Spark plasma sintering of alumina: Study of parameters, formal sintering analysis and hypotheses on the mechanism(s) involved in densification and grain growth

Sintering behavior of spark plasma sintered alumina with graphene nanoplatelet reinforcement

“…8b that the sintered grain size is smaller when the applied pressure is higher, which is contrary to the literature on the pressure effects on alumina [43,46,47,52] where sintered grain size is generally observed to stay the same or increase with increasing pressure. A mechanism for the observed behavior is proposed here and presented schematically in Fig.…”

“…The variable 'm' is the grain growth exponent [46], m ¼ 2 is used here as this corresponds to grain boundary diffusion. Volume diffusion (m ¼ 3) typically occurs for liquid phase diffusion, which is unlikely in the present case as GNP survive and no signs of liquid or glassy phases are observed.…”

“…SPS has been shown to fully densify a variety of ceramic systems effectively including Al 2 O 3 [43][44][45][46][47][48][49][50][51] often with improvements in mechanical and functional behavior. Alumina consolidated by SPS has been shown to have superior hardness [43], fracture toughness [43,49], plasticity [44,48] and optical translucency [47] compared to conventionally processed alumina.…”

Effect of amount of doping agent on sintering, microstructure and optical properties of Zr- and La-doped alumina sintered by SPS

“…Consequently, diffusion mechanisms of Al 3+ cations along these grain boundaries should be favoured. Some authors [28][29][30][31] have proved that the densification of ␣-alumina by SPS is controlled by grain boundary diffusion but the rate controlling species are not known for certain. Currently, no studies have been able to ascertain whether aluminium grain boundary diffusion is greater or smaller than oxygen grain boundary diffusion.…”

Fabricação de ferramentas de corte em gradação funcional por Spark Plasma Sintering (SPS).

“…A temperatura é medida por um pirômetro que só é sensível a valores acima de 570ºC, quando a máquina de SPS procura elevar a temperatura no ciclo térmico em função do tempo, uma forte descarga elétrica com tensão proporcional é aplicada aos pós e um segundo pico (2) pode ser notado na curva de taxa de deslocamento, temperatura, corrente e um leve aumento no deslocamento. Isto pode ser um indicativo de centelhamento (spark) causando um adicional rearranjo de partículas como observa Tokita (2000) e Santanach et al (2011), uma vez que a pressão já estava estabilizada em 80 MPa. Na sequência verifica-se uma nova descarga de corrente elétrica e a formação de um novo pico (3), um pouco mais destacado para o FGM AlZr do que para o FGM AlTiC.…”