Reaction sintered alumina-lanthanum hexaaluminate composites

Lanthanum hexaaluminate, abbreviated as LHA, with an ideal stoichiometry LaAl11O18 is a candidate coating material for fibre–matrix interface adjustment in fibre reinforced ceramic composites as well as an in-situ platelet reinforcement for dispersion reinforced composites. Fields of application are e. g., thermal barrier coatings and combustion catalysts. This work exhibits results of a study to investigate microstructure evolution in homogenous and functionally graded alumina/LHA composite ceramics containing 2.8 to 80 vol% LHA. The microstructure development in these ceramics was studied with respect to application of a modified green processing, various sintering parameters (i. e., temperature and atmosphere), and microwave assisted sintering. Based on measurements of phase composition, porosity, grain growth, and densification, the influence of the different utilized processing variables as well as of the LHA content on resulted mechanical and thermal properties of composite ceramics was investigated. The obtained mechanical and thermal properties achieved for the different homogenous composite ceramics were taken into consideration for designing of the functionally graded composite ceramic.