Effects of Re_2O_3 (Re = La, Nd, Y and Yb) addition in hot-pressed ZrB_2-SiC ceramics

摘要

ZrB_2-20 vol% SiC composites with 3 vol% Re_2O_3 rare-earth oxide (Re = La, Nd, Y or Yb) were hot pressed to near full-density at 1900 deg C. The La_2O_3 and Nd_2O_3 additions not only caused the formation of an amorphous grain boundary phase and enhanced densification, but also resulted in substantial ZrB_2 and SiC grain growth. In contrast, the Y_2O_3 and Yb_2O_3 additions resulted in the formation of crystalline (Y/Yb)_2Zr_2O_7 and enhanced densification without ZrB_2 and SiC grain growth. The hardness was improved by the rare-earth oxide addition, especially with Y_2O_3 and Yb_2O_3. The La_2O_3 and Nd_2O_3 only had a minor effect on the fracture toughness, whereas the Y_2O_3 and Yb_2O_3 additions increased the fracture toughness. The type of Re_2O_3 addition was found to influence the nature of the grain boundary and the concomitant fracture and toughening mechanisms.