Abstract:

The reaction thermodynamics for synthesizing the “312” and “413” o-MAX phases using the powder metallurgy are investigated using a linear programing optimization algorithm based on the high-throughput first principles phonon calculations. The validity and reliability of the current methodology are verified by correctly predicting the impurities in four experimentally known o-MAX systems including Cr-Ti-Al-C, Cr-V-Al-C, Mo-Sc-Al-C and Mo-Ti-Al-C. The formability of each investigated o-MAX phase is evaluated by means of formation enthalpy and formation Gibbs free energy in a temperature range from 0 K to 1700 K. It is revealed that the thermodynamic stability of the “413” o-MAX structure is no better than that of the “312” phase. The formability of “413” o-MAX is also reduced at high sintering temperature, compared to that of “312” phase. The optimal synthetic routes are predicted for all thermodynamically stable “312” and “413” o-MAX phases. It is found that most o-MAX phases considered could be prepared as the single phase using the non-conventional synthetic routes from the aspect of reaction thermodynamics. Few of them including Cr₂TaAlC₂, Nb₂HfAlC₂, Nb₂TaAlC₂, Nb₂Hf₂AlC₃, Nb₂Ta₂AlC₃, Mo₂V₂AlC₃ and Mo₂Ta₂AlC₃ are predicted to be either destabilized at high temperature or overwhelmed by the most competing side reaction.

Key words: Thermodynamics, First-principles calculation, Synthesis, o-MAX phase