Alumina disks with different surface finish: thermal shock behavior

Disks of commercial alumina powder were fabricated by slip casting and sintering (1600°C, 2 h). Two different surface treatments were performed: a coarse wear, using a 70 grit diamond wheel (CAW) and a fine one with SiC paper of 120 and 320 grit (FAW). The thermal shock resistance of the worn specimens was evaluated testing the disks by sudden cooling with a high-velocity air jet. The critical temperature differential (ΔTC) was determined increasing the initial temperature of the sample in 10°C until the crack propagation was detected. The values of the mean ΔTC were 940°C for FAW specimens and 765°C for CAW ones. The statistical distributions of the results were analyzed in function of the fracture strength of the specimens measured in biaxial flexion and the characteristics of the different surface finish determined by scanning electron microscopy, profilometry, and residual stresses measured by X-ray diffraction.