Key findings
|
Inconel 625 is the corrosion and weldability choice, strengthened by solid solution. Inconel 718 is the high-strength, high-temperature choice, strengthened by precipitation hardening and heavily dependent on specific heat treatments. Selecting between them dictates your maximum operating temperature, environmental resistance, and overall manufacturing lead time.
Engineers specifying nickel superalloys for heavy industrial components often face this exact choice. However, when transitioning from traditional foundries to wire arc additive manufacturing (WAAM), the decision criteria shift. Large part sizes, localized thermal cycles during printing, and the necessity of post-print furnace treatments mean that choosing between these two alloys directly impacts your production route.
Inconel 625 vs 718 at a Glance
The most effective way to compare these two materials is to view their core metallurgical mechanisms and typical WAAM properties side by side. While both alloys belong to the nickel-chromium family, their varying secondary elements dictate entirely different industrial use cases. The table below outlines the primary distinctions between printed 625 and printed 718, assuming standard post-print conditions.
Inconel 625 vs Inconel 718: properties of WAAM printed material
| Feature | Inconel 625 | Inconel 718 |
| UNS Number | N06625 | N07718 |
| Strengthening Mechanism | Solid Solution | Precipitation Hardening |
| Tensile Strength (Typical) | ~680 MPa | ~1,215 MPa |
| Yield Strength (Typical) | ~400 MPa | ~1,010 MPa |
| Elongation (Typical) | 55% | 20-25% |
| Max Service Temperature | Up to 980°C | Up to 700°C (for strength retention) |
| Corrosion Resistance | Exceptional in harsh chlorides | Good, but secondary to strength |
| Weldability / Printability | Highly forgiving | Requires strict thermal control |
| Heat Treatment After WAAM | Simple stress relief or annealing | Complex multi-stage aging |
| Typical Cost & Lead Time | Baseline | Higher cost, longer processing time |
Composition and How Each Alloy Gets Its Strength
The performance gap between these two materials originates in their chemical makeup. While both rely on a heavy nickel and chromium base to resist oxidation, their trace elements dictate how they behave under mechanical load.
- Nickel (Ni): Base element for both alloys.
- Chromium (Cr): High in both, providing crucial oxidation resistance.
- Molybdenum (Mo): Approximately 9% in 625, but only around 3% in 718.
- Niobium (Nb): Present in both, but utilized differently during thermal processing.
- Iron, Titanium, and Aluminum: Kept to a minimum in 625, but present in specific ratios in 718 to facilitate hardening.
Inconel 625 derives its strength through solid-solution strengthening. The high levels of molybdenum and niobium stiffen the nickel-chromium matrix without requiring precipitation phases. For 3D printing, manufacturers typically utilize standard ERNiCrMo-3 welding wire to deposit this alloy.
Conversely, Inconel 718 is a precipitation-hardened alloy. It relies on careful additions of titanium, aluminum, and niobium to form microscopic gamma prime and gamma double prime precipitates during heat treatment. These precipitates act as roadblocks to internal deformation, giving the alloy its massive tensile strength. To print this alloy, application engineers generally specify ERNiFeCr-2 wire classifications.
Mechanical Properties: As-Printed vs Heat-Treated
When evaluating Inconel 3D printing with WAAM, the mechanical properties of the final part depend heavily on its condition. Traditional wrought datasheets do not perfectly translate to as-deposited wire-arc material.
Printed Inconel 625 offers highly reliable and isotropic properties immediately upon deposition. Once stress-relieved or annealed, WAAM 625 routinely hits tensile strengths around 680 MPa and yield strengths near 400 MPa, boasting excellent ductility with elongation values frequently reaching 40%. This makes it a highly tough, resilient material capable of absorbing significant energy before failure, roughly 200J.
Printed Inconel 718 behaves differently. In its as-printed state, it is relatively soft. The material must undergo a rigorous solution annealing and aging process to unlock its true mechanical potential. Once fully aged, WAAM 718 can achieve massive tensile strengths near 1,215 MPa and yield strengths surpassing 1,010 MPa. However, this extreme strength comes at the cost of ductility, with elongation dropping to the 20% to 25% range.
A critical consideration for large-format metal 3D printing is anisotropy, which is the difference in mechanical strength depending on the testing direction (horizontal versus vertical build directions). Advanced software platforms like MetalXL mitigate this by planning intelligent, multi-directional toolpaths that optimize the grain structure and reduce directional weakness in the final near-net-shape part.
Corrosion and Temperature Performance
The choice between these alloys usually crystallizes when evaluating the operating environment.
Inconel 625 is the undisputed champion of extreme corrosion resistance. Its high molybdenum content makes it practically immune to chloride-ion pitting, crevice corrosion, and aggressive sour gas environments. If a component operates submerged in seawater or handles highly acidic chemicals, 625 is the premier specification.
Inconel 718 is engineered for structural integrity under extreme thermal stress. While 625 loses structural rigidity under high loads at elevated temperatures, the precipitation-hardened matrix of 718 retains massive yield strength up to 700°C. This makes it the default choice for sustained creep and fatigue resistance in demanding turbomachinery and propulsion systems.
There is a slight overlap in capabilities. Both alloys offer excellent general oxidation resistance. The deciding factor almost always comes down to mechanical load at high temperatures (favoring 718) versus aggressive chemical attack at moderate temperatures (favoring 625).
Printing Them with WAAM: Weldability, Heat Treatment and Lead Time
From a manufacturing perspective, the two alloys present vastly different operational challenges.
Because Inconel 625 relies on solid-solution strengthening, it is highly weldable and incredibly forgiving during robotic deposition. It resists hot cracking and does not require overly complex thermal management during the print. Following deposition, the part only requires a simple stress relief or standard anneal cycle before final machining.
Inconel 718 demands far stricter process control. The heat from the welding arc can cause localized stress and micro-cracking if thermal parameters are not perfectly managed. Furthermore, the heat treatment route for 718 is extensive. It requires a high-temperature solution anneal followed by a lengthy double aging process. For massive WAAM parts, finding industrial furnaces capable of running this long, multi-stage cycle can become a logistical bottleneck.
This directly impacts your project budget and timeline. Inconel 718 raw wire is generally more expensive than 625. When you factor in the 18-hour furnace cycles and the fact that fully aged 718 is notoriously difficult to machine due to its extreme hardness, the total WAAM vs casting and forging cost calculation shifts. 718 will require higher cutting tool consumption, slower CNC spindle speeds, and longer overall lead times compared to the more machinable 625. Regardless of the chosen alloy, both require rigorous inspection. Buyers should familiarize themselves with the non-destructive testing of WAAM parts to ensure structural integrity prior to deployment.
Which One Should You Choose?
Consult the WAAM material selection guide to ensure a nickel superalloy is actually required for your specific load case. If it is, the decision comes down to the primary failure risk of the component.
Caption: WAAM Alloy Decision Matrix
| Application / Environment | Recommended Alloy | Primary Reason |
| Subsea manifold or valve body | Inconel 625 | Maximum resistance to seawater pitting and chloride corrosion. |
| Turbine housing or exhaust component | Inconel 718 | Retains extreme yield strength and creep resistance at 700°C. |
| Chemical heat exchanger | Inconel 625 | Broad-spectrum resistance to both oxidizing and reducing acids. |
| High-load structural aerospace bracket | Inconel 718 | Precipitation hardening delivers the highest possible tensile strength. |
| Low-load corrosive offshore piping | Super duplex stainless steel | Provides adequate corrosion resistance at a significantly lower material cost. |
Get an Alloy Recommendation
Selecting the correct superalloy is only the first step. Ensuring that the component can be printed, heat-treated, and successfully machined requires deep application engineering. Whether you are exploring 3D printing in oil and gas for corrosive environments or aerospace 3D printing for high-temperature propulsion parts, expert guidance is critical.
Send our engineering team your digital CAD geometry, the anticipated operating temperature, and the chemical medium. We will evaluate the load cases, recommend either 625 or 718, and outline the precise heat treatment route required to ensure your component passes final inspection. When you are ready to bypass traditional foundry lead times, contact our team to order metal parts on demand and secure your industrial components in weeks rather than months.
FAQ
What is the difference between Inconel 625 and 718?
Inconel 625 is solid-solution strengthened, making it highly ductile, easy to weld, and exceptionally resistant to harsh corrosion. Inconel 718 is precipitation-hardened, requiring a multi-stage heat treatment to achieve massive tensile and yield strength for high-temperature structural applications.
What is Inconel 718 used for?
Inconel 718 is primarily used for high-stress components operating at elevated temperatures up to 700°C. Common WAAM applications include turbomachinery, gas turbine housings, aerospace propulsion components, and high-load structural brackets where creep resistance is mandatory.
What is the composition of Inconel 718?
Inconel 718 is a nickel-chromium base alloy heavily alloyed with iron, niobium, and molybdenum. Crucially, it contains small, precise additions of aluminum and titanium, which allow the material to form strengthening precipitates during its aging heat treatment cycle.
What is the hardness of Inconel 625?
Because it does not undergo precipitation hardening, Inconel 625 remains relatively soft compared to aged 718. In its standard annealed or stress-relieved condition, WAAM-printed 625 typically presents a hardness that allows for straightforward conventional CNC machining without excessive tool wear.
How to weld Inconel 625?
Inconel 625 is highly weldable and rarely suffers from hot cracking. In additive manufacturing, it is deposited using standard ERNiCrMo-3 wire through controlled robotic arc welding. WAAM systems can easily print massive 625 components without the strict thermal management required for more sensitive alloys. To answer whether can WAAM parts be certified for this process, review our WAAM materials and certification portal for current industrial standards.
