Effect of sintering technology in beta-eucryptite ceramics: Influence on fatigue life and effect of microcracks

Abstract

β-eucryptite ceramics with low negative or near-zero coefficient of thermal expansion (CTE) with excellent mechanical properties, such as Young’s modulus  100 GPa, have attracted attention for many important industrial applications. The extremely anisotropic thermal expansion behaviour of this material leads to thermal residual stresses, and causes spontaneous microcracking. These microcracks cause large negative CTE with mechanical weaknesses. The appearance of microcracks is due to different factors. The most important are prolonged sintering time and heating source used. The present work shows experimentally the evolution of grain microcracks and residual stresses of the sintered -eucryptite material going through many thermal fatigue cycles (3600). The effect of stresses applied on β-eucryptite crystals due to the thermal cycling could be considered for explaining the small change observed of β-eucryptite to β-spodumene phase, which is higher in the samples obtained by microwave sintering. Therefore, the study of residual stresses has suggested that the heating source employed, such as conventional or microwave, has a great influence on thermal fatigue life and the final mechanical and thermal properties. The microwave heating has a significant impact on β-eucryptite materials lifetime.