Improvement in the thermal shock resistance of alumina through the addition of submicron-sized aluminium nitride particles

The possibility of improving the thermal shock behaviour of alumina under mild thermal conditions due to the addition of submicron-sized and homogeneously dispersed AlN particles is studied. Processing conditions were adjusted in order to avoid the formation of AlON and, consequently, a decrease in the thermal conductivity of the composite. To evaluate the thermal shock behaviour, samples containing Vickers indentations were tested in quenching and the growth of the radial cracks was determined. Glycerine was chosen as the quenching fluid to minimize the effect of boiling on the heat transfer coefficient and to assure mild heat transfer conditions. A reference alumina material and a composite alumina+10 vol% AlN with similar microstructural characteristics were prepared. The materials properties controlling the thermal shock response of the materials, i.e. Youngʹs modulus, fracture toughness, coefficient of thermal expansion and thermal conductivity were determined and the theoretical relationships for the growth of the cracks were calculated and compared with the experimental results. The combination of thermal and mechanical properties of the composite leads to an improvement in the thermal shock resistance of alumina in terms of critical temperature increment (≅50%) which is in agreement with the value predicted by theory.