Abstract:

Using Ti₃AlC₂ as the precursor, a new MAX phase Ti₃ZnC₂ was synthesized via an A-elemental substitution reaction in a molten salts bath. Composition and crystal structure of Ti₃ZnC₂ were confirmed by XRD, SEM and TEM analysis. Its structure stability and lattice parameter of Ti₃ZnC₂ were further proved by a theoretical calculation based on density function theory (DFT). Moreover, thermodynamics of A-elemental substitution reactions based on Fe, Co, Ni, and Cu were investigated. All results indicated that the similar substitution reactions are feasible to form series of MAX phases whose A sites are Fe, Co, Ni, and Cu elements. The substitution reaction was achieved by diffusion of Zn atoms into A-layers of Ti₃AlC₂, which requires Al-Zn eutectic formation at high temperatures. The molten salts provided a moderate environment for substitution reaction and accelerated reaction dynamics. The major advantage of this substitution reaction is that MAX phase keeps individual metal carbide layers intact, thus the formation of competitive phases, such as MA alloys, was avoided. The proposed A-elemental substitution reactions approach opens a new door to design and synthesize novel MAX phases which could not be synthesized by the traditional methods.

Key words: MAX phase, elemental exchange reaction, Ti₃ZnC₂