High-entropy high-hardness metal carbides discovered by entropy descriptors

Abstract

High-entropy materials have attracted considerable interest due to the combination of useful properties and promising applications. Predicting their formation remains the major hindrance to the discovery of new systems. Here we propose a descriptor—entropy forming ability—for addressing synthesizability from first principles. The formalism, based on the energy distribution spectrum of randomized calculations, captures the accessibility of equally-sampled states near the ground state and quantifies configurational disorder capable of stabilizing high-entropy homogeneous phases. The methodology is applied to disordered refractory 5-metal carbides—promising candidates for high-hardness applications. The descriptor correctly predicts the ease with which compositions can be experimentally synthesized as rock-salt high-entropy homogeneous phases, validating the ansatz, and in some cases, going beyond intuition. Several of these materials exhibit hardness up to 50% higher than rule of mixtures estimations. The entropy descriptor method has the potential to accelerate the search for high-entropy systems by rationally combining first principles with experimental synthesis and characterization.

Low‐temperature sintering of single‐phase, high‐entropy carbide ceramics

“…The resulting ceramics had an average grain size of 16.4 ± 0.5 µm . Similarly, Sarker et al reported that (Hf, Zr, Ti, Ta, Nb)C ceramics produced by SPS at 2200°C using commercial carbide powders that were mixed by HEBM had an average grain size of more than 10 µm . In contrast, the (Hf, Zr, Ti, Ta, Nb)C ceramics in the present study had much finer grain sizes.…”

“…Young's modulus increased from 405 ± 10 GPa to 452 ± 6 GPa as the densification temperature increased from 1750°C to 1900°C, which was attributed to the increase in the relative density as the densification temperature increased. (Figure ) Modulus values were higher than the value of 436 ± 30 GPa predicted using a volumetric rule of mixture (ROM) calculation and the modulus values of the nominally pure constituent carbides reported in previous studies . This has been attributed to the disorder associated with the multi‐metal composition .…”

“…Vickers hardness measured under a load of 4.9 N increased from 23.7 ± 0.3 GPa to 24.8 ± 0.8 GPa when the sintering temperature increased from 1750°C to 1900°C, presumably due to the increase in relative density with increasing densification temperature. (Figure ) The resulting hardness values were higher than the value of 23 ± 2 GPa predicted from a ROM based on the binary carbides, which has been attributed to disorder among the metallic species and solid solution hardening . Vickers hardness of HECCs produced at 1900°C was also measured as a function of indentation load to evaluate the indentation size effect.…”

“…Castle et al reported that SPS of (Hf, Ta, Zr, Ti)C and (Hf, Ta, Zr, Nb)C ceramics with a relative density of ~99% required sintering temperatures about 2300°C . Similarly, Sarker et al produced (Hf, Zr, Ti, Ta, Nb)C ceramics with a relative density of ~99% at 2200°C by SPS . Commercial carbide powders with an average particle size of <45 µm were used for preparation of HECCs in the latter studies, which resulted in high densification temperatures.…”

One‐step synthesis of coral‐like high‐entropy metal carbide powders

“…As a member of high-entropy ceramics, the high-entropy metal carbides have recently aroused intensive research interests for their promising applications in various fields, such as aerospace, armors, and cutting tools. [8][9][10][11][12][13] The synthesis of high-entropy metal carbide powders is critical for implementing their extensive applications. To date, only two methods have been developed to synthesize high-entropy metal carbide powders.…”