Nickel-Cobalt Superalloys
Nickel-cobalt superalloys are nickel with 10–20 % cobalt, 15–20 % chromium, molybdenum or tungsten for solid-solution strength and 3–8 % aluminum plus titanium that precipitate as ordered gamma-prime, stable to far higher temperatures than the strengthening phase in Inconel 718. The result is the strongest class of metal at temperature: Waspaloy holds about 795 MPa yield at room temperature and useful strength to 760 °C, and cast MAR-M247 and single-crystal CMSX-4 blades run above 1,000 °C. They are forged, cast or printed rather than machined from bar, and they are the last step before ceramics.
Popular nickel superalloy grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Waspaloy | 520 | 930 | 8.19 | Poor | Fair | Forged discs, rings and fasteners to 760 °C; the default |
| Haynes 282 | 550 | 1,010 | 8.27 | Poor | Excellent | Weldable creep-resistant alloy for combustors to 930 °C |
| Rene 41 | 1,060 | 1,420 | 8.25 | Not recommended | Poor | Highest wrought strength to 870 °C; afterburner sheet |
| Haynes 230 | 390 | 870 | 8.97 | Poor | Very good | Solid-solution oxidation resistance to 1,150 °C |
| MAR-M247 | 815 | 965 | 8.54 | Not recommended | Not recommended | Cast and directionally solidified blades above 1,000 °C |
| CMSX-4 | 920 | 1,100 | 8.7 | Not recommended | Not recommended | Single-crystal blades for the hottest stages |
| MP35N | 1,790 | 1,930 | 8.43 | Not recommended | Poor | Cold-worked to 2,000 MPa; fasteners and medical wire |
Choose nickel superalloy for
Turbine discs, blades, vanes, seals, shrouds and casings; combustor liners and transition ducts; afterburner and exhaust structure; rocket-engine turbopumps; hot-section fasteners and springs; and the highest-strength non-magnetic fasteners and medical wire (MP35N) — parts that must carry load or hold shape at 700–1,100 °C.
Look elsewhere when
The part stays below about 650 °C — Inconel 718 gives more room-temperature strength, machines faster and welds better; the requirement is oxidation or corrosion without stress (Inconel 601, Inconel 625 or Hastelloy X, all far easier to fabricate); the part is a wet-corrosion problem (Hastelloy C276); or weight matters below 500 °C (a titanium alloy such as Ti-6242). A cast blade alloy such as MAR-M247 or CMSX-4 is never the answer for a machined-from-bar part — it is not made in that form.
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Nickel superalloy by application
- Discs, shafts and rings
- Waspaloy for forged rotating parts between the 650 °C limit of Inconel 718 and about 760 °C; Rene 95 and Astroloy as powder-metallurgy disc alloys where fatigue strength at temperature must be higher still; 718Plus as the drop-in step beyond 718.
- Combustors and hot sheet
- Haynes 282 and NiCo20Cr20MoTi (2.4650) where the sheet is welded and formed and then carries stress at 800–930 °C; Haynes 230 and Haynes 214 where oxidation to 1,150 °C or more matters more than strength; Rene 41 for the strongest thin structure.
- Blades and vanes
- IN-713C, IN-738LC and IN-939 investment-cast for industrial turbines and turbochargers; MAR-M247 and Rene 80 for aero hot stages; CMSX-4 single crystals with internal cooling for the first stages. Root and tip surfaces are ground, not milled.
- Fasteners, springs and wire
- Waspaloy and Rene 41 for hot-section bolts and studs; MP35N for the highest-strength corrosion-proof fasteners, medical implants and cable that must stay non-magnetic.
Working with nickel superalloy
- Machining
- Wrought alloys are machined solution-treated or aged at 38–45 HRC with whisker-reinforced ceramic or coated carbide at very low speeds, rigid fixturing and constant chip load — the slowest cutting of any metal family, with grinding and EDM planned for slots, fir-tree roots and holes. Cast blade alloys are cast to near-net shape and finished by grinding and EDM only.
- Welding
- Gamma-prime alloys with more than about 3 % aluminum plus titanium are prone to strain-age cracking: Waspaloy welds solution-treated and is aged afterwards; Rene 41 needs over-aged base metal and prompt post-weld treatment; Haynes 282 and alloy 263 were designed to weld and do so readily; Haynes 230 welds like a stainless with ERNiCrWMo-1. Cast alloys such as MAR-M247 and CMSX-4 are brazed or repaired by specialised processes, not fusion-welded.
- Heat treatment
- Waspaloy: solution 1,010–1,080 °C, stabilise 4 h at 845 °C, age 16 h at 760 °C. Haynes 282: anneal 1,120–1,150 °C, then 2 h at 1,010 °C and 8 h at 788 °C. Rene 41: 1,065 °C then 16 h at 760 °C. Vacuum or protective-atmosphere furnaces with certified charts; castings are hot-isostatically pressed before solution treatment. Cold-worked MP35N is aged 4 h at about 590 °C.
- Forming and finishing
- Sheet alloys (alloy 263, Haynes 282, Haynes 230, Rene 41) are formed annealed with intermediate anneals and a narrow hot-working window around 1,000–1,150 °C. Blades and vanes receive platinum-aluminide or MCrAlY bond coats and zirconia thermal-barrier coatings; fatigue-critical wrought parts are shot-peened.
Other nickel alloy series
Nickel-Cobalt Superalloys — frequently asked
What is nickel superalloy?
Nickel-cobalt superalloys are nickel with 10–20 % cobalt, 15–20 % chromium, molybdenum or tungsten for solid-solution strength and 3–8 % aluminum plus titanium that precipitate as ordered gamma-prime, stable to far higher temperatures than the strengthening phase in Inconel 718. The result is the strongest class of metal at temperature: Waspaloy holds about 795 MPa yield at room temperature and useful strength to 760 °C, and cast MAR-M247 and single-crystal CMSX-4 blades run above 1,000 °C. They are forged, cast or printed rather than machined from bar, and they are the last step before ceramics.
Which grade of nickel superalloy should I use?
Waspaloy when Inconel 718 is not enough: discs, shafts, rings, seals and fasteners at 650–760 °C, forged and heat-treated, still weldable with care. Rene 41 for higher strength to 870 °C in sheet and fasteners — afterburner parts and turbine shrouds — but difficult to weld and form. Haynes 282 is the newer wrought alloy with creep strength between the two and real weldability, for combustors, exhaust cases and land-based turbine parts to 930 °C; NiCo20Cr20MoTi (2.4650), better known as alloy 263, is the formable sheet grade for combustor liners to 850 °C. Haynes 230 and Haynes 214 are the solid-solution members for oxidation to 1,150 °C and beyond without high stress. For cast blades and vanes, IN-713C and IN-738LC serve industrial turbines and turbochargers, MAR-M247 and Rene 80 the hotter aero stages, and CMSX-4 is the rhenium-bearing single crystal for the hottest. Rene 95 and Astroloy are powder-metallurgy disc alloys; 718Plus extends 718 by about 55 °C. MP35N is the cobalt-nickel alloy cold-worked and aged to 1,800–2,000 MPa for fasteners, springs and medical wire.
Which grade of nickel superalloy is the strongest?
MP35N has the highest yield strength in the series at 1,790 MPa; Rene 95 follows at 1,240 MPa. Values are for each grade's default condition.
Which grade of nickel superalloy is easiest to machine?
Haynes 214 (machinability poor, 20/100), then Haynes 282 (20/100).
Waspaloy or Inconel 718?
Inconel 718 up to 650 °C: it has the higher room-temperature yield (about 1,035 MPa against 795 for Waspaloy), machines and welds better and costs less. Above 650 °C the niobium-rich gamma-double-prime in 718 coarsens into delta phase and its strength falls away, while the gamma-prime in Waspaloy holds to about 760 °C — so hot-section discs, rings and fasteners move to Waspaloy, and to Rene 41 or Haynes 282 beyond that. 718Plus is the intermediate step, buying about 55 °C over 718 with 718-like processing.
Why are turbine blades cast instead of machined from bar?
The blade alloys (MAR-M247, IN-738LC, CMSX-4) carry 6–8 % aluminum plus titanium and 60–70 % gamma-prime, which makes them impossible to forge and almost impossible to machine; investment casting gives the aerofoil, cored cooling passages and fir-tree root in one shot. Directional solidification aligns grain boundaries with the blade axis and single-crystal casting removes them entirely, worth roughly 25–50 °C of extra metal temperature in creep. Machining is limited to grinding the root and tip and drilling film-cooling holes by EDM or laser.