Inconel
Inconel 718
Age-hardenable superalloy. UTS 1240+ MPa post-HT — the dominant jet-engine alloy.
Inconel 718 is a Ni-Cr-Fe age-hardenable superalloy strengthened by Nb and Ti. The dominant alloy in jet engine hot-section static components — discs, blades, casings, bolts. Retains strength up to 700 °C; maintains ductility down to −250 °C (LH₂/LOX service).
Equivalent Designations
| Standard | Designation |
|---|---|
| UNS | N07718 |
| Werkstoff Nr. | 2.4668 |
Standards
ASTM B637 / ASME SB637 (precipitation-hardening bar, forgings)AMS 5662, 5663, 5664 (aerospace)AMS 5596 (sheet/strip)
Chemical Composition (% by mass)
| Ni | 50.0–55.0 |
| Cr | 17.0–21.0 |
| Fe | Balance |
| Mo | 2.8–3.3 |
| Nb (+ Ta) | 4.75–5.5 |
| Ti | 0.65–1.15 |
| Al | 0.20–0.80 |
| Co | 1.0 max |
| Cu | 0.30 max |
| Mn | 0.35 max |
| Si | 0.35 max |
| C | 0.08 max |
| P | 0.015 max |
| S | 0.015 max |
| B | 0.006 max |
Mechanical Properties
| Tensile Strength (annealed) | 930 MPa |
| Tensile Strength (after age) | 1240+ MPa |
| Yield Strength (annealed) | 482 MPa |
| Yield Strength (after age) | 1100+ MPa |
| Elongation | 45 % |
Physical Properties
| Density | 8.2 g/cm³ |
| Melting Point | 1260–1336 °C |
Available Forms & Sizes
| Form | Size Range | Notes |
|---|---|---|
| Round Bar | Ø5 mm to Ø500 mm | Tolerance H8/H9/H10/H11 |
| Sheet/Plate | 0.5 mm to 75 mm thick | — |
Use Cases
Gas turbine engine parts
Discs, blades, casings, bolts. The dominant superalloy in jet engine hot-section static components.
Liquid-fuel rocket motor components
Turbo-pump impellers, combustion chamber liners (e.g., Manastu Space, ISRO Vikas/CE-20 derivatives).
High-temperature springs, fasteners
Retains strength up to 700 °C.
Cryogenic tanks
Ductile down to −250 °C; LH₂/LOX pressure vessels.
Design Notes
- Heat treatment to spec: Solution at 980 °C / 1 h + age 720 °C / 8 h FC to 620 °C / 8 h, AC. Failure to follow exact ramp/hold gives wildly off-spec strength.
- Specify AMS 5663 or AMS 5664 to anchor heat-treatment requirements.
- Machining: rough machine in solution-annealed condition; finish after age-hardening if dimensional tolerances are tight (~0.0008%/°C contraction during age).