4J36 Alloy

4J36 (internationally known as Invar® 36) is a high-performance iron-nickel (Fe-Ni) based low-expansion alloy, belonging to the Invar family, specifically engineered for high-precision applications requiring ultra-low thermal expansion coefficient (CTE) and exceptional dimensional stability across a wide temperature range. Unlike Fe-Ni-Co based Kovar alloys (4J29, 4J32, optimized for glass sealing), 4J36 achieves its core function—near-zero expansion—through a precisely controlled nickel content (≈36%) that leverages the Invar effect (a unique magnetic anomaly that suppresses thermal expansion). This alloy excels in temperature-sensitive scenarios ranging from -269℃ to 200℃, making it the benchmark material for precision instruments, aerospace optical components, and high-precision molds where even micro-scale dimensional changes can compromise performance.

Notably, 4J36 maintains a near-constant volume over its service temperature range, with CTE as low as 0.5×10⁻⁶/℃ (20-100℃)—far lower than conventional metals and most low-expansion alloys. Its good cold workability and weldability enable manufacturing of complex high-precision components (e.g., optical lens mounts, laser alignment structures), while its moderate corrosion resistance suits controlled environments (e.g., cleanrooms, laboratory settings). It is widely used in aerospace, semiconductor manufacturing, metrology, and precision engineering, where dimensional stability directly determines the accuracy and reliability of critical systems. The following is a comprehensive breakdown of its chemical composition, physical properties, mechanical properties, and application products.

1. Chemical Composition (Mass Fraction, %)

2. Physical Properties

2.1 Basic Physical Parameters

• Density: Approximately 8.10g/cm³ at room temperature (25℃), lower than Fe-Ni-Co based 4J32 (8.90g/cm³) and 4J29 (8.30g/cm³) due to the absence of high-density cobalt, making it more suitable for weight-sensitive precision components (e.g., aerospace optical structures).
• Melting Temperature Range: 1430-1480℃ (liquidus: ~1480℃; solidus: ~1430℃). The narrow melting range ensures uniform composition during casting, avoiding segregation that would cause CTE variations (critical for batch consistency of high-precision parts).
• Thermal Expansion Coefficient (CTE) – Core Performance Indicator:

◦ 20-100℃: 0.5-1.0×10⁻⁶/℃ (near-zero expansion, the Invar effect peak)

◦ 20-200℃: 1.0-2.0×10⁻⁶/℃

◦ 20-300℃: 5.0-6.0×10⁻⁶/℃ (Invar effect fades above 200℃)

◦ -269℃ (liquid helium) to 20℃: -0.1 to 0.3×10⁻⁶/℃ (negative to near-zero expansion at cryogenic temperatures)

The ultra-low CTE in 20-100℃ (typical operating range for precision instruments) ensures dimensional variation ≤0.1μm/m per ℃—a level unmatched by most engineering materials, making it ideal for applications requiring micro-scale accuracy.

• Thermal Conductivity (λ):

◦ 100℃: ~10.0W/(m·K)

◦ 200℃: ~12.0W/(m·K)

◦ -269℃: ~2.0W/(m·K)

Extremely low thermal conductivity (1/5 of carbon steel) minimizes heat transfer, reducing thermal gradients within components (e.g., optical benches) and further enhancing dimensional stability.

• Electrical Resistivity (ρ):

◦ Room temperature (25℃): 80-90×10⁻⁸Ω·m

◦ 200℃: 95-105×10⁻⁶Ω·m

◦ -269℃: 150-160×10⁻⁸Ω·m

High resistivity reduces eddy current losses in high-frequency applications (e.g., microwave antenna structures) and minimizes thermal noise in precision sensors.

2.2 Magnetic Properties

The Invar effect is inherently linked to magnetic properties, which are critical for understanding 4J36’s performance:

• Magnetic Permeability (μ): ~300-500μ₀ (at H=800A/m, room temperature) — higher than Kovar alloys (4J29: ~100-200μ₀; 4J32: ~80-150μ₀), as the Invar effect relies on magnetic ordering;
• Coercivity (Hc): ~80-120A/m (room temperature) — lower than Kovar alloys, making it slightly magnetic but still suitable for most non-magnetically sensitive applications (magnetic shielding can be added for critical scenarios);
• Magnetic Saturation (Bs): ~0.60-0.70T (room temperature) — lower than 4J29 and 4J32, reducing magnetic interference risks;
• Curie Temperature (Tc): ~230-250℃ — marks the fading of the Invar effect (CTE increases sharply above Tc), defining the upper limit of its low-expansion service range (≤200℃ for precision applications).

2.3 Dimensional Stability (Key Performance Metric)

Key Notes:

• Ultra-low Dimensional Change: Dimensional variation ≤0.5μm/m over 1000 thermal cycles (20-100℃) ensures precision instruments (e.g., coordinate measuring machines) maintain accuracy over years of use;
• Negligible Long-term Drift: Long-term dimensional change ≤0.3μm/m after 10,000h eliminates the need for frequent recalibration of high-precision equipment.

3. Mechanical Properties (After Standard Heat Treatment: 850-900℃ annealing for 1h, air cooling)

Key Notes:

• Excellent Cold Workability: Room-temperature elongation (≥30%) and reduction of area (≥60%) allow manufacturing of ultra-thin sheets (minimum thickness ≥0.01mm) for micro-precision components (e.g., semiconductor wafer chucks) and complex formed parts (e.g., optical lens cells);
• Good Cryogenic Ductility: Even at -269℃, elongation (≥10%) prevents brittle fracture—critical for cryogenic precision instruments (e.g., space-based telescopes);
• Adequate Strength for Precision Applications: Tensile strength (≥450MPa) is sufficient to withstand mechanical stress during assembly and service without deformation, while low hardness (HV 120-150) simplifies precision machining (e.g., grinding to ±0.1μm tolerance).

4. Application Products & Industry Scenarios

4.1 Aerospace & Optical Engineering Field

As the gold standard for low-expansion aerospace and optical components, 4J36 is used for:

• Aerospace Optical Structures: Lens mounts, mirror cells, and optical benches for space telescopes (e.g., Hubble, James Webb) and airborne reconnaissance systems, maintaining optical alignment (≤0.1μm) under extreme thermal cycling (-150℃ to 80℃); the near-zero CTE minimizes thermal distortion of optical paths (wavefront error ≤λ/100, λ=632.8nm);
• Laser Alignment Components: Laser cavity mirrors, beam splitters, and optical fiber alignment structures for high-power laser systems (e.g., fusion reactors, laser communication), ensuring beam stability (pointing drift ≤1μrad/hour);
• Satellite Antenna Structures: Feed horns and reflector supports for satellite communication antennas, maintaining antenna gain (≤0.1dB loss) under space thermal variations.

4.2 Precision Metrology & Instrumentation Field

In metrology and precision instruments requiring unrivaled dimensional stability, 4J36 is applied to:

• Coordinate Measuring Machine (CMM) Components: Guide rails, scale supports, and probe arms for high-precision CMMs (accuracy ≤0.1μm), ensuring measurement error ≤0.05μm over 24 hours (room temperature variation ±2℃);
• Length Standards: Reference bars and gauge blocks for calibration laboratories, maintaining dimensional accuracy (≤0.01μm/m) for decades—certified as national length standards in many countries;
• Precision Clock Components: Pendulum rods for atomic clocks and balance wheels for high-precision mechanical clocks, minimizing time drift (≤1×10⁻¹⁰/day) caused by temperature changes.

4.3 Semiconductor & Electronics Manufacturing Field

In semiconductor manufacturing requiring micro-scale precision, 4J36 is used for:

• Semiconductor Wafer Chucks: Electrostatic chucks and vacuum chucks for EUV lithography and wafer inspection systems, maintaining wafer flatness (≤0.5μm over 300mm wafer) during thermal processing (20-150℃);
• Precision Mask Frames: Frames for photomasks (used in chip lithography), ensuring mask flatness (≤0.1μm) to prevent pattern distortion (overlay error ≤1nm);
• Electronic Packaging for High-Precision Sensors: Packages for MEMS accelerometers and gyroscopes (used in autonomous vehicles, aerospace navigation), minimizing thermal-induced zero drift (≤0.001°/hour).

4.4 Precision Engineering & Mold Manufacturing Field

In precision engineering and mold making, 4J36 is used for:

• Injection Molds for Micro-components: Mold inserts for micro-injection molding (e.g., medical micro-needles, electronic connectors), maintaining cavity dimensional accuracy (±1μm) over thousands of cycles (mold temperature 20-120℃);
• Die Casting Dies for High-Precision Parts: Dies for casting aerospace and medical components, reducing thermal expansion-induced die wear (service life extended by 30-50% compared to conventional die steels);
• Precision Gauges: Go/no-go gauges, thread gauges, and profile gauges for quality control in automotive and aerospace manufacturing, maintaining gauge tolerance (≤0.001mm) over years of use.

4.5 Cryogenic & Scientific Research Field

In cryogenic and scientific research requiring stable dimensions at ultra-low temperatures, 4J36 is used for:

• Cryogenic Sample Holders: Sample stages for cryo-electron microscopy (cryo-EM) and cryo-X-ray diffraction, maintaining sample position (≤0.1μm) at -196℃ to -269℃;
• Superconducting Magnet Components: Support structures for superconducting magnets (e.g., NMR spectrometers, particle accelerators), minimizing magnetic field distortion (≤0.01ppm) caused by thermal expansion;
• Quantum Experiment Apparatus: Frames for quantum computing experiments and ultra-cold atom traps, ensuring component alignment (≤0.05μm) during cooling to near-absolute zero.
• Smelting: Vacuum induction melting (VIM) is recommended to control nickel content accuracy (±0.2%) and reduce impurities (C ≤0.05%); air melting is acceptable for non-critical applications but may cause minor CTE variations;
• Cold Working:

5. Processing & Welding Recommendations

◦ Sheets/Wires: Cold rolling with 30-40% deformation per pass, followed by intermediate annealing (800-850℃, 1h, air cooling) after every 60-70% total deformation to restore ductility; final cold working (10-20% deformation) can be used to fine-tune CTE (slight deformation reduces CTE by 0.1-0.2×10⁻⁶/℃);

◦ Precision Machining: Machining should be performed at constant temperature (20±1℃) to avoid thermal expansion-induced errors; use sharp carbide or diamond tools, low cutting speeds (≤50m/min), and minimal cutting forces to prevent work hardening (which increases CTE);

• Welding: Suitable for TIG welding, laser welding, and electron beam welding (for high-precision parts);

◦ Welding filler metal: Matching 4J36 alloy wire (Ni36Fe);

◦ Preheating: Not required for thin sheets (<3mm); preheat to 150-200℃ for thick sections (>5mm) to avoid cracking;

◦ Post-weld heat treatment: 850-900℃ annealing for 1h, air cooling, to restore the Invar effect (welding can temporarily increase CTE by 0.5-1.0×10⁻⁶/℃);

• Surface Treatment: Passivation (using nitric acid solution) is recommended for corrosion-prone environments; electroplating (e.g., gold, nickel) can be applied for electrical conductivity or wear resistance, but plating thickness should be ≤5μm to avoid CTE interference.

This comprehensive performance and application profile establishes 4J36 as the premier low-expansion alloy for high-precision engineering. Its unique In