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2001 | PATENTS
| INTERNET
| Barsoum M. W., El-Raghy T. Room Temperature Ductile
Carbides // Met. Mat. Trans. - 1999. - 30A. - 363-369. Large-grained, oriented, polycrystalline samples of Ti3SiC2 loaded in compression at room temperature deform plastically. When the basal planes are oriented in such a way that allowed for slip, deformation occurs by the formation of shear bands. The minimum critical resolved shear stress at room temperature is = 36 MPa. When the slip planes are parallel to the applied load - a situation where ordinary glide is impossible - deformation occurs by a combination of delamination of, and kink band formation in individual grains, as well as shear band formation. It is this unique multiplicity of deformation modes that allows the material to deform plastically in any arbitrary orientation. |
| Barsoum M. W., El-Raghy T., Farber L., Amer M., Christini R., Adams A. The
Topotactic Transformation of Ti3SiC2
into a Partially Ordered Cubic Ti(C0.67Si0.06)
Phase by the Diffusion of Si into Molten Cryolite
// J. Electrochem. Soc. - 1999. - 146(10). - 3919-3923. Immersion of Ti3SiC2 samples in molten cryolite at 960 °C resulted in the preferential diffusion of Si atoms out of their basal planes to form a partially ordered, cubic phase with approximate chemistry Ti(C0.67,Si0.06). The latter forms in domains, wherein the (111) planes are related by mirror planes; i.e., the loss of Si results in the de-twinning of the Ti3C2 layers. Raman spectroscopy, X-ray diffraction, optical, scanning and transmission electron microscopy all indicate that the Si exists the structure topotactically, in such a way that the C-atoms remain partially in their ordered position in the cubic phase. |
| Barsoum M. W., El-Raghy T., Rawn C. J., Porter W. D., Payzant A., Hubbard
C. Thermal Properties of Ti3SiC2
// J. Phys. Chem. Solids - 1999. - 60. - 429-439. The thermal properties of polycrystalline Ti3SiC2 in the 25-1000 °C temperature range determined by Rietveld refinement of high temperature neutron diffraction data, show that at all temperatures, the amplitudes of vibration of the Si atoms are higher than those of the Ti and C atoms. Up to 700 °C, the vibrations of the Si atoms are quite isotropic but the vibrations of the other atoms are greater along the c- than along the a-axis. The amplitudes of vibration of the Ti atoms adjacent to the Si atoms are higher and more anisotropic than for the other Ti atom sandwiched between the C-layers. Good agreement is obtained between the bulk thermal expansion coefficients measured by dilatometry, 9.1 (± 0.2) x 10-6 °C-1, and the values from the neutron diffraction results, 8.9 (± 0.1) x 10-6 °C-1. The thermal expansion coefficients along the a- and c-axes are, respectively, 8.6 (± 0.1) x 10-6 °C-1 and 9.7 (± 0.1) x 10-6 °C-1. The heat capacity is 110 J/mol K at ambient temperatures and plateaus at = 160 J/mol K by 1200 °C. The room temperature thermal conductivity is 37 W/m.K and decreases linearly to 32 W/m.K at 1200 °C. The thermal conductivity is dominated by delocalized electrons. |
| Barsoum M. W., Farber L., Levin I., Procopio A., El-Raghy T., Berner A. High-Resolution
Transmission Electron Microscopy of Ti4AlN3,
or Ti3Al2N2
Revisited // J. Amer. Ceram. Soc. - 1999.
- 82(9). - 2545-2547. The structure and chemistry of what initially was proposed to be Ti3Al2N2 are incorrect. Using high-resolution transmission electron microscopy, together with chemical analysis, the stoichiometry of this compound is concluded to be Ti4AlN3-d (where d = 0.1). The structure is layered, wherein every four layers of almost-close-packed Ti atoms are separated by a layer of Al atoms. The N atoms occupy ~97.5% of the octahedral sites between the Ti atoms. The unit cell is comprised of eight layers of Ti atoms and two layers of Al atoms; the unit cell is hexagonal with P63/mmc symmetry (lattice parameters of a = 0.3 nm and c = 2.33 nm). This compound is machinable and closely related to other layered, ternary, machinable, hexagonal nitrides and carbides, namely M2AX and M3AX2 (where M is an early transition metal, A is an A-group element, and X is carbon and/or nitrogen). |
| Crossley
J. A. A., Kisi E. H., Summers J. W. B., Myhra S. Ultra-Low
Friction for a Layered Carbide-Derived Ceramic, Ti3SiC2,
Investigated by Lateral Force Microscopy (LFM)
// J. Phys. D: Appl. Phys. - 1999. - 32(6). - 632-638. [no abstract] |
| El-Raghy
S. M., Waheed A. F., El-Raghy T. S., Barsoum M. W. Preliminary
Report on the Electrochemical Behavior of Ti3SiC2
// J. Mater. Sci. Lett. - 1999. - 18. - 519-520. Polycrystalline samples of Ti3SiC2 produced by reactive hot isostatic pressing of Ti, SiC and graphite were subjected to potentiodynamic polarization and linear polarization resistance. The corrosion tests were performed at room temperature in 10% H2SO4 , 3% NaCl and a 3% NaCl solution to which 1.5% sodium thiosulfate, (Na2S2O3) was added to evaluate the localized corrosion. The potentiodynamic polarization runs showed that the corrosion potentials of Ti3SiC2 in 10 % H2SO4 were more noble than the corrosion potentials in the other two solutions. The linear polarization technique showed a lower corrosion rate in 10% H2SO4 than the other two solutions. The corrosion rate of Ti3SiC2 in the 10% H2SO4 solution was lower than that of Ti metal; in the 3% solution it was higher. |
| El-Raghy T., Barsoum M. W. Processing and Mechanical
Properties of Ti3SiC2.
Part I: Reaction Path and Microstructure Evolution
// J. Amer. Ceram. Soc. - 1999. - 82(10). - 2849-2854. In this article, the first part of a two-part study, we report the reaction path and microstructure evolution during the reactive hot isostatic pressing of Ti3SiC2, starting with ti-tanium, SiC, and graphite powders. A series of interrupted hot isostatic press runs have been conducted as a function of temperature (1200°–1600°C) and time (0 –24 h). Based on X-ray diffractometry and scanning electron microscopy, at 1200°C, the intermediate phases are TiCx and Ti5 Si3 Cx . Fully dense, essentially single-phase samples are fabricated in the 1450°–1700°C temperature range. The time–tem-perature processing envelope for fabricating microstruc-tures with small (3–5 µm), large (~200 µm), and duplex grains, in which large (100–200 µm) Ti3SiC2 grains are embedded in a much finer matrix, is delineated. The mi-crostructure evolution is, to a large extent, determined by (i) the presence of unreacted phases, mainly TiCx , which inhibits grain growth; (ii) a large anisotropy in growth rates along the c and a directions (at 1450°C, growth nor-mal to the basal planes is about an order of magnitude smaller than that parallel to these planes; at 1600°C, the ratio is 4); and (iii) the impingement of grains. Ti3SiC2 is thermally stable under vacuum and argon atmosphere at temperatures as high as 1600°C for as long as 24 h. The influence of grain size on the mechanical properties is dis-cussed in the second part of this study. |
| El-Raghy T., Barsoum M. W., Zavaliangos A., Kalidindi S. R. Processing
and Mechanical Properties of Ti3SiC2.
Part II: Effect of Grain Size and Deformation Temperature
// J. Amer. Ceram. Soc. - 1999. - 82(10). - 2855-2860. In this article, the second part of a two-part study, we report on the mechanical behavior of Ti3 SiC2 . In particu-lar, we have evaluated the mechanical response of fine-grained (3–5 µm) Ti3SiC2 in simple compression and flex-ure tests, and we have compared the results with those of coarse-grained (100–200 µm) Ti3 SiC2 . These tests have been conducted in the 25°–1300°C temperature range. At ambient temperature, the fine- and coarse-grained micro-structures exhibit excellent damage-tolerant properties. In both cases, failure is brittle up to ~1200°C. At 1300°C, both microstructures exhibit plastic deformation (>20%) in flex-ure and compression. The fine-grained material exhibits higher strength compared with the coarse-grained material at all temperatures. Although the coarse-grained material is not susceptible to thermal shock (up to 1400°C), the fine-grained material thermally shocks gradually between 750° and 1000°C. The results presented herein provide evidence for two important aspects of the mechanical behavior of Ti3SiC2 : (i) inelastic deformation entails basal slip and damage formation in the form of voids, grain-boundary cracks, kinking, and delamination of individual grains, and (ii) the initiation of damage does not result in catastrophic failure, because Ti3 SiC2 can confine the spatial extent of the damage. |
| Farber
L., Levin I., Barsoum M. W. HRTEM Study of a
Low-Angle Boundary in Plastically Deformed Ti3SiC2
// Phil. Mag. Letters. - 1999. - 79(4). -
163-170. The dislocation structure of a typical low angle boundary associated with a kink band in a sample of Ti3SiC2 deformed at room temperature was studied by high resolution transmission electron microscopy. The boundary had both tilt and twist components. To account for both, the boundary was interpreted to be composed of parallel, alternating, mixed perfect dislocations with two different Burger's vectors lying in the basal plane at an angle of 120° relative to one another. The boundary twist was provided by having an excess of one type of dislocation. This hitherto unreported structure of a low-angle boundary is attributed to the fact that all dislocations are confined to the basal planes. |
| Farber
L., Levin I., Barsoum M. W., El-Raghy T., Tzenov N. High
Resolution Transmission Electron Microscopy Study Of Some Tin+1AXn
Compounds (n = 1, 2; A = Al Or Si; X = C Or N)
// J. Appl. Phys. - 1999. - 86. - 2543-2540. The crystal structures of Ti2AlN, Ti3SiC2 and Ti3AlC1.8, studied by high resolution transmission electron microscopy (HRTEM) confirmed the P63/mmc space group and the layered nature of these ternaries. The structure of Ti2AlN agrees with that previously determined from analysis of X-ray and neutron diffraction data. Conversely, the crystal structures of thinned Ti3SiC2 and Ti3AlC1.8 samples differ from the bulk structure as determined from X-ray and neutron diffraction analysis. Since both structures have identical symmetries and lattice parameters, the differences - which involve the shearing of the Si or Al planes in opposite directions - are indistinguishable by conventional transmission electron microscopy. This polymorphic phase transformation in the Tin+1AXn compounds, for n ³ 2, is discussed in relation to dimensionally induced hexagonal close-packed to face-centered cubic (HCP-to-FCC) phase transformations in Ti-based thin multilayers. |
| Feng
A., Orling T., Munir Z. A. Field-Activated Pressure-Assisted
Combustion Synthesis of Polycrystalline Ti3SiC2
// J. Mater. Res. - 1999. - 14(3). - 925-939. The simultaneous synthesis and densification of the ternary Ti3SiC2 was investigated by the field-activated, pressure-assisted combustion method. Depending on temperature and time at temperature, relatively pure and nearly fully dense materials can be synthesized by this approach. The optimum conditions to produce this phase were a reaction temperature of 1525 °C and a time at temperature of 2 h. The product contained TiC as a second phase at a level of Ê2 mol%. The resulting ternary phase has the typically elongated grains which were about 25 <>mm in size. Within a range of applied force of 1Ç4 N, the microhardness of the product was relatively constant, ranging from 6 to 7 GPa. Investigations on the thermal and chemical stabilities of the ternary were also conducted. Vacuum annealing at temperatures of 1600 and 2000 °C resulted in the formation of a surface layer of TiC, while the air-annealing at 1000 °C resulted in the formation of TiO2. Oxidation studies on the prepared Ti3SiC2 were made at temperatures ranging from 800 to 1100 °C. The results suggest a two-mechanism process, one dominating in the approximate range of 800°C - 950 °C and the other in the range 950 °C - 1100 °C with corresponding activation energies of 137.7 and 312.5 kJ. mol-1. The results are explained in terms of two proposed reactions on the basis of microprobe analyses. |
|
Finkl P., Barsoum M. W., El-Raghy T. Low Temperature
Dependence of Elastic Properties of Ti3SiC2
// J. Appl. Phys. - 1999. - 85. - 7123-7126. In this work, the Young’s, E, and shear, m, moduli of Ti3SiC2 are measured ultrasonically in the 20–300 K temperature range. At room temperature, Young’s, E RT , and shear, mRT , moduli are 32262 and 133.660.8 GPa, respectively. Poisson’s ratio is 0.2. Both moduli increase slowly with decreasing temperature and plateau out at temperatures below '130 K. A least square fit of the data yields, m/ mRT 5121.42310 24 (T2298) and E/ E RT 5120.95310 24 (T2298) for temperatures greater than 140 K. The elastic Debye temperature is estimated to be 427 K, which is significantly lower than the value of 620 K calculated from heat capacity measurements. |
| Gamarnik
M., Barsoum M. W. Bond Lengths in the Ternary
Compounds Ti3SiC2,
Ti3GeC2
and Ti2GeC //
J. Mater. Sci. - 1999. - 34. - 169-174. The interatomic distances in the ternary compounds Ti3SiC2, Ti3GeC2 and Ti2GeC have been determined precisely by comparing the lattice parameters of Ti3GeC2 and Ti2GeC, on the one hand and Ti3GeC2 and Ti3SiC2, on the other. The assumptions made were that the Ti-Ge and Ti-C distances in the Ge-containing phases were identical, and that the differences in the Ti-Si and Ti-Ge distances in Ti3SiC2 and Ti3GeC2 phases were equal to the differences in the covalent radii of Si and Ge. And while the results clearly show that the TiC octahedra in the ternary phases are distorted, the extent of that distortion is smaller than previously reported. The extent of the distortion was found to depend on the type of atoms surrounding the TiC6 octahedrons; the deformation is larger in the Ge-containing than in the Si-containing compounds. However, the Ti-C-Ti distances appear to be insensitive to nature of the compound. |
| Gao
N. F., Miyamoto Y., Zhang D. Dense Ti3SiC2
Prepared by Reactive HIP // J. Mater. Sci.
- 1999. - 34(18). - 4385-4392. [no abstract] |
| Grigoryan H. E., Rogachev A. S., Sytschev A. E., Levashev E. A. SHS
and Composites Structure Formation in the Ternary Systems Ti-Si-C,
Ti-Si-N, Ti-B-N // Ogneupory i technicheskaya ceramica. - 1999.
- 11. - 7-11. (Russian). [no abstract] |
| Grigoryan
H. E., Rogachev
A. S. Some Peculiarities of Combustion
and Structure Formation in the Ternary Systems Ti-Si-C (Ti-SiC), Ti-Si3N4
and Ti-BN /
Proc. V Int. Symp. on Self-Propagating High-Temperature Synthesis
(SHS-99). - Moscow, Russia, 1999. New precursors for producing nitrides, carbides, and borides in SHS regime are proposed. The dependence of combustion velocity on composition of the initial mixture have been studied. The critical significance of mass ratios of the green mixture has been found. The maximum of combustion velocity has been found in the study of the dependence of the combustion velocity on density. Upon study of density effect on the SHS mode and combustion velocity, some new types of front instability were observed. They arise due to increase of green mixtures porosity. Microgravity conditions allows us to attain lower porosities for both the green mixture and product. This task was resolved experimentally on board Mir space station in January 1998.The optimum concentration ranges favorable for the production of the Ti3SiC2-based ceramics during combustion were determined. |
| Ho
J. C., Hamdeh H. H., Barsoum M. W. Low Temperature
Heat Capacities of Ti3Al1.1C1.8
,Ti4AlN3,
and Ti3SiC2
// J. Appl. Phys. - 1999. - 86. - 3609-3611. For the binary Ti–Al system, an ordering transformation in Ti3Al has been shown to result in a significant lowering of the electronic heat-capacity coefficient, g, by removing electrons from conducting states. When gis normalized to a per Ti atom basis, the same tendency is found in low temperature calorimetric studies of the conducting ternary carbides Ti3Al1.1C1.8, Ti4AlN3, and Ti3SiC2 reported herein. As a consequence of C- or N-induced covalent-like bond formation, the Debye temperatures in these ternaries are in excess of 700 K. |
| Ho
J. C., Hamdeh H. H., Barsoum M. W., El-Raghy T. Low
Temperature Heat Capacity of Ti3SiC2
// J. Appl. Phys. - 1999. - 85. - 7970-7971. Calorimetric measurements between 2 and 10 K have been made on Ti3SiC2. The molar heat capacity, c, data can be fitted to the sum of an electronic and a lattice contribution: c5 gT 1 bT 3 . The b value of 0.049 mJ/mol K 4 yields a Debye temperature of 620 K, typical of high stiffness and hardness ceramic materials such as TiC. This value is significantly higher than the Debye temperature measured from elastic measurements. The g value of 5.21 mJ/mol K 2 is a measure of the density of states at the Fermi level. This value, when normalized to a per Ti atom basis, is higher than that of TiC0.97, but roughly half that of Ti metal, implying that covalent-type bonding induced electron localization increases in going from Ti to Ti3SiC2 to TiC. It also partially explains the excellent electrical and thermal conductivities of Ti3SiC2. |
| Jondo
Yun, Hwancheol Bang, Cheolho Go, Tae-Hyeon Choi, Bongseob Kim. Preparation
of Carbide Fiber-Reinforced Composites by High Pressure Combustion
Sintering / 5th International Symposium on SHS, Moscow, Russia,
1999. Alumina ceramic or titanium metal composites reinforced with short fibers of titanium carbides were fabricated by high pressure combustion sintering method. The dense body of titanium matrix composites were produced by the self-propagating high temperature synthetic reaction between carbon fibers, and excessive titanium powders, under the conditions of high pressure and electrothermal heating. It was found that the fiber shape was well maintained after the reaction, and the fibers were aligned due to the pressure. The fibers were either of carbon with carbide shell, or all carbide, depending on the reaction time and temperature. Alumina ceramic matrix composites with carbide fibers were also fabricated in the same way from aluminum, titania powders and carbon fibers. The EDS analysis showed that the thin layers of aluminum oxycarbide were formed between the carbon core and carbide shell in case of C-TiC-Al2O3 composites. Mechanical properties, such as a strength, fracture toughness, and hardness were investigated and discussed in terms of the microstructure and compositional variation along the interface between the fibers and matrix. |
| Kooi B. J., Kabel M., Kloosterman A. B., De Hosson J. Th. M. Reaction
Layers Around SiC Particles In Ti: An Electron Microscopy Study
// Acta mater. -1999. - 47(10). - 3105-3116. A detailed description is given of the microstructure of the top layer of Ti±6Al±4V with SiC particles embedded with a high-power Nd:Yag laser system. Scanning electron microscopy (SEM), as well as conventional, analytical and high-resolution transmission electron microscopy (TEM) were used. An existing controversy about the presence or absence of Ti3SiC2 in the reactive SiC/Ti systems is clarifed and the frst observations of Ti5Si3 precipitation on stacking faults in Si supersaturated TiC are reported. The Si released during the reaction SiC+Ti4TiC+Si results in the formation of Ti5Si3. If in the reaction layer regions in between the TiC grains become enclosed, the rejected Si content increases locally and Ti3SiC2 plates with dominant (0001) facets nucleate. In the TiC grains particularly of the cellular reaction layer, a high density of widely extending stacking faults of the order of 100 nm is observed and on these faults in many instances small Ti5Si3 precipitates are present. |
| Li
J. T., Miyamoto Y. J. Fabrication of Monolithic
Ti3SiC2 Ceramic Through Reactive Sintering of Ti/Si/2TiC //
Mater. Synth. Process. - 1999. - 7(2). - 91-96. [no abstract] |
| Li
J.-F., Sato F., Watanabe R. Synthesis of Ti3SiC2
Polycrystals by Hot-Isostatic Pressing of the Elemental Powders
// J. Mater. Sci. Lett. - 1999. - 18(19). - 1595-1597. [no abstract] |
| Lihrmann J.-M., Tirlocq J., Descamps P., Cambier F. Thermodynamics
of the Al-C-O system and properties of SiC - AlN - Al2OC
composites // J. Europ. Ceram. Soc. - 1999.
- 19(16). - 2781-2787. Based on a recent thermodynamic evaluation of the Al-O-C system, the standard Gibbs free energies of formation of both aluminium oxicarbides Al4O4C and Al2OC are given, and a classical stability diagram is shown at 2100 K. Because Al2OC is unstable below 1715°C, the stable wurtzite compound 2AlN·Al2OC has been preferred, and formed in-situ as the second phase in SiC-based composites. Starting with commercial powders of a-SiC, AlN, Al2O3 and Al4C3, dence materials are obtained by pressureless sintering (up to 2020°C) or hot-pressing (up to 1950°C), owing to the liquid phase from Al2O3-Al4C3 system. The existence of miscibility gap is shown, and the microstructures are fine grained and equiaxed. Compared with SiC-Al2OC alloys, the hot pressed materials with 90 wt% SiC exhibit slightly higher mechanical properties and a good retention nearly up to 1500°C. |
| Lis J. Ceramic Nanolaminates Based on Ti3SiC2
//
Internet Journal of the High Pressure School,
Proc. IHPS3, Warsaw, 13-16 Sept. 1999. Composites with layered structures – laminates, because of specific properties, have an important, permanent place in a materials science research. Recently, an interesting group of laminates have been discussed and developed. They are called nanolaminates because of layered structure in a nanoscale. The paper summarises author’s works on preparation and testing of a new group of nanolaminates -ceramics based on Ti3SiC2. A possibility of preparation of sinterable Ti3SiC2 powders by Self-Propagating High-temperature Synthesis (SHS) from powdered substrates is shown. The powders can be densified into Ti3SiC2 -based polycrystals using pressureless sintering or hot-pressing. The final materials have a very specific laminar character in nano and micro scale. Such structure can be correlated with a relatively low hardness, high elastic modules, high fracture toughness, and high corrosion and thermal shock resistance. The examples of preparation of ceramic composite nanolaminates built with Ti3SiC2 and TiC using HIP and functionally gradient materials (FGM) Ti3SiC2- SiC by HP are discussed. |
| Meyer
F. D., Hillebrecht
H. Konstitutionsuntersuchen im System
Al / Si / C und der Einbau von BN im sogennanten 12R-Al4SiC4
// Werkstoffwoche 98, Verlag Wiley-VCH, Weinheim, Band 7 (1999). -
413 - 416. [no abstract] |
|
Meyer F. D., Hillebrecht H. Konstitutionsuntersuchen
im System Al / C / N und die Herstellung von blauem AlN //
Werkstoffwoche 98, Verlag Wiley-VCH, Weinheim, Band 7 (1999). - 425
- 430. [no abstract] |
| Myhra
S., Summers J. W. B., Kisi E. H. Ti3SiC2
- A Layered Ceramic Exhibiting Ultra-Low Friction
// Mater. Lett. - 1999. - 39(1). - 6-11. [no abstract] |
| Onodera
A., Hirano H., Yuasa T., Gao N. F., Miyamoto Y. Static
compression of Ti3SiC2
to 61 GPa // Applied Physics Letters - 1999.
- 74(25). - 3782-3784. Synchrotron x-ray diffraction measurements have been made on hexagonal crystal Ti3SiC2 under pressures up to 61 GPa and at room temperature. No phase transition was observed within the pressure range studied. Both the a and c axes exhibited decreases with pressure, accompanied by a decrease in the c/a ratio to about 50 GPa, beyond which the ratio increased. The bulk modulus deduced from the volume-versus-pressure data was 206 ± 6 GPa (with its pressure derivative 4.0 ± 0.3), being close to that of TiC. |
| Radhakrishnan
R., Williams J. J., Akinc M. Synthesis and High-Temperature
Stability of Ti3SiC2
// J. Alloys Compd. - 1999. - 285(1-2). - 85-88. [no abstract] |
| Sun
Z., Zhang Y., Zhou Y. Synthesis of Ti3SiC2
Powders by a Solid-Liquid Reaction Process //
Scripta Materialia - 1999. - 222. - 41(1). - 61-66. Ti3SiC2 is a novel ceramic material, which combines the merit of both metals and ceramics. Like metals it is thermal and electrical conductive, easy to machine with conventional tools, and resistant to thermal shock; like ceramics it has high strength, high melting point and thermal stability (1). Ti3SiC2 has hexagonal crystal structure with space group of P63/mmc. The theoretical density of Ti3SiC2 is 4.53g/cm3 and the melting point exceeds 3000 °C. The measured Young’s modulus is 320 GPa and microhardness is 4 GPa (2). Despite the remarkable properties, synthesis of Ti3SiC2 is difficult. Jeitschko et al (3) synthesized pure Ti3SiC2 through chemical reaction between TiH2, Si and graphite, but the method is limited to laboratory scale by its efficiency. Recently, a number of methods including self-propagating high temperature synthesis (SHS) (4), arc-melting (5) and solid-state reaction (6) have been utilized to synthesize Ti3SiC2. In most of these methods carbides (e.g. TiC or SiC) and silicides (e.g. Ti5Si3 , TiSi2 ) were co-existing with Ti3SiC2 in the product. Thus work is needed to develop new methods for the synthesis of Ti3SiC2. In this paper, a solid-liquid process for the formation of Ti3SiC2 powders was reported. The starting materials are Ti, Si and graphite powders, and the liquid phase was formed by the addition of fluorite, i.e., NaF. The Ti3SiC2 powders prepared using this process were characterized by X-ray diffraction and scanning electron microscopy. The effect of synthesis temper-ature on the composition of the reaction products was investigated by quantitative X-ray analysis. |
| Sun
Z., Zhou Y. Ab Initio Calculation of Titanium
Silicon Carbide // Phys. Rev. B, Condens. Matter - 1999. -
60(3). - 1441-1443. The electronic structure and properties of the layered ceramic Ti3SiC2 have been examined by ab initio linear combination of atomic orbital calculations. With the calculated results we predict that the electronic conductivity of Ti3SiC2 is metallic and anisotropic. The major factors governing the electronic properties are hybridized Ti 3d, Si 3p, and C 2p states and the p-d bonding stabilizes the structure. |
| Sun
Z., Zhou Y. Fluctuation Synthesis and Characterization
of Ti3SiC2
Powders // Mater. Res. Innovations - 1999.
- 2(4). - 227-231. A novel fluctuation method for the synthesis of Ti3SiC2 powders was developed. The raw materials used in this process are Ti, Si, and graphite powders. Fluctuation synthesis utilized Si as in-situ liquid forming phase (additive), which was formed by heating the powder mixtures to 1300°C and using the heat released from the exothermic reaction for Ti3SiC2 formation. The result demonstrated that the reaction time for the formation of Ti3SiC2 was dramatically shortened using fluctuation method and the powders produced using this method contained more than twice amount of Ti3SiC2 compared to the solid reaction synthesized powders. The powders prepared by fluctuation method are fiber-like in morphology with dimensions of 0.8-2 µm in width and 5-10 µm in length. The growth direction of the fiber-like Ti3SiC2 particulate is {101-1}*. The lattice parameters for Ti3SiC2 were determined by a trial-and-error method and are a=3.067 Å and c=17.645 Å. |
| Tomasi R., Munir Z. A. Effect of High-Energy Milling
Reactant on the Combustion Synthesis of Ti3SiC2
/ Proc. V Int. Symp. on Self-Propagating High-Temperature Synthesis
(SHS-99). - Moscow, Russia, 1999. The Ti3SiC2 is one interesting material due its high thermal and chemical resistance and good machinability and ductility at elevated temperatures. Most of the solid-state synthesis of Ti3SiC2, including the combustion synthesis, has resulted in the presence of TiC, TiSi2 or SiC as second phase. Although the reported good stability of the Ti3SiC2 up to 1600oC, the formation of a second phase during solid phase synthesis has explained by decomposition of the ternary phase at the temperature range of the synthesis process. In the combustion synthesis the velocity and the stability of combustion wave propagation can be significantly improved by decreasing reactant particle size. High-energy milling can also mechanically activate the reactivity in solid state process. In this work, it was studied the effect of high-energy milling the mixture of Ti, Si and graphite on the combustion synthesis of Ti3SiC2. Reactant mixtures were milled at different time and ball to powder mass ratio and the transformations during milling were characterized by X-ray diffraction. The combustion synthesis experiments were performed in cylindrical pressed pellets. It was observed the significant effect of milling on propagation velocity, probably due both the reactant particle size and the partial transformations, by mechanically induced reaction, during milling. The correspondent effect was also observed for final microstructure. |
| Tsuchida
T., Azuma Y. Oxidation Behavior of (Al2OC)1-x(AlN)x
and AlN in TG-DTA // Thermochimica Acta. -
1999. - 334(1/2). - 67-71. [no abstract] |
| Zhang
Y., Sun Z., Zhou Y. Cu/Ti3SiC2
Composite: a New Electrofriction Material
// Mater. Res. Innovations - 1999. - 3(2). - 80 -84. Cu/Ti3SiC2 composite, a new electrofriction material, was prepared, for the first time, by PM method. The microstructure, mechanical and electrical properties of the Cu/Ti3SiC2 composites were investigated and were compared with those of Cu/graphite composites. The results demonstrated that Cu/Ti3SiC2 composites had superior mechanical properties over Cu/graphite composites. At filer content of less than 20 vol%, the electrical conductivity for Cu/Ti3SiC2 composites was higher than that for Cu/graphite composites; at high filer content, the electrical conductivity for Cu/Ti3SiC2 composites was lower than that for Cu/graphite composites because of the presence of residual pores. It was found that like Cu/graphite composite, Cu/Ti3SiC2 was a self-lubricated material. The compressive yield strength, Brinell hardness, relative ratio of compressive for Cu-30 vol% Ti3SiC2 composites are 307 MPa, 140, 15.7% respectively. |
| Zhou Y., Sun Z. The Compressive Property and Brittle-to-Ductile
Transition of Ti3SiC2
Ceramics // Mater. Res. Innovations - 1999.
- 3(3). - 171-174. Compressive tests of polycrystalline Ti3SiC2 were performed from room temperature to 1423 K at strain rates of 1×10-4 s-1 and 2.5×10-5 s-1, respectively. The effect of strain rates on high-temperature compressive property was also investigated. Polycrystalline Ti3SiC2 exhibited positive temperature dependence of flow stress (flow stress anomaly) and showed a temperature peak at 1173 K. The brittle-to-ductile transition temperature (BDTT) for polycrystalline Ti3SiC2 was strain-rate sensitive, an approximately 100 K decrease in transition temperature was associated with four times of magnitude decrease in strain rate. In addition, the fracture morphology changed from predominately intergranular to mostly transgranular. The mechanism responsible for the brittle-to-ductile transition in Ti3SiC2 was involved in the onset of a thermally activated deformation process. |
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Zhou Y., Sun Z. Microstructure and Mechanism
of Damage Tolerance for Ti3SiC2
Bulk Ceramics // Mater. Res. Innovations -
1999. - 2(6). - 360-363. Titanium silicon carbide (Ti3SiC2) is a damage tolerance material that is expected to be used in a number of high temperature applications. In this work, the microstructure and damage tolerance mechanism of Ti3SiC2 was investigated. The result demonstrated that the Ti3SiC2 ceramics prepared by the in-situ hot pressing/solid-liquid reaction process had a dual microstructure, i.e., large laminated grains were distributed within small equiaxial grains. This microstructure is analogous to that of platelets reinforced ceramic matrix composites. The bending test using single-edge-notched-beam specimens revealed that Ti3SiC2 was a damage tolerance material. The damage tolerance mechanisms for Ti3SiC2 are basal plane slip, grain buckling, crack deflection, crack branching, pull-out and delamination of the laminated grains. |
