Toughening of commercial 85 wt.% Al 2O 3 by controlled heat treatments

Abstract

In order to evaluate the relative importance of various heat treatment parameters on the mechanical behaviour of commercial 85 wt.% Al 2O 3 (AD-85) it was decided to establish a three-dimensional matrix of test results based on three parameters varied within set limits. The three parameters chosen were (1) the solution treatment temperature which was varied from 1400 to 1600°C, (2) the stress relief (annealing) temperature which was varied from 750 to 900°C and (3) the precipitation temperature which was varied from 1050 to 1200°C. All other parameters (the time of exposure at temperature, the tile thickness and the cooling rate) were kept fixed. The transverse rupture strength σ trs and fracture toughness K Ic were measured Fractographic and ceramographic analyses were performed on test specimens after fracture. X-ray diffraction analysis of specimens was performed after different heat treatments. The maximum values of σ trs and K Ic were obtained for specimens that were rapidly cooled after solution treatment. Smooth fracture surfaces were observed for these specimens, compared with rough fracture surfaces for specimens showing low σ trs and K Ic values. The highest values of σ trs and K Ic observed are of the same order as for high performance ceramics.