% by 400°C. 304 stainless loses 30% by 600°C. Inconel 718 loses 20% by 650°C (its designed service temp). For design, use temperature-derated material data, not room-temperature values.
When is creep important?
Creep becomes dominant design consideration above ~30% of melting temperature (absolute scale, K). For room-temperature materials: aluminum above 100-150°C, mild steel above 400°C, stainless above 500°C, Inconel above 600°C. For applications with sustained load at elevated temperature, creep is the primary design criterion. Short-term or intermittent exposure: creep less critical.
Why does molybdenum oxidize badly in air?
Molybdenum oxide (MoO3) is volatile — sublimes away above 500°C in oxidizing atmosphere. Instead of forming protective layer, MoO3 evaporates, exposing fresh Mo metal which oxidizes further. Catastrophic mass loss. In vacuum or inert atmosphere, Mo is stable to 1800°C+. For Mo service in air above 500°C, silicide or aluminide coatings required. Same issue for tungsten and some other refractory metals.
Do plastics work at high temperature?
Yes, but limits. Standard thermoplastics: up to 100°C continuous. Engineering plastics (PEEK, Ultem, PPS): 150-260°C. Polyimides (Vespel, Meldin): up to 300°C. Above 300°C, plastics generally not viable — use metals or ceramics. For specific high-temperature polymer applications, consult specific material data sheets — temperature ratings vary with load and time.
How to specify high-temperature parts?
Specify: (1) Continuous service temperature, (2) Peak temperature (short-term excursion), (3) Atmosphere (air, vacuum, inert, reducing), (4) Loading (static, cyclic, pressure), (5) Expected service life, (6) Thermal cycling frequency. These together determine material. Never over-specify — high-temperature alloys are expensive ($50-150/kg vs $2-8/kg for steel).
Heat treatment for high-temperature parts?
High-temperature alloys often require specific heat treatment for optimal properties. Inconel 718: solution treat at 980°C + age at 720°C + age at 620°C to achieve full precipitation hardening. Without heat treatment, properties significantly lower. We coordinate heat treatment with NADCAP-qualified heat treat partners for aerospace parts.
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