Effect of preparation conditions on phase formation, densification, and microstructure evolution in La-β-Al₂O₃/Al₂O₃ composites

In situ development of La-β-Al₂O₃ (LBA) platelets in α-Al₂O₃ was studied as a function of the preparation method: a conventional solid-state reaction of commercial A1₂O₃ powder and La(NO₃)₃ as well as a sol-gel method starting with boehmite and the same La₂O₃ precursor. In both cases, homogeneous distribution of the reinforcing phase was achieved, and a noteworthy inhibition of A1₂O₃ grain growth resulted. However, samples prepared by solid-state reaction densified more easily than those prepared via sol-gel, but the formation of the LBA phase occurred at a lower temperature in samples prepared by the sol-gel approach. Results on the correlation of the onset of LBA grain growth and densification to microstructure are discussed.