Microstructural examination in high-strain-rate superplastically deformed tetragonal ZrO₂ dispersed with 30 vol% MgAl₂O₄ spinel

Abstract

The role of MgAl 2 O 4 spinel particle dispersion for attaining high-strain-rate superplasticity (HSRS) was examined in tetragonal ZrO 2 . Microstructural examination shows that the dispersed spinel particles provide the following positive factors to ZrO 2 simultaneously: (i) stable fine grain size by retarding grain growth due to pinning effect; and (ii) enhanced accommodation due to accelerated lattice diffusivity caused by the dissolution of aluminum and magnesium into ZrO 2 from the spinel particles, and accelerated relaxation of stress concentrations exerted by grain boundary sliding through dislocation motion. These positive factors make it possible to attain HSRS in ZrO 2 .

Development of High-Strain-Rate Superplastic Oxide Ceramics Based on Flow Mechanism

“…Figure 2(a) shows the typical TEM image of the ZrO 2 -30vol% spinel composite [22,23]. The fine spinel particles disperse homogeneously among the ZrO 2 grains.…”

“…2(b)]. The grain elongation became remarkable as deformation proceeds [22]. An important feature of the deformed substructure was activated intragranular dislocations, including aligned dislocations and sub-boundaries both in ZrO 2 and in the spinel grains [22,23].…”

“…For the present composite, since dislocation motion can also be observed in the present composite, the rate of deformation may be controlled by the slower dislocation recovery process limited by the lattice diffusion within harder ZrO 2 grains rather than within spinel grains. For the ZrO 2 -spinel composite, the lattice diffusivity of cations in ZrO 2 grains is enhanced by the dissolution of aluminum and magnesium [22]. This contributes to the accelerated recovery process of the dislocations and thereby accelerates the rate of deformation, resulting in HSRS.…”

Thermodynamic Strengthening of Heterointerfaces in Nanoceramics

“…This is a challenging experiment because multiphase oxides are expected to show limited coarsening as compared to single phase nanoceramics, limiting the heat released during the calorimetric study. 3,5,32,33 Figure 3 shows the DSC signal for the doped and undoped biphase composite upon heating. A distinguishable exothermic peak (or combination of many) is observed for both doped and undoped samples.…”

“…That is, no parallel reactions, redox, decomposition, or strain relaxation can take place, as previously discussed. ,, Here, we have applied this technique for the first time in a two-phase system, and the energetics of coarsening of the nanocomposite with and without the dopant were studied by carrying out the process inside a DSC (see the Supporting Information). This is a challenging experiment because multiphase oxides are expected to show limited coarsening as compared to single phase nanoceramics, limiting the heat released during the calorimetric study. ,,, …”