Low-temperature synthesis and mechanical performance analysis of single-phase high-entropy (Ti,Cr,V,Nb,Ta)B1.9 ceramics

Abstract

The structural stability of non-stoichiometric TiB1.5 was assessed using first principles calculations, followed by synthesis through the mechanical alloying method. Subsequently, TiB1.5 was combined with other transition metal borides to fabricate high-entropy ceramics (HEB1.9) consisting of multi-component transition metal borides (Ti, Cr, V, Nb, Ta)B1.9 via spark plasma sintering (SPS). The sintered bodies were prepared at various temperatures ranging from 1700 °C to 1900 °C and were subjected to characterization. Simulation results indicate that TiB1.5 exhibits a negative formation energy, signifying its stability. Experimental findings reveal that at relatively low sintering temperatures, the combined influence of temperature and pressure facilitates the diffusion of several other compounds into the TiB1.5 phase, resulting in the synthesis of a single-phase high-entropy diboride ceramic (HEDC) at 1700 °C. As the sintering temperature increases, the Vickers hardness and flexural strength of the sintered body initially increase and subsequently decrease, a trend influenced by both porosity and grain size. Concurrently, fracture toughness exhibits a pattern of decreasing, increasing, and then decreasing again. At a temperature of 1850 °C, the single-phase HEDC demonstrates peak values in Vickers hardness (23.28 GPa), fracture toughness (5.33 MPa m1/2), and flexural strength (681.39 MPa).