Multiscale aspects of the influence of yttrium on microstructure, sintering and creep of alumina

Titanium effect on phase transformation and sintering behavior of transition alumina

“…During this transition, the increase in densification rate is attributed, in the case of yttrium, to an increase in intergranular diffusivity resulting from an yttrium supersaturation at GBs leading to precipitation. 24,[53][54][55] Similar mechanisms with precipitation of Al 2 T i O 5 can be invoked for Ti-doped alumina. The temperature of this additional densification rate peak is higher for lower doping levels.…”

“…[18][19][20] Doping elements have generally a low solubility limit in ␣-alumina and segregate to grain boundaries (GBs) or precipitate when the GBs are saturated. [21][22][23][24] ␥-Alumina is a metastable phase with an open spinel structure that is known to incorporate a larger amount of various doping elements than ␣-alumina does. 25,26 Doping procedure should be considered in regards of this incorporation: sol-gel and coprecipitation are better routes than impregnation way.…”

Atomistic modeling of dopant segregation in α-alumina ceramics: Coverage dependent energy of segregation and nominal dopant solubility

“…Both dopants are known to decrease grain growth during sintering 42,43 and increase the high-temperature creep resistance [44][45][46][47][48][49] of ␣-alumina. Grain boundary segregation rather than second phase precipitation is the cause of these effects, as they occur below the solubility limit.…”

“…Grain boundary segregation rather than second phase precipitation is the cause of these effects, as they occur below the solubility limit. 43,46,47,50 Initial suggestions that La dopants promote the formation of low-energy, low-Σ boundaries could not be substantiated 38 and the prevalent opinion in recent literature is that both dopants reduce grain boundary diffusion 21,38,47,48 and grain boundary dislocation climb/slide 33,49 due to site blocking. Due to the higher segregation energy calculated here and elsewhere 35,36 the interface concentration of La at the same overall dopant concentration and grain size is expected to be higher than for Y.…”

Disconnection arrays in a rhombohedral twin in α-alumina

“…In fine-grained alumina, the main deformation process is grain boundary sliding, which involves GB dislocation glide and climb, processes that are controlled by GB diffusion [1,2]. Indeed, it has been found that the number of dislocation arrays in GBs increases after deformation.…”