Papers by Author: S.R. Kushan

Abstract: In this study, effect of seed addition on the microstructural development of Y-Sm α-SiAlON system has been investigated. Besides using pre-produced rod-like α-SiAlON seeds, growth in the glassy phase and harvested by chemical treatment, powdered Y-Sm/α-SiAlON was also used as nuclei. Microstructural results of both systems were compared with un-seeded samples. It was found that the powdered α-SiAlON addition has also caused the acicular α-SiAlON grain formation, which indicates the dominant effect of thermodynamic stability on the preferential growth of α-SiAlON grains in the c direction.

Abstract: In this study, textured α-SiAlON ceramic was produced by templated grain growth process. In order to enhance the alignment of the seeds, gated tape casting arrangement was utilized. Y-Ce codoped seeds were synthesized to induce the preferred orientation. For the production of the seeds, Ce3+ was used as a sintering additive due to its well-known effect on the formation of elongated α-SiAlON grains. In addition, Y3+ was used to stabilize Ce3+ in α-SiAlON structure. Gated tape casting arrangement was also used to enhance the alignment of the seeds in the green tape. After the lamination and sintering, preferentially aligned α-SiAlON grains were observed by the microstructural investigation. In addition, XRD results obtained from the planes parallel and perpendicular to the casting direction indicated the alignment of grains in α-SiAlON ceramics. Hardness measurements also confirmed that the alignment of the grains results in 8% increase in hardness value of the plane perpendicular to the casting direction with respect to that of the parallel one.

Abstract: In the present work, multi-cation doped (Sr2+-Mn4+) SiAlON ceramics were investigated. The mixture was sintered at in a gas pressure sintering furnace (GPS). XRD results showed that sintered samples were composed of β and α-SiAlON phases and this result is also confirmed by back scattered SEM images. EDX analysis of the individual α-SiAlON grains showed that Mn can incorporate into the α-SiAlON structure when it is codoped with Sr.