Thermal stability of phase-separated nanograin structure during heat treatment

摘要

A thermodynamic model was developed based on the first principles to describe the thermal stability in the phase-separated alloy systems. The distributions of the solute atoms in the nanocrystalline system were predicted for the heating process, using the typical phase-separating system of W-Cr alloy as an example. The effects of the re-dissolution and grain-boundary segregation processes on the thermal stability of the nanograin structure were investigated, based on which the critical conditions of grain size and solute concentration for controlling destabilization of nanostructure at high temperatures were proposed. The transformation of solute distribution from phase separation to grain-boundary segregation was described in detail by the present model without introducing any empirical parameters. The calculations indicated that the stabilization mechanisms are distinct for the single-and double-phase states of the nanocrystalline alloys even at the same composition. Thus the approach to inhibit nanograin growth is flexible by adjusting the solute distribution to reach either the thermodynamically stable or the meta-stable state. This study advanced the understanding of the doping effect and facilitated precise design of nanocrystalline alloys with high stability during high-temperature heat treatment.