High temperature thermomechanical properties of a microcracked model refractory material: A silica-doped aluminium titanate

Abstract

An aluminium titanate based (AT) material doped with silica was investigated as refractory model material in order to highlight its thermomechanical properties through various techniques of characterization operating at high temperature such as ultrasonic pulse echography technique operating in long bar mode, acoustic emission, dilatometry and tensile test measurements up to 1400 °C. Young's modulus (MoE) as a function of temperature evolves in the form of a large hysteresis loop with a maximum value of about 170 GPa due to the healing of diffuse microcracks during heating. A sharp decrease in MoE occurs on cooling at about 780 °C, corresponding to the re-opening of the microcracked network due to a high level of stress around AT grains. In addition, during cooling, the dilatometric analysis shows a quasi-linear shrinkage followed by a sudden non-linear expansion from 750 °C. The thermal expansion coefficient value determined between 1100 °C and 750 °C is about 8.8 10−6 °C−1. By recording the evolution of the cumulative number of hits as a function of temperature, the results of the acoustic emission clearly confirm the resurgence of microstructural defects at 780 °C. The incremental tensile loading test performed at 1400 °C shows a greater degree of nonlinearity suggesting a higher flexibility of the studied AT due to both the microcracks network and the low viscosity of intergranular glassy phase. Symmetric alternating loading tests have highlighted that the viscous contribution in the viscoelastic behaviour of such materials is increasing from 850 H °C to 1400 H °C as the viscosity of the silica-riched amorphous phase is decreasing. These results are very useful to understand the more sensitive parameters involved in the high thermal shock resistance of aluminium titanate.