UNS K94610 | Werkstoff Nr 1.3981 | DIN 17745 | ASTM F 15 | AMS 7726 | AFNOR NF A54-301 | S.E.W 385

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 hyperlink entitled “Mean Coefficient of Thermal Expansion: as annealed” contains the average coefficient of expansion properties after annealing in hydrogen for one hour at 1650°F (900°C) at 15 minutes at 2010°F (1099°C) and cooled to room temperature within one hour. Material heat treated using this procedure should not exhibit any transformation when cooled to -112°F (-80°C) for four hours. This was determined by means of metallographic examination.
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

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

Specifications

UNS K94610
Werkstoff Nr 1.3981
DIN 17745
ASTM F 15
AMS 7726 Wire
AMS 7727 Bars and Forgings
AMS 7728 Sheet, Strip and Plate
MIL-I-23011 class 1
AFNOR NF A54-301
S.E.W 385
DILVER P