Microstructural Characterization of Superplastic SiO₂‐doped TZP with a Small Amount of Oxide Addition

Abstract

The microstructures of 5 wt% SiO2‐doped TZP, 5 wt% (SiO2+ 2 wt% MgO)‐doped TZP, and 5 wt% (SiO2+ 2 wt% Al2O3)‐doped TZP are characterized by high‐resolution electron microscopy, energy‐dispersive X‐ray spectroscopy, and electron energy loss spectroscopy. An amorphous phase is formed at multiple grain junctions but not along the grain‐boundary faces in these three materials. A small addition of MgO and Al2O3 into the SiO2 phase results in a marked reduction in tensile ductility of SiO2‐doped TZP. This reduction seems to correlate with segregation of magnesium or aluminum ions at grain boundaries and a resultant change in the chemical bonding state.

Grain Boundary Energy and Tensile Ductility in Superplastic Cation-doped TZP

“…It has been reported that dopant cations are likely to segregate at grain boundaries in TZP. 10,11,27,28) The dependence of groove angle on dopant is supposed to result from segregation of dopant at grain boundaries.…”

“…As mentioned before, dopants are likely to segregate to grain boundaries in TZP. 10,11,27,28) The segregated dopant probably changes the covalent bonding state nearby grain boundaries. Effective covalency can be evaluated using total BOP of all bonds in a cluster.…”

“…On the other hand, it has been reported that the ductility of SiO 2 -doped TZP cannot be explained only from flow stress. [9][10][11] Recent studies have pointed out that covalent bonding states nearby grain boundaries correlate with the tensile ductility of TZP and Al 2 O 3 . [12][13][14] Further analyses to the grain boundaries are indispensable to fully understand the tensile ductility of TZP.…”

Mecanismos de deformación plástica en policristales cerámicos con fases secundarias vítreas

“…Basándose en resultados conocidos de la teoría de fluidos, estos autores derivan la siguiente ecuación de fluencia en tracción (15): [6] donde Q es una energía de activación efectiva y α un parámetro ajustable. De este modo se justifica la variación exponencial de la velocidad de deformación con la tensión aplicada, en buen acuerdo con buena parte de las observaciones experimentales.…”

“…La fase secundaria se localiza fundamentalmente en "bolsas" situadas en puntos de contacto entre varios granos (5)(6)(7). Además, una fracción de la fase secundaria vítrea se localiza también en las fronteras de grano, formando una película intergranular delgada (de entre 0.5 y 2 nm de espesor), capaz de soportar tensiones normales (8).…”