High-entropy (Y0.2Gd0.2Dy0.2Ho0.2Er0.2)Al3C3 ceramic: A noval promising ultra-high temperature structural material

High-entropy (Y0.2Gd0.2Dy0.2Ho0.2Er0.2)Al3C3 (HE(5RE1/5)Al3C3) with high purity, high density and high compositional uniformity was prepared by in-situ hot pressing process using Y, Gd, Dy, Ho, Er, Al and C as initial materials for the first time. The results show that its crystal structure is hexagonal system (P63/mmc) with lattice constants of a = b = 3.43 Å, c = 17.35 Å. The Vickers hardness, flexural strength, Young's modulus, thermal expansion coefficient, and thermal conductivity of HE(5RE1/5)Al3C3 are 13.2 ± 0.5 GPa, 148 ± 15 MPa, 375 GPa, 8.21 × 10−6 K−1, and 10.98 W m−1 K−1, respectively. The residual Young's modulus of HE(5RE1/5)Al3C3 remained approximately 83 % of its room temperature value even at 1500 °C Additionally, compared to YAl3C3, HE(5RE1/5)Al3C3 has a high Debye temperature (921 K) and a high initial oxidation temperature (980 °C). These results indicate HE(5RE1/5)Al3C3 is a highly promising oxidation resistant ultra-high temperature structural material.