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1.
We have determined the energetics of defect formation and migration in Mn+1AXn phases with M = Ti, A = Si or Al, X = C, and n = 3 using density functional theory calculations. In the Ti3SiC2 structure, the resulting Frenkel defect formation energies are 6.5 eV for Ti, 2.6 eV for Si, and 2.9 eV for C. All three interstitial species reside within the Si layer of the structure, the C interstitial in particular is coordinated to three Si atoms in a triangular configuration (C–Si = 1.889 Å) and to two apical Ti atoms (C–Ti = 2.057 Å). This carbon–metal bonding is typical of the bonding in the SiC and TiC binary carbides. Antisite defects were also considered, giving formation energies of 4.1 eV for Ti–Si, 17.3 eV for Ti–C, and 6.1 eV for Si–C. Broadly similar behavior was found for Frenkel and antisite defect energies in the Ti3AlC2 structure, with interstitial atoms preferentially lying in the analogous Al layer. Although the population of residual defects in both structures is expected to be dominated by C interstitials, the defect migration and Frenkel recombination mechanism in Ti3AlC2 is different and the energy is lower compared with the Ti3SiC2 structure. This effect, together with the observation of a stable C interstitial defect coordinated by three silicon species and two titanium species in Ti3SiC2, will have important implications for radiation damage response in these materials.  相似文献   

2.
(Cr2Ti)AlC2 is a newly discovered MAX phase with ordered occupations of Ti and Cr atoms on M sites. The Cr‐containing MAX phase is expected showing magnetic property, which provides functional applications in spintronics and as self‐monitoring smart coating. The magnetic states of (Cr2Ti)AlC2 are predicted by GGA and GGA + U methods and compared to those of Cr2AlC. The ground states are predicted as FM or AFM‐XX configurations depending on the calculation methods. Analysis of the electronic structure shows that the magnetic moments mainly originate from the net spins of Cr 3d valence electrons, whereas the contribution of other atoms is negligible. The calculated magnetic moments of Cr atoms in (Cr2Ti)AlC2 are higher than those in Cr2AlC due to the larger distance between the out‐plane Cr atoms separated by the intercalated nonmagnetic Ti–C slab. This work provides an insight on tailoring magnetic properties of MAX phases by modifying the crystal structure.  相似文献   

3.
Temperature dependences of thermal and elastic properties, such as the Grüneisen parameters, thermal expansion, bulk modulus, and heat capacity of Ti2AlC and Cr2AlC, are studied by combining first‐principles method and lattice dynamic calculation based on the quasi‐harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients of Ti2AlC and Cr2AlC show different trends: Ti2AlC exhibits anisotropic thermal expansion while Cr2AlC shows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Grüneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) of Ti2AlC and Cr2AlC. In addition, the calculated bulk modulus of Cr2AlC is higher at ambient temperature but decreases faster than the value of Ti2AlC as temperature increasing.  相似文献   

4.
Inspired by pressure resistance welding of metallic materials, herein we describe how two MAX phases—Ti3SiC2 and Ti3AlC2—were successfully joined by a rapid electric current heating method in a pulsed electric current sintering furnace. No welding agent was employed and the total processing time was less than 6 min. When the bulk temperature of the joint couple exceeded 1070°C, good joints, with shear strength above 50 MPa, were achieved in both homo‐ and heterojunction joints.  相似文献   

5.
The magnitude of the single‐crystal elastic constant c44 in the MAX phase Ti3SiC2 is under debate. In this paper, estimates for the magnitude of c44 for MAX phases Ti3AlC2 and Ti3SiC2 are determined from a partially oriented polycrystalline sample via coherent inelastic neutron scattering. The largely quasi‐isotropic nature of these Mn+1AXn phase elastic constants as previously predicted by density functional theory calculations is confirmed experimentally for Ti3AlC2 to be c44=115.3 ± 30.7 GPa. In contrast, Ti3SiC2 is confirmed to be shear stiff with c44=402.7 ± 78.3 GPa supporting results obtained by earlier elastic neutron diffraction experiments.  相似文献   

6.
新型层状陶瓷材料Ti3AlC2结合了金属和陶瓷的许多优异性质,既具有与金属相似的良好的导热、导电性,良好的可加工性,相对柔软,抗热震性好,可塑性变形等;同时又具有与陶瓷相似的抗氧化、耐腐蚀、耐高温等特性;并且还有很好的自润滑性和超低摩擦系数,被认为在许多领域有着广泛的应用前景。  相似文献   

7.
新型层状陶瓷Ti3AlC2的研究进展   总被引:4,自引:0,他引:4  
综述了可加工性Ti3A1C2陶瓷的研究进展。三元碳化物Ti3AlC2属于六方晶体结构,空间群为P6 3/mmc。它具有许多优良的性能,有较高的强度和弹性模量,还有高的导热和导电系数。室温下有抗损伤能力,高温下有良好的抗氧化性及显著的塑性变形。应用SHS、HP/HIP及SPS(等离子放电烧结)可制备该化合物。用HIP及SPS可制备高纯、致密的Ti3A1C2陶瓷材料。  相似文献   

8.
In this study, we report on the compressive behavior of Ti3AlC2 and Ti3Al0.8Sn0.2C2 MAX phases at room temperature. We found that these two phases could be classified as Kinking Nonlinear Elastic (KNE) solids. The cyclic compressive stress–strain loops for Ti3AlC2 and Ti3Al0.8Sn0.2C2 are typical hysteretic and fully reversible. At failure, both compositions fracture in shear with maximum stresses of 545 MPa for Ti3AlC2 and 839 MPa for Ti3Al0.8Sn0.2C2. Consequently, the macroshear stresses for failure, τc, are 185 MPa and 242 MPa for Ti3AlC2 and Ti3Al0.8Sn0.2C2, respectively. In addition to the grain size effects, the presence of a ductile TixAly intermetallic distributed in the grain boundaries plays an important role in the enhancement of the ultimate compressive and macroshear stresses for Ti3Al0.8Sn0.2C2. SEM observations reveal that these two MAX phases exhibit crack deflections, intragranular fractures, kink band formation and delaminations, grain push‐in and pull‐out.  相似文献   

9.
Alumina forming, oxidation and thermal shock resistant MAX phases are of a high interest for high temperature applications. Herein we report, on bonding and resulting interactions between a Ni-based superalloy, NSA, and two alumina forming MAX phases. The diffusion couples Cr2AlC/Inconel-718/Ti2AlC were assembled and heated to 1000 or 1100 °C in a vacuum hot press under loads corresponding to stresses of either 2 MPa or 20 MPa. The resulting interfaces were examined using X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Good bonding between Cr2AlC and NSA was achieved after hot pressing at 1000 °C and a contact pressure of only 2 MPa; in the case of Ti2AlC a higher temperature (1100 °C) and pressure (20 MPa) were needed. In both cases, a diffusion bond, in which mainly Ni and Cr out diffused from the NSA into the MAX phase and a concomittant out diffusion of Al from the latter, was realized with no evidence of interfacial damage or cracking after cooling to room temperature. The reactions paths were determined to be: Cr2AlC/Cr7C3/Cr7C3,β-NiAl/α-Cr(Mo)/NSA and Ti2AlC/Ti2AlC,Ti3NiAl2C/β-NiAl/α-Cr(Mo)/NSA. Twenty thermal cycles from room temperature to 1000 °C showed that Ti2AlC is a poor oxidation barrier for Inconel-718. However, in the case of Cr2AlC no cracks, delamination nor surface degradation was observed, suggesting that this material could be used to protect Inconel-718 from oxidation.  相似文献   

10.
综合介绍了一类三元纳米层状化合物Mn 1AXn的结构以及性能。其兼有金属和陶瓷的优良性能,既具有与金属相似的良好的导热性、导电性和加工性能等,同时又有与陶瓷相似的抗氧化性、耐高温和耐腐蚀等特性,还有自润滑性。这种三元纳米层状化合物Mn 1AXn将有着广泛的应用。  相似文献   

11.
Ti3SiC2及其复合材料的研究现状及发展趋势   总被引:4,自引:0,他引:4  
介绍了Ti3SiC2陶瓷材料的微观结构与性能,认为该材料良好的综合性能有望解决陶瓷材料的脆性问题.并概述了Ti3SiC2及Ti3SiC2基复合材料各种制备方法的特点和研究状况、应用前景和发展趋势.  相似文献   

12.
《Ceramics International》2023,49(1):168-178
Since the synthesis of non-oxidized ceramic and alloy powders requires both high temperature and oxygen insulation conditions, here we demonstrate a cost-efficient molten salt sealing/shielded synthesis method with dynamic gas tightness. Compared to conventional synthesis method, it can prevent the loss of reaction materials at high temperature, cut off the connection between reacting material and outside air, and does not require long-time ball milling mixing treatment or provision of applied pressing before or during heating. Only low-cost salts (e.g., NaCl, KCl), a few minutes of raw material mixing, and regular heating molds are required to obtain high-purity (>96 wt%), micron-sized Ti3AlC2 and Ti3SiC2 powders with narrow size distribution, which significantly decreased the complexity and production costs in the synthesis process. The effect of temperature and raw material content on the products were investigated. The mechanism of diffusion reaction between reactants in molten salt environment was analyzed. The new method developed here was also applicable to Ti2AlC, V2AlC and Cr2AlC MAX phases, as well as provided new ideas for the preparation of other MXenes precursors with certain stoichiometric ratios, air-sensitive materials and nanopowders.  相似文献   

13.
Commercially available Ti3SiC2 and Ti2AlC ceramics were used in this study to investigate their wet corrosion and mechanical behaviour as they were under investigation for years for their applications in the field of nuclear as cladding materials and aerospace. The test coupons of dimension 3 × 4 × 40 mm3 and 3 × 4 × 20 mm3 were machined out from commercially available samples for the 3-pt bend test and wet corrosion test, respectively. The water vapour corrosion studies of these samples were carried out at 800 ℃, 1000 ℃, 1200 ℃ for 10, 20 and 100 h in gas flow condition containing 50 % steam + 50 % air. Phase analysis of the as-received Ti3SiC2 and Ti2AlC ceramics revealed the presence of other impurity phases such as TiC and TiSi2. The XRD patterns of the oxidised samples show the formation of rutile as the major phase in both materials. The oxidation layer formed on Ti3SiC2 sample was measured to be 280 μm after exposing the sample in steam for 100 h at 1200 °C. The water vapour corrosion studies reveal that Ti2AlC has high oxidation resistance compared with the Ti3SiC2 due to the formation of protective layers of TiO2 and Al2O3 which resulted in reduced weight gain and oxidation layer thickness. Three-point bend tests were conducted at room temperature for the samples after the water vapour corrosion test at 1000 °C/100 h. The TAC samples showed no degradation in the bending strength (244 MPa) whereas the TSC samples showed reduced strength of 320 MPa. The tensile strength of the samples was measured at room temperature and hydrothermal condition (250 °C and 250 bars pressure) and it was observed that Ti3SiC2 had high tensile strength (190 MPa) in hydrothermal conditions. The tensile strength results were validated using Finite element analysis (FEA) using ANSYS and the FEA results showed a negligible variance of 7 % compared with experimental method. Mathematical modelling based on one dimensional solution of diffusion equation combined with Deal-Grove model was employed to study and compare the oxidation thickness for the linear and parabolic models for the ceramics. The model was effective in validating the oxidation thickness of Ti3SiC2 showing that the experimental thickness was closer to that of mathematical model.  相似文献   

14.
Two new MAX compounds, (Cr2/3Ti1/3)3AlC2 and (Cr5/8Ti3/8)4AlC3, were successfully synthesized by hot‐pressing elemental powders at 1500°C for 1 h under 30 MPa in a flowing argon atmosphere. Their crystal structures were indentified and characterized by X‐ray diffraction and transmission electron microscopy analysis. (Cr2/3Ti1/3)3AlC2 and (Cr5/8Ti3/8)4AlC3 have the same crystal structures with the well‐characterized Ti3AlC2 and Ti4AlN3, respectively.  相似文献   

15.
Ti3SiC2陶瓷的制备及性能研究   总被引:6,自引:0,他引:6  
层状陶瓷材料Ti,SiC2结合了金属和陶瓷的许多优异性质,既具有与金属相似的良好的导热、导电性,良好的可加工性,相对柔软,抗热震性好,可塑性变形等性能,同时又具有与陶瓷相似的抗氧化、耐腐蚀、耐高温等特性;并且还有很好的自润滑性和超低磨擦系数,被认为在许多领域有着广泛的应用前景。  相似文献   

16.
The susceptibility of Ti2AlN and Ti4AlN3 to high-temperature thermal dissociation in a dynamic environment of high-vacuum has been investigated using in situ neutron diffraction. Under high vacuum, these ternary nitrides decomposed above 1400 °C through the sublimation of Al, and possibly Ti, to form a surface coating of TiNx (0.5  x  0.75). The kinetics of isothermal phase decomposition were modelled using the Avrami equation and the Avrami exponents (n) of isothermal decomposition of Ti2AlN and Ti4AlN3 were determined to be 0.62 and 0.18, respectively. The characteristics of thermal stability and phase transitions in Ti2AlN and Ti4AlN3 are compared in terms of the rate of decomposition, phase relations and microstructures.  相似文献   

17.
(Cr,Mn)2AlC solid solutions have attracted much attention due to their magnetic property which will be enhanced with increasing Mn solubility. So far, only 3?at.-% Mn solubility in (Cr,Mn)2AlC bulk materials has been reported. This work reports on the synthesis of (Cr,Mn)2AlC solid solutions via a new reaction route with AlCr2, C and Mn as starting materials. The Mn solubility increases with increasing the starting Mn content. The maximum solubility of Mn in (Cr,Mn)2AlC was 8.3?at.-%, corresponding to a resultant solid solution (Cr0.83Mn0.17)2AlC. However, increasing the Mn content in the starting mixture caused the formation of impurities in the sintered samples. A dense (Cr0.95Mn0.05)2AlC ceramic has been achieved by hot-pressing the mixture of AlCr2/C/0.1Mn. The mechanical properties and thermal expansion coefficient of (Cr0.95Mn0.05)2AlC were measured.  相似文献   

18.
Oxidation resistance of textured Ti3AlC2 ceramics was measured in the temperature range 1273–1573?K. It was found that the oxidation was markedly anisotropic and the samples exhibited a better oxidation resistance when tested along a direction transverse to the c-axis. This behavior was attributed to the rapid diffusion of Al within its basal planes to form a passivating Al2O3 scale and it respected Ellingham diagrams. The scales formed had different compositions depending on the testing direction; this response was clearly resulting from the crystallographic orientation. Even at 1473?K after 20?h exposure, the samples tested in a direction transverse to the c-axis showed a reduced weight gain which was 45 times lower than one seen on a basal plane.  相似文献   

19.
20.
以TiC/TiO2/Si/Al/Ti等为主要原料,采用热压法原位合成Ti2SiC2/Al2O3复合材料,分别探讨了Al掺入量和工艺制度对Ti3SiC2/Al2O3复合材料物相、显微结构以及性能的影响。结果表明:原位合成制备的Ti3SiC2/Al2O3复合材料与传统方法合成制备的纯Ti3SiC2材料相比,材料的硬度和致密度均有很大的提高。  相似文献   

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