Nickel Alloy Alloy 684 vs Inconel 718
Nickel Alloy · grade comparison
Nickel Alloy Alloy 684 and Inconel 718 are both nickel alloy grades. Alloy 684 is the stronger of the two: yield strength 860 MPa (125 ksi) against 550 MPa (79.8 ksi) for Inconel 718, about 56% more; tensile strength follows at 1,310 MPa (190 ksi) vs 965 MPa (140 ksi). In exchange, Inconel 718 is the more ductile: elongation 45% versus 16% for Alloy 684, and Alloy 684 is harder (355 HB vs 200 HB). Alloy 684 is stiffer (213 GPa vs 200 GPa) and Alloy 684 runs hotter in service (870°C vs 540°C continuous). On the shop floor, Inconel 718 welds better (very good vs poor) and Inconel 718 sits in a lower cost tier (premium, $$$) than Alloy 684 (high, $$$$).
Alloy 684Choose it when strength drives the design, or when the part sees heat.
Inconel 718Choose it when the part is bent, formed or impact-loaded, or when it will be welded.
Alloy 684 vs Inconel 718: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all nickel alloy grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all nickel alloy grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Shear Modulus
Bulk Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Hardness, Rockwell B
Physical
Density and transition temperatures.
Density
Melting Point (Solidus)
Liquidus Temperature
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Latent Heat of Fusion
Max Service Temperature (continuous)
Min Service Temperature
Electrical
Conductivity and insulation.
Electrical Resistivity
Same in both: Electrical Conductivity 1.4 % IACS
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Galvanic Potential (seawater, vs SCE)
Corrosion Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Weldability
Formability (cold)
Castability
Brazeability / Solderability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Same in both: Typical Recycled Content 35%
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Thermal Diffusivity
Thermal Shock Resistance Index
Strength versus weight
Yield strength against density for every nickel alloy grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | Alloy 684 | Inconel 718 |
|---|---|---|
| CNC machining | — | Yes |
| Sheet metal | — | Yes |
| 3D printing | — | Yes |
| Default condition | — | Solution Annealed |
| Relative cost | $$$$ High | $$$ Premium |
| Min. machined wall | — | 1.5 mm |
| Best machined surface | — | Ra 1.6 µm |
| Electropolishing | — | Yes |
| HVOF Coating | — | Yes |
They share 3 finishes: Gold Plating, Plasma Spray, Silver Plating.
Alloy 684 vs Inconel 718 — frequently asked
Is Alloy 684 stronger than Inconel 718?
Yes. Alloy 684 has a typical yield strength of 860 MPa (125 ksi) against 550 MPa (79.8 ksi) for Inconel 718 — about 56% more. Tensile strength is 1,310 MPa (190 ksi) vs 965 MPa (140 ksi).
Which is cheaper, Alloy 684 or Inconel 718?
Inconel 718 is the lower-cost material: it sits in the premium tier ($$$) while Alloy 684 is high ($$$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
Which is easier to machine, Alloy 684 or Inconel 718?
Inconel 718. Its machinability rates poor (18/100) against not recommended (12/100) for Alloy 684; for welding the order is Inconel 718 first (very good, 70/100) then Alloy 684 (poor, 20/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in Alloy 684 and Inconel 718 side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.