Microstructure and mechanical properties of Al2O3-YSZ and Al2O3-YAG directionally solidified eutectic plates

Plates of Al2O3-YSZ and Al2O3-YAG eutectic composition with a thickness from 0.1 to 1 mm were prepared by directional solidification using a diode laser stack. The melt processed regions of plates exhibited colony microstructure consisting of finely dispersed phases. Due to the curved shape of the melted pool, the growth rate depends on the distance to the surface plate, decreasing from top to bottom. In this way, the microstructure characteristic length changes as a function of the distance to the plate surface. Vickers indentations and piezo-spectroscopy measurements were done on longitudinal and transverse cross-sections of the samples at different depths. From these measurements, we concluded that the Vickers hardness (HV), indentation fracture toughness (KIC) and residual stresses (σh) of the plates were mainly independent from the distance to the surface. The mean values that we obtained in the Al2O3-YSZ plates were HV = 16 GPa, KIC = 4.2 MPa m1/2 and σh = −0.33 GPa, and in the Al2O3-YAG plates were HV = 16 GPa, KIC = 2.0 MPa m1/2, and σh = −0.1 GPa. These values are similar to those found in directionally solidified eutectic rods.