Nanoscale stacking fault–assisted room temperature plasticity in flash-sintered TiO ₂

Abstract

Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures and fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here, we have investigated the deformability of TiO2 prepared by a flash-sintering technique. Our in situ studies show that the flash-sintered TiO2 can be compressed to ~10% strain under room temperature without noticeable crack formation. The room temperature plasticity in flash-sintered TiO2 is attributed to the formation of nanoscale stacking faults and nanotwins, which may be assisted by the high-density preexisting defects and oxygen vacancies introduced by the flash-sintering process. Distinct deformation behaviors have been observed in flash-sintered TiO2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed.

Linking far-from-equilibrium defect structures in ceramics to electromagnetic driving forces

“…17,18 The application of electric elds also led to high oxygen atomic displacement parameters attributed to the presence of oxygen defects, 19 phase transitions to substoichiometric Magnéli phases in TiO 2 , 20 and improved plasticity in TiO 2 due to eld-induced stacking faults. 21 While these studies represent a growing body of literature reporting on the multiscale effects of EM elds on materials, they do not directly connect external eld parameters to changes in local atomic structure and phase stability.…”

Far-from-equilibrium effects of electric and electromagnetic fields in ceramics synthesis and processing

“…However, in conventional ceramics, the fracture strain is low at room temperature and increases with temperature. 27 the order of 10 2 K/s enable the ultrafast densification. 29 The Raj et al article introduces the possible generation of Frenkel defects, electroluminescence, and the critical power density, 28 and the article by Guillon et al discusses fundamentals of nonthermal effects.…”

“…57 Electric fields created metastable cubic structures in yttria-stabilized ZrO 2 , 25 phase transitions to oxygen deficient Magnéli phases in TiO 2 , 102 and enhanced mechanical properties of ceramics through defect-mediated inelastic deformation mechanisms. 27 The article by Phuah et al in this issue describes in situ studies on the temperature-dependent transition of deformation mechanisms that can produce room temperature plasticity in TiO 2 from stacking faults, potentially generated under the electric field. MWR exposure leads to a decrease in the Sn-Cl/O peak intensity (vertical dashed line) relative to the starting intensity, which is not observed in the conventional synthesis condition.…”

“…At room temperature, micropillars of flash-sintered TiO 2 could deform plastically up to a strain of 8%, unlike conventionally sintered samples that fractured elastically at 2% strain (Figure 1c). 27 We do not fully understand if these abnormal albeit technologically appealing phenomena can be attributed simply to ultrahigh heating/cooling rates that emerge during synthesis or if far-from-equilibrium effects of a nonthermal nature, such as the hypothesized field-induced nucleation of defects, are involved. [1][2][3]17 The articles in this issue of MRS Bulletin focus on direct electric fields, particularly for densification and sintering.…”

Flash sintering of additively manufactured 3YSZ gears

“…1 Additionally, flash-sintered (FS) ceramics have shown improved mechanical deformability at room temperature compared to their conventional-sintered counterparts due to additional defects, such as dislocations and stacking faults, introduced during flash sintering. 2,3 Although flash sintering has many advantages over conventional sintering, the applications of this technique are limited by several factors, one of which is the sample geometry. Currently, the most common sample geometry used for the flash sintering process is dog-bone shape 1,[4][5][6] since the electrical contacts can be easily provided to opposing ends of the dogbone and the electrical current can flow uniformly through the thin cross section of the gauge area.…”