Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

A technique for forming step-graded Al2O3-ZrO2 composites from aqueous suspensions

In Biograd-Dip the aim was to prepare ceramic functionally graded ball-heads using a technique alternative to electrophoretic deposition. The basic idea was to use an adapted dip-coating technique that combines the principles of several conventional shaping methods: a porous core material is dipped into aqueous suspensions with gradually changing compositions. After encouraging preliminary experiments with samples of simple geometry, several problems appeared in shaping of larger discs and ball-heads. For this reason we implemented another shaping technique: sequential slip casting, where the part is built layer by layer by casting of the suspensions with different composition in porous mould. In numerous experiments, conditions for preparation of green parts without major defects were determined. Special attention was paid to the most critical phases - drying and sintering. Using the suspensions with adapted properties, resulting in similar green densities of the layers, step-graded discs and ball-heads were prepared. The results of the analysis showed, that the residual compressive stress at the alumina surface are typically 100-150 MPa that yield in a decreased wear rate. The test step-graded ball-heads that survived the machining reached the proposed burst strength. Reliability is, however, still low that indicates a need of optimisation of the process with special attention given to elimination of defects.

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