P. Henits

Structural characterization of gel-derived calcium silicate systems

The main aim of this study is to synthesize calcium silicate ceramics that exhibit suitable properties to be used for biomedical applications. In the present work, attention was paid to the understanding of processing-structure relationships. A particular effort was made to clarify the identification of Ca-O-Si bonds by means of spectroscopy. The calcium silicate systems were prepared via a sol-gel route, varying the chemical compositions, the catalyst concentration, and the temperature and time of aging and heat treatment. The processes and the phases evolved during the sol-gel procedure were determined. The bond systems were investigated by Fourier transform infrared (FTIR) and (29)Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and the aggregate structures by scanning electron microscopy (SEM), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and X-ray diffraction (XRD) measurements.

Microstructural characterization of the crystallization sequence of a severe plastically deformed Al-Ce-Ni-Co amorphous alloy

Discs of Al85Ce8Ni5Co2 amorphous alloy were severely deformed by high pressure torsion. Severe plastic deformation exceeding equivalent strain of 8.2 induces the formation of nanocrystalline fcc-Al in a more stable residual amorphous matrix. Calorimetric and X-ray diffraction measurements revealed that the deformed outer part of the disc crystallizes into a mixture of equilibrium phases during the first thermal event. However, in the amorphous ribbon the same crystalline mixture develops only after the second stage.

Correlation between microstructural evolution during high-pressure torsion and isothermal heat treatment of amorphous Al85Gd8Ni5Co2 alloy

þ a-Al phase mixture to primary a-Al by increasing the annealingtemperature above 555 K. This thermal sensitivity predestinates the composition toidentify the controversial thermal contribution of the plastic deformation in metallicglasses. Thermal stability and structure of the partially devitrified samples weresystematically analyzed and compared by calorimetry, x-ray diffraction, and electronmicroscopy. It seems that the effect of severe deformation cannot be singled out by asimple isothermal heat treatment; i.e., high-pressure torsion acts as a spectrum of heattreatments performed at different annealing temperatures.I. INTRODUCTIONAmorphous Al-based aluminum–transition-metal–rare-earth alloys (Al–TM–RE) have successfully beensynthesized over a wide composition range in the lastdecades.

Nanocrystallization in Al85Ce8Ni5Co2 amorphous alloy induced by heat treatment and severe plastic deformation

Al85Ce8Ni5Co2 metallic glass ribbon was devitrified by heat treatments just below its glass transition temperature and by severe plastic deformation applying ball milling and high pressure torsion. Evolution of the microstructure, thermal stability and further thermal history were compared for the different devitrification processes. Based on this mapping of phase selection processes, microstructural changes can be predicted for high temperature and/or high stress compaction which are often required for application of this light weight alloy.