Jul 12 2013
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Forming
Welding
Annealing
Cold Working
Applications
Introduction
Super alloys are built to function well in high temperature applications. Some of the components that use super alloys include gas turbine engines, rocket motors, nuclear reactors, submarines, and petroleum equipment.
Super alloy KOVAR is an iron-based alloy with nickel and cobalt. The chemical composition is well controlled so as to provide low, uniform, thermal expansion property for this alloy.
The following sections will discuss in detail about super alloy KOVAR.
Chemical Composition
The chemical composition of KOVAR is outlined in the following table.
|
Element |
Content (%) |
|
Nickel, Ni |
29 |
|
Cobalt, Co |
17 |
|
Silicon, Si |
0.2 |
|
Chromium, Cr |
0.2 |
|
Carbon, C |
0.02 |
|
Iron, Fe |
Remainder |
Physical Properties
The physical properties of super alloy KOVAR are tabulated below.
|
Properties |
Metric |
Imperial |
|
Density |
8.3 g/cm3 |
0.302 lb/in3 |
|
Melting point |
1449°C |
2640°F |
Mechanical Properties
The following table shows mechanical properties of super alloy KOVAR.
|
Properties |
Metric |
Imperial |
|
Tensile strength |
518 MPa |
75 ksi |
|
Yield strength |
276 MPA |
40 ksi |
|
Elongation |
30% |
30% |
|
Hardness, (HRB) |
80 |
80 |
Other Designations
Equivalent materials to super alloy KOVAR are listed below:
-
AMS 7726
-
AMS 7727
-
AMS 7728
-
ASTM F15
-
MIL I-23011 Class 1
Fabrication and Heat Treatment
Machinability
Super alloy KOVAR can be machined easily using the conventional methods.
Forming
Good ductility makes KOVAR readily formable.
Welding
Welding of super alloy KOVAR can be performed using all the traditional welding methods.
Annealing
Annealing can be performed at 788°C (2000°F) followed by air cooling. In case annealing is performed after cold working, the end product’s thermal expansion characteristics may get affected. To restore to original condition, the material has to be annealed in hydrogen atmosphere at 899°C (1650° F) for 1 h. Then the temperature has to be raised to 1099°C (2010°F) and held for 15 min followed by cooling to room temperature for less than 1 h.
Cold Working
KOVAR can be easily cold worked using conventional processes as the alloy is ductile.
Applications
KOVAR’s expansion properties are useful in Pyrex glasses as well as alumina ceramics, thus making this super alloy one of the popular controlled expansion alloys that can be adapted for hermetic sealing applications.
Super alloy KOVAR is also applied in the following:
-
Glass sealing of metal components or lead wires, into hard glass or ceramic devices
-
In applications where low expansion with temperature change is an essential characteristic e.g. integrated circuits packaging
-
Scientific instruments
-
Microwave tubes
-
Hybrid packages
-
Power tubes
-
Transistors
-
Diodes