High Temperature Evaluation of Mechanical Properties of Refractory Castables: Impact of Eutectic Aggregates and Testing Methods
Within the framework of service life improvement of unshaped materials, those formulations must be designed in order to favour microstructural mechanisms at the origin of fracture toughness increase.
In the study herein, functional aggregates are incorporated in a common low cement castable based on tabular alumina. Such grog grains aim to, according to their nature, chemistry, hardness and shape, counter the crack propagation by creating new stable interfaces between cracks and aggregates. The fracture energy of those studied materials increase according to the present microstructural phenomenon: crack deviation, crack bridging, bridging of liquid phase, internal friction, and crack closure in contact with partially stabilized zirconia particles. The fundamental approach of such toughening enhancement is to improve the strengthening mechanisms occurring in the wake region of the crack while the crack tip is held responsible for material damaging after progressive quenching tests. As refractory castables are continuously subjected to severe and cycling thermal gradients, crack nucleation cannot be avoided. Therefore, the incorporation of functional aggregates turns out to be essential to affect the shielding effect occurring at the crack tip with increasing crack length.
Considering this aspect, the addition of eutectic aggregates of Al2O3–ZrO2–SiO2 and Al2O3–ZrO2 and andalusite is investigated to study in another step the relevance of the ensuing toughening mechanism on the thermal shock resistance of high alumina castable.