![]() ![]() For instance, entropy forming ability (EFA) from the first principles has been proposed to address the probability of the formation of single-phase HECs 15. To facilitate the design of stable solid solution HECs, several descriptors have been proposed in recent years 14. Thus, they are anticipated to be used in diversified extreme conditions, such as in hypervelocity finishing cutter, hypersonic aircraft, nuclear reactor, and refractory crucibles 9, 12, 13. Recently, HECs have attracted significant interests due to their significant properties, e.g., high hardness, low thermal conductivity, excellent thermal stability, outstanding wear resistance, and ultra-high melting point 6, 7, 8, 9, 10, 11. In single-phase HECs, metal components randomly occupy the cation sites, and C atoms are located on the anion sublattice. The concept of high-entropy carbides (HECs), proposed based on the original idea of high-entropy alloys (HEAs) 1, 2, 3, 4, usually refers to solid solution ceramics containing more than four species of carbides in equimolar or near-equimolar proportions with relatively high configurational entropy 5, 6. The work demonstrates the concept of using in-situ metastable particles for toughening bulk high-entropy ceramics by taking advantage of their compositional flexibility. The toughening effect is primarily attributed to the transformation of the metastable tetragonal ZrO 2 particles under mechanical loading, which promotes crack tip shielding mechanisms including crack deflection, crack bridging and crack branching. m 1/2, significantly exceeding the value predicted by rule of mixture and that of other reported HECs. ![]() Apart from a high hardness of 21.0 GPa, the HEC can obtain an enhanced fracture toughness of 5.89 MPa This is realized by developing a (WTaNbZrTi)C HEC showing a solid solution matrix with uniformly dispersed in-situ tetragonal and monoclinic ZrO 2 particles. Here, we introduce a metastability engineering strategy to achieve superhard HECs with enhanced toughness via in-situ metastable particles. Despite the extremely high hardness of recently proposed high-entropy carbides (HECs), the low fracture toughness limits their applications in harsh mechanical environment. ![]()
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