Effect of the Granule Properties and Compaction Pressure on the Green and Sintered Densities of Al₂O₃/15vol% ZrO₂

Abstract

The dependence of green and sintered densities of zirconia-toughened alumina (ZTA: Al2O3/15vol% ZrO2) on the properties of spray-dried granules and compaction pressures was studied to differentiate the domi nant processing parameter controlling sintered properties. Two sets of spray-dried granules, which differed largely in terms of the morphology and yield stress of granules, were compacted at various uniaxial pressures in the range of 80MPa to 120MPa. The green and sintered densities varied depending on the granule properties and compaction pressure. However, both sets of granules formed by cold isostatic press ing at 500MPa exhibited the same green and sintered densities of about 63% and 99%, respectively, relative to the theoretical density, regardless of the variation of granule properties. This work confirmed that high cold isostatic pressure could overcome the effect of granule properties on the green and sintered densities. The strength of sintered specimens was determined from the size of large hollows in the spray-dried granules remaining after compaction. Details of the compaction behavior in terms of the granule properties were discussed.

Morphology of alumina granules obtained by spray freeze drying with twin‐fluid atomization

“…At a pressure of 100 MPa, delamination was detected between a layer of material close to the punch and the volume of the material. Similar granule behavior was shown 36 when pressing SD ZTA granules without binder additives. Next, we observed delaminations in the pressing of SFD granules that did not include a binder additive or included a 4‐wt.% PVA.…”

Characterization and production of slip casts mullite–zirconia composites

“…It is thought that this causes the reactions not to be completed especially during sintering at 1450 °C since packing and intergranular interactions between grains in a composition containing 45% solids by weight are low. One possible mechanism is segregation of particles of different sizes, which is increased when solid loading is low and, thus, hindered settling is reduced [27,28]. Another reason for this situation is the lack of any additive in the prepared mixture.…”