Understanding the Synergistic Co-Mo Effect in Maraging Steels: An Atomistic Simulation

Abstract

Maraging steels are renowned for their exceptional strength. Particularly, in these steels, Co plays a crucial role in enhancing their strength by promoting the precipitation of Mo-based intermetallic compounds. This phenomenon, known as the synergistic Co-Mo effect, lies at the heart of achieving their exceptional strength. However, the precise mechanism by which Co promotes the precipitation of Mo- based intermetallic compounds has remained unclear. During the initial stages of aging, the heat treatment for precipitation hardening, solute atoms undergo redistribution, leading to the formation of clusters that can later transform into precipitates. This suggests that the redistribution phenomenon of solute atoms can provide valuable insights into the formation of precipitates. Therefore, the present work focused on investigating the redistribution of solute atoms to identify the cause of the synergistic Co-Mo effect. To achieve this, neural network potentials, a type of machine learning potentials, were developed, and atomistic Monte Carlo simulations were conducted using these potentials. The findings revealed that the co-addition of Co and Mo leads to compositional separation, resulting in the formation of Mo-rich/Co-lean and Mo-lean/Co-rich regions. In particular, it is worth noting that the high Mo concentration in the Mo- rich/Co-lean regions promotes the precipitation of Mo-based intermetallic compounds. Therefore, the present work proposes that this compositional separation is the reason for the synergistic Co-Mo effect. Moreover, the present work has clearly demonstrated that the interactions among solute atoms are responsible for this compositional separation.