Probe characterization of ceramics: microstructure, chemistry, morphology, Projeto Tecnologias Italianas, Seminário sobre a Inovação de Produtos Cerâmicos Industriais

Innovative coatings, need to be investigated and understood by the use of a lot of different techniques; a huge amount of interest is concerned with the use of microscopy techniques due to: semi-quantitative elemental analyses coupled with morphological characterization, extended up to wide regions of interest and tracking while rising up magnification (from LM up to TEM resolution); low cost and quick response if proper sample preparation is used also for standard SEM analyses. Two case studies of combined LM, SEM, TEM, SPM and related techniques are presented. The first one is an example of thick coating and is related to the determination of microstructures and nano-phases obtained during the deposition of UHTC ZrB2-SiC composite mixture by Inert Plasma Spray (IPS). The use of ZrB2-SiC mixtures is aimed to promote the formation of a stable silica based oxides in order to protect ZrB2 from oxidation. Due to the lack of a stable liquid phase, these type of mixtures were supposed not to be suitable for plasma spraying. However, sample produced with this technique showed an almost complete retention of SiC within the sprayed deposit. Scanning and Transmission Electron Microscopy (BF, DF, SAD and Nanoprobe) were used to investigate coating microstructure and composition aimed to correlate mechanical properties (eg. toughness, hardness, wear behaviour) to IPS process parameters. The second one is an example of a thin coating and is related to the production of CrN/NbN superlattice coatings by Cathode Switching Reactive Cathodic Arc Evaporation (the term superlattice indicate a particular case of multilayer film that is a repeated layered structure of two materials with nanometric scale dimensions). High hardness and high fracture resistance as well as an improved corrosion resistance and decreased abrasive and erosive wear rates due to superlattice coatings are reported in literature for both metallic-ceramic and ceramicceramic couples, and their properties are strongly dependent on their nano/micro structure, especially on layers period. Also surface defects, formed during deposition, change in number and properties and this can be a further reason for the improved mechanical performances. Several microscopy and related Image Analysis techniques were used in this case study to characterize coating and its defects. Latter was investigated focussing on shape, dimension, density, clustering and other process-sensitive features. In CrN/NbN superlattice coatings a separation between defects and the surrounding bulk coating was evident, in fact SEM analysis revealed a different microstructure and chemical composition in this area.