Fabrication of bulk Al2O3 dispersed ultrafine-grained Cu matrix composite by self-propagating high-temperature synthesis casting route

Bulk Al₂O₃ dispersed ultrafine-grained (UFG) Cu matrix composite has been fabricated by self-propagating high-temperature synthesis (SHS) casting route. The microstructures and mechanical properties of the as-fabricated materials have been investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, and microhardness measurements and compression tests, respectively. The results show that the as-fabricated material has small amount of entrapped Al₂O₃ particles in uniform microstructure Cu having a grain size ranging from 200-500 nm with an elevated compressive yield stress (298 MPa) and an improved microhardness value (1.06 GPa). The possible strengthening mechanism of the product has been discussed.     

磁场诱导自蔓延高温合成钡铁氧体

本文采用外加磁场诱导自蔓延高温合成钡铁氧体,试验用的电磁场强度最高可达1.3T,对无磁场和不同磁场强度下合成的铁氧体的形貌、相组成和磁性能分别进行了表征.研究结果表明:外加磁场对燃烧温度有影响,燃烧温度影响产物转换,燃烧温度较低时,产物为BaFe2O4与BaFe12O19相共存;本试验条件下,磁场强度为0.86T时,合成为M型的钡铁氧体(BaFe12O19),产物结晶完整,有六角片状的钡铁氧体,且性能达到了最佳,矫顽力达到1083(4π)-1·kA·m-1,比剩余磁化强度为16.16 A·m2/kg,比不加磁场条件下分别提高50%和提高32%,说明适当的磁场强度诱导自蔓延高温合成可以改善BaFe12O19的磁性能.     

Effect of substitution of Si by Al on microstructure and synthesis behavior of Ti5Si3 based alloys fabricated by mechanically activated self-propagating high-temperature synthesis

The effect of substitution of Si by Al and mechanical activation on microstructure, phase composition, ignition and combustion temperature of Ti₅Si₃ based alloys and composites that were prepared by mechanically activated self-propagating high-temperature synthesis (MASHS) method was investigated. For this purpose elemental powders of titanium, silicon and aluminum were mixed according to the 5Ti + 3(1 − X)Si + 3XAl formula, where X = 0, 0.2, 0.4, 0.6. The samples were characterized by X-ray diffraction (XRD) analytical technique and scanning electron microscope (SEM) equipped with an energy-dispersive spectrum (EDS) analyzer. The results have shown that formation of Ti₅Si₃ during milling stage is postponed by adding Al into the system. Presence of Al in the Ti–Si system have a significant effect on the phase composition of the final products. Substitutional solid solution of Ti₅(Si, Al)₃ and Ti₅Si₃–Ti₃Al composite are formed by increasing Al amount in the system. Furthermore combustion temperature and crystallites size of Ti₅Si₃ is reduced with addition of Al into the Ti–Si system. Moreover, solubility of Al in Ti₅Si₃ is increased with enhancing the X up to 0.4, after that, the solubility of Al in Ti₅Si₃ is ceased, due to achieving the solubility limit of Al in the Ti₅Si₃. The average crystallites size of Ti₅Si₃ are decreased with increasing milling time prior to the reaction.     

Wear behaviors of an (TiB + TiC)/Ti composite coating fabricated on Ti6Al4V by laser cladding

A titanium-based composite coating reinforced by in situ synthesized TiB whiskers and TiC particles was successfully fabricated on Ti6Al4V by laser cladding. The coating is mainly composed of α-Ti cellular dendrites and a eutectic in which a large number of needle-shaped TiB whiskers and a few equiaxial TiC particles are uniformly embedded. The wear resistance of the coating is significantly superior to that of Ti6Al4V under the dry sliding wear condition at room temperature.     

自蔓延工艺参数对TiNi合金多孔体孔洞均匀性的影响

研究了自蔓延高温合成工艺制备了ＴｉＮｉ合金均匀多也体－人造骨材料的可能性。通过对工艺参数的优化，制备出整体均匀的钛镍合金多孔体，从而证明了应用自蔓延工艺制备ＴｉＮｉ合金多孔的可能性。     

High temperature flow behavior and constitutive model of alloy transition layer in composite steel tube prepared by centrifugal self-propagating high-temperature synthesis (SHS)

Centrifugal self-propagation high-temperature synthesis (SHS) is a newly developed composite preparation technique by which a ceramic-alloy-carbon steel multilayer composite tube can be prepared. The hot deformation behaviors of the alloy steel layer at 800 °C–1000 °C, strain rates of 0.01 s⁻¹, 0.1 s⁻¹, 1.0 s⁻¹ and 10 s⁻¹ were studied by Gleeble-1500 thermal simulator. Rheological curve characteristics were analyzed under different thermal compression processes and a phenomenological hyperbolic sinusoidal Arrhenius constitutive equation was established to characterize the rheological mechanics of the material. The results show that the alloy steel is sensitive to temperature and strain rate, and its value of true stress decreases with the increase of temperature and strain rate. Thermal deformation process is the interaction between work hardening and dynamic softening, which is accompanied by the increase and extinction of dislocations. Under the strain rate of 10 s⁻¹, the stress-strain curve has a significant decrease when the strain exceeds 0.5. According to the observation of microstructure, this phenomenon can be attributed to the micro-crack generated by the local instability flow in the denatured zone. With the strain rate decreases, the softening mechanism of the alloy changes from dynamic recovery to dynamic recrystallization. The calculation results of the Arrhenius constitutive equation (AARE = 6.54 %, R = 0.99452) indicate that the model can predict the flow stress of the alloy accurately.     

Effect of Ti/C additions on the formation of Al3Ti of in situ TiC/Al composites

A novel technique for fabricating TiC particulate-reinforced commercial purity Al composites was introduced. The mechanism of formation of brittle Al₃Ti up to 30 μm in size produced in the composites was studied and a method of eliminating them was put forward. The results show that: (1) the brittle Al₃Ti phase is always present in the composites when the Ti:C molar ratio is 1:1. In this case, the tensile elongation of the composite was only 4%, much lower than the value of unreinforced aluminum (20%); and (2) the formation of the brittle Al₃Ti phase can be eliminated entirely from the final product by using a proper Ti:C molar ratio of 1:1.3 in the Ti–C–Al preforms. In this case, the tensile elongation of this composite was 10%, higher than the value of the composite with a lot of Al₃Ti (4%). Moreover, improvement in the tensile elongation of the composite was accompanied by an increase of the ultimate tensile strength.     

Ti-C含量对多孔TiC/FeAl复合材料孔型结构和力学性能的影响

以尿素为造孔剂,利用自蔓延高温合成技术制备了多孔TiC/FeAl复合材料,主要考察了Ti-C含量（质量分数为15wt%~35wt%）对多孔TiC/FeAl复合材料孔型结构和压缩性能的影响。当Ti-C含量不高于25wt%时,多孔TiC/FeAl复合材料由毫米孔和孔壁微孔组成规则的复合孔型结构。相互连通的毫米孔产生于尿素颗粒的挥发和液相迁移;微孔尺寸为10~50 μm,产生于Fe-Al-Ti-C粉末的自蔓延过程,孔径随Ti-C含量的增加而增大。通过调整尿素的体积分数,多孔TiC/FeAl复合材料的孔隙率可控制在56.64%~85.35%。当Ti-C含量不高于25wt%时,多孔TiC/FeAl复合材料的抗压强度随Ti-C含量的增加而增大。当Ti-C含量高于25wt%时,多孔TiC/FeAl复合材料壁面微孔形状很不规则,且抗压强度下降。孔隙率约为64.3%时,多孔Fe-Al金属间化合物和TiC/FeAl复合材料（Ti-C含量为25wt%）的抗压强度分别为20.03 MPa和66.68 MPa,对应的应变值分别为4.77%和8.21%。另外,多孔TiC/FeAl复合材料的压缩性能可用Gibson-Ashby模型来解释。     

Influence of Cu addition on the self-propagating high-temperature synthesis of Ti5Si3 in Cu–Ti–Si system

The self-propagating high-temperature synthesis (SHS) reactions can take place in Cu–Ti–Si systems with Cu additions of 10–50 wt.%, and the products only consist of Ti₅Si₃ and Cu phases, without any transient phase. In Ti–Si system, most of the Ti₅Si₃ grains synthesized exhibit the polygon-shaped coarse appearance with an obviously sintered morphology. When Cu content increases from 10 to 50 wt.%, however, the Ti₅Si₃ exhibits cobblestone-like shape with a relatively smooth surface, and its average size decreases significantly from 15 to 2 μm or less. The formation mechanism of Ti₅Si₃ in Cu–Ti–Si system is characterized by the solution, reaction and precipitation processes. Furthermore, the addition of Cu has a great influence on the volume change between green and reacted preforms. The volume change increases with Cu content increasing from 0 to 20 wt.%, and then decreases with the content further increasing from 20 to 50 wt.%. The addition of Cu to Ti–Si system significantly decreases the onset temperature of the reaction during differential scanning calorimetry process, which is even much lower than the α → β transition temperature of Ti (882 °C), suggesting that the reaction could be greatly facilitated by Cu addition. As a result, the role of Cu serves not only as a diluent but also as a reactant and participates in the self-propagating high-temperature synthesis reaction process.     

硼砂对自蔓延高温合成ZrB2粉体的影响

以ZrO_2、Mg、B_2O_3及Na_2B4O_7为原料,采用自蔓延高温合成技术制备ZrB2粉体。通过FactSage7.0软件计算,从热力学角度研究了该反应体系发生自蔓延反应的可能性。采用X射线粉末衍射物相分析仪、场发射电子扫描电镜-能谱分析对最终产物的物相组成及显微形貌进行检测。分析结果显示,过量的Mg、B_2O_3可有效提高产物中ZrB_2的含量,Mg和B_2O_3分别过量40%(质量分数)、30%(质量分数)为Mg-ZrO_2-B_2O_3体系的较佳配比。基于上述优化配比,研究了用无水硼砂(Na_2B_4O_7)替换原料中B_2O_3对产物ZrB_2含量及晶粒尺寸的影响,当替换量达到15%(质量分数)时,ZrB_2的含量最高,并且随着Na_2B_4O_7替换量的增加,产物的晶粒尺寸由2μm减小至不足0.5μm。     

Effect of Ti/C ratio on the SHS reaction of Cr–Ti–C system

The effect of Ti/C molar ratio on the SHS reaction of the Cr–Ti–C system was investigated. With the Ti/C ratio increasing, the type of products synthesized by SHS varied, and the amount of solid solution (Ti,Cr)C_ss increased in the final products; furthermore, also the lattice parameter of (Ti,Cr)C_ss increased due to the reduction in the solubility of Cr in TiC. Moreover, the combustion temperature increased, resulting in the increase of average grain size of (Ti,Cr)C_ss from ∼ 1 μm to ∼ 5 μm as well as the grain shape looked more and more like spherical.     

Effect of Nanosized Powders on the Structure and Properties of Electrospark Alloyed Coatings

The influence of nanosized additives ZrO₂, Al₂O₃, W, WC, WC-Co, NbC, Si₃N₄ on mass transfer of the SHS electrode material of the Ti-Cr-Ni-C system (SHIM-3B alloy trade mark) is considered. The thickness, continuity, and microhardness of the electrospark coatings alloyed onto the nickel alloy, as well as the coating structure, wear resistance, and the nanosized powder distribution in the coating have been studied. The coatings obtained have been subjected to X-ray analysis. An optimum performance regime of the ALIER-METAL setup for high-frequency electrospark alloying has been determined. It has been found that addition of nanosized powders to the electrode material facilitates thickening of the electrospark alloying (ESA) coatings and improvement of their continuity, hardness, and wear resistance.     

Effect of HCl concentration on TiB2 separation from a self-propagating high-temperature synthesis (SHS) product

This paper presents a synthesis of TiB₂ powder via self-propagating high-temperature synthesis (SHS) method using a mixture of TiO₂, B₂O₃ and Mg followed by acid leaching. In the acid leaching step, the MgO content in the SHS product was leached in different HCl concentrations. X-ray diffraction (XRD) analysis showed that when 9.3 M HCl was used, the leached SHS product was found similar to that of the commercial TiB₂ powder. However, scanning electron microscopy (SEM) and BET surface area analysis revealed that the leached product was agglomerated and exhibited very high surface area.     

Effect of in situ reaction conditions on the microstructure changes of Cu-TiB2 alloys by combining in situ reaction and rapid solidification

A new short flow technique combining in situ reaction and rapid solidification has been developed and used to prepare Cu-TiB₂ (0.45, 1.6 and 2.5 wt% TiB₂) alloys. The effects of in situ reaction conditions, cooling rate and solute concentration on the microstructure change of Cu-TiB₂ alloys were systematically investigated and analyzed by modeling. It is shown that the size and distribution of TiB₂ particles are strongly dependent on the choice of reactor shape, in situ reaction conditions and solute concentration, specifically, the size and aggregation level of TiB₂ particles tend to increase as increasing normal volume percent of TiB₂ particles when the same in situ reaction condition is used. Some different in situ reaction mechanisms, based on the microstructure change and TiB₂ particle distribution under different conditions, were also established and analyzed, which can be used to quantitatively predict the size of melt micelles needed for synthesizing uniformly distributed TiB₂ particles with different sizes in the copper matrix.     

Nano iron oxide (Fe2O3)/carbon black electrodes as electrode material for electrochemical capacitors: Effect of the nanoparticles dispersion quality

In the present study, nano Fe₂O₃/carbon black electrodes are proposed for electrochemical capacitors and the effect of nanoparticles dispersion quality on the surface morphology, nature and electrochemical properties of the electrodes are investigated. Mechanical pressing is accompanied by different mixing (mechanical and sonication) processes to prepare the electrode. Electrochemical properties of the produced nanocomposites are studied using cyclic voltammetry and electrochemical impedance spectroscopy tests in 2 M KCl electrolyte. Scanning electron microscopy is used to characterize the microstructure and the nature of the nanoparticles on the nanocomposites produced. Results obtained show that the sonicated and unsonicated 10:80:10 (CB:Fe₂O₃:PTFE) electrodes have specific capacitance of 22.02 and 22.35 F g⁻¹ respectively, at scan rate of 10 mV s⁻¹. Sonication process breaks the agglomerated particles and disperses them on the electrode surface, uniformly. This increases the specific surface area and the electrical resistance of the electrodes. The sonicated electrodes show a higher charge separation capability at electrolyte/electrode interfaces, lower ratio of outer to total charge (q_O*/q_T*) of 0.13 and lower current response at end potentials. Energy density was increased after the sonication process from 0.686 to 1.498 (Wh kg⁻¹). Charge/discharge cycling results confirmed that the uniform dispersion of active material on the electrode surface postpones the electrolyte decomposition and improves the electrical conductivity during cycling.     

Effect of the TiO2 nanoparticle size on the decomposition behaviors in aluminum matrix composites

The decomposition behaviors and the effect of particle size on the kinetic rate are studied for Al–3 vol.% titanium dioxide (TiO₂) composites by using three different types of TiO₂ particles (15, 50, and 300 nm). Thermal analysis shows that the reaction is stepwise with the first reaction starting before the melting temperature of Al. Since the high chemical potential of nanoparticles enhances reactivity, the TiO, Al₃Ti, and α-Al₂O₃ phases are found to be formed during the first reaction regardless of particle size. Based on observations of microstructure, the formation mechanism of Al₃Ti and α-Al₂O₃ is understood to be solution precipitation. Non-isothermal kinetic analysis reveals that the reaction mechanism is closely related to the three-dimensional continuous nucleation and the growth limited by diffusion. Particle size is found to be having considerable effect on the kinetic rate. As the particle size decreases, the rate constant increases, while the pre-exponential factor and the activation energy decreases. A non-linear relationship between the rate constant and the reciprocal of the size is found and evaluated.     

Effect of maleic anhydride modified MWCNTs on the morphology and dynamic mechanical properties of its PMMA composites

This study successfully grafted multiwalled carbon nanotubes (MWCNTs) with maleic anhydride (Mah-g-MWCNTs) via Friedel–Crafts acylation with the aluminum chloride catalyst (AlCl₃), investigated by Raman and TGA analysis. The covalent bonds and carboxylic groups of maleic anhydride provided additional active species, improving adhesion between the MWCNTs and poly(methyl methacrylate) (PMMA). This investigation also studied the morphology and dynamic mechanical properties of pristine MWCNTs (P-MWCNTs) and modified MWCNTs (Mah-g-MWCNTs) reinforced with PMMA. Findings show a homogeneous distribution of MWCNTs throughout the matrix for Mah-g-MWCNTs/PMMA composites, as revealed by transmission electron microscope (TEM). The addition of both MWCNTs influenced the molecular arrangement of the PMMA matrix and also increased the dynamic mechanical properties of MWCNTs/PMMA composites. Glass transition temperature (Tg) and storage moduli (E′) of the Mah-g-MWCNTs/PMMA composites increased significantly comparing with P-MWCNTs/PMMA composites, attributed to improved interfacial adhesion between the reinforcement and the matrix. DMA studies revealed that adding 4.76 wt% Mah-g-MWCNTs into PMMA generates a 184% enhancement in the storage modulus and a 19 °C increase in Tg. However, adding 4.76 wt% P-MWCNTs into PMMA only generates 108% enhancement in the storage modulus and a 14 °C increase in Tg.     

Effect of the microstructure on the cutting performance of superhard (Ti,Si,Al)N nanocomposite films

A d.c. reactive magnetron sputtering technique was used to deposit (Ti,Si,Al)N coatings onto WC-Co cutting tools. The microstructure of the coatings was analysed using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) measurement. Before the cutting experiments, the XRD results revealed a structure indexed to an fcc TiN. The results obtained by the XRD tests, with detector variation in asymmetric mode (rocking curves) showed a decrease in the quality of the fiber texture in the (111) grains with the change on deposition chamber geometry (two magnetrons in place of four magnetrons). Cross-sectional HRTEM images of the (Ti,Al)N sample showed grains with a diameter between 16 and 30 nm, while for the (Ti,Si,Al)N samples grains with a diameter between 6 and 10 nm were observed. Furthermore, through the visualization of bright field images it was possible to discern a columnar structure. For samples prepared at high deposition rates (2 μm/h), HRTEM micrographs revealed the formation of the multilayer stacking of (Ti,Si)N/(Ti,Al)N.     

Effect of Heat Treatment on the Microstructure and Residual Stresses in (Ti,Al)N Films

(Ti,Al)N films were fabricated by arc ion plating (AIP) and then annealed within a range of temperatures from 200 to 500~0C for 30 min in vacuum. The results indicate that the average residual stresses decrease slightly from -5.84 to -4.98 GPa with increasing annealing temperature. The stress depth distribution evolves from a sharp bell shape to a mild bell shape, suggesting a more uniform stress state in the annealed films. The microstructure of the films was also investigated in detail. The as-deposited film consists of fine columnar crystals with an amorphous phase at the interface. During heat treatment, the columnar subgrain growth was observed; meanwhile, the phenomenon of crystallization has been identified at the interface. Further more, the relationship between the residual stresses and the microstructure of the films was explored and highlighted. In addition, there is no hardness degradation of the films during heat treatment.     

Effect of CH4 and H2 on CVD of SiC and TiC for possible fabrication of SiC/TiC/C FGM

SiC and TiC coatings were deposited by CVD on graphite substrates and the effect of the variation of the methane (CH₄) and hydrogen (H₂) ratio on deposition was investigated. SiCl₄, TiCl₄ and CH₄ were used as sources of Si, Ti and C. In case of the SiC coatings, stoichiometric SiC was obtained when the ratios of CH₄/(SiCl₄ + CH₄)andH₂/(SiCl₄ + CH₄) are 0.4 and 10, respectively. Stoichiometric TiC was also obtained under similar conditions. In order to obtain non-stoichiometric materials for possible fabrication of functionally gradient materials (FGM), a change of microstructure and composition was observed with changes of the CH₄ and H₂ ratio. As a result, SiC, TiC and C contents were more easily controlled by a change of the H₂ ratio compared to the CH₄ ratio for SiC and TiC deposition. It has been verified that the change of the H₂ ratio is more desirable for possible manufacturing of SiC/TiC/C FGM.