EFINEA has been a Kovar supplier to engineers, metallurgists, and procurement teams who need reliable access to ASTM F15 alloy since 1965. This page consolidates the technical reference material most often requested for ASTM F15 alloy, including thermal characteristics, physical properties, chemistry, mechanical properties, specifications, and applications where Kovar alloy remains the material of choice.
If you have questions about whether Kovar fits your design, our sales engineers and metallurgists are available at 800-348-6268. We stock Kovar in plate, sheet, round bar, and rod for fast shipment. No order quantity is too small.
Kovar® Properties
Engineers evaluating Kovar properties typically look at four data sets: thermal expansion behavior, physical properties such as density and thermal conductivity, mechanical properties under tension, and chemical composition. The tables below summarize the typical values for ASTM F15 alloy as annealed.
Mean Coefficient of Thermal Expansion (As Annealed)
The thermal expansion behavior of Kovar is the property most engineers reference first. Kovar exhibits a low and relatively flat expansion coefficient from room temperature up to approximately 450°C, which is the working range for sealing to borosilicate glasses such as Corning 7052.
Above the inflection point near 450°C, expansion increases significantly, which is expected behavior and reflects the magnetic transition at the Curie temperature.
Mean Coefficient of Thermal Expansion As Annealed |
|||||
|---|---|---|---|---|---|
| Temp Range 77°F to | Coefficient 10-6/°F | Temp Range 25°C to | Coefficient 10-6/°C | ASTM F15 CTE* 30°C to | µm/m • °C |
| 212°F | 3.25 | 100°C | 5.86 | ||
| 392°F | 2.89 | 200°C | 5.20 | ||
| 572°F | 2.85 | 300°C | 5.13 | ||
| 662°F | 2.72 | 350°C | 4.89 | ||
| 752°F | 2.81 | 400°C | 5.06 | 400°C | 4.60 to 5.20* |
| 842°F | 2.92 | 450°C | 5.25 | 450°C | 5.10 to 5.50* |
| 932°F | 3.41 | 500°C | 6.15 | ||
| 1112°F | 4.34 | 600°C | 7.80 | ||
| 1292°F | 5.06 | 700°C | 9.12 | ||
| 1472°F | 5.73 | 800°C | 10.31 | ||
| 1652°F | 6.25 | 900°C | 11.26 | ||
| Average coefficient of expansion properties after annealing in hydrogen for one hour at 1650 °F (900°C) at 15 minutes at 2010° F (1099°C) and cooled to room temperature within one hour. | |||||
| Source: CarTech® Kovar Alloy Data Sheet v. 10/90. *ASTM F15 Table 4 | |||||
To compare the linear coefficient of thermal expansion across our line of controlled expansion glass and sealing alloys, please refer to the Thermal Expansion Table.
Typical Physical Properties
Physical properties describe how Kovar behaves as a bulk material, independent of applied load. These values matter when calculating heat transfer, electrical resistance, and weight for a finished component.
ASTM F15 Alloy (Kovar®) Typical Physical Properties |
||
|---|---|---|
| Density | lb/cu in | 0.302 |
| Specific Gravity | 8.36 | |
| Curie Temp | °F | 815 |
| °C | 435 | |
| Melting Point | °F | 2640 |
| °C | 1450 | |
| Electrical Resistivity (70°F) | ohm-cir mil/ft | 294 |
| microhm-cm | 49 | |
| Thermal Conductivity | BTU-in/sq. ft-hr-°F | 120 |
| W/cm °C | 0.17 | |
| Specific Heat | Cal/gm °C | 0.11 |
| BTU/lbm- °F | 0.11 | |
| Source: CarTech® Kovar Alloy Data Sheet v.10/90. | ASTM F15 | ||
It’s worth noting that the Curie temperature of 435°C sits very close to the upper end of Kovar’s useful sealing range. This is not coincidental. The magnetic transition at the Curie point is what causes expansion to rise sharply above 450°C, so designers should keep operating service temperatures below this threshold when seal integrity is critical.
Typical Mechanical Properties
Mechanical properties guide how Kovar will behave during forming, machining, and service loading. The annealed condition is the standard delivery state for sealing applications.
ASTM F15 Alloy (Kovar®) Typical Mechanical Properties | ||
|---|---|---|
| *Tensile Strength | ksi (MPa) | 75 (517) |
| **Sheet + Strip, Temper A, Annealed | ksi (MPa) | 82 (570) max |
| **Rod + Wire, Temper A, Annealed | ksi (MPa) | 85 (585) max |
| *Yield Strength | ksi (MPa) | 50 (345) |
| *Elongation | % in 2" | 30 |
| *Typical Hardness (Annealed) | Rockwell B | 68 |
| Modulus of Elasticity | ksi (GPa) | 20,000 (138) |
| Poisson's Ratio | 0.317 | |
| *Kovar strip tested parallel to the direction of rolling. Material annealed 1830 °F (999°C) for 30 minutes, then furnace cooled. ** Per ASTM F15, Temper A, Annealed |
||
| Source: CarTech® Kovar Alloy Data Sheet v.10/90. | ASTM F15 | ||
Kovar alloy is readily deep-drawn, stamped, and machined when the proper feeds, speeds, and tooling are selected. Because of its work hardening rate, intermediate anneals are often required during heavy forming operations.
Kovar® Chemistry (ASTM F15)
The chemistry of Kovar is closely controlled because even small deviations in nickel and cobalt content will shift the thermal expansion curve away from the borosilicate glass match.
ASTM F15 (Kovar®) Chemistry | Composition % |
|---|---|
| Iron, nominal | 53.00 |
| Nickel, nominal | 29.00 |
| Cobalt, nominal | 17.00 |
| Manganese, max | 0.50 |
| Silicon, max | 0.20 |
| Carbon, max | 0.04 |
| Copper, max | 0.20 |
| Chromium, max | 0.20 |
| Molybdenum, max | 0.20 |
| Aluminum, max | 0.10 |
| Magnesium, max | 0.10 |
| Zirconium, max | 0.10 |
| Titanium, max | 0.10 |
| The iron, nickel and cobalt % listed are nominal. They shall be adjusted by the manufacturer so that the alloy meets the requirements for coefficient of thermal expansion | |
| The total aluminum, magnesium, zirconium and titanium shall not exceed 0.20% | |
| Source: ASTM F15-04 (2017) Table 1 | |
The iron, nickel, and cobalt percentages listed are nominal. They shall be adjusted by the manufacturer so that the alloy meets the requirements for the coefficient of thermal expansion. The total aluminum, magnesium, zirconium, and titanium shall not exceed 0.20%. Source: ASTM F15-04 (2017) Table 1.
Specifications and Cross-References
ASTM F15 (Kovar®) Specifications | |||
|---|---|---|---|
| ASTM F15 | UNS K94610 | AMS 1-23011 CL1 | MIL 1-23011 CL1 |
ASTM F15 (Kovar®) Specifications- Historic Cross- Reference | ||
|---|---|---|
| ASTM F1466 | UNS K94360 | AMS 7726B, 7727, 7728C |
For additional context on specifications, visit the websites of ASTM International and ASM International, which develop and publish the technical standards governing Kovar alloy and related controlled expansion materials.
Kovar® Applications
Kovar applications span any industry where a reliable seal between metal and glass or metal and ceramic is required to maintain hermeticity through repeated thermal cycling. The combination of controlled expansion, good machinability, and excellent deep-drawing characteristics has kept Kovar in service for decades across communications, defense, semiconductor, medical, and aerospace markets.
Power Tubes
The power tube market has long relied on Kovar alloy for glass-to-metal and ceramic-to-metal construction. These tubes function as power amplifiers in radio and television transmitters, induction heating equipment, navigational aides, and high-frequency industrial generators.
In communication equipment, Kovar is also used in relay links and waveguide assemblies where the seal must survive both mechanical vibration and thermal cycling without losing vacuum integrity.
Microwave Tubes
Microwave tubes convert kinetic energy into electromagnetic energy at microwave frequencies and operate as oscillators, amplifiers, and converters. The development of microwave tubes enabled a generation of technologies, including radar systems, tropospheric scatter propagation, electronic countermeasure equipment, navigational systems, and long-range communication links.
Klystrons, magnetrons, and traveling wave tubes (TWTs) all use Kovar in their hermetic seal assemblies, and the alloy remains specified for replacement parts in legacy military and satellite systems.
Medical Devices and Implantables
Implantable pacemakers, cochlear implants, neurostimulators, and infusion pumps all rely on hermetic enclosures to protect electronics from body fluids. Kovar housings and feedthroughs, sealed to alumina ceramic insulators, provide the long-term hermeticity required for devices that must function reliably inside the body for a decade or more.
Sensors and Vacuum Equipment
Pressure sensors, ion gauges, mass spectrometer components, and vacuum flanges are routinely fabricated from Kovar where ceramic or glass insulator interfaces are present. The alloy’s compatibility with brazing alloys and its low outgassing behavior after proper cleaning make it a good choice for ultra-high vacuum service.
Aerospace and Defense Electronics
Avionics, missile guidance systems, and satellite electronics use Kovar for hermetic packages that protect sensitive circuitry from humidity, pressure swings, and radiation. Because spaceflight hardware undergoes wide temperature excursions, the matched expansion behavior of Kovar against borosilicate glass and aluminum oxide ceramics is essential for long mission lifetimes.
Kovar alloy is also found in feedthroughs for pressurized cabin instrumentation and in connector shells that require vacuum compatibility.
Integrated Circuits and Semiconductor Packaging
Flatpack and dual-in-line (DIP) packages use Kovar alloy as the structural housing material, providing both mechanical access for the lead frame and electrical isolation for the semiconducting chip. Kovar lids and bases are also used in hermetic seam-welded packages for MEMS devices, optoelectronic components, and crystal oscillators, where moisture ingress would degrade performance. Gold plating over a nickel underplate is the standard surface finish for solderability and corrosion resistance.
Photonics and Optoelectronics
Laser diode packages, fiber optic transmitter and receiver modules, and photodetector housings use Kovar to maintain optical alignment under thermal load. The matched expansion characteristics keep lensing elements and fiber pigtails properly positioned across the operating temperature range, which is critical for telecom-grade signal integrity.
Why Source Kovar® from EFINEA Metals?
EFINEA Metals has supplied controlled expansion alloys to high-technology industries since 1965.
As a Kovar alloy supplier with stock across four ISO 9001:2015 and AS9100D-certified facilities in New Jersey and California, we can ship standard inventory within 24 hours of order confirmation and offer precision cutting, shearing, slitting, and waterjet services to support both prototype quantities and production runs. Every shipment is accompanied by mill certifications, and our metallurgists are available to consult on specification interpretation, alternative alloy selection, and fabrication guidance.
To request a quote, download the EFINEA Kovar® data sheet from our Technical Library, or speak with a sales engineer, contact us at 800-348-6268.
Frequently Asked Questions About Kovar® Alloy Properties, Applications, and Specifications
Yes. Kovar can be TIG-welded, electron beam-welded, laser-welded, and resistance-welded. For hermetic packaging, laser seam welding and electron beam welding are most common because they produce narrow heat-affected zones and preserve dimensional stability. Filler metal is generally not required for autogenous welds between Kovar parts.
The standard finish is electroplated nickel (typically 50 to 150 microinches) followed by gold (typically 50 to 100 microinches). The nickel underplate prevents iron diffusion into the gold, and the gold layer provides solderability and corrosion protection. Plating specifications are typically called out to MIL-DTL-45204 or ASTM B488.
EFINEA stocks Kovar in plate, sheet, round bar, and rod. We also offer custom cutting, shearing, slitting, and waterjet services to produce near-net-size blanks, which reduces machining time and material waste for customers running high-volume programs.