INFLUENCE OF STOICHIOMETRY ON FRACTURE-BEHAVIOR OF MAGNESIUM ALUMINATE SPINELS AT 1200-DEGREES-C

The mechanical behaviour at 1200 degrees C of one stoichiometric and t wo alumina rich polycrystalline magnesium aluminate spinels is studied . Similar microstructures have been obtained for both spinel compositi ons. Lattice parameters have been determined and related to the solid solution stoichiometry for all materials. Microstructures have been ch aracterized by scanning electron microscopy. Fracture toughness measur ements at 1200 degrees C as a function of strain rate and observations of polished and fracture surfaces have been performed Relationships b etween fracture behaviour and microstructure and solid solution compos ition have been established In spite of similarities between microstru cture (porosity, grain size), two differentiated fracture behaviours a s a function of composition have been found. The stoichiometric spinel presents intergranular fracture and crack bridging at all strain rate s used, whereas high alumina spinels show mostly transgranular fractur e. (C) 1997 Elsevier Science Limited.