Papers by Author: D. Grossin

Abstract: In the field of advanced ceramics, Spark Plasma Sintering (SPS) is known to be very efficient for superfast and full densification of ceramic nanopowders. This property is attributed to the simultaneous application of high density dc pulsed current and load, even though the sintering mechanisms involved remain unclear. In the first part of the paper, the mechanisms involved during SPS of two insulating oxide nanopowders (Al₂O₃ and Y₂O₃) are discussed while in the second part illustrations of the potential of SPS will be given for (i) Consolidation of mesoporous or unstable nanomaterials like SBA-15 or biomimetic apatite, respectively; (ii) Densification of core (BT or BST)/shell (SiO₂ or Al₂O₃) nanoparticles with limited or controlled reaction at the interface. (iii) In-situ preparation of surface-tailored Fe–FeAl₂O₄–Al₂O₃ nanocomposites, and finally (iv) One-step preparation of multilayer materials like a complete thermal barrier system on single crystal Ni-based superalloy.

Abstract: The orientation distributions of α-Al2O3 textured ceramics are determined from neutron diffraction and SEM-EBSD. A curved position-sensitive detector coupled to a tilt angle (χ) scan allowed the whole neutron diffraction pattern treatment in the combined Rietveld-WIMV-Popa algorithm. Analyses from neutron and electron diffraction data gave similar results if EBSD data are smoothed to account for grain statistics. Four textured alumina ceramics were prepared by slipcasting under a high magnetic field and sintered at 800°C, 1300°C, 1400°C and 1600°C. The inverse pole figures and EBSD-mapping highlights the influence of the magnetic field and sintering temperature on the texture development. The inverse pole figures calculated for the fiber direction show a major (001) component for all the samples. With the increasing sintering temperature, the texture strength is enhanced and the c-axis distribution is sharper. The effectiveness of the combined approach for determining the crystallite size is also evident. As a global trend, the calculated crystallite size and observed grain size are similar and increase with the increasing sintering temperature. The mechanism of the texture development in the sintered specimens is certainly initiated from the preferred orientation of the green body after slip-casting under a high magnetic field. The basal texture is enhanced during sintering by selective anisotropic grain growth. We evidenced here the powerfulness of the Rietveld texture analysis correlated to SEM-EBSD calculation to provide a basis for the correlation of texture, microstructural parameters and anisotropic properties.