Nilo K (Kovar)

Nilo K (Kovar) ASTM F15, UNS K94610 is a controlled expansion alloy. It is a Nickel Iron alloy with 29% Nickel, 17% Cobalt and the remaining balance is Iron. The expansion characteristics of  Nilo k (Kovar) match both borosilicate (or Pyrex) glasses and alumina ceramics, making it one of the most popular of the controlled expansion alloys for hermetic sealing applications (Glass to Metals Sealing). Nilo K (Kovar) is produced to ensure good properties for machining and deep drawing, and is a porosity free product.

Kovar (Nilo K) Specifications

ASTM F15UNS K94610AMS-I-23011 CLASS 1 W. 1.3981

Stock Sizes

Sheet0.1mmTo3.2mm Thick
Strip in Coil 0.1mmTo1.0mmThick
Tube2mm O/D x 0.2mm WallTo25.4mm O/D x 1mm Wall

Kovar (Nilo K) 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.

Kovar (Nilo K) is typically used in power tubes, microwave tubes, transistor and diodes, Hybrid circuit casings, optoelectronic component cases and bases, and hemetic feedthroughs are amoung some of Kovar (Nilo K) 

Typical Chemistry

Nickel Ni29 %
CobaltCo17 %
Manganese Mn0.5 %
SiliconSi0.2 %
CarbonC0.1 %
AluminiumAl0.1 %
MagnesiumMg0.1 %
ZirconiumZr0.1 %
TitaniumTi0.1 %
Copper Cu0.2 %
Molybdenum Mo0.2 %

Coefficient of thermal expansion

Degree CDegree C
30 - 100-30 - 450 5.1 - 5.5
30 - 150-30 - 475-
30 - 2005.530 - 500
30 - 250-30 - 525-
30 - 3005.130 - 550-
30 - 325-30 - 6007.9
30 - 350-30 - 7009.3
30 - 375 -30 - 80010.4
30 -4004.6 - 5.2 30 -90011.5
30 - 425-30 - 1000-

“If we say we keep it
then we actually
do keep it”

Mechanical Properties

Yield Strength(0.2%) offset3300 MPa
Tensile Strength380 MPa

Physical Properties

Densityg/cm³8.26Thermal ConductivityW.m-¹°C16.7
Melting Point°C1448.9Thermal Exspansion µm.m-¹°C-¹6
Specific Heatj/Kg°K385Youngs ModulusGPa130



Kovar is a Trademark of Carpenter Technology Corporation, Pernifer is a Trademark of ThyseenKrupp-VDM Germany,
Dilaton 29/18 is a Trademark of Deutsche Nickel, Dilvar is a Trademarks of Imphy Alloys France.