Experimental Investigations and Thermodynamic Evaluation of the Sn-Cu-O System (original) (raw)
2001, Key Engineering Materials
Thermodynamic calculations of the structural-phase equilibrium in the Ti-Si-C system at 1100-1400°C are performed using the CALPHAD method. Calculated phase diagrams of this system are presented. It is established that 100% of the Ti 3 SiC 2 phase is formed with the stoichiometric component ratio. With the deviation of the carbon or silicon content, titanium carbide, titanium disilicide, or silicon carbide appear in the system. The temperature almost does not affect the phase composition in the studied temperature range. The calculated data are compared with the experimental determination of the phase composition of the samples of the mentioned system after the spark-plasma sintering of the mechanically activated powder composition. In practice, the process temperature and duration of high-temperature holding substantially affect the phase composition of the final product, which is associated with the limited rate of solid-phase reactions during the synthesis of compounds. The samples have a grain size of 1-5 μm and hardness of 4-15 GPa, depending the phase composition.
Related papers
Preparation and firing of a TiC/Si powder mixture
IOP Conference Series: Materials Science and Engineering, 2009
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 → Ti 3 SiC 2 + 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 Ti 3 SiC 2. 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. Ti 3 SiC 2 , TiC and SiC are dominant in the final products. The highest amount of Ti 3 SiC 2 is achieved for short holding times (2-4 hours) at high temperatures (1350-1400ºC). Ti 3 SiC 2 appears to decompose at elevated temperatures or extended times, through a Ti 3 SiC 2 → TiC + Si(g) type reaction. The activation energy of Ti 3 SiC 2 phase formation is determined to be 289 kJ/mol, using the Mehl-Avrami-Johnson model.
The effect of preceding mechanical alloying on titanium silicon carbide (Ti 3 SiC 2 ) formation from a powder mixture of 5Ti/2Si/3C through spark plasma sintering technique as well as the mechanical property of the bulk material was investigated in this paper. The results showed that mechanical alloying can significantly improve the density of the obtained bulk material via the particles refinement as well as the microhardness by increasing the TiC content. The corresponding relative density of the spark plasma sintered samples from elemental powders of Ti/Si/C and the previously mechanically alloyed ones were calculated to be respectively 93.20% and 99.82%. The measured microhardness values of the different samples were respectively about 462 and 955 Hv.
Phase reactions associated with the formation of Ti3SiC2 from TiC/Si powders
Ceramics International, 2011
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 Ti 3 SiC 2 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 8C 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 TiSi 2 , which was consumed in the Ti 3 SiC 2 forming reactions. No decomposition of Ti 3 SiC 2 was observed at temperatures below 1450 8C. Evaporation of CO(g) and small amounts of Si(g) were detected at 1430 8C.
Ti 3 SiC 2 was elaborated by two different methods: (i) Spark plasma sintering of 5Ti/2SiC/C powders and (ii) mechanical alloying of powders followed by Spark plasma sintering. The results showed that mechanical alloying was not advantageous for pure Ti 3 SiC 2 formation but it can significantly improve the density of the obtained bulk material via the particles refinement as well as the microhardness by increasing the TiC content. It was found that the relative density was increased up to 98.58% for the sintered mechanically alloyed sample whereas it was not more than 96.04% for the sintered 5Ti/2SiC/C starting powders. The Vickers microhardness measured for both bulk samples demonstrates a high improvement for the previously mechanically alloyed powder mixture, as it was of about 1282 Hv and only 581.2 Hv for the alloy obtained from 5Ti/2SiC/C starting powders.
Journal of Advanced Ceramics, 2019
In this paper, the synthesis of Ti 3 SiC 2 from SiC/Ti powder using reactive spark plasma sintering (R-SPS) in the temperature range of 1300-1400 ℃ is reported. The results show that the purity of Ti 3 SiC 2 is improved up to 75 wt% when the holding time is increased from 10 to 20 min at 1400 ℃. The thermodynamic and experimental results indicate that Ti 3 SiC 2 formation takes place via the reaction of a pre-formed TiC phase with the silicides, formed from the eutectic compositions. Detailed analysis of mechanical behaviour indicates that samples with higher percentage of secondary phases exhibit higher microhardness and better resistance compared to the near single phase Ti 3 SiC 2 .
Synthesis of Ti3SiC2 by Reaction of TiC and Si Powders
Ceramic Engineering and Science Proceedings, 2009
The MAX phase Ti 3 SiC 2 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 Ti 3 SiC 2 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 TiSi 2 is an intermediate phase to the formation of Ti 3 SiC 2 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 Ti 3 SiC 2 was found to decompose into TiC and gaseous Si at high temperatures.
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2010
Binary phase TiC/Ti3SiC2 composites have been synthesized by reactive hot-pressed sintering (HPS) with the aim of developing a new hard product. Raw powders of TiC, Ti and Si with compositions 2TiC/1Ti/1Si (2:1:1) and 2TiC/1Ti/1.1Si (2:1:1.1) have been used as the starting materials for the synthesis. The phase content and microstructure of synthesized composites have been analyzed using X-ray diffractometer (XRD) and scanning electron microscope (SEM). The mechanical properties such as four-point flexural strength and fracture toughness have been investigated for different processing parameters. The phase content (Ti3SiC2:TiC) of the composite synthesized from (2:1:1) powder vary from (81:19) to (71:29) with the hot pressing temperature increased from 1500 to 1700 °C. This sample exhibits maximum flexural strength of 627 MPa and fracture toughness of 6.84 MPa m1/2. The maximum apparent density is found to be 4.65 g/cm3 for this sample at optimum hot pressing temperature of 1500 °C. The composite synthesized from (2:1:1.1) composition shows improvement in the mechanical properties compared to 2:1:1 composition. The relationship between the phase content and mechanical properties has been investigated.
The liquidus temperatures and enthalpies of fusion for Cu–Sn alloys are systematically measured across the whole composition range by differential scanning calorimetry (DSC). The liquidus slope vs. Sn content is derived on the basis of the measured results. The measured enthalpy of fusion is related to the Sn content by polynomial functions, which exhibit one maximum value at 55 wt.% Sn and two minimum values around 28.9 wt.% Sn and 90 wt.% Sn, respectively. The undercoolability of those liquid alloys solidifying with primary a (Cu) solid solution phase is stronger and can be further enhanced by increasing the cooling rate. However, other alloys with the preferential nucleation of intermetallic compounds display smaller undercoolings and are not influenced by cooling rate. Microstructural observations reveal that peritectic reactions can rarely be completed. With the increase in undercooling, the primary a (Cu) dendrites are refined in the peritectic Cu–22 wt.% Sn alloy. For the hyperperitectic Cu–70 wt.% Sn alloy, typical peritectic cells are formed in which the peritectic g(Cu 6 Sn 5) phase has wrapped the primary e(Cu 3 Sn) phase. The DSC curves of metatectic-type Cu–Sn alloys indicate that the metatectic transformation c ! e + L upon cooling is an exothermic event, and a large undercooling of 70 K is required to initiate this transformation in metatectic Cu–42.5 wt.% Sn alloy. The metatectic microstructures are characterized by (e + g) composite structures. The g phase is mainly distributed at the grain boundaries of the coarse e phase, but are also dispersed as small particles inside e grains. The volume fraction of the g phase increases with the Sn content.
Experimental investigation and thermodynamic assessment of the Cu–Sn–Ti ternary system
Calphad
The Cu–Sn–Ti ternary system has been studied via experiments and thermodynamic modelling. In the experimental section, the composition of the alloys was selected based on the preliminary calculations and available literature data. Metallography, scanning electron microscopy and electron probe microanalysis were employed to analyse alloy samples prepared by arc-melting after annealing at 800 °C for 760 h. Solid phase relations at 800 °C were established. In contrast to earlier reports, the CuSn3Ti5 phase was interpreted as a binary intermetallic compound (Sn3Ti5) with extended Cu solubility. In the modelling section, three binary sub-systems were critically evaluated and updated according to the new experimental data and theoretical calculations reported in literature. According to their crystal structures and homogeneity ranges, appropriate sublattice models were proposed for SnTi3,SnTi2,Sn3Ti5 and Sn5Ti6. A set of self-consistent thermodynamic parameters for the Cu–Sn–Ti ternary sy...
Transactions of the Indian Ceramic Society, 2018
Liquid phase sintering (LPS) often yield an amorphous grain boundary region which deteriorates the high temperature properties of the sintered ceramics and thus ceramists prefer to obtain a crystalline grain boundary after LPS. This paper deals with LPS of silicon carbide ceramics to near theoretical density, understanding the densification behavior, evolution of gehlenite phase and subsequent evaluation of their mechanical properties. High density SiC ceramics were fabricated from submicrometre -SiC powders with the aid of refractory phase forming metal oxide additives by spark plasma sintering. Sintering temperature and holding time at peak temperature were varied to study their effect on densification and mechanical properties. Density of the sintered ceramics reached ~97% at 1800 o C. Microstructural features and crack propagation mode were studied using scanning electron microscopy. XRD analysis confirmed the presence of crystalline gehlenite phase in the sintered samples. Hardness, fracture toughness and flexural strength of the sintered ceramics were determined by standard test procedures.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.