ZrO2/ZrO2 layered composites for crack bifurcation

Laminates containing a thin layer (5 to 200 mu m thick) sandwiched between two thick layers (2 mm thick) were fabricated by sequential slip casting in order to study crack bifurcation, The thin layer was formed with a mixture of a pure ZrO2 powder (MZ) and Zr(Y)O-2 powder containing 3 mol% Y2O3 (TZ) . The thick layers were formed with TZ powder containing 0.05 volume fracti on of Al2O3 powder to distinguish the interfaces between the different laye rs in the scanning electron microscope. Dilatometry data for monolithic spe cimens formed with the mixed MZ and TZ powders (0.30 to 1.00 volume fractio n MZ) showed that the monoclinic-to-tetragonal transformation temperature a nd strain varied with the MZ content, suggesting the yttria in the TZ powde r diffused into the MZ powder during processing at 1500 degrees C/2 h, Thes e data also showed that large compressive stresses developed in the thin la yer due to the transformation, Conditions (thin layer composition and thick ness) for observing edge cracks produced along the center line of the thin layer and for observing crack bifurcation during flexural failure were dete rmined, Delamination occurred during cooling for layers fabricated with gre ater than or equal to 0.40 volume fraction of the MZ powder when the thin l ayers mere 200 mu m thick, Edge cracking, which occurred during cooling, an d crack bifurcation, which occurred during flexural loading, occurred for t hin layer com;positions containing greater than or equal to 0.40 volume fra ction MZ powder,when the thickness of the thin layer was between approximat e to 50 and 150 mu m, Crack bifurcation was not observed in thinner layers. With decreasing layer thickness, thin layers fabricated with >0.60 volume fraction of the MZ powder contained multiple microcracks, parallel to the c enter line, on the surface, instead of a single edge crack. The flexural st rength of all specimens depended on the strength of the thicker Zr(Y)O-2 la yers, regardless of whether bifurcation occurred.