Evaluation of novel interphases for oxide/oxide ceramic matrix composites

Stoichiometric MXO4 type compounds, where M represents a rare earth or yttrium ion and X a pentavalent cation, have been prepared using mixed oxide and liquid precursor methods. Their stability in relation to Al2O3, mullite, and yttrium-aluminium garnet (YAG) has been determined by examining interfaces exposed in reaction couples after heating to 1400°C. Complex oxides of the phosphate and vanadate type are shown to possess the desired chemical stability with some of the candidate oxides and can be considered as suitable interphase materials. Close control over composition and homogeneity is shown to be important in determining their performance as potential interphases due to the possible formation of a liquid phase which can react readily with the oxide matrix or fibre. Selected MXO4 compounds have also been successfully deposited on to oxide substrates and woven oxide fibres using liquid precursors and RF magnetron sputtering techniques, yielding controlled and uniform fibre coatings. BCT/338