Nickel Alloy Alloy 684 vs Inconel 725
Nickel Alloy · grade comparison
Nickel Alloy Alloy 684 and Inconel 725 are both nickel alloy grades. Alloy 684 is the stronger of the two: tensile strength 1,310 MPa (190 ksi) against 1,240 MPa (180 ksi) for Inconel 725, about 6% more. In exchange, Inconel 725 is the more ductile: elongation 25% versus 16% for Alloy 684, and Alloy 684 is harder (355 HB vs 330 HB). Alloy 684 is lighter (8.02 g/cm³ vs 8.31 g/cm³ for Inconel 725) and Alloy 684 runs hotter in service (870°C vs 650°C continuous). On the shop floor, Inconel 725 welds better (good vs poor).
Alloy 684Choose it when strength drives the design, or when weight is the constraint.
Inconel 725Choose it when the part is bent, formed or impact-loaded, or when it will be welded.
Alloy 684 vs Inconel 725: 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
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Same in both: Fatigue Strength (Endurance Limit) 480 MPa69.6 ksi
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)
Max Service Temperature (continuous)
Same in both: Latent Heat of Fusion 290 J/g125 BTU/lb · Min Service Temperature -196°C-321 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
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
Typical Recycled Content
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 725 |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$$ High | $$$$ High |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Both take the same 3 finishes: Gold Plating, Plasma Spray, Silver Plating.
Alloy 684 vs Inconel 725 — frequently asked
Is Alloy 684 stronger than Inconel 725?
Yes. Alloy 684 has a typical tensile strength of 1,310 MPa (190 ksi) against 1,240 MPa (180 ksi) for Inconel 725 — about 6% more.
Which is cheaper, Alloy 684 or Inconel 725?
Both sit in the same relative cost tier ($$$$, high); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which welds better, Alloy 684 or Inconel 725?
Inconel 725. Its weldability rates good (55/100) against poor (20/100) for Alloy 684.
Ready to make it?
Upload a CAD file and FabDigit prices the part in Alloy 684 and Inconel 725 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.