Material : Kovar

Identification
UNS Number
  • K94610
Type Analysis
Single figures are nominal except where noted.
Carbon (Maximum) 0.02 % Manganese 0.30 %
Silicon 0.20 % Nickel 29.00 %
Cobalt 17.00 % Iron Balance
General Information
Description
Kovar® alloy is a vacuum melted, iron-nickel-cobalt, low expansion alloy whose chemical composition is controlled within narrow limits to assure precise uniform thermal expansion properties. Extensive quality controls are employed in the manufacture of this alloy to ensure uniform physical and mechanical properties for ease in deep drawing, stamping and machining.

NOTE: Kovar® Alloy is a Glass and Ceramic Sealing Alloy.

Applications
Kovar alloy has been used for making hermetic seals with the harder Pyrex glasses and ceramic materials.

This alloy has found wide application in power tubes, microwave tubes, transistors and diodes. In integrated circuits, it has been used for the flat pack and the dual-in-line package.

Preparation for Sealing
All degreased, fabricated Kovar alloy parts should be degassed and annealed in a wet hydrogen atmosphere.

Atmosphere is to be made moist by bubbling the hydrogen through water at room temperature. Care must be taken to prevent surface carbon pickup. Furnace should have a cooling chamber provided with the same atmosphere.

Heating should be conducted within the 1540/2010°F (838/1099°C) temperature range. Time at temperature should be approximately two hours for lowest temperature to 20 minutes for the highest temperature. Parts should then be transferred to the cooling zone and held until below 570°F (299°C), then removed.

An oxide film on the metallic part is preferred for metal-to-hard glass sealing. The best oxide film is thin and tightly adhering. The film can be produced by heating the parts to 1200/1290°F (650/700°C) in regular ambient atmosphere for a time sufficient to form a dark gray to slight brown oxide.

Corrosion Resistance
Important Note:The following 4-level rating scale is intended for comparative purposes only. Corrosion testing is recommended; factors which affect corrosion resistance include temperature, concentration, pH, impurities, aeration, velocity, crevices, deposits, metallurgical condition, stress, surface finish and dissimilar metal contact.
Humidity Moderate
Properties
Physical Properties
The hyperlink entitled “Mean Coefficient of Thermal Expansion: as annealed” contains the 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. Material heat treated using this procedure should not exhibit any transformation when cooled to -112°F (-80°C) for four hours. This was determined by means of metallographic examination.
Specific Gravity
8.36
Density
0.3020 lb/in³
Mean CTE
77 to 212°F, Annealed 3.25 x 10-6 in/in/°F
77 to 392°F, Annealed 2.89 x 10-6 in/in/°F
77 to 572°F, Annealed 2.85 x 10-6 in/in/°F
77 to 662°F, Annealed 2.72 x 10-6 in/in/°F
77 to 752°F, Annealed 2.81 x 10-6 in/in/°F
77 to 842°F, Annealed 2.92 x 10-6 in/in/°F
77 to 932°F, Annealed 3.41 x 10-6 in/in/°F
77 to 1112°F, Annealed 4.34 x 10-6 in/in/°F
77 to 1292°F, Annealed 5.06 x 10-6 in/in/°F
77 to 1472°F, Annealed 5.73 x 10-6 in/in/°F
77 to 1652°F, Annealed 6.25 x 10-6 in/in/°F
Thermal Conductivity
120.0 BTU-in/hr/ft²/°F
Modulus of Elasticity (E)
20.0 x 103 ksi
Electrical Resistivity
70°F 294.0 ohm-cir-mil/ft
Curie Temperature
815 °F
Melting Range
2640 °F
Magnetic Properties
Kovar alloy is magnetic at all temperatures below the Curie point. Magnetic properties will depend upon heat treatment; the lower the hardness, the higher the permeability values and lower hysteresis loss.
Magnetic Permeability
2010°F, 500.00 G 1900.0 Mu
1830°F, 500.00 G 1000.0 Mu
2010°F, 1000.0 G 3500.0 Mu
1830°F, 1000.0 G 1400.0 Mu
2010°F, 2000.0 G 5800.0 Mu
1830°F, 2000.0 G 2000.0 Mu
1830°F, 5000.0 G 2300.0 Mu
2010°F, 5000.0 G 10000 Mu
1830°F, 10000 G 3400.0 Mu
2010°F, 10000 G 8200.0 Mu
2010°F, 12000 G 5000.0 Mu
1830°F, 12000 G 3000.0 Mu

Disclaimer:
The information and data presented herein are typical or average values and are not a guarantee of maximum or minimum values. Applications specifically suggested for material described herein are made solely for the purpose of illustration to enable the reader to make his/her own evaluation and are not intended as warranties, either express or implied, of fitness for these or other purposes. There is no representation that the recipient of this literature will receive updated editions as they become available.