Stacking behavior of the close-packed Ta-atom planes and its effects on formation of 'hybrid grains' in TaC0.66-0.7 ceramics
| Autor: | Faqiang Shi, Yujin Wang, Jinfu Ma, Jiandong Wu, Limeng Liu, Zhonghua Li |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
010302 applied physics
Materials science Process Chemistry and Technology Diffusion Stacking 02 engineering and technology 021001 nanoscience & nanotechnology Hot pressing 01 natural sciences Surfaces Coatings and Films Electronic Optical and Magnetic Materials chemistry.chemical_compound Crystallography Fracture toughness chemistry Phase (matter) visual_art 0103 physical sciences Materials Chemistry Ceramics and Composites visual_art.visual_art_medium Ceramic 0210 nano-technology High-resolution transmission electron microscopy Tantalum carbide |
| Zdroj: | Ceramics International. 46:19092-19102 |
| ISSN: | 0272-8842 |
| DOI: | 10.1016/j.ceramint.2020.04.244 |
| Popis: | In previous works, it was found hard to synthesize “phase pure” ζ-Ta4C3-z at relatively low temperatures even by prolonged heating, though ζ-Ta4C3-z was believed stable till decomposition at ~2130°C. When the samples were subjected to TEM, vast richness of locally disordered structures in close relation with stacking of the close-pacted Ta-atom planes was observed. Although kinetic factors including diffusion of C atoms/vacancies and re-stacking of the Ta-atom planes explain the densely disordered structures, the richness of local disorders is a scenario that shows cohabitant of the cubic, rhombohedral, and hexagonal structures in a single grain, i.e. formation of a “hybrid grain” consisted of the three symmetries, indicating a transitional or intermediate stage before complete formation of the final phase of rhombohedral ζ-Ta4C3-z. This time tantalum carbide ceramics TaCx with C:Ta atomic ratios x = 0.66 and 0.7 were prepared by reaction hot pressing of TaC and Ta powder mixtures. 5–30 mol% Cu/Ag additives and heat treatments were used to reproduce “hybrid grains” to facilitate further TEM and HRTEM observations on the disordered hybrid grains to argue for the transitional/intermediate stage. The cohabitant cubic, rhombohedral, and hexagonal structures in single grains may also help explain the difficulty in identification of the various phases by XRD in the transitional/intermediate stage of ζ-Ta4C3-z reaction. Microstructural evolution and fracture toughness of the composites were also investigated. |
| Databáze: | OpenAIRE |
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