Anomalous high activation energy for creep in nanostructured 3YTZP/Ni cermets

The plastic behavior of cermets based on a 3 mol% yttria-stabilized tetragonal zirconia matrix that incorporates nanometric nickel inclusions (3YTZP/n-Ni), with 2.5, 5 and 10 vol.% of nickel content, has been studied by constant load tests in compression carried out in argon atmosphere. The microstructure of these composites consists of nanometric nickel inclusions homogeneously dispersed into a fine-grained zirconia matrix (about 200 nm). The microstructural and mechanical results obtained show that the creep behavior is controlled by the zirconia matrix as in 3YTZP-based cermets with micrometric Ni inclusions (3YTZP/μ-Ni); whereas the stress exponent values are similar to those of high-purity monolithic 3YTZPs, anomalous high values of the activation energy have been measured. The ceramic/metal interface plays a crucial role for creep properties; the strong TZP/n-Ni interface matching can be at the origin of these high values of the activation energies for creep.Ministerio de Educación y Ciencia MAT2003-04199-CO

Slow crack growth resistance and bridging stress determination in alumina-rich magnesium aluminate spinel/tungsten composites

International audienc

Epitaxial growth of tungsten nanoparticles on alumina and spinel surfaces

International audienceIsolated tungsten nanoparticles (a-W and ß-W phase) were synthesized and epitaxially grown on alumina and spinel particle surfaces with an average tungsten size of =20 nm for a low tungsten content (of =1.5 vol%). Using tungsten (VI) ethoxide alcoholic solutions, tungsten trioxide hydrated precursors were attached to a ceramic grains surface as a nanoparticle coating. High-resolution transmission electron microscopy (HRTEM) micrographs showed epitaxial interfaces between alumina, spinel and metallic tungsten. This epitaxial growth is assumed to be due to the effect of water vapour on the sublimation of ortho-tungstic acid during the reduction process in a hydrogen atmosphere. The planes involved in the epitaxy were found to be (220) Al2O3||(121)W and (311)MgAl2O4||(110) W