WAAM nickel alloys compared: when to pick Inconel 625 or 718

MX3D has published a selection guide for wire arc additive manufacturing (WAAM) parts in two nickel superalloys. Inconel 625 suits corrosive service and easy processing, while Inconel 718 suits high loads at elevated temperature but needs a long heat treatment route. The choice sets operating limits, cost and lead time.

Context WAAM deposits metal wire with an electric arc, layer by layer, to build large near-net-shape parts that are then machined.

How do the two alloys gain their strength?

Both are nickel-chromium alloys, but they harden differently. Inconel 625 relies on solid-solution strengthening: roughly 9% molybdenum plus niobium stiffens the matrix, and no precipitates are needed. It is deposited with standard ERNiCrMo-3 wire. Inconel 718 contains only about 3% molybdenum and depends on titanium, aluminium and niobium additions that form fine strengthening precipitates during heat treatment. Its wire class is ERNiFeCr-2.

What do the mechanical figures look like?

MX3D gives typical values for printed material after post-print treatment. Aged 718 reaches roughly 1,215 MPa tensile and above 1,010 MPa yield, with elongation of 20 to 25%. Printed 625, after a stress relief or anneal, sits near 680 MPa tensile and 400 MPa yield, but stretches up to about 40% and absorbs around 200 J before failure. As deposited, 718 is comparatively soft and only gains its strength through the full heat treatment. The article also notes that anisotropy matters in large WAAM parts and that multi-directional toolpath planning in MetalXL can reduce it.

Which environment favours which alloy?

The deciding factor is usually the service condition. The molybdenum content makes 625 very resistant to chloride pitting, crevice attack and sour gas, which suits seawater and aggressive chemicals, with a temperature ceiling of about 980 °C. Alloy 718 holds its yield strength and creep resistance up to about 700 °C, which is why it is the default for turbomachinery and propulsion parts. Both resist general oxidation.

What changes in production, cost and lead time?

Alloy 625 is forgiving: it resists hot cracking and needs only a stress relief or anneal before machining. Alloy 718 demands tighter thermal control during deposition to avoid micro-cracking, then a high-temperature solution treatment and a two-step ageing cycle of roughly 18 hours in the furnace. For large parts, furnace capacity can become a bottleneck. Wire is dearer, aged 718 is harder to machine, and tool wear and cycle times rise, so cost and lead time both increase. MX3D advises checking first whether a nickel superalloy is needed at all, and notes that non-destructive testing applies to either alloy.

What it means

For manufacturers considering WAAM nickel parts, the alloy decision is also a route decision. Alloy 625 keeps the process chain short and suits repair, marine or chemical parts. Alloy 718 adds furnace access, thermal control expertise and harder machining, all of which affect quote, qualification effort and delivery time. Figures come from a service provider's guide and describe typical material, not design values, so project-specific testing and supplier data remain necessary.

Frequently asked questions

Which Inconel is better for hot structural parts in WAAM?

Inconel 718, according to MX3D, because it keeps its strength and creep resistance up to about 700 °C. It needs a solution treatment and two-step ageing to reach that strength.

When is Inconel 625 the better choice?

When the main risk is corrosion, for example chlorides, seawater or sour gas. It is also easier to print and machine, and needs only a stress relief or anneal.

Why does 718 cost more and take longer?

The wire costs more, the deposition needs stricter thermal control, the heat treatment involves long furnace cycles, and the aged material is harder to machine.