High-entropy rare-earth diborodicarbide: A novel class of high-entropy (Y0.25Yb0.25Dy0.25Er0.25)B2C2 ceramics

Abstract

A novel class of high-entropy rare-earth metal diborodicarbide (Y0.25Yb0.25Dy0.25Er0.25)B2C2 (HE-REB2C2) ceramics was successfully fabricated using the in-situ reactive spark plasma sintering (SPS) technology for the first time. Single solid solution with a typical tetragonal structure was formed, having a homogeneous distribution of four rare-earth elements, such as Y, Yb, Dy, and Er. Coefficients of thermal expansion (CTEs) along the a and c directions (αa and αc) were determined to be 4.18 and 16.06 μK−1, respectively. Thermal expansion anisotropy of the as-obtained HE-REB2C2 was attributed to anisotropy of the crystal structure of HE-REB2C2. The thermal conductivity (k) of HE-REB2C2 was 9.2±0.09 W·m−1·K−1, which was lower than that of YB2C2 (19.2±0.07 W·m−1·K−1), DyB2C2 (11.9±0.06 W·m−1·K−1), and ErB2C2 (12.1±0.03 W·m−1·K−1), due to high-entropy effect and sluggish diffusion effect of high-entropy ceramics (HECs). Furthermore, Vickers hardness of HE-REB2C2 was slightly higher than that of REB2C2 owing to the solid solution hardening mechanism of HECs. Typical nano-laminated fracture morphologies, such as kink boundaries, delamination, and slipping were observed at the tip of Vickers indents, suggesting ductile behavior of HE-REB2C2. This newly investigated class of ductile HE-REB2C2 ceramics expanded the family of HECs to diboridcarbide compounds, which can lead to more research works on high-entropy rare-earth diboridcarbides in the near future.

Keywords

• high-entropy rare-earth diboridcarbide
• (y0.25yb0.25dy0.25er0.25)b2c2 (reb2c2)
• high-entropy ceramics (hecs)
• thermal property
• damage tolerance