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用燃烧波淬熄法研究了TiC-Al金属陶瓷自蔓延高温合成中显微组织的转变,淬熄试样中保留了未反应区、反应区及反应完成区.用扫描电子显微镜观察了燃烧反应中的显微组织转变过程,用能谱仪分析了各微区的成分变化,测量了燃烧温度和燃烧波蔓延速度,并用XRD分析了反应产物相的组成.结果表明,Ti-C-Al系燃烧反应起始于铝粉熔化后与固态钛粉反应生成Al3Ti,并随着反应温度的升高,TiC颗粒从溶有钛和碳的铝熔体中析出;当Al3Ti熔化后,从熔体中也析出TiC颗粒,最终产物组织中除大量的TiC颗粒分布于铝基体中外,还发现有少量的Al3Ti存在,可能与使用的钛粉和铝粉的原料颗粒较粗有关. 相似文献
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自蔓延高温合成碳化铬金属陶瓷熔覆层 总被引:6,自引:2,他引:6
利用自蔓延高温合成(SHS)熔铸技术,将碳化铬的高温熔体铺展在平面样品的钢表面上,从而形成厚度为几毫米的熔覆层。为克服碳化铬与底材的润湿问题,采用与Fe有良好互溶性的Cr作为润湿功能层,在此基础上,使Cr-C合金层中的碳作阶梯改变,从而获得了梯度熔覆层结构。来用N2加压(<20MPa)和预热工艺(≤300℃)等措施,控制反应燃烧温度,改善熔体流动性,增大熔渣分离速度,有利于提高熔覆层表面平滑程度。研究认为,良好的结合强度来源于界面间强烈的冶金作用以及梯度成分分布。 相似文献
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在研究Ti,C,A1摩尔比为2:1:1的混合粉末自蔓延高温合成Ti2A1C过程中的组织演变中,将在试样中蔓延的燃烧波强制淬熄.用扫描电镜观察了淬熄试样中的显微组织演变,测定了其燃烧温度,并用X射线衍射检测了燃烧合成产物的相组成.结果表明:合成反应以Al的熔化为先导;反应过程可用溶解-析出-熔化结晶机制描述;该反应具有不完全性,可能是由于实验中使用了较粗的钛粉和铝粉所致. 相似文献
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Ni3Al金属间化合物自蔓延高温合成中的显微组织演变 总被引:1,自引:0,他引:1
为了研究用Ni粉和Al粉自蔓延高温合成(SHS)Ni3Al过程中的显微组织演变,用燃烧波淬熄法使蔓延的燃烧波自行熄灭,用扫描电子显微镜(SEM)及能谱仪(EDS)观察和分析了淬熄试样中的显微组织,测试了燃烧温度,并用X射线衍射(XRD)分析了合成产物的相组成.结果表明,合成反应开始于Al的熔化,从而使Ni粉粒开始部分溶解,Ni与Al原子间的互扩散导致Ni3Al反应扩散层在未溶解的Ni粉粒表面形成并逐渐增厚.该反应具有不完全性,可能是实验中使用了较粗的Ni粉和Al粉的缘故. 相似文献
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用燃烧波淬熄法研究了TiC-Ti金属陶瓷自蔓延高温合成(SHS法)中的组织转变和反应机理。淬熄试样中保留了未反应区、反应区及已反应区。用扫描电子显微镜观察了燃烧反应中的显微组织转变过程,用能谱仪分析了各微区的成分变化,测量了燃烧温度Tc,并用XRD分析了反应产物的相组成。实验结果表明:TiC-Ti复合材料的自蔓延高温合成机理可以用溶解-析出机制来描述:Ti首先部分熔化,C溶解在Ti液中,并和Ti发生反应生成TiCx,随着温度的升高,TiCx熔化,形成Ti-C熔体,在降温过程中,细小的TiC大量从Ti-C熔体中析出并聚集,最终形成TiC增强Ti基复合材料。 相似文献
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自蔓延高温合成TiC-Ni金属陶瓷的热力学编程计算与分析 总被引:2,自引:0,他引:2
根据热力学原理对Ti、C、Ni三元体系进行热力学编程计算,绘出了标准反应自由焓随温度变化的曲线、绝热温度随Ni含量变化的曲线以及绝热温度随预热温度变化的曲线,通过对曲线进行分析认为:Ti、C、Ni三元体系的主反应是Ti C=TiC;体系的绝热温度随Ni含量的增加而下降,当预热温度为600K时,最佳的理论Ni含量约40%;体系的绝热温度随预热温度的升高而升高,当Ni含量过大,体系的绝热温度小于1800K时,可以适当提高预热温度,来确保反应的自发进行。 相似文献
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自蔓延高温合成(SHS)技术发展和应用 总被引:1,自引:0,他引:1
详细地叙述了自蔓延高温合成(SHS)技术的基本原理,特点及国内外发展情况,并对SHS工艺在工业领域中应用的情况进行了介绍。 相似文献
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J. H. Ouyang Xiaodong Li T. C. Lei 《Journal of Materials Engineering and Performance》2000,9(2):234-246
The microstructure of a laser-clad TiC-Ni particle-reinforced coating on 1045 steel was studied by scanning electron microscopy
(SEM), transmission electron microscopy (TEM), and ion microprobe mass spectroscopy (IMMS). The microstructural constituents
of the clad layers (CLs) were analyzed to be TiC particles, γ-Ni primary dendrites, and interdendritic eutectics of γ
e
-Ni plus M23(CB)6 and M6(CB) carboborides. Three growth mechanisms of the original TiC particles were found: (1) stepped lateral growth at the edges,
(2) radiated and cylindrically coupled growth at the edges, and (3) bridging growth of the clustered particles. Ordered and
modulated structures were found in the original TiC particles. In addition to the original TiC particles, fine TiC particles
precipitated from the liquid phase and γ-Ni solid solution during laser cladding. The microstructures of the bonding zones (BZs) were intimately associated with laser
processing parameters. The BZs of the clad coatings can be categorized into three types according to the combination of the
CL with heat-affected zone (HAZ): (1) straight interface combination, (2) zigzag connection, and (3) combination by partial
melting of prior austenitic grain boundaries of the substrate. The straight interface BZ consists of the γ-Ni solid solution only, but in the other two types of combinations, the BZs consist of γ-Ni primary dendrites, γ-(Fe, Ni)/M23(C, B)6 eutectics, and martensite of the substrate. The microstructural evolution of the CLs was discussed. The formation and phase
transformation models of the BZs were proposed. 相似文献
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Microstructural development during high-temperature oxidation of Ti2AlC below 1300 °C involves gradual formation of an outer discontinuous TiO2 layer and an inner dense and continuous α-Al2O3 layer. After heating at 1400 °C, an outer layer of mixed TiO2 and Al2TiO5 phases and a cracked α-Al2O3 inner layer were formed. After heating to 1200 °C and cooling to room temperature, two types of planar defect were identified in surface TiO2 grains: twins with (2 0 0) twin planes, and stacking faults bounded by partial dislocations. Formation of planar defects released the thermal stresses that had generated in TiO2 grains due to thermal expansion mismatch of the phases (TiO2, α-Al2O3 and Al2TiO5) in the oxide scale. After heating to 1400 °C and cooling to room temperature, crack propagation in TiO2 grains resulted from the thermal expansion mismatch of the phases in the oxide scale, the high anisotropy of thermal expansion in Al2TiO5 and the volume changes associated with the reactions during Ti2AlC oxidation. An atomistic oxidation mechanism is proposed, in which the growth of oxide scale is caused by inward diffusion of O2? and outward diffusion of Al3+ and Ti4+. The weakly bound Al leaves the Al atom plane in the layered structure of Ti2AlC, and diffuses outward to form a protective inner α-Al2O3 layer between 1100 and 1300 °C. However, the α-Al2O3 layer becomes cracked at 1400 °C, providing channels for rapid ingress of oxygen to the body, leading to severe oxidation. 相似文献
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A phase-field model is developed and used to simulate high-temperature synthesis of intermetallic compounds. The model is based on a thermodynamic formulation, which incorporates the formation of chemically ordered phases and the associated heat generation. In contrast to previous approaches to modelling of high-temperature synthesis of intermetallics, the present model can be used to analyse the kinetics of the process at the microstructure level. The model takes general thermodynamic and kinetic parameters as input and gives as output a spatially resolved sequence of phase formation, from which the overall reaction kinetics can be inferred. Thus, no additional assumption has to be made on the nature of the kinetic mechanisms or on the magnitude of the overall reaction rate. Beside prediction of the microstructure, the model captures the key thermal characteristics of the combustion synthesis in both modes of thermal explosion and self-propagation. The results of simulations, as applied to the case of intermetallic formation in a simplified Ni–Al system, are shown to be consistent with the existing experimental data. 相似文献
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采用自蔓延高温合成技术实现了TiAl合金的连接。在连接过程中采用了具有很高放热量的Ti-Al-C中间层以及外加电磁场辅助连接。连接接头包括3个典型的反应区域,靠近TiAl母材界面处发现了深灰色的TiAl,反应层,在中间层内观察到了TiC颗粒以及Ti-Al系化合物。直接连接时由于产物和反应物之间的比热差,杂质的气化和孔隙中束缚气体的释放而导致孔隙无法避免。为了提高致密度,在粉末压坯和TiAl母材之间添加了Ag-Cu钎料箔。在SHS反应过程中熔化的钎料改善了中间层对TiAl母材的润湿同时填充到了中间层反应产物的孔隙中,采用这种方法能够提高反应产物的致密度和连接质量。 相似文献
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1 INTRODUCTIONSHS ,theself propagatinghigh temperaturesyn thesis,wasfirstdiscoveredbyMerzhanovandBorovinskayawhentheystudiedsolidfu 相似文献