Microstructure tailoring of Nb-based MAX phase by low temperature synthesis with layer-structured Nb₂C powder and molten salt method

This study introduced a novel method to synthesize the Nb₂AlC, i.e., MAX phase, using the molten salt method. The Nb₂C phase was preferentially prepared using the Nb, Al, and graphite powders as starting materials. The parametric study enables the optimization of the synthesis condition, including the type of salt, the ratio of powder mixture to salt, synthesis temperature and time. High-quality Nb₂C powder was prepared following the optimized recipe, which was used to synthesize the Nb₂AlC powder. We confirmed that the Nb₂C phase using the molten salt method offers several advantages for Nb₂AlC MAX phase synthesis, compared to the NbC phase; Molten salt provided the diffusion path for the Al element to form a MAX phase while solid-to-solid diffusion required in the synthesis process without salt. In addition, the MAX phase was successfully synthesized at a relatively low temperature, 1100 °C, for 2 h.