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Microwave sintering and characterization of alumina and alumina matrix ceramic nanocomposites

Kayıplar, Burcu
Efficiency of microwave heating on the sintering of ceramic materials has been investigated in comparison to conventional processing. Monolithic alumina with or without sintering additives such as MgO, CaO, Y2O3 were fabricated by both conventional and microwave sintering at temperatures ranging from 1000°C to 1600°C with a constant soaking time of 1 hour. Based on the densification results on monolithic alumina, nanometer-sized SiC or stabilized ZrO2 particle-dispersed alumina matrix ceramic nanocomposites were sintered by both methods at 1300°C and 1500°C for 1 hour. Sintered ceramic materials were characterized in terms of densification, microstructural evolution, chemical composition and mechanical properties such as hardness and indentation fracture toughness. Microwave sintering was determined to be a remarkably effective method in the production of Al2O3 ceramics at considerably low temperatures (≤1400°C) compared to conventional sintering in achieving enhanced relative densities reaching to ~97% with improved microstructural characteristics and mechanical properties. Usage of sintering additives at temperatures higher than 1400°C was determined to be effective in densifiying Al2O3 by both methods. Second phase particle incorporation yielded poor densification resulting in a decrease of hardness of the fabricated ceramic nanocomposites; however, their fracture toughness improved considerably caused by the crack deflection at the dispersed particles and grain boundaries reaching to ~4 MPa·m1/2 in the case of SiC particledispersed nanocomposites. Compared to conventional sintering, microwave sintering is more effective in the processing of alumina and alumina matrix nanocomposites leading to similar densification values along with improved microstructural and mechanical characteristics at lower temperatures in shorter soaking periods.