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

Abstract

In this research, series of carbonitride ceramics with a high entropy solid solution powder were designed using an open dynamic carbothermal reduction nitriding method. The influence of nitrogen on the high entropy configuration was assessed through experimental methods and first principles calculations. The influence of nitrogen on the high entropy configuration was assessed through experimental methods and ab-intio modeling. DFT calculation was used by both SQS and AFLOW-POCC method to explore the effects of nitrogen on the formability and stability from the perspective of phase composition. Accompanied with the intrinsic mechanical properties of HECN, the correlation between elastic modulus and electronic structure was established by iDOS( E pg , E F ) descriptor. Calculation results illustrated that, the composition inhomogeneity induced phase deviation were primarily attributed to the covalent preference between group IV elements and N, and aggravative charge distribution for nitrogen around Mo atom. Thus, for HECN ceramic containing VIB group element, low label nitrogen content could obtain better mechanical properties by the synergistic enhancement of shear modulus and Young’s modulus. • The role of the multi-anionic component in the formation and phase composition of (Ti, Zr, Nb, Mo, Ta)C x N 1-x high entropy carbonitride was investigated using a bottom-up strategy. • The compositional differential induced by nitrogen on the bulk properties of HECN was evaluated, and the correlation has been established with electronic structure and mechanical properties. • The effect of nitrogen content on the structural stability and mechanical properties of HECN configuration were investigated using experimental methods and ab-intio modeling. Influence of nitrogen on the synthesis and mechanical properties of high-entropy carbonitride are evaluated in (Ti, Zr, Nb, Mo, Ta)C x N 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 0.9 N 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.

Topics & Concepts