共查询到20条相似文献,搜索用时 0 毫秒
1.
Preparation of the ternary carbide Cr2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from the Cr2O3-Al-Al4C3 powder compact. Effects of the contents of Al and Al4C3 on the product composition and combustion behavior were studied by formulating the reactant mixture with a stoichiometric proportion of Cr2O3:Al:Al4C3 = 3:5x:y, where x and y varied from 1.0 to 1.5. When compared to those of the powder compact with Cr2O3:Al:Al4C3 = 3:5:1 (i.e., x = y = 1.0), the combustion temperature and reaction front velocity increased with content of Al, but decreased with that of Al4C3. Besides Cr2AlC and Al2O3, the final products always contained a secondary phase Cr7C3 that was substantially reduced by adopting additional Al and Al4C3 in the reactant compacts. For the sample with Cr2O3:Al:Al4C3 = 3:7.5:1 (x = 1.5), solid state combustion reached a peak temperature of 1245 °C and yielded Cr2AlC with a trivial amount of Cr7C3. Although Cr7C3 was lessened by introducing extra Al4C3, the increase of Al4C3 from y = 1.1 to 1.5 produced almost no further reduction of Cr7C3 in the final product. This is partly attributed to the low combustion temperature in the range of 1065-1095 °C for the samples with additional Al4C3, and in part, due to the role of Al4C3 which might react with Cr to form Cr7C3, Cr2Al, and Cr2AlC. 相似文献
2.
Preparation of the ternary carbide Ta2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from elemental powder compacts of different compositions. The synthesis reaction is characterized by a nearly planar combustion front traversing the entire sample in a self-sustaining manner. When compared with those of the reactant compact with stoichiometry of Ta:Al:C = 2:1:1, lower combustion front velocities and temperatures were observed for the samples containing more Al than the stoichiometric amount. The as-synthesized products are generally composed of Ta2AlC as the dominant phase along with two minor carbides Ta2C and Ta4AlC3, both of which can be reduced by increasing the amount of Al in the sample. On the other hand, an aluminide compound Ta2Al was detected in the final product when the green compact contained carbon less than the stoichiometric quantity. Finally, an optimum composition arrived at Ta:Al:C = 2:1.6:1, with which the powder compact produced single-phase Ta2AlC through SHS. The grains of Ta2AlC are typically plate-like with a size of 5–10 μm and the layered structure consisting of closely packed Ta2AlC is evident in the product obtained from the sample with sufficient Al. In addition, a set of possible reaction paths to produce Ta2AlC was proposed, including the reactions of Ta2C with Al and Ta2Al with carbon, as well as the interaction between Ta4AlC3, Ta2Al, and Al. 相似文献
3.
Formation of Ti3SiC2 was conducted by self-propagating high-temperature synthesis (SHS) from both the elemental powder compacts of Ti:Si:C = 3:1:2 and the TiC-containing samples compressed from powder mixtures of Ti/Si/C/TiC with TiC content ranging from 4.3 to 33.3 mol%. The effect of TiC addition was studied on combustion characteristics and the degree of phase conversion. For the elemental powder compacts, with the progress of combustion wave the sample experiences substantial deformation, including axial elongation and radial contraction. The extent of sample deformation and flame-front propagation velocity were considerably reduced for the samples with TiC addition, because the dilution effect of TiC lowered the reaction temperature. Two reaction mechanisms were adopted to explain the formation of Ti3SiC2, one involving the reaction of a Ti–Si liquid phase with solid reactants for the elemental powder compact and the other dominated by the interaction of solid-phase species for the TiC-containing sample. For all products synthesized in this study, the XRD analysis identifies formation of Ti3SiC2 along with a major impurity TiC and a small amount of Ti5Si3. The resulting Ti3SiC2 is typically elongated grains. Based upon the XRD profile, the Ti3SiC2 content at a level of 71.5 vol.% was obtained in the product from the elemental powder compact. With the addition of TiC, an improvement in the yield of Ti3SiC2 was observed and an optimal conversion reaching 85 vol.% was achieved by the sample with 20 mol% of TiC. However, further increase of the TiC amount led to a decrease in the Ti3SiC2 content, because of the low reaction temperature around 1150 °C. 相似文献
4.
Preparation of the Ti3Si1−xAlxC2 solid solution with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS) using TiC-, SiC-, and Al4C3-containing powder compacts. Due to the variation of reaction exothermicity with sample stoichiometry, the combustion temperature and reaction front velocity decreased with increasing Al content of Ti3Si1−xAlxC2 for the TiC- and Al4C3-added samples, but increased for the samples with SiC. In contrast to the formation of Ti3(Si,Al)C2 as the dominant phase for the TiC- and SiC-added samples, TiC was identified as the major constituent in the final products of samples adopting Al4C3. In addition, the evolution of Ti3(Si,Al)C2 was improved by increasing the Al content of the TiC- and SiC-added powder compacts, but deteriorated considerably upon the increase of Al4C3 in the Al4C3-containing sample. 相似文献
5.
通过2TiC-Ti-1.2Al体系的原位热压反应制备了Ti3AlC2陶瓷,然后以59.2Ti-30.8Al-10Ti3AlC2(wt%)为反应体系,采用放电等离子烧结技术制备出Ti2AlC/TiAl基复合材料。借助XRD、SEM分析了产物的相组成和微观结构,并测量了其室温力学性能。结果表明:原位热压烧结产物由Ti3AlC2和TiC相组成,Ti3AlC2呈典型的层状结构,TiC颗粒分布在其间。SPS法制备的Ti2AlC/TiAl基复合材料主要由TiAl、Ti3Al和Ti2AlC相组成,Ti2AlC增强相主要分布于基体晶界处,表现为晶界/晶内强化作用。力学性能测试表明:Ti2AlC/TiAl基复合材料的密度、维氏硬度、断裂韧性和抗弯强度分别为3.85 g/cm3、5.37 GPa、7.17 MPa?m1/2和494.85 MPa。 相似文献
6.
Ti2AlC is strengthened by substituting Ti with V to form (Ti,V)2AlC solid solutions. The Vickers hardness, flexural strength, shear strength and compressive strength are enhanced by 29%, 36% and 45% for (Ti0.8,V0.2)2AlC solid solution, respectively. The strengthening mechanism is discussed. 相似文献
7.
以热压烧结后球磨粉碎的Ti_2AlC亚微米粉末为原料,通过水热处理使其团聚成微米级粉末,并运用冷喷涂技术在Zr-4合金基体上沉积Ti_2AlC涂层。采用扫描电子显微镜、金相显微镜、XRD衍射仪、激光粒度分析仪等对Ti_2AlC颗粒和涂层微观结构进行表征;采用显微硬度仪和拉伸测试系统对Ti_2AlC涂层的基本力学性能进行测试;采用N2吸附法测涂层孔隙,采用电化学工作站测涂层的贯通孔隙。结果表明:对平均粒径0.3μm的Ti_2AlC粉末进行水热处理时,添加硫酸铵能够促进亚微米颗粒的团聚,团聚粉末的平均粒度可达到6μm。此粉末的冷喷涂特性最好,沉积的Ti_2AlC涂层厚度达到100μm,涂层中有微孔和介孔但没有贯通孔隙,涂层和基体结合强度达到了44MPa。 相似文献
8.
以Ti,Al和TiC为原材料,用无压煅烧合成法制备三元化合物Ti3AlC2。详细讨论了煅烧温度和铝含量对多晶Ti3AlC2纯度的影响。利用X射线衍射仪、场发射扫描电镜和场发射透射电镜研究了粉末材料的组织结构、晶粒大小、层板厚度和选区电子衍射花样。结果表明1300℃是合成Ti3AlC2粉末的最佳煅烧温度,1:1.2:2是Ti/Al/TiC原材料的最佳摩尔比。用热压法制备了不同烧结温度下的Ti3AlC2块体试样,在1300℃热压制备的Ti3AlC2块体的相对密度可达99.9%,其维氏硬度和三点抗弯强度分别为5.7 GPa和630 MPa。通过场发射扫面电镜观察材料的断口形貌,进一步分析了Ti3AlC2块体材料的强化机理。 相似文献
9.
Guobing YingXiaodong He Mingwei LiShanyi Du Wenbo HanFei He 《Journal of Alloys and Compounds》2011,509(31):8022-8027
In this work, phase pure Cr2AlC and impure Cr2AlC with Cr7C3 have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10−5 K−1 in the temperature range of 25-1200 °C. The thermal conductivity of the Cr2AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr2AlC decreases from 1.8 × 106 Ω−1 m−1 to 5.6 × 105 Ω−1 m−1. For the impure phase of Cr7C3, it has a strengthening and embrittlement effect on the bulk Cr2AlC. And the Cr2AlC with Cr7C3 would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity. 相似文献
10.
Jun Yang Xiaoci LiJunyi Zhou Yu TangYuanming Zhang Yongwang Li 《Journal of Alloys and Compounds》2011,509(37):9271-9277
Bismuth ferric oxide nanopowders were prepared through combustion method. Pure phase and well-crystallized BiFeO3 can be obtained by controlling the combustion process, fuel type and fuel-to-oxidant ratio. The evolutions of phase constitution and structural characteristics of the as-resulted nanopowders were investigated by X-ray diffraction, scanning electron microscope, and simultaneous thermogravimetric analysis. The results revealed that both the type and amount of fuel have to be carefully considered because they play an important role in total reaction characteristics. Among all tested fuels, l-α-alanine and glycine are the suitable fuels for BiFeO3 synthesis. For α-alanine, the optimal fuel-to-oxidant ratio is 0.22, which results in a suitable flame temperature for BiFeO3 formation. Still, too little fuel would result in only amorphous phase powders due to the low flame temperature and too much fuel would lead to transformation of the BiFeO3 phase to impurities because of the high flame temperature involved. The resulting BiFeO3 nanopowders exhibited strong H2O2-activiting ability and weak magnetism. When BiFeO3 nanopowders were used as a heterogeneous Fenton-like catalyst to degrade rhodamine B (RhB), the apparent rate constant for RhB degradation in the presence of H2O2 at pH 5.0 was evaluated to be 0.048 min−1. 相似文献
11.
Jianhui Yang Linsen Han Yixiang ChenGuanghua Liu Zhiming LinJiangtao Li 《Journal of Alloys and Compounds》2012,511(1):81-84
Reactants were pelletized, and then combustion synthesis of Si3N4 powder was achieved under the N2 pressure of 3.0 MPa. Effects of the pelletization of reactants and Si3N4 diluents on the combustion process parameters and the characteristics of products were studied. The combustion mode of single reactant pellet was preliminarily discussed. The results indicated that the combustion reaction of single pellet was layer-by-layer from the surface to the core, which led to two peaks on the combustion temperature variation waves. With increasing the diluents content, the morphologies of Si3N4 particles changed from short rods into equiaxed grains, and residual Si in the final products obviously decreased. Single phase β-Si3N4 powder mainly contained equiaxed grains was prepared when 58 wt.% diluents was added. 相似文献
12.
SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba3Si4C2. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba3Si4C2 has the Ba3Ge4C2 type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO3), and contains isolated anion groups of slightly compressed [Si4]4− tetrahedra and [C2]2− dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10−2–7 × 10−3 S cm−1 in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K−1. 相似文献
13.
Jianing LiChuanzhong Chen Zhaoqing LinTiziano Squartini 《Journal of Alloys and Compounds》2011,509(14):4882-4886
Laser cladding of the Fe3Al + TiB2/Al2O3 pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti3Al/Fe3Al + TiB2/Al2O3 ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti3Al/Fe3Al + TiB2/Al2O3 ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al2O3 can react with TiB2 leading to formation of amount of Ti3Al and B. This principle can be used to improve the Fe3Al + TiB2 laser cladded coating, it was found that with addition of Al2O3, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases. 相似文献
14.
Di Shan Guo Yan Lian Zhou Chengshan LiJinshan Li Guoqing LiuJianqing Feng 《Journal of Alloys and Compounds》2011,509(8):3602-3605
T3SiC2 bulks have been synthesized by infiltrating Si liquid into porous precursor pellets composed of solid TiC and Ti powders. Silicon pellets were placed at the bottom of the precursor pellets as the liquid source. The starting compositions can be represented by the formula 2TiC + Ti + xSi, where x = 1.0, 1.2, 1.5 and 1.8, respectively. The phase formation and microstructure of the bulks were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) system. The results demonstrated that the TiC/Ti precursor pellet could only react with Si completely when the x value is 1.8. Impurities SiC, Ti-Si binary compounds and Ti8C5 appeared along the silicon diffusion direction. It is found that the compositions of impurities strongly depended on the Si-concentration. Reaction mechanism of this Ti3SiC2 infiltration synthesis has also been discussed based on the Si-concentration changes on the diffusion path. 相似文献
15.
In this study, we fabricated high purity Ti3SiC2 ceramic by mechanical alloying (MA) and spark plasma sintering (SPS), and investigated the effect of trace amount of Al on these processes. Our results show that addition of proper amount of Al significantly increases the purity of Ti3SiC2 in the MA and subsequent SPS products, and remarkably reduces the sintering temperature for Ti3SiC2. Ti3SiC2 sintered compact with a purity of 96.5 wt% was obtained by 10 h of MA and subsequent SPS from a starting mixture composed of n(Ti):n(Si):n(Al):n(c) = 3:1:0.2:2 at 850 °C. At 1100 °C, Ti3SiC2 with a purity of 99.3 wt% and a relative density of 98.9% was obtained. 相似文献
16.
Baoyan Liang Mingzhi Wang Jinfeng Sun Qin Zou Xin Han 《International Journal of Refractory Metals and Hard Materials》2009,27(5):927-930
The mechanically activated sintering process was adapted to synthesize Ti3AlC2 using 3Ti/Al/2C/0.05Sn powder mixtures. The result showed that the powders containing TiC, Ti3AlC2 and Ti2AlC were obtained by mechanical alloying (MA) 3Ti/Al/2C powders. Addition of appropriate Sn reduced the content of Ti2AlC and enhanced the synthesis of Ti3AlC2 significantly. The powders with highest content of Ti3AlC2 were obtained by MA 3Ti/Al/2C/0.05Sn powders. Through pressureless sintering the mechanical alloyed powders at 900–1100 °C for 2 h, the high purity Ti3AlC2 material with fine organization was produced. 相似文献
17.
In this paper we report on the electrochemical corrosion of select MAX phases, namely Ti2AlC, (Ti,Nb)2AlC, V2AlC, V2GeC, Cr2AlC, Ti2AlN, Ti4AlN3, Ti3SiC2 and Ti3GeC2 in 1 M NaOH, 1 M HCl and 1 M H2SO4 solutions. Polarization characteristics recorded in 1 M NaOH show that V2AlC, V2GeC and Cr2AlC undergo active dissolution at potentials more positive than the corrosion potential, while Ti2AlC, (Ti,Nb)2AlC, Ti3SiC2 and Ti3GeC2 passivate. In the 1 M HCl solutions, Ti2AlC, V2AlC and V2GeC actively dissolve; Ti3SiC2 and Ti3GeC2 passivate. Depending on potential, (Ti,Nb)2AlC and Cr2AlC showed trans-passive behavior. In 1 M H2SO4 solutions, Ti2AlC, (Ti,Nb)2AlC, Ti3SiC2 and Ti3GeC2 passivate, V2AlC and V2GeC show active dissolution, while Cr2AlC exhibits trans-passive behavior. Ti2AlN and Ti4AlN3 were passive in all solutions except in 1 M HCl, where Ti2AlN showed trans-passive behavior. Given that the corrosion behavior of (Ti,Nb)2AlC is unlike either Ti or Nb, the behavior of the former cannot be predicted from that of the latter. 相似文献
18.
Sung Sic HwangJaeHo Han Dongyun Lee Sang-Whan Park 《Journal of Alloys and Compounds》2011,509(35):L336
High-purity Ti3SiC2 compounds have been fabricated by infiltration of molten Si into a precursor, a partially sintered TiCx (x = 0.67) preform. The Si source and the TiCx preform were placed side by side on carbon cloth, and the system was heated to 1550 °C. Molten Si infiltrated the preform through the carbon cloth, and a direct reaction between TiCx and molten Si immediately occurred at the reaction temperature to yield pure Ti3SiC2. We could observe phase formation and the microstructure of the bulk products with time, which were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). Pure Ti3SiC2 compounds were formed on the exterior of the TiCx preform at 1550 °C when the sintered TiCx:Si ingot molar ratio was 3:1.4. At 1550 °C, no other minor phases were detected for any of the sintering time ranges. 相似文献
19.
氧化铝/氧化铝复合材料(Al2O3/Al2O3)是20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,已经发展为与SiC/SiC、C/SiC等非氧化物陶瓷基复合材料并列的一类陶瓷基复合材料。与非氧化物陶瓷基复合材料相比,Al2O3/Al2O3具有长时抗氧化、高温耐腐蚀、低成本等独特优势,已经在航空发动机、地面燃气轮机等军民两用热结构材料领域展现出广阔的应用前景。本文从材料应用的角度出发,系统分析阐述了目前在Al2O3/Al2O3占主导地位的多孔基体Al2O3/Al2O3(P-Al2O3/Al2O3)的增韧机制、成型工艺和性能特点,重点归纳了国外近年来P-Al2O3/Al2O3的工程化应用进展及前景,最后指出了P-Al2O3/Al2O3存在的局限性并展望了未来发展方向,旨在为国内Al2O3/Al2O3体系发展提供借鉴和参考。 相似文献
20.
MoSi2/WSi2 nanocrystalline powder has been successfully synthesized by the mechanical-assistant combustion synthesis method. This method includes a ball-milling process followed by combustion synthesis. The composition and microstructure of the as-milled powder mixture were detected by X-ray diffraction and scanning electron microscopy analyses. Their results show that the Mo(W) solid solution and Si nanocrystals could be obtained during the ball-milling process. Compared with normal powder mixture (Mo + Si + W), it could be easily ignited and high maximum combustion temperature was achieved. It was also confirmed that MoSi2/WSi2 solid solution powder with nanometric structure could be prepared through combustion synthesis method from the mechanical activated powder mixture. 相似文献