Tuning anionic components to control the phase stability and mechanical properties of High-Entropy carbonitrides

Abstract

Influence of nitrogen on the synthesis and mechanical properties of high-entropy carbonitride are evaluated in (Ti, Zr, Nb, Mo, Ta)C_xN_1-x solid solution (denoted as HECN) through experimental method, thermodynamic calculations and ab-intio modeling. HECN powders with varying nitrogen content are fabricated using an open dynamic carbothermal reduction nitriding method. Both the calculation and experiment results indicate that the higher nitrogen content alters the bonding behavior and charge distribution difference of HECN due to the highly distorted crystal lattice. Leading the increase of formation energy between the HECN and sub-system configurations, resulting in decreased phase stability. Due to the correlation between electronic structure and mechanical properties calculated by Density functional theory and integrated density of states, HEC_0.9N_0.1 exhibits the highest mechanical properties, with a hardness of 20.1 ± 0.1 GPa at 49N and an indentation fracture resistance (K_IC) of 5.54 ± 0.16 MPa∙m^1/2. The weak bonding characteristic between Mo and N atoms contributes to the reduced phase stability and the random atomic occupation. This work reveals the nitridation characteristics critical for the design and preparation of high entropy systems and elucidates the correlation between nitrogen content and intrinsic properties, providing a feasible strategy for guiding the design and synthesis of HECN ceramics.