Grain Growth Phenomena in the Interface Region of α‐Alumina Bilayer Composites

Abstract

Microstructural development in the interface region of ␣-Al 2 O 3 bilayer composites has been systematically investigated in terms of the sintering additive CaO-SiO 2 , residual impurity level in the starting powders (particularly MgO), and sintering conditions. The interfacial microstructure is strongly related to relative CaO-SiO 2 doping levels in the two constituting layers and to residual impurities in the starting powders. The presence of high levels of impurities in the starting powder can substantially modify the features of CaO-SiO 2 -Al 2 O 3 liquid at the interface region, thereby strongly influencing ␣-Al 2 O 3 grain growth across the interface. Three grain growth modes in the interface region thus have been identified for different combinations of impurity level and CaO-SiO 2 dopant in the ␣-Al 2 O 3 bilayer. This provides an important mechanism for controlling two-dimensional structures in coatings, films, and layered ceramic materials for various engineering applications.

Surface Modification and Microstructure Design of Alumina Ceramics

“…(d), we believe that the presence of MgO effectively increase the diffusivity and the orientation growth of the Al 2 O 3 –MgO–SiO 2 liquid, which is in good agreement with previous work . The anisotropic phenomena are similar to what have been found in the Al 2 O 3 –CaO–SiO 2 system . Figure (f) shows the alumina surface modified by the TiO 2 /SiO 2 slip.…”

“…The mechanisms of the surface microstructure modification are akin to those when those oxides are added uniformly in the ceramic powders before sintering. However, special “boundary” effects may exist as shown previously and also in the present study, and such effects should be further explored. The preliminary results show that MgO and SiO 2 inhibit alumina grains growth, whereas TiO 2 promotes the grain growth.…”

“…Our proposed method utilizes the micro‐porous feature of an alumina green body pre‐sintered at 1000°C, and deposits ultra‐low‐density sintering additive slips onto the micro‐porous substrate, so that the microstructures of the surface layer can be specially designed. It should be pointed out that the “boundary‐effect” of sintering additives can be very different from that in a bulk ceramic as shown by the special effects on alumina grain growth in the interfacial region of bi‐layer alumina composites …”