Mechanical properties of mullite-zirconia ceramics made from rapidly solidified powder

Mullite ceramics containing zirconia were rapidly solidified (RS) to obtain amorphous ceramic powder using plasma centrifugal atomization (PCA). The RS powder was hot-pressed into disk specimens at various temperatures ranging from 1623 to 1823 K. For comparison, non-RS mullite-zirconia disk specimens were also produced. Test pieces were machined from the disks. Transverse rupture strength (TRS), Vickers hardness and fracture toughness (K-IC) of RS and non-RS hot-pressed samples were measured at room temperture. The TRS of the RS samples increased with increasing hot-pressing temperature from 1623 to 1723 K. A maximum TRS of 550 MPa was recorded at 1723 K. A similar trend of TRS was observed for the non-RS samples; the maximum TRS also obtained at 1723 K, was lower than that of the RS compacts. SEM observations revealed that the mullite-zirconia samples produced from the RS powder had a much finer microstructure than the non-RS samples. The higher TRS of the RS samples compared to the non-RS samples was attributed to the finer microstructure of the RS samples. The fracture toughness, obtained using the indentation fracture (IF) method, was approximately 3 MPa . m(1/2) for both materials. Although the RS samples exhibited higher TRS values than the non-RS samples, there was no appreciable difference in fracture toughness.