For the Czech surname, see Kovář

Kovar

Kovar is a nickel-cobalt ferrous alloy designed to be compatible with the thermal expansion characteristics of borosilicate glass in order to allow direct mechanical connections over a range of temperatures...

.

Kovar (trademark of Carpenter Technology Corporation

Carpenter Technology Corporation

Carpenter Technology Corporation is a globally recognized developer, manufacturer and distributor of cast wrought and powder metallurgy specialty alloys/metals including superalloys, ultra-high strength steels, and stainless steel, as well as titanium alloys in a range of product forms...

) is a nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

-cobalt

Cobalt

Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

 ferrous

Ferrous

Ferrous , in chemistry, indicates a divalent iron compound , as opposed to ferric, which indicates a trivalent iron compound ....

 alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 designed to be compatible with the thermal expansion

Thermal expansion

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...

 characteristics of borosilicate glass

Borosilicate glass

Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common 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

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 and microwave

Microwave

Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...

 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

Invar

Invar, also known generically as FeNi36 , is a nickel steel alloy notable for its uniquely low coefficient of thermal expansion . The name, Invar, comes from the word invariable, referring to its lack of expansion or contraction with temperature changes.It was invented in 1896 by Swiss scientist...

 which exhibits minimum thermal expansion.

Typical composition

Given in weight %

Fe FE Fe or FE may refer to:* Iron * Fe , the f-rune of the Younger Futhark* Fe * Fe * "Fe" , a song by Jorge González...	Ni Nickel Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...	Co Cobalt Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....	C Carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...	Si Silicon Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...	Mn Manganese Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
balance	29%	17%	<0.01%	0.2 %	0.3 %

Properties

Property	sintered Sintering Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...	HIP Hot isostatic pressing Hot isostatic pressing is a manufacturing process used to reduce the porosity of metals and influence the density of many ceramic materials. This improves the material's mechanical properties and workability.... ed
Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...  / g cm3	8.0	8.35
Hardness / HV1	160	150
Youngs Modulus / GPa	159	159
reduction of area at fracture / %	30	30
yield strength / MPa	270	270
thermal conductivity Thermal conductivity In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....  / W/Km	17
Curie Temperature Curie point In physics and materials science, the Curie temperature , or Curie point, is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic on heating; the effect is reversible. A magnet will lose its magnetism if heated above the Curie temperature...  / °C	435
electrical resistivity Ω mm2 / m	0.49
specific heat J/gK	0.46
thermal expansion coefficient/10-6 K-1 (25 – 200°C)	5.5
(25 – 300°C)	5.1
(25 – 400°C)	4.9
(25 – 450°C)	5.3
(25 – 500°C)	6.2

External links

• Kovar specification page