Effect of Internal Lubricants on Defects in Compacts Made from Spray-Dried Powders

The role of internal lubricants in the closure of large intergranular pores during dry-pressing was investigated. Alumina was spray-dried with and without an internal lubricant to yield granules with similar characteristics other than lubricant effects. Green and sintered microstructures were evaluated at different compaction pressures. The defects were quantified by evaluating the fracture surface of ∼90% dense sintered compacts. The samples that contained an internal lubricant had higher green densities and fewer defects at comparable compaction pressures. The internal lubricant did not cause any significant reduction in green strength or increase in springback.