Invar 36
metaliron-nickel low-expansion alloy
FeNi36Nilo 36Pernifer 36UNS K93600DIN 1.3912Alloy 36Invar
Composition — UNS K93600 / ASTM F1684
| Element | Min % | Max % | Notes |
|---|---|---|---|
| Fe | bal. | balance | |
| Ni | 35.00 | 37.000 | 36% Ni is the critical inflection point for minimum CTE; deviations of ±1% change CTE significantly |
| Mn | — | 0.600 | Improves hot workability; minor solid-solution strengthener |
| Si | — | 0.350 | |
| C | — | 0.050 | Low carbon avoids carbide precipitation which degrades CTE stability |
| P | — | 0.025 | |
| S | — | 0.025 | |
| Co | — | 0.500 | Small additions can tailor the Curie temperature |
Mechanical & thermal properties — 2 conditions
| Property | LPBF as-built (XY) | LPBF stress-relieved (850°C / 1h / furnace cool) |
|---|---|---|
| Elastic modulus | 140–155 GPa | — |
| Yield strength (0.2%) | 280–370 MPa | 250–330 MPa |
| Ultimate tensile strength | 430–520 MPa | 400–480 MPa |
| Elongation at break | 20.0–40.0 % | 25.0–45.0 % |
| Hardness (HV) | 160–200 HV10 | — |
| Density | 8.11 g/cm³ | — |
| Relative density | 99.0–99.9 % | — |
| Thermal conductivity | 12.0–14.5 W/m·K | — |
| CTE | 0.9–1.8 µm/m·K | 0.9–1.8 µm/m·K |
| Melting / solidus point | 1420–1450 °C | — |
| As-built surface Ra | 7.0–18.0 µm | — |
Values shown as min–max where a spread is reported, otherwise as typical ± unit. Ranges reflect inter-source variation, not single-sample scatter. All values are for AM-processed specimens unless noted.
Engineering considerations
- CTE must be confirmed by measurement on the final LPBF part — do not rely solely on powder composition certificates
- Stress relief at 850°C/1h before final machining is the industry-standard post-process for LPBF Invar tooling
- Design autoclave tooling with the coefficient mismatch between Invar (1.3 µm/m·°C) and composite mandrel in mind — typical CFRP CTE is 0–2 µm/m·°C in-plane
- Confirm magnetic behaviour is acceptable for the application — Invar 36 is ferromagnetic at RT and becomes paramagnetic above ~277°C
- Minimum wall thickness: ~0.4 mm achievable but thicker walls (>1.5 mm) recommended for tooling structural integrity
- Residual oxygen in build chamber must be <50 ppm to prevent oxidation of the nickel-rich alloy
- Creep at elevated temperatures (>200°C) is a design consideration for long autoclave cycles — refer to pröbstle-2018-invar-creep for data
- Powder reuse: characterise CTE of recycled powder batches — oxidation can shift Ni/Fe ratio and alter CTE
Advantages
- Lowest CTE of any commercial LPBF metal (~1.3 µm/m·°C) — 7× lower than stainless steel
- Dimensional stability across temperature cycles — essential for composite tooling in autoclaves (up to 180°C)
- Good ductility (elongation ≥30%) — complex thin-walled tooling features are feasible
- LPBF allows integration of complex cooling/venting channels not achievable in wrought Invar
- Near-wrought CTE maintained in LPBF condition when composition is well controlled
- No phase transformation between room temperature and autoclave service temperatures
Limitations
- Extremely high raw material cost — Ni content makes Invar powder 3–5× more expensive than stainless steel powder per kg
- High residual stress in as-built LPBF condition — stress relief before final machining is mandatory
- Magnetic at room temperature — cannot be used in MRI environments or near magnetically sensitive equipment below Curie temperature (~277°C)
- Low hardness (~180 HV) — not suitable for wear surfaces without hard coating
- Low thermal conductivity (13 W/m·K) — residual stress accumulates rapidly; requires preheat and optimised scan strategy
- Limited published LPBF parameter databases compared to Ti-6Al-4V or 316L — expect parameter development effort
- CTE is highly sensitive to Ni content — powder composition control to ±0.5% Ni is essential
- Susceptible to hot cracking in LPBF if scan strategy and parameters are not optimised
Typical applications
Composite lay-up jigs and fixtures for aerospace (CFRP, GFRP structures)Autoclave tooling masters and mandrels for composite structuresMetrological tooling and precision gauges requiring dimensional stabilitySatellite and space optical bench structuresLaser and interferometric equipment framesBimetallic thermostat elements and temperature-compensating devicesPrecision mould tooling inserts for optics manufacturingShadow masks for cathode ray tube and display manufacturing (legacy)
Industries
aerospacetoolingindustrialelectronics
Compatible AM processes (2)
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Related calculators
NDT SelectorSelect the right non-destructive testing method for your AM part. Inputs: material class, defect focus, geometry, production volume, and criticality. Ranked scorecard across CT, X-ray, UT, FPI, MPI, eddy current, and visual inspection with detection limits and standard references.DistortionEstimate residual stress and distortion risk index (σ/σ_y) for LPBF and DED builds. Mercelis-Kruth model with preheat sensitivity table.LPBF Porosity PredictorPredict lack-of-fusion and keyhole porosity from laser parameters. Maps VED and normalised enthalpy to relative density and flags dangerous regimes.Powder Characterisation TrackerScore a powder batch against key qualification metrics — particle size distribution, flowability, apparent/tap density, moisture, and oxygen content.Surface Treatment SelectorRank post-print surface treatments (shot peening, electropolishing, tumbling, PVD, and more) against Ra target, material, fatigue criticality, and corrosion requirements.
Last reviewed: 2026-05-13 · v1 · Sources: aperam-invar-36-2022, yakout-2020-invar-lpbf, pröbstle-2018-invar-creep
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