Structure evolution and degradation mechanism of compressive strength for (Zr0.25Hf0.25Ti0.25Ta0.25)C high-entropy ceramics with ultra-strength of 3.62 GPa

(Zr0.25Hf0.25Ti0.25Ta0.25)C high-entropy ceramics (ZHTTC) with exceptional compressive strength were prepared by spark plasma sintering at different temperatures (1900–2200 ℃). The effect of average grain size on compressive strength were investigated. The results indicate that the compressive strength degrades with the increase of the average grain size. The grain growth from 3.309 ± 0.603–9.25 ± 1.98 µm as the temperature elevated from 1900 to 2200 ℃. The ZHTTC-1900 achieves the maximum compressive strength of 3620 ± 180 MPa, while the compressive strength of ZHTTC-2200 is 1912 ± 203 MPa, which is 47 % lower than that of ZHTTC-1900. The increase of sintering temperature not only causes the increased average grain size, but also induces the decrease of grain boundary precipitation sites and adhesion of grain boundaries. The above reasons result in the degradation of compression properties.