Common materials
ASTM F-15 alloy is an iron-nickel-cobalt, controlled expansion alloy whose chemical composition is controlled to assure uniform thermal expansion properties. It is the most common material used in “matched” seals for both the eyelet and leads. There are a number of other alloys such as Alloy #48 with slightly different characteristics but with the similar thermal expansion properties.
Alloy #52 is a 50/50 nickel-iron alloy developed for glass-to-metal seals. The alloy's rate of thermal expansion is virtually constant to a temperature of about 1050°F (565°C) and is often used as a pin material in “compression” seals.
Plain carbon steel is the most common non alloy used in hermetic applications. It has the advantage of a low cost material however it has poor corrosion resistance qualities. It is often used in low cost “compression” seal applications as an eyelet material.
Copper, copper based and molybdenum alloys provide very good heat dissipating and current capacity properties. They are not suitable for direct sealing however provides a suitable base material.
Aluminum Silicon Carbide (AlSiC) composite materials are designed to have a high thermal conductivity with the added benefit of low density.
There are numerous specialty materials available for unique applications. Please contact Design Engineering for more information.
Table 1 - Selected Material Data
|
Material
|
Density
(g/cc)
|
CTE
(ppm/°C)
|
TC
(W/m/K)
|
Electrical.
Resistance (µΩ-mm)
|
|
ASTM F-15 (Kovar)
|
8.36
|
10.4 (@800°C)
|
17
|
489
|
|
Alloy #48
|
8.25
|
12.1 (@800°C)
|
13
|
482
|
|
Alloy # 52
|
8.30
|
10.4 (@800°C)
|
14
|
429
|
|
CRS
|
7.87
|
13.8 (@400°C)
|
52
|
143
|
|
Copper
|
8.96
|
17.7 (@300°C)
|
391
|
171
|
| Tungsten-Copper |
14.87-16.98*
|
6.7-9.6*(@400°C)
|
172-205* |
|
|
Molybdenum-Copper
|
9.90-10.01*
|
10.4 (@800°C)
|
165-185* |
|
|
Molybdenum
|
10.22
|
10.4 (@800°C)
|
138
|
|
|
AlSiC
|
2.89-3.01*
|
10.4 (@800°C)
|
160-180*
|
207
|
* - actual value depends on specific composition
Table 2 - Common Material Combinations
|
Frame
|
Base
|
Leads/Pins
|
Seal Type
|
| ASTM F-15 |
ASTM F-15
|
ASTM F-15
|
Matched
|
| ASTM F-15 |
Tungsten-Copper
|
ASTM F-15
|
Matched
|
|
ASTM F-15
|
Molybdenum
|
ASTM F-15
|
Matched
|
|
Alloy 48
|
AlSiC
|
ASTM F-15
|
Compression
|
|
CRS
|
CRS
|
Alloy #52
|
Compression
|
|
CRS
|
Copper
|
Alloy #52
|
Compression
|