Functionally graded TiC-based cermets via combustion synthesis and quasi-isostatic pressing

Experimental results on the preparation of functionally graded TiC-based cermets obtained by combustion synthesis (also known as Self-Propagating High-Temperature Synthesis, SHS) followed by quasi-isostatic (QIP) pressing in a granulate medium are presented. Pellets of TiC-Fe graded cermets are produced by stacking layers of Ti and C powder mixtures in which the content of a NiFe alloy (50 wt% Ni and 50 wt% Fe) is varied from 5 up to 25 vol %. X-ray diffraction showed that the NiFe alloy did not react with the TiC, thus preserving its special properties. Scanning electron microscopy results show a graded material with pores increasing in size towards the side with the highest ceramic fraction

Spectroscopic studies of dynamically compacted monoclinic ZrO2

The properties of dynamically compacted monoclinic zirconia have been studied by X-ray powder diffraction, IR, Raman, EPR and luminescence spectroscopy. Compaction introduces a large number of defects into the sample, which leads to a broadening of the X-ray lines, and IR and Raman bands. Besides, Raman spectra of compacted samples recorded with both 1064 and 488 nm excitation show additional bands in comparison with original monoclinic zirconia. The bands in the region 540-730 nm with 488 nm excitation are ascribed to electronic transitions of Sm3+ ions. The nature of the extra bands in the 3000-1830 cm-1 region observed with 1064 nm excitation is unknown. Their intensity depends on the concentration of defects, but these bands are still observed for a sample containing no paramagnetic defects. In contrast to uncompacted zirconia, the EPR spectrum of the dynamically compacted material shows defects, most likely related to V′o (oxygen vacancies), which might be an indication for ionic conduction. As monoclinic zirconia is not an ionic conductor, it could be that shock-compaction introduces sample conductivity, e.g. ionic conduction, which can be important for the development of new applications such as batteries. © 1999 Published by Elsevier Science Ltd. All rights reserved