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Kovar it was invented to meet the need for a reliable glass-to-metal seal, which is required in electronic devices such as light bulbs, vacuum tubes, cathode ray tubes, and in vacuum systems in chemistry and other scientific research. Most metals cannot seal to glass because their coefficient of thermal expansion is not the same as glass, so as the joint cools after fabrication the stresses due to the differential expansion rates of the glass and metal cause the joint to crack.

Chemical composition

composition % Fe Ni Co C P Mn Si P S Cu Cr Mo
content min Bal 28.5 16.8 - - - - - - - - -
content max Bal 29.5 17.8 0.03 0.02 0.5 0.3 0.02 0.02 0.2 0.2 0.2

Typical Physical properties

Property Name Value
Density (g/cm3) 8.2
Electrical resistivity at 20ºC(OMmm2/m) 0.48
Melting point ºC 1450
Curie point Tc/ ºC 430
Elastic Modulus, E/ Gpa 138
Delivery status There are rods, tube, rods, strip and wire.

Application overview and special requirements

The kovar alloy is a typical fe-ni Co glass sealing alloy for international use.Long used by the aviation factory, the performance is stable.Mainly used in electric vacuum components such as tube, shock tube, ignitron, magnetron, transistors, the wires of a sealing plug, relays, integrated circuits, chassis, such as shell, support glass sealing.In the application, the selected glass should match the expansion coefficient of the alloy.The stability of the cryogenic tissue is strictly tested by using temperature.Proper heat treatment should be done during the process to ensure that the material has good deep drawing performance.

Tensile Strength, MPa

Code of condition Condition Wire Strip
R Soft ≤585 ≤570
1/4I 1/4 Hard 585~725 520~630
1/2I 1/2 Hard 655~795 590~700
3/4I 3/4 Hard 725~860 600~770
I Hard ≥850 ≥700

The heat treatment process

Annealing for stress relief Annealing Holding time Cooling rate
Heated to 470~540ºC and hold 1~2 h. Cold down In vacuum heated to 750~900ºC 14 min~1h. No more than 10 ºC/min cooled to 200 ºC

Coefficient of expansion

θ/ºC α1/10-6ºC-1 θ/ºC α1/10-6ºC-1
20~60 7.8 20~500 6.2
20~100 6.4 20~550 7.1
20~200 5.9 20~600 7.8
20~300 5.3 20~700 9.2
20~400 5.1 20~800 10.2
20~450 5.3 20~900 11.4

Thermal conductivity

θ/ºC 100 200 300 400 500
λ/ W/(m*ºC) 20.6 21.5 22.7 23.7 25.4

Style of supply

Type Dimension
Wire D= 0.1~8mm
Strip W= 5~250mm, T= 0.1mm
Foil W= 10~100mm, T= 0.01~0.1mm
Bar Dia= 8~100mm, L= 50~1000mm