Papers by Author: Alpagut Kara

Abstract: An effective approach for preparing electrically conductive SiAlON-TiN composites was developed. Granules of a designed composition of α- SiAlON was obtained by spray drying and coated with varying amounts of TiO2 powder homogenously by mechanical mixing. Fully dense composites were obtained by spark plasma sintering (SPS) under a pressure of 50 MPa at 1650°C for 5min. According to the SEM analysis, unique microstructures containing continuously segregated in-situ formed TiN phase in 3-D were achieved. Additionally, XRD studies revealed that all TiO2 was successfully converted to TiN. The resistivity of the α-β SiAlON (1x1011 .m) was drastically reduced with the addition of only 5 vol. % TiO2 (2x10-4 .m).

Abstract: Si3N4-B4C composites containing fine and coarse B4C particles were produced using Al2O3 and Y2O3 as sintering additives via spark plasma sintering (SPS) technique. Phase assemblages of the produced composites were determined by XRD analysis. Si3N4, B4C and in situ formed SiC, h-BN and Si phases were observed. Even when incorporated in significant amounts, B4C was consumed readily in the Si3N4 based system. Consequently, full densification of these composites was found to be a very difficult task due to the simultaneous in-situ reactions, even in fast sintering process. Electrical resistivity measurements carried out at room temperature indicated that addition of both fine and coarse B4C particles decreased the electrical resistivity by several orders of magnitude due to the formation of electrically conductive in-situ phases, mainly SiC and metallic Si.

Abstract: 25α:75β SiAlON composition was designed with different cations and at different molar ratios. Effect of the type of cations both on the composition and the type of intergranular phase investigated after gas pressure sintering and further post sintering heat treatment.