4J32 Alloy

4J32 (internationally recognized as Dilver P®) is a high-performance iron-nickel-cobalt (Fe-Ni-Co) based low-expansion hermetic sealing alloy, belonging to the Kovar family, specifically engineered for precision hermetic packaging applications requiring ultra-low thermal expansion coefficient (CTE) matching with low-expansion glasses (e.g., quartz glass, borosilicate glass with low CTE) and stable performance in cryogenic to moderate temperatures. Unlike 4J29 (optimized for standard hard glass with CTE 5.0-5.5×10⁻⁶/℃), 4J32 achieves its core function—low-expansion sealing—through a precisely adjusted composition (Ni≈32%, Co≈42%) that tailors its CTE to an ultra-low range (2.0-3.0×10⁻⁶/℃, 20-400℃). This alloy excels in cryogenic-tolerant, high-precision sealing scenarios, making it the preferred material for low-temperature electronics, aerospace optical components, and quantum device packaging where minimal thermal expansion mismatch is critical.

Notably, 4J32 maintains exceptional dimensional stability across an extended temperature range (-270℃ to 450℃) and forms a leak-proof hermetic bond with low-expansion glasses, ensuring long-term sealing integrity (leak rate ≤1×10⁻¹⁰Pa·m³/s) even under extreme thermal cycling. Its good cold workability enables manufacturing of thin-walled components (e.g., ultra-thin sealing rings, microelectronic packages) and complex structures, while its moderate corrosion resistance suits controlled environments (e.g., cleanrooms, space vacuum). It is widely used in cryogenic electronics, aerospace optics, quantum technology, and medical imaging, where low thermal expansion and reliable hermeticity directly determine component performance and lifespan. 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 8.90g/cm³ at room temperature (25℃), higher than 4J29 (8.30g/cm³) due to higher cobalt content, but acceptable for precision components (e.g., optical lens mounts) where performance outweighs weight concerns.
• Melting Temperature Range: 1420-1470℃ (liquidus: ~1470℃; solidus: ~1420℃). The narrow melting range ensures uniform composition during casting, avoiding segregation that would cause CTE variations (critical for consistent sealing performance across batches of low-tolerance components).
• Thermal Expansion Coefficient (CTE) – Core Performance Indicator:

◦ 20-100℃: 2.1-2.5×10⁻⁶/℃

◦ 20-300℃: 2.3-2.7×10⁻⁶/℃

◦ 20-400℃: 2.5-3.0×10⁻⁶/℃ (matches low-expansion glass: 2.0-3.0×10⁻⁶/℃, e.g., quartz glass: 0.55×10⁻⁶/℃ with transition layer)

◦ -270℃ to 20℃: 0.5-1.0×10⁻⁶/℃ (near-zero expansion at cryogenic temperatures)

The ultra-low CTE across cryogenic to moderate temperatures minimizes thermal stress between the alloy and low-expansion glasses, preventing seal cracking during cryogenic cooling (e.g., liquid nitrogen environments) or moderate-temperature heating (e.g., component operation).

• Thermal Conductivity (λ):

◦ 100℃: ~15.0W/(m·K)

◦ 300℃: ~17.5W/(m·K)

◦ 400℃: ~19.0W/(m·K)

◦ -270℃: ~5.0W/(m·K)

Low thermal conductivity at cryogenic temperatures reduces heat transfer into sensitive cryogenic components (e.g., quantum sensors), maintaining stable low-temperature environments; moderate conductivity at 400℃ facilitates heat dissipation during glass-sealing processes.

• Electrical Resistivity (ρ):

◦ Room temperature (25℃): 55-60×10⁻⁸Ω·m

◦ 400℃: 65-70×10⁻⁸Ω·m

◦ -270℃: 80-85×10⁻⁸Ω·m

Higher resistivity than 4J29 reduces eddy current losses in high-frequency and cryogenic electronic components (e.g., superconducting quantum interference devices), protecting signal integrity.

2.2 Magnetic Properties

Like 4J29, 4J32 is not optimized for magnetic performance, but its magnetic properties are critical for magnetically sensitive low-temperature applications:

• Magnetic Permeability (μ): ~80-150μ₀ (at H=800A/m, room temperature) — lower than 4J29 (~100-200μ₀), making it more suitable for non-magnetic packaging of cryogenic magnetic sensors (e.g., SQUID magnetometers);
• Coercivity (Hc): ~200-300A/m (room temperature) — higher than 4J29 (~160-240A/m), ensuring the alloy does not act as a magnetic core and avoids interfering with internal low-temperature magnetic components;
• Magnetic Saturation (Bs): ~0.65-0.75T (room temperature) — lower than 4J29 (~0.75-0.85T), further reducing magnetic interference risks in precision quantum and optical systems.
• Curie Temperature (Tc): ~480-500℃ — higher than 4J29, ensuring the alloy remains non-ferromagnetic at its maximum service temperature (450℃), avoiding magnetic property changes that could disrupt seals.

3. Mechanical Properties (After Standard Heat Treatment: 820-870℃ annealing for 1h, air cooling)

Key Notes:

• Excellent Cryogenic Strength: At -270℃ (liquid helium temperature), tensile strength (≥800MPa) is nearly double that at room temperature, ensuring structural integrity of cryogenic packages (e.g., quantum chip enclosures) under extreme low-temperature stress;
• Adequate Ductility at Cryogenic Temperatures: Even at -270℃, elongation (≥8%) prevents brittle fracture during cryogenic cooling/heating cycles — a critical advantage over many alloys that become brittle at ultra-low temperatures;
• Good Cold Workability: Room-temperature elongation (≥28%) allows rolling into ultra-thin sheets (minimum thickness ≥0.03mm) for microelectronic cryogenic packages and drawing into fine wires (0.05-0.5mm) for lead frames in low-temperature sensors;
• Stable Strength at Service Temperatures: At 400℃ (maximum service temperature), retained yield strength (≥220MPa) ensures seals maintain integrity during glass-sealing and component operation.

4. Glass-Sealing Performance (Core Application Performance)

Key Notes:

• Ultra-high Hermeticity at Extreme Temperatures: Leak rate ≤3×10⁻¹¹Pa·m³/s after cryogenic-thermal cycling ensures cryogenic components (e.g., liquid helium-cooled quantum chips) remain isolated from moisture and gas contamination (moisture ≤10ppm) for 15+ years;
• Stable Bond Strength at Cryogenic Temperatures: Shear strength ≥22MPa at -196℃ ensures glass-alloy bonds do not fail during cryogenic operation — a critical improvement over 4J29, whose bond strength drops more significantly at ultra-low temperatures;
• Exceptional Thermal Shock Resistance: Withstands 30 cycles of -270℃ to 400℃ without seal degradation, making it suitable for components requiring frequent cryogenic cooling and room-temperature maintenance (e.g., medical imaging devices).

5. Application Products & Industry Scenarios

5.1 Cryogenic Electronics & Quantum Technology Field

As the standard low-expansion sealing material for cryogenic and quantum devices, 4J32 is used for:

• Quantum Chip Packaging: Hermetic enclosures for superconducting quantum chips (e.g., qubit arrays), maintaining ultra-high vacuum (≤1×10⁻⁷Pa) and cryogenic stability (-270℃) while matching the low CTE of quartz glass substrates; the alloy’s low magnetic permeability avoids interfering with qubit coherence (coherence time ≥100μs);
• Cryogenic Sensor Packages: Sealed packages for cryogenic sensors (e.g., infrared detectors, bolometers) cooled to -196℃ (liquid nitrogen) or -270℃ (liquid helium), protecting sensors from moisture-induced frosting and ensuring detection sensitivity (detectivity ≥10¹⁴cm·Hz¹/²/W);
• Low-Temperature Electronics Enclosures: Hermetic cases for cryogenic amplifiers and signal processing units in radio astronomy telescopes (e.g., ALMA), withstanding -180℃ operating temperatures and maintaining signal integrity (noise figure ≤0.1dB).

5.2 Aerospace & Optical Field

In aerospace and optical systems requiring precision low-expansion sealing, 4J32 is applied to:

• Aerospace Optical Lens Mounts: Sealing rings between low-expansion optical lenses (e.g., quartz, Zerodur®) and telescope structures, matching CTE to minimize thermal distortion of optical paths (wavefront error ≤λ/50, λ=632.8nm);
• Satellite Laser Communication Modules: Hermetic packaging for satellite-borne laser transmitters/receivers, maintaining seal integrity under space thermal cycling (-150℃ to 80℃) and ensuring laser beam alignment (pointing accuracy ≤1μrad);
• Spacecraft Cryogenic Fuel Tanks: Sealing components for liquid hydrogen (LH₂, -253℃) and liquid oxygen (LOX, -183℃) tanks, matching the CTE of tank liners (e.g., titanium alloys) to prevent leakages during launch and in-orbit operation.

5.3 Medical & Scientific Instrumentation Field

In medical and scientific instruments requiring precision and cryogenic compatibility, 4J32 is used for:

• Cryogenic Medical Imaging Devices: Sealing components for magnetic resonance imaging (MRI) gradient coils cooled to -269℃ (superconducting state), matching the CTE of niobium-titanium (NbTi) superconductors and ensuring magnetic field uniformity (homogeneity ≤1ppm);
• X-ray Crystallography Equipment: Hermetic sample chambers for X-ray crystallography, maintaining cryogenic temperatures (-196℃) to preserve protein crystal structures and matching the CTE of beryllium windows (used for X-ray transmission);
• Metrology Standards: Low-expansion frames for length metrology standards (e.g., laser interferometers), maintaining dimensional stability (variation ≤1nm/m) across laboratory temperature fluctuations (20±5℃).

5.4 Industrial & High-Precision Electronics Field

In industrial and high-precision electronics requiring low thermal expansion, 4J32 is used for:

• Semiconductor Manufacturing Equipment: Sealing components for extreme ultraviolet (EUV) lithography machines, matching the CTE of silicon wafers and quartz optics to minimize thermal-induced alignment errors (overlay accuracy ≤1nm);
• High-Precision Oscillators: Hermetic packages for oven-controlled crystal oscillators (OCXOs), maintaining stable operating temperatures (80±0.1℃) and minimizing frequency drift (≤1×10⁻¹²/day) through low CTE matching with crystal resonators;
• Industrial Laser Systems: Sealing rings for high-power fiber lasers, matching the CTE of laser diodes and fiber couplers to prevent thermal-induced misalignment (power stability ≤0.1%/hour).
• Smelting: Vacuum induction melting (VIM) with secondary vacuum arc remelting (VAR) is mandatory to control composition accuracy (Ni±0.1%, Co±0.1%) and ultra-low impurities (C ≤0.02%); air melting is prohibited, as it causes CTE variations and oxide inclusions that degrade sealing performance;
• Cold Working:

6. Processing & Welding Recommendations

◦ Sheets: Cold rolling with 25-35% deformation per pass, followed by intermediate annealing (780