LOW TEMPERATURE FABRICATION OF TRANSPARENT MAGNESIUM ALUIMINATE SPINEL BY HIGH PRESSURE SPARK PLASMA SINTERING

Magnesium aluminate spinet specimens were fabricated at temperatures lower than 1100 degrees C using a high pressure (up to 650 MPa) SPS approach. Nanostructured ceramics with grain size of 80-100 nm, in-line transmittance higher than 80% in the visible range and hardness higher than 18 GPa were successfully fabricated under applied pressure of 650 MPa at 1025 degrees C. Vickers hardness values obtained at wide loading range from 100 to 2000 g, remained constant and for the grain size between tens of microns and 80 nm the hardness values strictly follow the Hall- Petch relation. The fracture toughness of the SPS-processed magnesium aluminate spinet obtained by measuring the extent of cracking associated with a Vickers indentation is about 2.7 MPa.m(1/2) and doesn't depend on the average grain size in the 80-100 nm range.