Investigation of sintering mechanisms of alumina using kinetic field and master sintering diagrams

Strain rates during sintering of alumina at different heating rates between 0.2 and 20 K/min have been measured non-contact using a thermooptical measuring technique. The shrinkage data were represented in a kinetic field diagram. It was shown that coarsening effects can be indirectly derived from the position and slope of iso-strain lines identified in the kinetic field. In addition temperature gradients which frequently lead to an erroneous interpretation of shrinkage kinetics were identified. Uni-axial loads up to 6 MPa were applied during sintering. The strain rates were measured parallel and perpendicular to the load. They were processed in separate kinetic field diagrams. It was shown that creep leads to a parallel shift of the iso-strain lines either to lower temperatures, for the strain rates parallel to the load, or to higher temperatures, for the strain rates perpendicular to the load. The individual kinetic field diagrams for a specific load were assembled in 3d, with the load used as z-axis. They formed a master sintering diagram (MSD) where the iso-strain lines were replaced by iso-strain surfaces. The parallel shift of the iso-strain lines with load enabled a simple representation of sintering kinetics for various loads during the entire range of densification, temperatures and heating rates.