Super Alloy KOVAR (UNS K94610)

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

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit