共查询到20条相似文献,搜索用时 62 毫秒
1.
Erich H. Kisi Erdong Wu Jennifer S. Zobec Jennifer S. Forrester Daniel P. Riley 《Journal of the American Ceramic Society》2007,90(6):1912-1916
It is demonstrated that the M n +1 AX n phase Ti3 AlC2 may be readily synthesized by sintering a stoichiometric mixture of the lower order MAX phase Ti2 AlC mixed with a stoichiometric amount of TiC in the temperature range 1350°–1450 °C. High-quality Ti3 AlC2 was readily produced using sintering times in the range 2–5 h. In general, <2% of unwanted or remnant phases were found to be present and in some samples none could be detected at all. 相似文献
2.
The phase domain of Ti3 O5 –Ti2 O3 –Ti(CO) at 1580 K was determined from the formation energies of Ti(C x O y ), as calculated via the Gibbs–Duhem equation. An extensive Ti(CO) domain is attributed to the high affinity between TiC and TiO. The phase domain of Ti3 O5 –Ti2 O3 –Ti(CN) was obtained at 1673 K using the formation energies of Ti(C x N y ). This study shows that the stable region for Ti2 O3 is significantly small in the Ti3 O5 –Ti2 O3 –Ti(CN) phase domain. It demonstrates the absence of TiO and Ti2 O3 in the normal syntheses of TiC and Ti(CN) from TiO2 , respectively. 相似文献
3.
Chunfeng Hu Jie Zhang Jiemin Wang Fangzhi Li Jingyang Wang Yanchun Zhou 《Journal of the American Ceramic Society》2008,91(2):636-639
V4 AlC3 , a new MAX phase, was synthesized by reactive hot pressing of a V, Al, and C powder mixture at 1700°C. Using a combination of Rietveld refinement with X-ray diffraction data and ab initio calculations, the crystal structure was determinated. It was found that V4 AlC3 has a Ti4 AlN3 -type crystal structure. The lattice constants are a =0.29310 nm and c =2.27192 nm. And the atomic positions are V1 at (4 f ) (1/3, 2/3, 0.0544), V2 at (4 e ) (0, 0, 0.1548), Al at (2 c ) (1/3, 2/3, 1/4), C1 at (2 a ) (0, 0, 0), and C2 at (4 f ) (2/3, 1/3, 0.1080). 相似文献
4.
Shahram Amini Michel W. Barsoum Tamer El-Raghy 《Journal of the American Ceramic Society》2007,90(12):3953-3958
Because the layered machinable ternary carbide, Ti2 SC, has a significantly shorter c -lattice parameter—as compared with most of the 50+ other so-called Mn+1 AXn (MAX) phase family (M=early transition metal; A=A group element and X=C or N and n=1–3) to which it belongs—it was postulated that its mechanical properties would be significantly different than the other MAX phases. In this work, fine-grained (FG) and coarse-grained (CG) polycrystalline fully dense Ti2 SC samples were fabricated. Hot pressing Ti2 SC powders, at 1500°C under a stress of ∼45 MPa for 5 h resulted in FG (2–4 μm) samples which and upon further annealing for 20 h at 1600°C resulted in CG (10–20 μm) ones. No peaks other than those associated with Ti2 SC and an impurity anatase phase, with a volume fraction of ∼6 vol% were observed in the XRD patterns and micrographs. The average Vickers hardness in the 2–300 N range is 8±2 GPa with the FG samples being slightly harder. This hardness is the highest of any of the MAX phases characterized to date. Also in contrast to all MAX phases, cracks extended from the corners of Vickers indents in the FG samples. From these cracks the fracture toughness was estimated and found to increase more or less linearly with load from ≈4 to 6 MPa·m1/2 as the Vickers force was increased from 50 to 300 N, respectively. The room temperature compressive stress of the FG samples was 1.4±0.2 GPa; the failure mode was brittle. Its Young's modulus—also one of the highest for a M2 AX phase measured to date—was 316±2 GPa. There was no evidence for incipient kink band formation during simple compression. The latter is attributed, in part, to the fine grain size of the hot-pressed material. 相似文献
5.
The quenching technique was used to study subliquidus and subsolidus phase relations in the pseudobinary system Na2 Ti2 Si2 O11 -Na2 Ti2 Si2 O9 . Both narsarukite (Na2 TiSi4 O11 ) and lorenzenite (Na2 Ti2 Si2 O9 ) melt incongruently. Narsarsukite melts at 911°±°C to SiO2 +liquid, with the liquidus at 1016°C. Lorenzenite melts at 910°±5°C to Na2 Ti6 O13 +liquid; Na2 Ti6 O13 reacts with liquid to form TiO2 and is thus consumed by 985°±5°C. The liquidus occurs at 1252°C. 相似文献
6.
Michel W. Barsoum Leonid Farber Igor Levin Adam Procopio Tamer El-Raghy Alex Berner 《Journal of the American Ceramic Society》1999,82(9):2545-2547
The structure and chemistry of what initially was proposed to be Ti3 Al2 N2 are incorrect. Using high-resolution transmission electron microscopy, together with chemical analysis, the stoichiometry of this compound is concluded to be Ti4 AlN3-delta (where delta = 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 P 63 / 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 M2 AX and M3 AX2 (where M is an early transition metal, A is an A-group element, and X is carbon and/or nitrogen). 相似文献
7.
Jing-Feng Li Toshiro Matsuki Ryuzo Watanabe 《Journal of the American Ceramic Society》2002,85(4):1004-1006
Mechanical alloying (MA) has been used to synthesize Ti3 SiC2 powder from the elemental Ti, Si, and C powders. The MA formation conditions of Ti3 SiC2 were strongly affected by the ball size for the conditions used. MA using large balls (20.6 mm in diameter) enhanced the formation of Ti3 SiC2 , probably via an MA-triggered combustion reaction, but the Ti3 SiC2 phase was not synthesized only by the MA process using small balls (12.7 mm in diameter). Fine powders containing 95.8 vol% Ti3 SiC2 can be obtained by annealing the mechanically alloyed powder at relatively low temperatures. 相似文献
8.
Adrish Ganguly Michel W. Barsoum Roger D. Doherty 《Journal of the American Ceramic Society》2007,90(7):2200-2204
In this work, we report on the interdiffusion of Ge and Si in Ti3 SiC2 and Ti3 GeC2 , as well as that of Nb and Ti in Ti2 AlC and Nb2 AlC. The interdiffusion coefficient, D int , measured by analyzing the diffusion profiles of Si and Ge obtained when Ti3 SiC2 –Ti3 GeC2 diffusion couples are annealed in the 1473–1773 K temperature range at the Matano interface composition (≈Ti3 Ge0.5 Si0.5 C2 ), was found to be given by
Dint increased with increasing Ge composition. At the highest temperatures, diffusion was halted after a short time, apparently by the formation of a diffusion barrier of TiC. Similarly, the interdiffusion of Ti and Nb in Ti2 AlC–Nb2 AlC couples was measured in the 1723–1873 K temperature range. The D int for the Matano interface composition, viz. ≈(Ti0.5 ,Nb0.5 )2 AlC, was found to be given by
At 1773 K, the diffusivity of the transition metal atoms was ≈7 times smaller than those of the Si and Ge atoms, suggesting that the former are better bound in the structure than the latter. 相似文献
D
At 1773 K, the diffusivity of the transition metal atoms was ≈7 times smaller than those of the Si and Ge atoms, suggesting that the former are better bound in the structure than the latter. 相似文献
9.
The effect of vacuum annealing on the thermal stability and phase transition of Ti3 SiC2 has been investigated by X-ray diffraction (XRD), neutron diffraction, synchrotron radiation diffraction, and secondary ion mass spectroscopy (SIMS). In the presence of vacuum or a controlled atmosphere of low oxygen partial pressure, Ti3 SiC2 undergoes a surface dissociation to form nonstoichiometric TiC and/or Ti5 Si3 C x that commences at ∼1200°C and becomes very pronounced at ≥1500°C. Composition depth profiling at the near surface of vacuum-annealed Ti3 SiC2 by XRD and SIMS revealed a distinct gradation in the phase distribution of TiC and Ti5 Si3 C x with depth. 相似文献
10.
pela Kunej Sreo D. kapin Danilo Suvorov 《Journal of the American Ceramic Society》2009,92(10):2373-2377
In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi2 O3 −TiO2 −Nd2 O3 system at 1100°C. The samples were analyzed using X-ray powder diffraction and scanning electron microscopy with energy- and wavelength-dispersive spectroscopy. A single-phase pyrochlore ceramic was obtained with the addition of 4.5 mol% of Nd2 O3 . We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi(1.6–1.08 x ) Nd x Ti2 O(6.4+0.3 x ) , where 0.25< x <0.96; (ii) the solid solution Bi4− x Nd x Ti3 O12 , where 0< x <2.6; and (iii) the Nd2− x Bi x Ti2 O7 solid solution, where 0< x <0.35. The determined phase relations in the pyrochlore-rich part are presented in a partial phase diagram of the Bi2 O3 −TiO2 −Nd2 O3 system in air at 1100°C. 相似文献
11.
P. Mogilevsky Tai-Il Mah T. A. Parthasarathy C. M. Cooke 《Journal of the American Ceramic Society》2006,89(2):633-637
Composites in the SiC–TiC–Ti3 SiC2 system were synthesized using reactive hot pressing at 1600°C. The results indicate that addition of Ti3 SiC2 to SiC leads to improved fracture toughness. In addition, high microhardness can be retained if TiC is added to the material. The best combination of properties obtained in this study is K I c =8.3 MPa·m1/2 and H v =17.6 GPa. The composition can be tailored in situ using the decomposition of Ti3 SiC2 . Ti3 SiC2 decomposed rapidly at temperatures above 1800°C, but the decomposition could be conducted in a controlled manner at 1750°C. This can be used for synthesis of fully dense composites with improved properties by first consolidating to full density a softer Ti3 SiC2 -rich initial composition, and then using controlled decomposition of Ti3 SiC2 to achieve the desired combination of microhardness and fracture toughness. 相似文献
12.
In this paper, we report a machinable Ti3 SiC2 /hydroxyapatite (HAp) composite prepared by spark plasma sintering. The experimental results of a drilling test demonstrated that the composites exhibit excellent machinability when the Ti3 SiC2 content is higher than 20 vol%, which can be attributed to the improvement in the mechanical and machinable properties of the composites by addition of Ti3 SiC2 phase, which possessess unique mechanical and machinable properties and energy-absorbing mechanisms. The superior mechanical and machinable properties of Ti3 SiC2 /HAp composites suggest that the composite system could be attractive for practical applications of novel biomaterials. 相似文献
13.
Ceramic samples with the nominal composition (1− x ) BaTiO3 + x Ba3 Ti2 YO8.5 ( x =0−0.535) were prepared by the mixed oxide method. X-ray diffraction (XRD) analysis shows that the materials are of single phase with a cubic symmetry as x ≤0.16. The compositions of the solid solutions ( x ≤0.16) can be expressed equivalently as Ba(Ti1− y Y y )O3−δ ( y ≤0.122, y = x /(1+2 x )). For x >0.16, the materials are diphasic composites consisting of Ba(Ti1− y Y y )O3 ( y =0.122) and Ba3 Ti2 YO8.5 . The microstructure observation by scanning electron microscopy supports the XRD result. The dielectric behavior and phase transitions of the solid solutions ( x ≤0.16) vary with different Y concentrations. The dielectric constant of the composites ( x >0.16) follows approximately the Lichteneker relation in a wide temperature range. 相似文献
14.
José M. Córdoba María J. Sayagués María D. Alcalá Francisco J. Gotor 《Journal of the American Ceramic Society》2007,90(3):825-830
Titanium silicon carbide (Ti3 SiC2 ) and Ti3 SiC2 -based composite powders were synthesized by isothermal treatment in an inert atmosphere as a function of initial compositions (mixtures). A high content of TiC was obtained in the final product when the initial mixtures contained free carbon. The use of TiC as a reagent was unsuccessful in obtaining Ti3 SiC2 . High Ti3 SiC2 conversion was found for the initial mixtures containing SiC as the main source for silicon and carbon. An initial mixture with a large excess of silicon, 3Ti/1.5SiC/0.5C, was needed to obtain high-purity Ti3 SiC2 . A reaction mechanism, where Ti3 SiC2 nucleates on Ti5 Si3 C crystals and grows by long-range diffusion of Ti and C, is proposed. The reaction mechanism was proposed to be based on silicon loss during the formation of Ti3 SiC2 . 相似文献
15.
Véronique Gauthier Benoît Cochepin Sylvain Dubois Dominique Vrel 《Journal of the American Ceramic Society》2006,89(9):2899-2907
Ti3 SiC2 is synthesized by self-propagating high-temperature synthesis (SHS) of elemental titanium, silicon, and graphite powders. The reaction paths and structure evolution are studied in situ during the SHS of the 3Ti+Si+2C mixture by time-resolved X-ray diffraction coupled with infrared thermography. The proposed reaction mechanism suggests that Ti3 SiC2 might be formed from Ti–Si liquid phase and solid TiC x . Finally, the effect of the powders starting composition on the Ti3 SiC2 synthesis is studied. For the investigated initial mixtures, TiC x is always formed as a major impurity together with the Ti3 SiC2 phase. 相似文献
16.
Kathleen B. Alexander Fred J. Walker Rodney A. McKee Fred A. List III 《Journal of the American Ceramic Society》1990,73(6):1737-1743
Titanium oxide/aluminum oxide films have been deposited using molecular beam epitaxy methods and characterized by reflection high-energy electron diffraction and transmission electron microscopy techniques. Growth on silicon substrates below 973 K resulted in primarily amorphous multilayers. At 1323 K, the deposition of titanium in an oxygen atmosphere on (0001) Al2 O3 substrates resulted in films of Ti2 O3 . These films consisted of small domains, up to 60 nm, slightly misoriented from a [1120] ∥ [1120] orientation relationship. Two variants of Ti2 O3 were observed due to multiple positioning during growth. Closing the titanium shutter during growth resulted in an oriented TiO2 film. 相似文献
17.
The microstructure of (Sr,Ca)TiO3 capacitor-varistor materials has been investigated by employing electron microscopy techniques (TEM, STEM, HREM, EDX, and EPA). The material is found to contain (Sr,Ca)TiO3 grains (∼30 μm) having perovskite crystal structure with domains, a Na+ -diffused layer at the grain boundaries which is dependent on thermal diffusion conditions, and multiple-grain junctions in which the Ti n O2n–1 Magneli phase coexists with an amorphous intergranular phase. In addition, wider grain boundaries (10–30 nm), thin grain boundaries (∼1 nm), and clean grain boundaries which are free from intergranular phase were observed, and the effects of different grain boundaries on the diffusion of Na+ are discussed. 相似文献
18.
Sui Lin Shi Wei Pan Ming Hao Fang Zhen Yi Fang 《Journal of the American Ceramic Society》2006,89(2):743-745
Ti3 SiC2 /HAp composites with different Ti3 SiC2 volume fractions were fabricated by spark plasma sintering (SPS) at 1200°C. The effects of Ti3 SiC2 addition on the mechanical properties and microstructures of the composites were investigated. The bending strength and fracture toughness of the composites increased with increasing of Ti3 SiC2 content, whereas the Vickers hardness decreased. The bending strength and fracture toughness reached 252±10 MPa and 3.9±0.1 MPa·m1/2 , respectively, with the addition of 50 vol% Ti3 SiC2 . The increases in the mechanical properties were attributed to the matrix strengthening and interactions between cracks and the Ti3 SiC2 platelets. 相似文献
19.
Xiaowei Yin Nahum Travitzky Peter Greil 《Journal of the American Ceramic Society》2007,90(7):2128-2134
Nanolaminates with a layered M N +1 AX N crystal structure (with M: transition metal, A: group element, X: carbon or nitrogen, and N =1, 2, 3) offer great potential to toughen ceramic composites. A ternary Ti3 AlC2 carbide containing ceramic composite was fabricated by three-dimensional printing of a TiC+TiO2 powder mixture and dextrin as a binder. Subsequent pressureless infiltration of the porous ceramic preform with an Al melt at 800°–1400°C in an inert atmosphere, followed by reaction of Al with TiC and TiO2 finally resulted in the formation of a dense multiphase composite of Ti3 AlC2 –TiAl3 –Al2 O3 . A controlled flaw/strength technique was utilized to determine fracture resistance as a function of crack extension. Rising R -curve behavior with increasing crack extension was observed, confirming the operation of wake-toughening effects on the crack growth resistance. Observations of crack/microstructure interactions revealed that extensive crack deflection along the (0001) lamellar sheets of Ti3 AlC2 was the mechanism responsible for the rising R -curve behavior. 相似文献
20.
L. M. Peng 《Journal of the American Ceramic Society》2007,90(4):1312-1314
A layered ternary carbide phase, Ti3 AlC2 , was synthesized by hot pressing from the starting materials of Ti, aluminum, and activated carbon at 1400°C for 2 h. Its composites were also fabricated through addition of micro-sized SiC and partially stabilized zirconia particulates to the pulverized Ti3 AlC2 powders. The polycrystalline Ti3 AlC2 ceramic obtained has a flexural strength of 172 MPa and a fracture toughness of 4.6 MPa·m1/2 , respectively. This compound is relatively soft (Vikers hardness of 2.7 GPa) and exhibits good electrical conductivity with an electrical resistivity of 8.2 μΩ·m. Both the Ti3 AlC2 /SiC and Ti3 AlC2 /ZrO2 composites are superior to the monolithic Ti3 AlC2 ceramic in strength, fracture toughness, and micro-hardness. 相似文献