Micro-structure control in polycrystal MgAl2O4 transparent ceramic armours

The main objective of this thesis is to develop a sintering protocol for pressure assisted sintering systems that will allow to control the microstructure of MgAl2O4 ceramics to achieve high mechanical properties. For this purpose, it is necessary to understand the dominant sintering mechanisms of MgAl2O4. Quantitative sintering analysis were carried out by using modified creep equation to determine the sintering mechanisms. In these studies, performed at temperatures between 1200 and 1250 ºC, the stress exponent value for low densities (below 80%) was calculated as n≥3, indicating the dominant mechanism is plastic flow. For high densities (80-90%), the stress exponent is calculated as n=2, and the activation energy required for sintering is 530kJ/mol. The obtained data indicate that the dominant sintering mechanism for this region is the grain boundary sliding induced by oxygen diffusion. On the other hand, quantitative sintering analysis approach has been evaluated in pressure assisted sintering systems such as SPS (spark plasma sintering), HP (hot pressing). It has been studied how to eliminate possible errors and deviations that this analysis method causes, and a methodology has been developed to reduce the error margin to a minimum.