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Kovar Alloy

Kovar Alloy

OHMALLOYOhmAlloy-4J29 (Expansion alloy)(Common Name: Kovar, Nilo K, KV-1, Dilver Po, Vacon 12)OhmAlloy-4J29 also known as Kovar alloy. it was invented to meet the need for a reliable glass-to-metal s

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OHMALLOY

OhmAlloy-4J29  (Expansion alloy)
(Common Name: Kovar, Nilo K, KV-1, Dilver Po, Vacon 12)

OhmAlloy-4J29 also known as Kovar alloy. 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.

(链接-Kovar合金)

Kovar  is a nickel–cobalt ferrous alloy compositionally identical to Fernico, designed to be compatible with the thermal expansion characteristics of borosilicate glass (~5 × 10−6 /K between 30 and 200 °C, to ~10 × 10−6 /K at 800 °C) in order to allow direct mechanical connections over a range of temperatures. It finds application in electroplated conductors entering glass envelopes of electronic parts such as vacuum tubes (valves), X-ray and microwave tubes and some lightbulbs.

The name Kovar is often used as a general term for Fe–Ni alloys with these particular thermal expansion properties. Note the related particular Fe–Ni alloy Invar which exhibits minimum thermal expansion.

OhmAlloy-4J29was 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.

OhmAlloy-4J29 not only has thermal expansion similar to glass, but its nonlinear thermal expansion curve can often be made to match a glass, thus allowing the joint to tolerate a wide temperature range. Chemically, it bonds to glass via the intermediate oxide layer of nickel oxide and cobalt oxide; the proportion of iron oxide is low due to its reduction with cobalt. The bond strength is highly dependent on the oxide layer thickness and character. The presence of cobalt makes the oxide layer easier to melt and dissolve in the molten glass. A grey, grey-blue or grey-brown color indicates a good seal. A metallic color indicates lack of oxide, while black color indicates overly oxidized metal, in both cases leading to a weak joint.

Mainly used in electric vacuum components and emission control, shock tube, igniting tube, glass magnetron, transistors, seal plug, relay, integrated circuits lead, chassis, brackets and other housing sealing.

Normal composition%

Ni

28.5~29.5

Fe

Bal.

Co

16.8~17.8

Si

≤0.3

Mo

≤0.2

Cu

≤0.2

Cr

≤0.2

Mn

≤0.5

C

≤0.03

P

≤0.02

S

≤0.02




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


Typical Physical properties

Density (g/cm3)

8.2

Electrical resistivity at 20℃(Ωmm2/m)

0.48

Temperature factor of resistivity(20℃~100℃)X10-5/℃

3.7~3.9

Curie point   Tc/ ℃

430

Elastic Modulus,  E/ Gpa

138


Coefficient of expansion

θ/℃

α1/10-6℃-1

θ/℃

α1/10-6℃-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/

100

200

300

400

500

λ/ W/(m*℃)

20.6

21.5

22.7

23.7

25.4


The heat treatment process

Annealing for stress relief

Heated to 470~540℃ and hold 1~2 h. Cold down

annealing

In vacuum heated to 750~900℃

Holding time

14 min~1h.

Cooling rate

No more than  10 ℃/min cooled to 200 ℃

Style of supply

Alloys Name

Type

Dimension

OhmAlloy-4J29

Wire

D= 0.1~8mm

OhmAlloy-4J29

Strip

W= 5~250mm

T= 0.1mm

OhmAlloy-4J29

Foil

W= 10~100mm

T= 0.01~0.1

OhmAlloy-4J29

Bar

Dia= 8~100mm

L= 50~1000

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