Case Stories

The fcc-hcp phase transition in Co and Co-alloys

Cobalt and Co-based alloys are important materials that have been subjected to considerable use because of their outstanding mechanical and magnetic properties. In particular, these alloys have found their way into industrial applications where high temperature strength and hardness, excellent wear, galling, corrosion, and erosion resistance are required properties. Unfortunately, serious health concerns related to Co dust and material availability issues may dramatically change the market scenario for Co and hence the search for alternatives has become a need. Finding a replacement for a material or a part of a material is not easy, specially when a material has been carefully crafted for a specific application.

Therefore, in order to find a replacement for a certain material, one needs to identify first a property that is related to the intended functionality of the material. For example, the performance of cutting tools made out
of cemented carbides; composite materials that typically use Co as a binder phase, is believed to be related to the low stacking faults energies and the hcp-fcc phase transition in Co.

Recently, Tian studied stacking fault energies in fcc Co-based binary alloys CoM, where M = Fe, Ni, Pd, Mo, W, Cr, Ru and Rh, by performing density functional theory and thermodynamical calculations.
They showed that the alloying effect of Fe, Ni, and Pd is to stabilize the fcc phase, whereas Cr, Ru and Rh tend to stabilize the hcp phase.

For more information contact:

Raquel Lizárraga
Coordinator of QM-FORMa

Researcher
Unit of Properties
Department of Materials Science and Engineering
Royal Institute of Technology (KTH)
Brinellvägen 23, SE-10044 Stockholm, Sweden

Phone: 070 593 77 56
Email: raqli@kth.se