Superplasticity and Joining of Zirconia-Based Ceramics

Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1,250 and 1,350 C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1,200 C

High-temperature mechanical behavior of proton-conducting yttrium-doped barium zirconate perovskite

International audienceThe high-temperature mechanical properties of yttrium doped barium zirconate obtained by two different routes are reported in this work. Polycrystals with composition BaZr0.85Y0.15O2.925 have been fabricated from nanopowders synthesized by a modified EDTA-citrate complexing method and conventionally sintered at 1600 °C for 24 h. The material exhibits a single cubic perovskite phase, with a homogeneous, dense and fine-grained microstructure consisting of equiaxed grains with an average size of 0.2 μm. Mechanical tests were carried out in compression between 1100 and 1325 °C in air at constant initial strain rate and at constant load. As the temperature increases and/or the strain rate decreases, a gradual transition from brittle-to-ductile behavior was found. In the brittle regime, the fracture is governed by an intergranular failure mode. In the ductile region, grain boundary sliding is the main deformation mechanism, characterized by a stress exponent of 2 and an activation energy of 570 kJ/mol

Influence of indium on the dissociation of dislocations in GaAs at high temperature

Dislocations have been introduced in GaAs doped with indium, by plastic deformation between 773 K and 1 373 K. Transmission electron microscope observations have shown that indium increases the width of dissociation. This can explain the reduction of as-grown dislocations in In doped GaAs.Des dislocations ont été introduites dans GaAs dopé à l'indium par déformation plastique entre 773 K et 1 373 K. Des observations en microscopie électronique en transmission ont montré que l'indium augmente la largeur de dissociation. Cela permet d'expliquer la réduction de densité de dislocations de croissance dans GaAs dopé à l'indium

Superplasticity and joining of zirconia-based ceramics

Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1,250 and 1,350 C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1,200 C

Electron microscopy characterization of yttrium-doped barium zirconate electrolytes prepared with Ni additive: Influence of hydrogen treatment

International audienceProton‐conducting Fuel or Electrolysis Cells (PCFCs) are thought to be a promising alternative to Solid Oxide Fuel/Electrolysis Cells [1‐2]. The most interesting proton conducting materials for electrolytes include doped barium zirconate, doped barium cerate or their solid solution. Recently, an innovative approach was proposed which allowed obtaining dense ceramics with grain size of typically 2‐4 µm. This new process is based on the reactive sintering of all oxide precursors with the use of NiO as sintering aid [2‐4]. Besides being dense, the samples obtained, such as yttrium‐doped barium zirconate (BZY), show a very high proton conduction with little influence of Ni‐species on conduction properties.We tested the mechanical properties of this BZY material for application as PCFCs electrolyte and we showed that materials made from this process present a fast degradation of mechanical properties when put in hydrogen‐rich conditions.The objective of the present work was thus to understand the atomic‐scale origin of this fast degradation. For this purpose, different electron microscopy techniques have used such as Scanning Transmission Electron Microscopy (STEM‐HAADF), Energy dispersive spectroscopy (EDS), Electron Energy Loss spectroscopy (EELS). Structural and chemical microscopy analysis show that the sample failure is due to the reduction of NiO nanoparticles at grain boundaries (Figure 1, 2)