Nickel Alloys and Superalloys

Nickel alloys are what you buy when steel has run out of temperature or chemistry. Inconel 718 holds nearly its full strength at 650 °C where stainless has halved; Hastelloy C-276 sits in boiling hydrochloric acid that would dissolve 316L in hours; Monel shrugs off seawater and hydrofluoric acid; Invar barely expands when heated. They are heavy (about the density of steel), expensive (five to twenty times stainless), and among the hardest metals to machine — so they are specified by the environment, never by default.

Nickel alloys by group

Commercially pure nickel≥ 99 % Ni · Nickel 200, 20112105 – 1,240Caustic-soda plant, food processing, electroplating anodes, battery and electronic components — magnetic, ductile, excellent in alkalis and dry halogens.

Monel (Ni-Cu)~67 % Ni, 30 % Cu · Monel 400, K-50012170 – 550Seawater pump shafts, valve trim, marine fasteners, hydrofluoric-acid equipment — immune to chloride stress cracking; K-500 age-hardens to stainless-like strength.

Inconel & Incoloy (Ni-Cr-Fe)Ni + 15–25 % Cr, Fe, Mo, Nb · 600, 625, 718, X-750, 800H81160 – 1,170Gas-turbine discs and casings, exhaust and afterburner parts, furnace fixtures, nuclear steam generators — oxidation resistance to 1,000 °C; 718 and X-750 age-harden for strength to 650 °C.

Hastelloy (Ni-Mo-Cr)Ni + 15–30 % Mo, 0–22 % Cr, W · C-276, C-22, B-3, X49235 – 520Chemical reactors, scrubbers, pickling tanks, flue-gas desulfurization — the corrosion champions in mixed acids, wet chlorine and hot chlorides; Hastelloy X for combustor cans.

Ni-Co superalloysNi + Co, Cr, Mo, Ti, Al · Waspaloy, René 41, Haynes 28221390 – 1,790Turbine blades, discs, seals and fasteners at 700–870 °C — the strongest metals at temperature; forged, cast or printed, rarely bar-stock machined.

Controlled-expansion (Ni-Fe)36–50 % Ni + Fe, Co · Invar 36, Kovar, Alloy 4216200 – 550Metrology and optical structures, laser and lithography frames, glass-to-metal and ceramic seals, bimetal strips — Invar expands a tenth as much as steel; Kovar matches borosilicate glass.

Shape-memory (Ni-Ti)~55 % Ni, 45 % Ti · Nitinol1—Stents, guidewires, orthodontic wire, eyeglass frames, actuators — superelastic (8 % recoverable strain) or thermally shape-recovering by composition.

Nitinol

Choose a nickel alloy for

Turbine and exhaust components, combustor liners and afterburner parts above 600 °C; chemical-plant valves, pumps and vessels in strong acids, chlorides or mixed oxidizing-reducing media; seawater pump shafts and marine fasteners (Monel); metrology frames, optical benches and glass-to-metal seals that must not move with temperature (Invar, Kovar); electrodes and cathodes in caustic (pure nickel); and medical or actuator parts that need shape memory (Nitinol).

Look elsewhere when

A stainless or duplex grade survives the environment (it will cost a fraction and machine three times faster), the temperature stays under ~500 °C (heat-resistant stainless or Cr-Mo steel), weight matters (titanium to 500 °C), or the part is large and mostly bulk. Nickel alloys also work-harden severely and have low thermal conductivity, so thin walls, deep pockets and small threads carry a machining premium far above the material price.

Yield strength against max service temp, every nickel alloy grade

No materials in view have both of these properties.

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Nickel Alloy by application

Heat above 600 °C: 718 for anything structural to 650 °C; Hastelloy X and 625 for sheet-metal combustor and exhaust parts to 1,000 °C without needing strength; Waspaloy for rotating parts hotter than 718 allows.
Acids, chlorides and mixed chemistry: C-276 when the chemistry is unknown or mixed; 625 for chloride pitting with high strength and good welding; Nickel 200 specifically for caustic and dry chlorine.
Seawater and marine hardware: Monel 400 for shafts, valve seats and fasteners immersed for decades; K-500 where the same part must also carry load — pump shafts, doctor blades, oil-tool components.
Dimensional stability with temperature: Invar for optical benches, mold masters for carbon-fiber layup and metrology fixtures; Kovar for hermetic packages and feedthroughs sealed to glass or alumina.
Medical and superelastic devices: Superelastic Nitinol for stents, guidewires and orthodontic archwire; shape-memory grades for actuators and couplings. Laser-cut or ground, rarely milled.

FabAgentAI

AI suggestions — verify with an engineer before ordering. Estimates are indicative; the quote page prices your exact geometry.

Manufacturing notes

CNC machining: Nickel alloys are the slowest common metals to cut — 10–20 % of the speed of mild steel — because they work-harden instantly, conduct heat poorly and abrade the tool. Rigid setups, sharp carbide or ceramic inserts, heavy constant feed, no dwelling. Machine 718 and K-500 in the solution-annealed condition and age afterwards; leave grinding stock on tight features because aging moves them slightly. Invar and Kovar are gummy but soft.
Welding: Solid-solution alloys (625, C-276, 600, Monel 400, Nickel 200) weld well by TIG / MIG with matching filler. Age-hardening alloys (718, X-750, K-500, Waspaloy) weld in the annealed state and are heat-treated afterwards; strain-age cracking is the risk. Nitinol and Invar are welded by laser or EB only.
Heat treatment: Solution anneal, then one or two aging steps: 718 at 720 / 620 °C for eight hours each, X-750 and Waspaloy similarly, K-500 at 600 °C. Precise ramp and atmosphere control is mandatory — we heat-treat to AMS specification with certification. Invar is stabilized by a low-temperature anneal after machining to lock its expansion coefficient.
Sheet and fabrication: 625, Hastelloy X and 600 sheet form and bend like a stiff stainless and are used for combustor liners, ducts and heat shields; 718 sheet forms in the annealed state only. Invar and Kovar sheet form easily for enclosures and lids.
Finishing: Passivate or pickle after welding; electropolish for cleanliness; aluminide or thermal-barrier coatings for turbine parts; gold or nickel plating on Kovar for hermetic packages. Nickel alloys are not anodized and rarely need a corrosion coating.

Most-quoted nickel alloy grades

Grade	Group	Yield, MPa	Tensile, MPa	Density, g/cm³	Machinability	Weldability	Best for
Inconel 718	Inconel & Incoloy (Ni-Cr-Fe)	550	965	8.19	Poor	Very good	Structural parts to 650 °C
Inconel 625	Inconel & Incoloy (Ni-Cr-Fe)	490	930	8.44	Poor	Excellent	Corrosion + heat, weldments
Hastelloy C276	Hastelloy (Ni-Mo-Cr)	360	790	8.89	Poor	Excellent	Aggressive chemical service
Monel 400	Monel (Ni-Cu)	240	550	8.8	Poor	Very good	Seawater shafts and valve trim
Invar 36	Controlled-expansion (Ni-Fe)	280	490	8.1	Poor	Very good	Near-zero thermal expansion
Kovar	Controlled-expansion (Ni-Fe)	345	520	8.36	Poor	Very good	Glass-to-metal seals
Nitinol	Shape-memory (Ni-Ti)	400	950	6.45	Not recommended	Fair	Superelastic medical devices
Nickel 200	Commercially pure nickel	148	462	8.89	Fair	Excellent	Pure nickel chemical plate
Waspaloy	Ni-Co superalloys	520	930	8.19	Poor	Fair	Disc-grade aerospace superalloy
Hastelloy X	Hastelloy (Ni-Mo-Cr)	360	755	8.22	Poor	Excellent	Hot-section combustor alloy

Finishes for nickel alloy

All 111 finishes

9 of our 111 surface finishes take nickel alloy: 5 recommended outright, 4 with process care. Each finish opens to its datasheet — thickness, hardness, salt-spray hours, spec codes and the nickel alloy-specific notes — and the configurator prices it on the grade you pick.

Finish	Group	On nickel alloy	Thickness, µm	Hardness, HV	Salt spray, h	Cost
Electropolishing	Anodizing, conversion & passivation	With care	removes 5–25	—	—	$$$
Gold Plating	Plating & metallizing	Yes	0.5–5	60–200	—	$$$$
Silver Plating	Plating & metallizing	Yes	5–20	60–200	—	$$$$
Hard Chrome Plating	Plating & metallizing	With care	10–500	850–1,050	24–96	$$$$
HVOF Carbide Coating	PVD, CVD & thermal spray	Yes	50–500	1,000–1,400	—	$$$$
Plasma Spray Coating	PVD, CVD & thermal spray	Yes	50–500	500–900	—	$$$$
Shot Peening	Mechanical finishing & post-processing	Yes	—	—	—	$$$
Honing	Mechanical finishing & post-processing	With care	0	—	—	$$$
Superfinishing and Isotropic Superfinishing	Mechanical finishing & post-processing	With care	0	—	—	$$$$

Nickel Alloy — frequently asked

Inconel 718 or 625 — which one?

718 when the part carries load hot: it age-hardens to roughly 1,000 MPa yield and keeps most of it to 650 °C, so it is the turbine-disc, fastener and structural-bracket alloy. 625 when the job is corrosion or oxidation resistance with good weldability and formability — it stays single-phase, cannot be hardened, and is the choice for sheet-metal exhaust, bellows, and chemical-plant welds.

What is the difference between Inconel, Hastelloy and Monel?

They are trade names for three alloy families. Inconel (Ni-Cr-Fe) is for heat and oxidation; Hastelloy (Ni-Mo-Cr) is for aggressive wet chemistry — acids, chlorine, mixed oxidizers; Monel (Ni-Cu) is for seawater and hydrofluoric acid. Overlap exists (625 corrodes well, Hastelloy X runs hot), but the family name still tells you what the alloy was designed to survive.

Why are nickel alloys so hard to machine?

They work-harden the instant the tool touches them, they carry heat into the cutting edge instead of the chip, and their carbides abrade carbide tooling. Cutting speeds are a tenth of mild steel, tool life is short, and thin features deflect. Expect the machining cost to exceed the material cost on most parts; design with generous radii, avoid deep narrow pockets and small threads, and let us machine soft and age afterwards.

What is Invar used for?

Anything that must not change size with temperature: optical and laser benches, lithography stages, metrology fixtures, composite layup tooling, and precision instrument frames. Invar 36 expands about 1.2 µm/m per °C — a tenth of steel and a twentieth of aluminum. Kovar is the related alloy whose expansion matches borosilicate glass and alumina, used for hermetic electronic packages.

Can nickel alloys be welded?

Yes, with care. Solid-solution grades (625, C-276, 600, Monel 400) weld like a slow stainless with matching filler. Age-hardenable grades (718, X-750, K-500) are welded in the annealed condition and heat-treated afterwards to avoid strain-age cracking. All need cleanliness — sulfur and lead contamination embrittle nickel — and interpass temperature control.