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- Kero, Ida
(författare)
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Ti3SiC2 synthesis by powder metallurgical methods
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The MAX phases constitute a group of ternary ceramics which has received intense attention over the last decade due to their unique combination of properties. The Ti3SiC2 is the most well studied MAX phase to date and it has turned out to be a promising candidate for high temperature applications. It is oxidation resistant, refractory and not susceptible to thermal shock, while at the same time it can be machined with conventional tools which is of great technological importance. Most attempts to synthesize bulk Ti3SiC2 have involved pure titanium in the starting powder mixtures, but Ti powder is oxidising and requires an inert atmosphere throughout the synthesis process which makes the procedures unsuitable for large scale production. The aim of the first part of this study was to delineate the influence of sintering time and temperature on the formation of Ti3SiC2 from a starting powder which does not contain pure titanium. Titanium silicon carbide MAX phase was synthesised from ball milled TiC/Si powders, sintered under vacuum for different times and temperatures. After heat treatment the samples were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD). This study showed that TiC was always present in the final products whereas TiSi2 was an intermediate phase to the Ti3SiC2 formation. The highest amount of Ti3SiC2 was achieved for short holding times of 2-4 hours, at high temperatures, 1350-1400¢ªC. More elevated temperatures or extended times resulted in silicon loss and decomposition of Ti3SiC2. In the second part of this study the sintering reactions and the mechanisms of formation of Ti3SiC2 were investigated by x-ray diffractometry, thermodilatometry, thermogravimetry, differential scanning calorimetry and mass spectrometry. TiC/Si powders of the different ratios; 3:2 and 3:2.2, were heated to different temperatures under flowing argon gas in a dilatometer and examined by XRD. The TiC/Si powder samples of the ratio 3:2 were further investigated by the other thermal analysis methods. The results confirmed the presence of the intermediate phase TiSi2. From 1500¢ªC silicon evaporation and MAX phase decomposition were observed, and the results show that the MAX phase formation may be concurrent with the melting of silicon. TiC was always present in the final products, either as a reactant or as a decomposition product. The extra silicon of the 3:2.2 TiC/Si powder significantly increased the Ti3SiC2 conversion and no intermediate phases were observed for this powder mixture. The Si of these samples did not melt or evaporate, and only minor decomposition was observed even at 1700¢ªC. These results indicate that the silicon content of the initial powder mixture is decisive to the reaction mechanisms of the sintering process.
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| 2. |
- Kero, Ida, et al.
(författare)
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Ti3SiC2 Synthesis by Powder Metallurgical Methods
- 2007
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Ingår i: European School of Materials Science and Engineering, fourth research conference. - Barcelona : CPDA-ETSEIB. - 8496616207
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Konferensbidrag (refereegranskat)abstract
- Titanium silicon carbide MAX phase was synthesised by a powder metallurgical method from ball milled TiC/Si powders of two different compositions, with TiC/Si ratios of 3:2 and 3:2.2 respectively. The cold pressed samples were analysed by dilatometry under flowing argon or sintered under vacuum for different times. The sintered samples were evaluated using x-ray diffraction (XRD). This study showed that titanium carbide was always present as a secondary phase and silicon carbide accompanied the Ti3SiC2 formation. Titanium silicide was observed in the samples of TiC/Si ratio 3:2 and is suggested to be an intermediate phase to the Ti3SiC2 formation in these samples. The melting of Si is essentially concurrent with the MAX phase formation in these samples and the evaporation of Si with its decomposition. The activation energy of Ti3SiC2 formation from 3TiC/2Si starting powders was determined to be 289 kJ/mol, using the Mehl-Avrami-Johnson model.The samples of TiC/Si ratio 3:2.2 extra silicon resulted in Ti3SiC2 of higher purity and the Si of the samples did not melt or evaporate. Furthermore, the thermochemical stability of the samples was increased by the extra silicon.
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