Inconel 718 and Waspaloy are two superalloys used side by side in the hot section of gas turbines. Both are precipitation hardening, but the type of precipitate differs — and that difference sets the temperature to which the material will hold up.
Niobium precipitate, or gamma prime?
Inconel 718 takes its strength largely from the precipitates formed by 4.75–5.50% niobium + tantalum. That phase is very favourable for manufacturing and welding — the weldability of 718 is among the best of the superalloys. However, it begins to lose its stability above roughly 650 °C.
There is no niobium in Waspaloy. In its place are 2.75–3.50% titanium and 1.20–1.60% aluminium; these combine with nickel to form the classic gamma prime phase. That phase stays stable at far higher temperatures. On top of it, 12–15% cobalt is added — cobalt delays the softening of the matrix at high temperature.
According to our datasheet, Waspaloy shows superior creep stability in the 750–870 °C range. Its tensile strength is 1200–1500 MPa and its hardness 35–45 HRC.
The price is machinability and welding: alloys with a high gamma prime content are prone to cracking during welding and are difficult to machine. In addition, the 12.0–24.0% iron in the composition of 718 is only max 2.0% in Waspaloy — which raises the cost markedly.
Comparison in numbers
| PROPERTY | Inconel 718 | Waspaloy |
|---|---|---|
| Nickel (Ni) | 50.0 – 55.0% | 58 – 61% |
| Chromium (Cr) | 17.0 – 21.0% | 18 – 21% |
| Cobalt (Co) | max 1.00% | 12 – 15% |
| Iron (Fe) | 12.0 – 24.0% | max 2.0% |
| Molybdenum (Mo) | 2.80 – 3.30% | 3.5 – 5.0% |
| Niobium + Tantalum | 4.75 – 5.50% | — |
| Titanium (Ti) | 0.65 – 1.15% | 2.75 – 3.50% |
| Aluminium (Al) | 0.20 – 0.80% | 1.20 – 1.60% |
| Carbon (C) | max 0.08% | 0.02 – 0.10% |
| Tensile strength Rm | — | 1200 – 1500 MPa |
| Yield strength Rp0.2 | — | ~1000 MPa |
| Hardness | — | 35 – 45 HRC |
| Density | — | 8.19 g/cm³ |
| Melting range | — | 1320 – 1380 °C |
| Creep strength | — | superior stability in the 750 – 870 °C range |
| UNS | N07718 | N07001 |
| W.Nr (DIN/EN) | 2.4668 | 2.4654 |
| AMS | 5596 · 5663 | 5544 · 5706 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Inconel 718 is sufficient — turbine discs, compressor parts, highly stressed fasteners, rocket engine components, cryogenic applications. Anywhere below 650 °C, 718 is both more economical and far easier to manufacture. It is the most widely used superalloy in the industry.
Waspaloy is required — turbine discs and shaft connections, parts around the combustion chamber, components carrying continuous load above 700 °C. If the specification calls out AMS 5544 or AMS 5706, 718 is not an acceptable substitute.
Neighbouring alloys
For an alternative in the same temperature class there is Nimonic 80A, and for a more economical precipitation hardening option Incoloy A286. For the solid solution equivalent of 718, see our Inconel 625 – 718 comparison.
Technical datasheets
Inconel 718 — chemical composition, mechanical values, standard equivalents
Waspaloy — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.