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2001 | PATENTS
| INTERNET
| Alexandrescu
R., Borsella E., Botti S., Cesile M. C., Martelli S., Giorgi R., Turtu
S., Zappa G. Synthesis of Aluminum Oxide - based
Ceramics by Laser Photoinduced Reactions from Gaseous Precursors
// J. Mater. Res. - 1997. - 12(3). - 774. Laser-driven synthesis of Al2O3 based ceramic powders from gaseous precursors has been accurately investigated. Different concentrations of the reactant gaseous precursors are shown to in uence both the process yield and the synthesized powder composition. Depending on the relative concentration of TMA: Al(CH3)3 and N2O, the process leads either to the formation of nanocrystalline g–Al2O3 with large free carbon contamination and traces of the Al3O3N phase or to the formation of a mixed g–Al2O3, Al2OC compound.The different reaction paths have been attributed to the intermediate formation of aluminum carbide. Particular attention has been paid to the gaseous reaction products to correctly interpret the source of carbon contamination observed in the formed powders. Calcining at moderate (900 °C) and high (1400 °C) temperatures induces nanosized g–Al2O3 powder and the g -> a-Al2O3 transition with particle coalescence and growth. |
|
Barsoum M. W., Brodkin D., El-Raghy
T. Layered
Machinable Ceramics For High Temperature Applications // Scripta
Materialia - 1997. - 36. - 535-541. Two classes of ternary compounds, the "312" phases namely, Ti3SiC2 and Ti3GeC2. and the H-phases (M2BX, where M is a transition metal and B a B-group element and X is either C or N) were fabricated and characterized. These phases are characterized by having the B-group elements exist in close-packed planes that separate planes of transition carbide or nitride octahedra. Electrical conductivity measurements, together with compelling microstructural evidence, lead to the conclusion that delocalized electrons parallel to the B-planes and the relatively weak bonding between the latter and the transition metal carbide or nitride layers sandwiched between them, are instrumental in endowing these compounds with a combination of truly remarkable properties. To date we fabricated the following ternaries: Ti3SiC2, Ti3GeC2, Ti2GeC, Ti2AlC and Ti2AlN. As a class these compounds are good electrical conductors (2 to 4 x106 ___m-1), relatively soft (3-6 GPa) and are as readily machinable as graphite. The microstructural evidence obtained to date leaves little doubt that these compounds are true polycrystalline nanolaminates. We also fabricated V2AlC, Ta2AlC and Nb2AlC and found them to be quite readily machinable as well. |
|
Barsoum
M. W.,
El-Raghy
T. A
Progress Report on Ti3SiC2,
Ti3GeC2 and the
H-Phases, M2BX // J. Mater.
Synth. and Process. - 1997. - 5. - 197-216. Recently we reported on two classes of layered ternary compounds, namely Ti3SiC2, Ti3GeC2 and Ti3AlC2 henceforth referred to as the 312's, and the H-phases, M2BX where M is a transition metal, B is a group B element and X is either C or nitrogen. In both cases, the structure is hexagonal with alternating layers of transition metal carbide (or nitride) layers interleaved with close-packed planes of the B-group element. In this paper we expand on our original findings and summarize our understanding of these layered materials to date. As a class these ternaries have relatively low hardnesses (4-6 GPa), high electrical conductivities (2-5 x 106 ___m-1) and are as readily machinable as graphite. At temperatures above 1200 °C they deform plastically with yield points that are quite high ( 100 MPa at 1300 °C) for that temperature. In addition, Ti3SiC2 is not susceptible to thermal shock, has good oxidation resistance (1 x 10-8 kg2m-4s-1 at 1000 °C) and is a good thermal conductor (43 W/m K). It is also a damage tolerant material. At this time there is little doubt that the deformation mechanism in these materials is dominated by slip along the basal planes. An apt descriptor of these materials is "polycrystalline nanolaminates", if it is understood that the lamina are flexible and can shear with ease relative to each other. |
|
Barsoum
M. W.,
El-Raghy
T.,
Ogbuji L. Oxidation of Ti3SiC2
in Air // J. Electrochem. Soc. - 1997. - 144(7). - 2508-2516. Polycrystalline samples of Ti3SiC2 were oxidized in air in the 900-1400 ºC temperature range. The oxidation was parabolic with parabolic rate constants, kp, that increased from 1x10-9 to 1x10-4 kg2m-4s-1 as the temperature increased from 900 to 1400 °C, respectively, which yielded an activation energy of 370ñ20 kJ/mol. The scale that forms was dense, adhesive, and resistant to thermal cycling and layered. The outer layer was pure TiO2 (rutile), and the inner layer consisted of mixture of SiO2 and TiO2. The results are consistent with a model in which growth of the oxide layer occurs by the inward diffusion of oxygen and the simultaneous outward diffusion of titanium and carbon. The presence of small volume fractions (÷ 2%) of TiCx in Ti3SiC2 were found to have a deleterious effect on the oxidation kinetics. |
|
Barsoum
M. W.,
Yaroschuck G., Tyagi S. Fabrication and Characterization
of M2SnC
(M = Ti, Zr, Hf and Nb) // Scripta Materialia - 1997.
- 37. - 1583-1591. Dense single phase polycrystalline samples of M2SnC, where M = Ti, Zr, Hf and Nb, were fabricated and preliminarily characterized for the first time. The fabrication process entailed the reactive hot-isostatic pressing of Sn powders with the appropriate transition metal and graphite powders. The fabrication of these ternaries is complicated by the fact that at low temperatures (divide; 1000 °C) the reaction kinetics for their formation are slow, while at higher temperatures (divide; 1350 °C) they tend to dissociate into Sn and the transition metal carbide. The exact decomposition temperature varied but was in the range of 1330 °C. The uniqueness of these layered compounds lies in the fact that they are all as readily machinable as graphite and are excellent electrical conductors with conductivities that range from 2.4 x 106 to 14 x 106 (__m)-1, with the least conductive phase being Hf2SnC and the most conductive Ti2SnC and the other two in between. The temperature dependence of the resistivity was metallic-like, with temperature coefficients of resistivity that varied from 0.003-0.009 K-1 As a class these ternaries were found to posses hardnesses in the range 3-5 GPa and were as readily machinable as graphite. |
| Barsoum
M. W., El-Raghy
T. Ternary Carbide of Titanium and
Silicon // Advanced materials un processes - 1997. - 152(1).
- 51 – 52. [no abstract] |
| Bialoskorski
J., Lis J., Piekarczyk J. Mechanical Properties
of the Ti3SiC2-TiC
Material // Key Eng. Mater. - 1997.- 132-136
(Pt. 1, Euro Ceramics V). - 508-511. Ti3SiC2-based ceramic materials were prepd. by pressureless sintering and hot pressing of the powders obtained by the SHS (self-propagating high-temp. synthesis) method. The material consisted of Ti3SiC2, TiC, TiSi2 and Ti2Si3. The elastic properties of the samples (E, G, .mu.) were tested by the use of the pulse ultrasonic technique, and the load-independent and crack free Knoop hardness values were used in the KIc calcns. according to a formula for Palmqvist crack geometry. The bending of the single edge notched beam method was also used for KIc detn. The fracture toughness of the evaluated materials ranged from 6.2 MPa*m0.5 for pressureless sintered samples to 9.4 MPa*m0.5 for hot pressed samples. The brittleness index for hot-pressed material was lower, but the indexes for sintered and hot pressed materials were rather closer to the ones of ceramic composites. These high values were connected with complex, transgranular fracture of the layered hexagonal Ti3SiC2 grains in the investigated materials. Comparatively high fracture toughness was connected mainly with a formation of a rough surface and steps along the cleavage face in the hexagonal Ti3SiC2 grains. |
| Borsella
E., Botti S., Martelli S., Alexandrescu R., Cesile M.C., Nesterenko
A., Giorgi R., Turtu S., Zappa G. Laser Synthesis
of Ceramic Nanocomposite Powders // Silic. Ind. - 1997. - 62(1-2).
- 3-10. [no abstract] |
| El-Raghy
T., Zavaliangos
A., Barsoum
M. W.,
Kalidindi
S. R. Damage Mechanisms Around Hardness
Indentations in Ti3SiC2
// J. Amer. Cer. Soc. - 1997. - 80. - 513-516. Microstructural observations of damage around indentations in Ti3SiC2 are presented. The Vickers hardness decreased with increasing load and asymptotically approached 4 GPa at the highest loads. No indentation cracks were observed even at loads as high as 300 N. Preliminary strength versus indentation plots indicate that, at least for the large-grained material (÷ 100 mm) studied here, Ti3SiC2 is a damage tolerant material able to contain the extent of microdamage to a small area around the indent The following multiple energy-absorbing mechanisms have been identified from scanning electron micrographs of areas in the vicinity of the indentation: diffuse microcracking, delamination, crack deflection, grain push-out, grain pull-out and the buckling of individual grains. |
| Faryna
M., Lis J., Kornikb R. SEM Studies of Microstructural
Development during Sintering of Ti3SiC2-based
Composites // J. Trace Microprobe Tech. -
1997. - 15(4). - 453-457. A densification of the bulk material obtained from powders prepd. by a combustion technique using pressureless sintering occurs with some secondary phenomena such as liq.-phase reactions with transient intermetallic phase and recrystn. of grains. As a result, the material with controlled microstructure in form of particulate composites, consisting of Ti3SiC2 matrix and TiC inclusions, can be obtained. This paper reports SEM and EDS studies of microstructure development during sintering. |
| Goldin B. A., Istomin P. V., Ryabkov Yu. I. Reduction
Solid-State Synthesis of Titanium Silicide Carbide, Ti3SiC2
// Neorg. Mater. - 1997. - 33(6). - 691-693. (Russian). Carbon reduction of leucoxene concentrate was used to prepare titanium silicide carbide. Synthesis of Ti3SiC2 was found to proceed in two stages. The conditions necessary for increasing the yield of Ti3SiC2 are discussed. |
| Grigoryan H. E., Rogachev A. S., Sytschev A. E. Gasless
Combustion in the Ti-C-Si System // International Journal of
SHS. - 1997. - 7(1). - 29-39. [no abstract] |
| Kellerman
D. G., Gorshkov V. S., Blinovskov Ya. N., Grigorov I. G., Perelyaev
V. A., Shveikin G. P. Synthesis and Properties
of the Ternary Phase Ti3SiC2
// Neorg. Mater. - 1997. - 33(3). - 329-332. (Russian). Ti3SiC2 can be prepared in vacuum from both elements and binary compounds. This carbosilicide is found to be stable up to 1600 K in vacuum. The microstructure of Ti3SiC2 materials obtained by hot pressing at different temperatures is studied by electron microscopy. |
| Lis J., Pampuch R., Rudnik T., Wegrzyn Z. Reaction
Sintering Phenomena of Self-Propagating High-Temperature Synthesis-Derived
Ceramic Powders in the Ti-Si-C System // Solid State Ionics
- 1997. - 101-103 (Pt. 1). - 59-64. Sintering phenomena of self-propagating high-temp. synthesis (SHS)-derived powders often have a character of densification accompanied by a reaction in solid and / or liq. phase. The problem is discussed in the case of prepn. of Ti3SiC2-based materials. This novel laminated ceramic has some unique properties like low hardness, high fracture toughness, corrosion resistance and ductile character at elevated temp. Because of specific mechanisms during rapid combustion-type SHS reactions, it is possible to prep. Ti3SiC2-rich powders that can be used as precursors for prepn. of Ti3SiC2-based polycrystals. Densification of these powders occurs with formation of transient metallic liq. phase. As a result, dense polycrystals with controlled microstructures in form of particulate composites with Ti3SiC2 matrix and controlled TiC inclusions can be obtained. The reactions occurring during prepn. of Ti3SiC2-based composites with WC and B4C are also discussed. |
| Naka
M., Feng J. C., Schuster J. C. Phase Reaction
and Diffusion Path of the SiC/Ti System // Metall. Mater. Trans.
A - 1997. - 28A(6). - 1385-1391. [no abstract] |
| Qiu
C., Metselaar R. Phase Relations in the Aluminum
Carbide - Aluminum Nitride - Aluminum Oxide System // J. Am.
Ceram. Soc. - 1997. - 80(8). - 2013-2020. The phase diagram of the pseudobinary Al4C3-AlN system was predicted using thermodynamic models. It was combined with previous thermodynamic descriptions of the pseudobinary Al4C3-Al2O3 and Al4C3-AlN systems, and then thermodynamic properties of the pseudoternary Al4C3-AlN-Al2O3 system were assessed by modeling the Gibbs energy of the various phases. An ionic-liquid model was applied to the liquid phase and a compound-energy model was applied to the solid solution phase (2H) that formed between Al2OC and AlN. A series of isothermal sections of the system were calculated in the temperature range of 1000°-2100°C, and reasonable phase relations were established. The calculated isothermal section at 1600°C showed satisfactory agreement with experimental results. The calculated liquidus projection in the Al2O3-rich corner can explain the experimental observation of microstructure after solidification very well. However, the present description cannot account for the phase segregation inside the solution phase but could be modified in the future, when more experimental information would be available. |
| Rudnik
T., Lis J. The Ti3SiC2
Based Structural Ceramics // Arch. Metall.
- 1997. - 42(1). - 59-66. A review, with 18 refs., of prepn. and testing of a new group of ceramic materials based on Ti3SiC2. The titanium silicon carbide, Ti3SiC2, belongs to relatively unknown group of complex carbides with laminar structure having unique properties. The presented works shows a possibility of prepn. of sinterable Ti3SiC2 powders by the Self-Propagating High-Temp. Synthesis (SHS) from powd. substrates. The powders can be densified into Ti3SiC2-based polycrystals using pressureless sintering or hot-pressing. Densification occurs by sintering with a liq. phase. The final materials have low hardness, high elastic modules, high fracture toughness, and high corrosion resistance. |
| Takashima
T., Washida M., Yamamoto T., Narita T. Metalizing
of Silicon-Carbide Ceramics with Titanium Vapor // J. Ceram.
Soc. Jpn. - 1997. - 105 (Jan.). - 68-72. (Japanese). Silicon carbide ceramic was metalized with titanium by the vapor-diffusion method, where pure titanium powder was used as a vapor source at 973-1323 K for up to 296.1 ks in a dynamic vacuum atm. The structure and compn. of the metalized layers were investigated by SEM, electron-probe microanal., and X-ray diffraction anal. At the initial stage of the metalization, titanium vapor reacted preferentially with the so-called free carbon in the grain boundaries of SiC ceramics to form a titanium carbide, and then a metalized layer was grown laterally, forming the sublayer structures. This sub-layer structure was composed of five sub-layers; TiC (top surface), Ti5Si3 contg. TiC (outer layer), TiC contg. Ti5Si3 (middle layer), Ti5Si3 (inner layer) and Ti3SiC2 (bottom layer). Growth kinetics of each sub-layer and their total thicknesses obeyed the parabolic rate law, and the parabolic rate consts. (kp) for the total layer varied between 10-16 m2.s-1 at 1173 K and 10-15 m2.cntdot.s-1 at 1323 K. The activation energy (Qkp) obtained for the metalized layer was 153 kJ.cntdot.mol-1. |
| Urretavizcaya
G., Porto Lopez J. M., Cavalieri A. L. Pressureless
Sintering of Al2O3/SiCW
Materials: Effect of the Reducing Atmosphere
// J. Europ. Ceram. Soc. - 1997. - 17(13). - 1555-1563. [no abstract] |
| Zurbuchen
M. A., Carim A. H. Microstructure in Brazed
Joints of Al2O3/SiC
Composites // Ceram. Trans. - 1997. - 77 (Ceramic
Joining). - 107-115. Com. Al2O3 / SiC whisker composites were brazed using com. Ag-Cu-Ti alloys and the resulting joint microstructures were characterized by electron microprobe and transmission electron microscopy. A model of the system has been developed from the data gathered to date. A continuous reaction layer of (Ti,Cu,Al)6O forms adjacent to the braze alloy. Small islands of reaction product were obsd. within this phase and adjacent to the ceramic. These islands were found to be composed of a layer of Ti3SiC2, with TiC beneath. Ti had reacted preferentially with SiC to form a TiC cap extending outward along the interface. Titanium oxides were found at the Al2O3 surface in contact with Ti3SiC2, TiC, and the overlying (Ti,Cu,Al)6O. |
