Kovar alloy, also known as Kovar alloy, is an Fe-Ni-Cobalt alloy with a density of 8.36g/cm3;In the range of 20~500℃, the linear expansion[TJC STEEL] coefficient is equal to that of glass and ceramics.

 

Standard:

CHINA	YB/T 5231-2005	4J29
AMERICA	ASTM F15-2004	K94610
GERMANY	DIN 17745:2002	NiCo 29 18 1.3981

 

Chemical Composition(%)

GRADE	4J29	K94610	1.3981
C	≤0.03	≤0.04	≤0.05
Si	≤0.30	≤0.20	≤0.30
Mn	≤0.50[TJC STEEL]	≤0.50	≤0.50
P	≤0.020	—	—
S	≤0.020	—	—
Ni	28.5~29.5	29.0*	28.0~30.0
Co	16.8~17.8	17.0*	16.0~18.0
Cr	≤0.20	≤0.20	—
Cu	≤0.20	≤0.20	—
Mo	≤0.20	≤0.20	—
Al	—	≤0.10	—
Mg	—	≤0.10	—
Zr	—	≤0.10	—
Ti	—	≤0.10	—
Fe	REST	Bal.*	Rest

*：Is a typical value, can be adjusted according to the requirements of thermal expansion coefficient。

 

Grades

AMERICA	CARPENTER[TJC STEEL]	Kovar® Rodar®
	Special Metals	Nilo® K
FRANCE	Aperam Alloys Imphy (Imphy Alloys)	Dilver P1®
GERMANY	VDM Metals	Pernifer® 2918
JAPAN	NIPPON YAKIN	NAS 29CO

 

TYPICAL LINEAR EXPANSION COEFFICIENT（YB/T 5231-2005）

TEM	AVERAGE COEFFICIENT OF LINEAR EXPANSION ā，10-6/℃
20℃~200℃	5.9
20℃~300℃	5.3
20℃~400℃	5.1
20℃~450℃	5.3
20℃~500℃	6.2
20℃~600℃	7.8
20℃~700℃	9.2
20℃~800℃	10.2

 

Alloy Principle

Most metals cannot be sealed with glass because their coefficient of thermal expansion is different from that of glass, so[TJC STEEL] when the joint is cooled, the stress caused by the different expansion rates of glass and metal causes the joint to break.The nonlinear thermal expansion curves of Kovar alloys can usually be matched with glass, allowing the joints to withstand a wide temperature range.

Chemically, the Kovar alloy is bonded to the glass through intermediate oxide layers of nickel oxide and cobalt oxide;The bonding [TJC STEEL]strength is highly dependent on the thickness of the oxide layer.The proportion of iron oxide is lower due to the reduction of cobalt, and the presence of cobalt makes the oxide layer more likely to melt and dissolve in the molten glass.Judging by color, gray, gray-blue or taupe indicate good seal;Metallic colors indicate a lack of oxides and black indicates an overoxidized alloy, both of which will result in weak bonding.

 

Applications

Kovar alloys allow for tight mechanical connections between two materials over a range of temperatures and are suitable for glass/ceramic-metal seals in scientific equipment, as well as conductors entering glass envelopes [TJC STEEL]in electronic components such as vacuum tubes (valves), X-ray and microwave tubes, transistors, diode integrated circuits, etc.