Creep mechanisms of laminated alumina/zirconia-toughened alumina composites

摘要

High-temperature plastic deformation of laminar composites containing alternate layers of Al_2O_3 and a mixture of 60 vol. percent Al_2O_3 + 40 vol. percent 3 mol percent Y_2O_3-stabilized tetragonal ZrO_2 (ZTA) produced by tape casting is investigated in isostrain compression testing at temperatures between 1400 and 1500 deg C. The stress exponent n and the creep activation energy Q are close to 1 and 700 kJ/mol, respectively. Microstructual observations reveal the lack of differential features in the ZTA layers and a general creep damage of the Al_2O_3 layers, with little microcracking by cavity coalescence even up to strains of 30 percent. The layer interfaces maintain their initial structural integrity after testing. An isostrain composite creep model predicts correctly the overall mechanical behavior of the laminates, which is dictated by the alumina phase via diffusional creep controlled by oxygen grain boundary diffusion.