Cobalt Based High Performance Alloys

Question 1

What elements are present in cobalt based high performance alloys?

Answer 1

50-60% Co
20-30% Cr
5-10% W
0.1-1% C
Some Ni, Ta, Fe and Nb

Question 2

How do cobalt based high performance alloys compare to nickel based?

Answer 2

Not as high strength as Ni based but maintain their properties at higher temperatures.

Good for long life static parts at low stress and high temperatures.

Cobalt based have lower strength at intermediate temperatures due to the lack of coherent gamma prime precipitation which, all the Ni superalloys have.

Cobalt based only has carbides and solid solution strengthening, hence it cannot compete in the high stress applications.

Question 3

What is the microstructure of cobalt based?

Answer 3

A gamma matrix and carbide precipitates.

No gamma prime precipitate.

Question 4

What are the main carbides of cobalt based?

Answer 4

M23C6 - M= W, Mo

MC - M= Ta, Ti, Zr, Nb

M6C - M= W, Mo(only at high contents)

Question 5

Where does its strength come from?

Answer 5

Solid solution strengthening and carbide precipitation.

Main strengthening carbide is M23C6 which both pins the grain boundaries and stops dislocation movement when precipitate within the grains.

Question 6

What type of applications are cobalt based used for?

Answer 6

Used for low stress, high temperature, long life applications.