Controlled Crack Propagation Experiments with a Novel Alumina-Based Refractory

Innovative, carbon-reduced and carbon-free refractory materials are currently under development within the framework of the DFG priority program FIRE. Among various novel material solutions an alumina-based refractory with titania and zirconia additives (AZT) has gained special interest for application in high temperature processes under thermal shock conditions. The resistance against fracture of the AZT material and, for comparison, of a pure alumina refractory was examined by controlled crack propagation experiments. Wedge splitting and compact tension tests with in situ crack growth observation, partially on microstructural level, have been performed for both materials. Based on the measured room temperature values of dissipated energy, refractory stiffness and fracture stress, the Hasselman thermal shock parameter R?? was determined. The results allow to predict that AZT is less prone to scale thermal shock damage than pure alumina. The microstructural observations reveal that growth and opening displacement of the main crack is accompanied in AZT by pronounced microcracking, branching and bridging processes. First efforts are also directed towards a mechanical quantification of this fracture behavior in terms of an R-curve representation (fracture resistance as a function of apparent crack length). The specific problems of R-curve evaluation that exist in AZT due to nonlinear deformation behavior are addressed and the influence of the observed crack growth mechanisms is discussed.