Three-dimensional atom probe observations and thermodynamic calculations revealed that the mechanism of gamma-phase stabilization by N addition in the Co-29Cr-6Mo alloy is different from that in stainless steel: N addition does not lower the free energy of the gamma phase in Co-29Cr-6Mo but increases the energy barrier and thus lowers the kinetic rate of the gamma -> epsilon transition through the formation of Cr-N short range order. (C) 2012 Elsevier B.V. All rights reserved.