Kovar Alloy Product Introduction
Product Overview
Kovar (UNS K94610) is a iron-nickel-cobalt (Fe-Ni-Co) low-thermal-expansion sealing alloy engineered exclusively for hermetic sealing with glass, ceramics, or other brittle materials. Unlike Invar (Ni-Fe, ultra-low CTE for dimensional stability) or Nickel 201 (high-purity Ni for corrosion resistance), Kovar features a precise ternary composition (Fe: 53-56%, Ni: 28-31%, Co: 16-18%)—a design that tunes its coefficient of thermal expansion (CTE) to match common sealing materials (e.g., borosilicate glass: ~5.5×10⁻⁶/℃, alumina ceramic: ~6.0×10⁻⁶/℃) in the critical sealing temperature range (20-400℃). This matching eliminates thermal stress at the metal-ceramic/glass interface, ensuring long-term vacuum tightness. It retains moderate mechanical strength and good weldability, making it the industry standard for hermetic packaging in electronics, optics, and aerospace—where “thermal expansion matching + hermetic sealing” are irreplaceable.
International Grade Comparison
Standard System | Grade | Description |
ASTM (USA) | F15 / K94610 | ASTM F15 (specification); UNS K94610 (unified number) |
EN (EU) | FeNi29Co17 | EN 10088-1 Standard Grade (hermetic sealing alloy) |
JIS (Japan) | NW49461 | JIS G4902 Standard Grade (equivalent to Kovar) |
DIN (Germany) | 1.3981 | DIN 17745 Standard Grade (classic sealing alloy) |
ISO (International) | FeNi29Co17 | ISO 6363 Standard Grade (glass/ceramic sealing alloy) |
Physical Properties (Room Temperature & Sealing-Critical Highlights)
Property Indicator | Typical Value (Room Temp) | Unit | Sealing Performance Advantage |
Tensile Strength | ≥480 | MPa | Retains ≥350 MPa at 400℃ (sealing temp); avoids deformation during bonding |
Yield Strength (0.2% Offset) | ≥240 | MPa | Prevents interface stress from plastic deformation |
Elongation (50mm Gauge Length) | ≥25 | % | Enables precision forming (e.g., sealing rings, pins) |
CTE (20-400℃) | 5.0-6.0×10⁻⁶ | /℃ | Matches borosilicate glass (5.5×10⁻⁶/℃) and alumina ceramic (6.0×10⁻⁶/℃) |
Density | 8.3 | g/cm³ | Lower than Ni-Co alloys; balances weight for miniaturized packaging |
Melting Point | 1420-1450 | ℃ | Stable above typical glass sealing temps (800-1000℃) |
Thermal Conductivity (20℃) | 17.0 | W/(m·K) | Low conductivity reduces heat loss in vacuum devices |
Chemical Composition (Mass Fraction, Sealing-Optimized Ternary Ratio)
Chemical Symbol | Composition Range (%) | Role in Hermetic Sealing |
Fe | 53.0-56.0 | Matrix base; adjusts CTE to match brittle materials |
Ni | 28.0-31.0 | Lowers CTE; enhances adhesion to glass/ceramic |
Co | 16.0-18.0 | Fine-tunes CTE; improves high-temp sealing stability |
C | ≤0.03 | Ultra-low content prevents carbide-induced CTE variation |
Mn | ≤0.5 | Improves hot workability; reduces sealing defects |
Si | ≤0.3 | Minimizes oxide inclusions; ensures uniform bonding |
S/P | ≤0.01/≤0.02 | Ultra-low impurities avoid interface voids |
Cu | ≤0.2 | Trace addition enhances weldability for sealing joints |
Product Characteristics
1.Precise Thermal Expansion Matching: CTE of 5.0-6.0×10⁻⁶/℃ (20-400℃) perfectly aligns with borosilicate glass, alumina ceramic, and quartz—eliminating thermal stress at the metal-brittle material interface, a critical factor for vacuum tightness;
2.Superior Hermetic Sealing: Forms airtight, leak-tight joints (leak rate ≤1×10⁻¹⁰ Pa·m³/s) with glass/ceramic via brazing or fusion bonding; maintains seal integrity in extreme environments (-270℃ to 450℃);
3.Balanced Mechanical Properties: Tensile strength (≥480 MPa) and ductility (≥25% elongation) enable precision machining of small sealing components (e.g., pin grids, tube bases) without cracking;
4.Good Processability: Compatible with cold/hot forming (rolling, stamping, wire drawing) and welding (TIG, spot welding); surface plating (Ni, Au) enhances corrosion resistance and bonding;
5.Wide Temperature Adaptability: Stable CTE and structure from cryogenic temps (-270℃, liquid helium) to 450℃ (long-term service)—suitable for aerospace and deep-space electronic packaging.
Metallographic Structure
At room temperature, Kovar features a single-phase body-centered cubic (BCC) ferritic matrix with uniform fine grains (ASTM 6-9 grades). The Fe-Ni-Co ternary solid solution ensures no phase transformations in the service range (-270℃ to 450℃)—avoiding CTE spikes that would disrupt the sealed interface. No secondary phases (e.g., carbides, intermetallics) form due to ultra-low carbon content, ensuring consistent thermal and mechanical properties across the material.
Product Forms and Executive Standards
Product Form | Main International Executive Standards | Application Reference |
Bars/Rods | ASTM F15, EN 10269 | Sealing rings for vacuum tubes, ceramic package frames |
Strips/Foils | ASTM F30, EN 10106 | Precision sealing pins, semiconductor lead frames |
Wires | ASTM F28, EN 10250-3 | Glass-to-metal seal wires, microelectronic bonding pins |
Tubes/Pipes | ASTM F171, EN 10216-5 | Vacuum feedthrough tubes, optical fiber sealing sleeves |
Forgings | ASTM F29, EN 10222-5 | Large glass envelope flanges (e.g., X-ray tubes) |
