| 1. |
- Antti, Marta-Lena, et al.
(author)
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Phase reactions in a hot pressed TiC/Si powder mixture
- 2012
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 38:3, s. 1999-2003
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Journal article (peer-reviewed)abstract
- This work investigated the possibility of producing dense Ti3SiC2 by hot pressing TiC/Si powders. A hot press with graphite heating elements was used for densification and the phase reactions of some hot pressed samples were further evaluated by pressureless heating in a dilatometer. The density and phase composition of the heat treated samples were evaluated using Archimedes principle and by x-ray diffractometry respectively. Hot pressing resulted in a low Ti3SiC2 yield; the main phases were TiC and TiSi2 regardless of starting powder composition, temperature, holding time or pressure. A second heating without pressure resulted in Ti3SiC2 formation, but only in samples initially hot pressed at 1300 °C or lower. At higher hot pressing temperatures, thin oxide layers on particle surfaces were locked into the structure. Acting as diffusion barriers, they prevented the Ti3SiC2 forming reaction. In hot pressed samples the density was significantly higher than in samples sintered without pressure.
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| 2. |
- Engberg, Göran, et al.
(author)
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Modeling microstructure development during hot working of an austenitic stainless steel
- 2013
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In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 753, s. 423-426
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Journal article (peer-reviewed)abstract
- A number of physically based models are combined in order to predict microstructure development during hot deformation. The models treat average values for the generation and recovery of vacancies and dislocations, recrystallization and grain growth and the dissolution and precipitation of second phase particles. The models are applied to a number of laboratory experiments made on 304 austenitic stainless steel and the model parameters are adjusted from those used for low alloyed steel mainly in order to obtain the right kinetics for the influence of solute drag on climb of dislocations and on grain growth. The thermodynamic data are obtained using Thermo-Calc© to create solubility products for the possible secondary phases. One case of wire rolling has been analyzed mainly concerning the evolution of recrystallization and grain size. The time, temperature and strain history has been derived using process information. The models are shown to give a fair description of the microstructure development during hot working of the studied austenitic stainless steel. © (2013) Trans Tech Publications, Switzerland.
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| 3. |
- Kero, Ida, et al.
(author)
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Carbon atmosphere effect on on Ti3SiC2 based composites made from TiC/Si powders
- 2010
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 36:4, s. 1259-1263
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Journal article (peer-reviewed)abstract
- The previous termeffect of carbonnext term activity and CO pressure in the furnace previous termatmospherenext term is investigated with respect to the phase reactions during heat treatment of TiC/Si powders. Special attention is given to the production and decomposition of Ti3SiC2. Samples were heated in graphite and alumina furnaces, connected to a dilatometer which enabled the in-situ analysis of the phase reactions. The phase compositions of the heat treated samples were determined by x-ray diffraction. The reducing previous termatmospherenext term of the graphite furnace enhanced the reactivity of the starting powder and enabled phase reactions to take place at a lower temperature than in the alumina furnace. TiSi2 and SiC phases formed at temperatures below the melting point of Si and were continuously consumed at higher temperatures. Ti3SiC2 formed at the melting point of Si regardless of furnace previous termatmosphere.next term No decomposition of the Ti3SiC2 was observed in either furnace.
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| 4. |
- Kero, Ida, et al.
(author)
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Effect of the amounts of silicon on the in situ synthesis of Ti3SiC2 based composites made from TiC/Si powder mixtures
- 2010
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 36:1, s. 375-379
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Journal article (peer-reviewed)abstract
- This paper describes how variations in silicon content and heat treatment influence on the phase composition of TiC/Si powder mixtures during heat treatment. The sintering procedure is investigated with respect to the phases produced with a particular emphasis on maximisation of the Ti3SiC2 content. The heat treated products have been analysed using scanning electron microscopy, energy dispersive spectroscopy and x-ray diffractometry. In the heat treated products Ti3SiC2 and TiC are the dominant phases and SiC and TiSi2 are found in smaller (0-30vol%) amounts. The composition was found to depend on both Si content and heat treatment temperature and time. The silicon content can be optimised with respect to maximum Ti3SiC2 production, but its value changes with different temperature programs. The highest amount (56 vol%) of Ti3SiC2 is achieved by heat treating powder mixtures of initial composition 3TiC/2.2Si at 1350° for 1 h. Heat treatment at lower temperatures (1250-1300 °C) results in an incomplete reaction and production of TiSi2.
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| 5. |
- Kero, Ida, et al.
(author)
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Phase reactions associated with the formation of Ti3SiC2 from TiC/Si powders
- 2011
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 37:7, s. 2615-2619
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Journal article (peer-reviewed)abstract
- The objective of this paper was to investigate the high temperature phase reactions that take place in a 3TiC/2Si powder mixture during heating. Special attention was paid to the formation of Ti3SiC2 and to the evaporation of gases. Differential scanning calorimetry and thermogravimetry were used for in situ analysis of the phase reactions. Samples were heated at a rate of 5 K/min to various temperatures between 890 and 1450 °C and then cooled at a rate of 20 K/min. Heat treated samples were analysed by X-ray diffractometry. The first phase to form was TiSi2, which was consumed in the Ti3SiC2 forming reactions. No decomposition of Ti3SiC2 was observed at temperatures below 1450 °C. Evaporation of CO(g) and small amounts of Si(g) were detected at 1430 °C.
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| 6. |
- Kero, Ida, et al.
(author)
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Preparation and firing of a TiC/Si powder mixture
- 2009
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In: 5th International EEIGM/AMASE/FORGEMAT Conference on Advanced Materials Research. - Bristol : IOP Publishing Ltd. ; 5, s. 012016-
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Conference paper (peer-reviewed)abstract
- This paper describes how the preparation and heat treatment of TiC/Si powders influences the phase reactions during firing. The powders are prepared by milling and some effects of powder preparation are discussed. A solid state displacement reaction according to: 3TiC + 2Si → Ti3SiC2 + SiC is a priori expected to take place during heat treatment. The firing procedure is investigated with respect to the effect of heat treatment time and temperature on the phases produced, especially Ti3SiC2. Samples were heat treated in a graphite lined furnace. Heat treated samples are analysed by x-ray diffraction, scanning electron microscope and energy dispersive spectroscopy. Ti3SiC2, TiC and SiC are dominant in the final products. The highest amount of Ti3SiC2 is achieved for short holding times (2-4 hours) at high temperatures (1350-1400°C). Ti3SiC2 appears to decompose at elevated temperatures or extended times, through a Ti3SiC2 → TiC + Si(g) type reaction. The activation energy of Ti3SiC2 phase formation is determined to be 289 kJ/mol, using the Mehl-Avrami-Johnson model.
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| 7. |
- Kero, Ida, et al.
(author)
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Synthesis of Ti3SiC2 by reaction of TiC and Si powders
- 2009
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In: Mechanical properties and processing of ceramic binary, ternary and composite systems. - Hoboken, NJ : John Wiley & Sons. - 9780470344927 ; , s. 21-30
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Conference paper (peer-reviewed)abstract
- The MAX phase Ti3SiC2 has been synthesized from starting powder mixtures which do not include pure titanium. The presence of pure titanium in a powder is problematic because of its oxidizing, and in the form of a finely divided powder, explosive nature. The aim of this study was to evaluate the synthesis of bulk polycrystalline samples of Ti3SiC2 from a starting powder mixture which is more suited for large scale production. Titanium silicon carbide MAX phase was synthesized by pressureless sintering of ball milled TiC and Si powders of six different compositions. The sintering reactions were evaluated in situ by dilatometer analysis under flowing argon gas. The as-sintered samples were evaluated using mainly x-ray diffraction (XRD) analysis. This study showed that titanium carbide, silicon carbide and titanium disilicide were present as intermediate or secondary phases in the samples.Our results indicate that TiSi2 is an intermediate phase to the formation of Ti3SiC2 when excess Si is present. The excess of silicon also proved beneficial for the synthesis of the MAX phase and there is a Si content which is optimal with respect to the maximum MAX phase content of the final product. The Ti3SiC2 was found to decompose into TiC and gaseous Si at high temperatures.
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| 8. |
- Kero, Ida
(author)
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Ti3SiC2 synthesis by powder metallurgical methods
- 2007
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Licentiate thesis (other academic/artistic)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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| 9. |
- Kero, Ida, et al.
(author)
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Ti3SiC2 Synthesis by Powder Metallurgical Methods
- 2007
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In: European School of Materials Science and Engineering, fourth research conference. - Barcelona : CPDA-ETSEIB. - 8496616207
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Conference paper (peer-reviewed)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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| 10. |
- Kero, Ida
(author)
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Ti3SiC2 synthesis from TiC and Si powders
- 2010
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Doctoral thesis (other academic/artistic)abstract
- The aim of this work was to produce Ti3SiC2 from TiC and Si powders and to investigate process parameters with respect to optimised Ti3SiC2 yield. The reaction pathway of Ti3SiC2 formation and the thermochemical degradation reactions were examined. Various material characterization and analysis methods have been applied, including x-ray diffractometry, dilatometry, calorimetry, scanning electron microscopy, energy dispersive spectroscopy and mass spectroscopy. Through the work performed it has been found that Ti3SiC2 may be produced in relatively large quantities (96.8 vol%) from TiC and Si powders. Short holding times (0-3 hours) and relatively high temperatures (1350-1400°C) produce the largest amounts of Ti3SiC2 when pressureless sintering is applied.The effect of varying the silicon contents on yield was investigated; excess silicon may be beneficial for the Ti3SiC2 yield if combined with appropriate heat treatments. TiSi2 is found to play a key role in the formation of Ti3SiC2 from TiC and Si powders. TiSi2 is present in samples heat treated at relatively low temperatures with short holding times. It is consumed in the formation of Ti3SiC2. Decomposition of Ti3SiC2 may occur at relatively low temperatures (1300°C) when there is oxygen present in the furnace atmosphere. The effect becomes more significant with long holding times (> 5 hours) and is also significant at very high temperatures (1500°C). When the partial pressure of oxygen is limited, no decomposition has been observed below 1450°C. At these temperatures, the presence of carbon in the furnace atmosphere induced no detrimental effect on the thermochemical stability of Ti3SiC2.
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