TiC/Ni/TiC材料的SHS合成研究

通过ＳＨＳ结合准等静压法得到了ＴｉＣ／Ｎｉ／ＴｉＣ材料,在ＳＨＳ过程中,Ｎｉ沿试样厚度方向向两层ＴｉＣ中对称渗流,在生层ＴｉＣ当中,Ｎｉ呈梯度分布,材料的硬度从中心向两边呈对称分布。理论上分析了Ｎｉ在两层ＴｉＣ中呈梯度分布所需的渗流动力。     

激光引燃自蔓延合成TiC／Al基复合材料研究

采用激光引燃自蔓延高温合成法,通过改变激光功率和成分配比制备了TiC陶瓷颗粒增强的Al基复合材料。利用X射线衍射（XRD）和扫描电镜（SEM）对自蔓延合成产物的相组成和显微组织进行研究。结果表明,通过激光引燃自蔓延法可以合成高纯度的TiC／Al基复合材料。随着激光功率升高,引燃时间缩短,合成的复合材料中TiC颗粒的尺寸和孔隙率增大;激光参数不变时,随着Al含量的增多合成TiC颗粒尺寸逐渐变小,形貌由球状转变为多角状。     

Role of iron addition in the combustion synthesis of TiC–Fe cermet

Coarse iron powders were incorporated into a mixture of titanium and carbon black powders, and the mixture was used for a combustion front quenching test. The quenched sample was analysed by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis to study the microstructural evolution in the iron powders. Also, the phase constituent of the combustion-synthesized product was analysed by X-ray diffraction (XRD). The results showed that the microstructural evolution in the iron powders could be described by the solution–precipitation model. Diffusion of carbon into the iron powders brought about a decrease in the melting point of the Fe–C alloy and a melt of the Fe powders, thus accelerating the solution of Ti into the molten droplets; then, TiC particles precipitated out of the saturated droplets. Therefore, it was suggested that iron addition mainly played the role of a source of reaction, i.e. it not only made necessary preparations for the combustion reaction of Ti + C, but also it provided another source for the precipitation of TiC particles. This revised version was published online in November 2006 with corrections to the Cover Date.     

The self-propagating high-temperature synthesis (SHS) of ultrafine high-purity TiC powder from TiO2+Mg+C

The self-propagating high-temperature synthesis (SHS) method has been applied to the preparation of TiC powder from mixtures of TiO₂, Mg, and C. The TiC/MgO product is leached by hydrochloric acid to remove the MgO. The optimum mixing ratio was TiO₂MgC=12.21.5. The final product TiC had > 99.9% purity and relatively uniform particle size of 0.3–0.4 m.     

SHS／PHIP技术制备TiC—30Fe金属陶瓷的显微组织及形成过程研究

通过自蔓延高温合成结合准热等静压法制备出了致密度为９６．３％的ＴｉＣ－３０ｗｔ％Ｆｅ金属陶瓷。分析了金属陶瓷的结构和组织，讨论了ＳＨＳ／ＰＨＩＰ制备金属陶瓷的材料结构形成过程。结果表明，金属陶瓷由近乎球形ＴｉＣ颗粒和Ｆｅ粘结相组成。粘结相Ｆｅ与ＴｉＣ之间有一较薄扩散层。     

Ni 含量对SHS 法合成TiC-Ni 基金属陶瓷的影响

利用SHS 结合准热等静压(PH IP) 技术制备了TiC-Ni 基金属陶瓷, 理论分析和实验显示, 绝热温度T_ad和燃烧温度T c 随Ni 含量的增加而降低, 反应温度影响产物的组织形貌,Ni 含量的增加使合成的TiC 颗粒尺寸变小, 并且逐渐趋向于规则的球形。最后的产物均由TiC 和Ni 两相组成。产物的致密度随Ni 含量的增加逐渐提高, 硬度值随Ni 含量的变化而变化, 两种因素的作用使硬度值在Ni 含量为20% 时达到最大。     

Combustion synthesis/quasi-isostatic pressing of TiC–NiTi cermets: processing and mechanical response

TiC–NiTi composites were produced by a technique combining self-propagating high-temperature synthesis (SHS) of elemental powders of Ni, Ti, and C with densification by quasi-isostatic pressing (QIP). In order to create a one-step synthesis/densification process, the Ti + Ni + C reactant material was surrounded in a bed of graphite and alumina particulate before initiation of the combustion reaction. The sample was ignited within the particulate and subjected to a uniaxial load immediately after passage of the combustion wave. The constitutive response, composition and resulting structures of the composites with varying volume fractions of NiTi are characterized. Powder mixtures prepared anticipating the formation of stoichiometric TiC result in the formation of composites with a eutectic matrix of Ni₃Ti and NiTi. This titanium impoverishment of the matrix is consistent with the formation of nonstoichiometric TiC _x during the combustion reaction. The Ni₃Ti phase can be suppressed by anticipating the formation of TiC_0.7 and adjusting the chemical content of the reactant mixture to include additional titanium. These cermets combine the high hardness of the ceramic phase with the possible shape memory and superelastic effects of NiTi.     

An investigation of the synthesis,consolidation and mechanical behaviour of Al 6061 nanocomposites reinforced by TiC via mechanical alloying

Nanostructured Al 6061–x wt.% TiC (x = 0.5, 1.0, 1.5 and 2.0 wt.%) composites were synthesised by mechanical alloying with a milling time of 30 h. The milled powders were consolidated by cold uniaxial compaction followed by sintering at various temperatures (723, 798 and 873 K). The uniform distribution and dispersion of TiC particles in the Al 6061 matrix was confirmed by characterising these nanocomposite powders by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The mechanical properties, specifically the green compressive strength and hardness, were tested. A maximum hardness of 1180 MPa was obtained for the Al 6061–2 wt.% TiC nanocomposite sintered at 873 K, which was approximately four times higher than that of the Al 6061 microcrystalline material. A maximum green compressive strength of 233 MPa was obtained when 2 wt.% TiC was added. The effect of reinforcement on the densification was studied and reported in terms of the relative density, sinterability, green compressive strength, compressibility and Vickers hardness of the nanocomposites. The compressibility curves of the developed nanocomposite powders were also plotted and investigated using the Heckel, Panelli and Ambrosio Filho and Ge equations.     

Microstructure and mechanical properties of an Al–TiC metal matrix composite obtained by reactive synthesis

A metal matrix composite has been obtained by a novel synthesis route, reacting Al₃Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%.     

Structural and mechanical properties of TiB2 and TiC prepared by self-propagating high-temperature synthesis/dynamic compaction

Titanium-diboride and titanium-carbide compacts with diameters of 100 mm and thicknesses of 25 mm were fabricated by self-propagating high-temperature synthesis/dynamic compaction (SHS/DC) of the elemental powders. Under the best conditions, the densities were greater than 99% and 96.8% of the theoretical densities for TiB₂ and TiC, respectively. The microhardness, compressive strength, and elastic modulus of the TiB₂ prepared by the SHS/DC method were comparable to reported values for hot-pressed TiB₂. While the microhardness and elastic modulus of the TiC compacts were comparable to those for hotpressed TiC, the compressive strength was lower due to extensive cracks in the compacts. The TiB₂ prepared using a low-purity boron powder (1–5% carbon impurity) compacted to higher densities and had less cracking than that prepared using a high-purity boron powder (0.2% carbon). This result could have an impact on the cost of producing TiB₂/TiC structural components by the SHS/DC process.     

Self-propagating high-temperature synthesis of AlN in a graphite crucible in air by mechanical activation

Powders of Al and C were mixed in a molar ratio of Al :C = 3:1 and were then ground in a planetary ball mill. When the thus mechanically activated mixtures were transferred into a graphite crucible and exposed to air, they spontaneously ignited and self-propagating high-temperature synthesis took place in two successive steps. The products were sliced along the depth direction and examined by X-ray diffraction. Depending on the depth of the crucible, aluminium nitride, aluminium carbide, aluminium oxynitride, aluminium oxycarbide and alpha alumina were detected. From measurements of the lattice constant, it was found that aluminium nitride with a 97% purity could be obtained at the bottom of the graphite crucible. This revised version was published online in November 2006 with corrections to the Cover Date.     

TiC/NiCrMoAlTi金属陶瓷的微观结构与力学性能

采用粉末冶金真空烧结方法制备了TiC/NiCrMoAlTi金属陶瓷.研究了Mo含量对TiC/NiCrAlTi金属陶瓷的微观结构与力学性能的影响.结果表明,在TiC/NiCrAlTi金属陶瓷中添加Mo后,在金属陶瓷的硬质相颗粒周围出现了典型的环形相,随着Mo含量的增加,环形相增多变厚,致使金属陶瓷的硬度线性增加,环形相的生成使金属陶瓷硬质相的颗粒细化、尖角钝化,从而提高了金属陶瓷的抗弯强度,当环形相过度发达时由于其本身较脆,金属陶瓷的抗弯强度降低,Mo含量为4%(质量分数)时抗弯强度达到最大值.     

机械振动对SHS陶瓷内衬复合管显微结构和力学性能的影响

通过在重力分离SHS法制备陶瓷内衬复合管过程中施以不同振幅与振频的单自由度上下往复式机械振动 ,研究了机械振动对SHS铝热燃烧、陶瓷凝固及复合管组织性能的影响 .研究发现 ,机械振动并相应提高振频可以提高燃烧温度、燃烧速率和反应转化率 ,促进Al2 O3 Fe液相重力分离和陶瓷致密过程 ,并使陶瓷层的凝固组织发生改变 ;性能测试结果表明机械振动并相应提高振频可以提高复合管的各项力学性能指标和内衬陶瓷层的表面质量 .     

Chemical activation of the SHS process in the Nb−C system

The phenomenon of chemical activation is investigated using combustion of the Nb–C system in the presence of an activating additive, namely, polytetrafluoroethylene, as an example. Regions of the parameters of the process are found where the interaction occurs by two different mechanisms. The characteristic features of the process are established and the role of the activating additive in each region is determined.Institute of Chemical Physics, Academy of Sciences of Armenia, Yerevan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No.5, pp.590–593, November, 1993.     

Unconventional synthesis of Mg x C y Ni3: Synergic combination of mechanical alloying, SHS and isothermal heating

Several methods have been tested in order to prepare the perovskite type compound Mg _x C _y Ni₃ applying the mechanical alloying (MA), the self-propagating high-temperature synthesis (SHS) and the isothermal heating techniques in the different steps of preparation. These methods may be summarized as follows: method MCN-1) synthesis of the Mg _x C _y Ni₃ phase through MA of Mg₂Ni (previously synthesised by isothermal heating) and selected amounts of graphite and Ni, followed by isothermal treatment; method MCN-2) synthesis of the Mg _x C _y Ni₃ phase applying the SHS technique using powder compacts; method MCN-3) synthesis of an eutectic sample composed of Ni and MgNi₂ by means of isothermal heating, subsequent MA with graphite and final synthesis of Mg _x C _y Ni₃ by means of SHS. The methods MCN-2 and MCN-3 proved their validity to the synthesis of the desired compound with two main important results: complete conversion of the reactants into Mg _x C _y Ni₃ and control of the stoichiometry in the final product. For instance method MCN-1 shows instead a very low degree of conversion of the reactants. All the phases obtained after each preparation step (MA, SHS, isothermal heating) have been characterized by means of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS).     

In situ synthesis of Al–TiC in aluminum melt

In situ technology for the preparation of Al–TiC composite by self-propagating high-temperature synthesis is considered in this paper. It involves the synthesis of the reinforcement phase TiC from elemental powders directly in aluminum melt. Based on thermodynamic calculations, the composition and molar ratio of powders were chosen for the experiments. The effects of initial melt temperature and fluxes on the character of SHS reaction and TiC recovery were studied. The synthesis was shown to result in the formation of Al and TiC phases. The composites Al–TiC with the uncontaminated macrofracture, with the best TiC recovery and with the smallest TiC particles, can be produced at 1000 °C with fluxes.     

SHS/QC法制备TiC/Al2O3复合陶瓷的显微组织研究

通过自蔓延高温合成结合快速加压法（ＳＨＳ／ＱＣ）制备了ＴｉＣ／Ａｌ２Ｏ３复合陶瓷。研究了在不同预热温度、不同稀释剂加入条件下制备的ＴｉＣ／Ａｌ２Ｏ３复合陶瓷的 相、组织特征。结果表明,随着预热温度的升高,燃烧由不稳定的螺旋燃烧向稳定的平面燃烧过渡,材料易于压实成型且反应充分,但生成的材料组织粗大。反之,生成的ＴｉＣ、Ａｌ２Ｏ３颗粒细小,但加压成型时易出现裂纹。试验测定了该体系的燃烧特性参数,并对反     

Self-propagating high temperature synthesis (SHS) of titanium carbide

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.