Mechanical properties of nanostructured Mg–5 wt%Al–x wt%AlN composite synthesized from Mg chips

In the present investigation, Mg chips are recycled to produce nanostructured Mg–5wt%Al reinforced with 1, 2 and 5 wt% nanosized AlN particulates by mechanical milling (MM). Each batch of composite mixture was milled for different milling durations to produce different degrees of grain refinement. The mechanical properties such as tensile strength, ductility and hardness with respect to the effect of grain refinement, in other words, milling duration were studied. It was found that grain size played an important role in controlling ductility of the composites.     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 μm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macro- and microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^′ (Al₃Li) and S^′ (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

Investigation on solar photocatalytic activity of TiO2 loaded composite: TiO2/Eggshell, TiO2/Clamshell and TiO2/CaCO3

The TiO₂/Eggshell, TiO₂/Clamshell and TiO₂/CaCO₃ loaded composites were prepared by sol-gel method and characterized by XRD and SEM. Their photocatalytic activities were measured through the degradation of Acid Red B under solar light irradiation. The influences of TiO₂ loaded content, heat-treated temperature and time on the photocatalytic activities were reviewed. The effects of irradiation time and dye initial concentration on the photocatalytic degradation were also investigated. The results showed that the photocatalytic activity can be greatly enhanced by appropriate TiO₂ loaded content.     

Thermal conductivity and thermal contact conductance studies on Al2O3/Al–AlN metal matrix composite

Al₂O₃/Al–AlN is a metal matrix composite (MMC) used for making heat sink of electronic devices. This paper presents the detailed investigations carried out on thermal contact resistance across this MMC contact in vacuum at different contact pressures. The experimental results are compared with the theoretical models available in the literature for metallic contacts and they are found to be in good agreement with each other.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.     

Effect of preparation conditions on properties of atomic layer deposited TiO2 films in Mo–TiO2–Al stacks

TiO₂ films were grown by atomic layer deposition on Mo electrodes in order to elucidate the dominating conductance mechanism and its dependence on the growth chemistry. TiCl₄ and Ti(OC₂H₅)₄ served as titanium precursors, and H₂O or H₂O₂ as oxygen precursors. The films grown at lower temperatures were amorphous. With increasing growth temperatures the crystallization first started in the TiCl₄–H₂O process. The films grown in this process were clearly leakier compared to the films grown from Ti(OC₂H₅)₄ and H₂O and from Ti(OC₂H₅)₄ and H₂O₂. In the Ti(OC₂H₅)₄-based processes, the application of H₂O₂ instead of H₂O resulted in the films with considerably lowered conductivity, although structural differences in these films were insignificant. Space–charge-limited currents were prevailing in all our amorphous Mo–TiO₂–Al packages. Measurements at different temperatures suggested quite high trap densities likely due to the presence of impurities and structural disorder, while the strong differences in conductivity seemed to be due to different densities of gap states.     

WO3/TiO2复合薄膜的制备及其电致变色性能

使用水热法在掺氟SnO₂涂覆的导电玻璃（FTO）基板上生长TiO₂纳米线,随后在TiO₂纳米线上采用水热法生长WO₃纳米线,制备出WO₃/TiO₂复合薄膜。通过循环伏安法（CV）、计时电流法（CA）、计时电量法（CC）等电化学测试技术研究了WO₃/TiO₂复合薄膜的电致变色性能;采用紫外分光光度计对薄膜的着色﹑漂白状态的响应时间进行测试。通过以上测试,计算得到了薄膜的循环稳定性﹑光调制﹑着色效率和切换时间（Y和X）等参数。结果显示WO₃/TiO₂复合薄膜的电致变色性明显提高,其中WO₃/TiO₂复合薄膜可逆性增加了6%,着色效率提高了40.96 cm2/C。      

Analysis of strain rate dependence of tensile elongation for a mechanical milling Al–1.1Mg–1.2Cu alloy tested at 748 K from a dislocation dynamics viewpoint

Tensile deformation was carried out for a mechanically milled and thermo-mechanically treated Al–1.1Mg–1.2Cu (at.%) alloy at 748 K and three nominal strain rates of 10⁻³, 10⁰, and 10² s⁻¹. Despite the prevailing belief that superplasticity occurs by grain boundary sliding which requires slow strain rates at high temperatures, the maximum elongation was observed at the intermediate strain rate of 10⁰ s⁻¹, neither at the lowest nor the highest strain rates. In order to explain this phenomenon, the true stress–true strain behaviors at these three nominal strain rates were analyzed from a viewpoint of dislocation dynamics by computer-simulation with four variables of the thermal stress component σ*, dislocation immobilization rate U, re-mobilization probability of unlocked, immobile dislocations Ω and dislocation density at yielding ρ₀. It can then be concluded that the large elongation (>400% in nominal strain) at the intermediate strain rate is produced by a combination of a very large Ω and a moderate U, resulting in a large strain rate sensitivity m value.     

TiO2/Bi2WO6复合光催化剂的制备及光催化性能研究

TiO₂/Bi₂WO₆异质结是当前最具潜力的一种可见光响应半导体光催化剂。以富含缺陷的TiO2纳米带为基体,采用水热法,诱导Bi2WO6在基体缺陷位点进行异质生长,从而合成具有异质结构的TiO₂/Bi₂WO₆复合材料。利用XRD、SEM、UV-Vis等技术,分析了基体表面缺陷、Bi2WO6负载量对TiO₂/Bi₂WO₆复合材料微观结构和性能的影响。结果表明,在基体表面引入缺陷,可以使TiO₂/Bi₂WO₆复合材料在可见光下对有机污染物Rh B的降解速率提高约50%。Bi2WO6负载量为0.12时的TiO₂/Bi₂WO₆复合材料,在可见光下,辐照6 min后对Rh B的降解率达99.3%,辐照30 min后对MB的降解率达99.7%,辐照15 min后对TC-HCl的降解率达87.7%。     

Preparation of SiO2/TiO2 composite fibers by sol-gel reaction and electrospinning

Submicron scale composite fibers of SiO₂/TiO₂ with various compositions have been prepared by electrospinning a sol-gel precursor of tetraethyl orthosilicate(TEOS) and titanium(IV) isopropoxide(TiP), followed by calcination. Any gelator or binder has not been used in this direct preparation process for composite fibers, and the maximum amount of titania for suitable fiber formation was about 50 mol%. The sintered composite fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy. Our results show that the surface morphology and crystallization behavior of electrospun fibers are largely influenced by the calcination temperature and the content of TiO₂. XRD results also reveal that the anatase phase in composite fibers can be preserved even after high temperature processing at lower content (x = 0.1, 0.2) of titania.     

The mechanical response of Al–Si–Mg/SiCp composite: influence of porosity

The effect of porosity on the mechanical and fracture behaviour in Al–Si matrix alloy and composites reinforced with SiC particles of 10 and 20 vol.% in the as-cast state and after extrusion process has been studied. Matrix alloy and composites were fabricated by compocasting and extrusion. Samples were characterized by optical microscopy, image analyzer, scanning electron microscopy and tensile tests. The results demonstrate that hot extrusion considerably reduces the porosity, while size and distribution of the reinforcement particles are also affected. In the point of fracture behaviour, the existence of large porosity is more effective.     

聚苯胺/TiO2复合纳米膜电极的制备及其光电性能

采用原位化学氧化法,在酸性TiO2溶胶中未加分散剂制备了聚苯胺修饰的TiO2稳定溶胶,并以涂刮法在柔性导电塑料薄膜上成膜。利用FT-IR、XRD、TEM、选区电子衍射、紫外-可见光谱、光电流-电压曲线对所制备的复合溶胶及复合膜进行了表征。结果表明TiO2与聚苯胺之间实现了结构上的复合,聚苯胺的引入改善了TiO2膜对太阳光的利用率,提高了TiO2膜的光电响应性能。这种用复合溶胶制备聚苯胺/TiO2复合膜的方式扩大了成膜基底的范围。     

聚苯乙烯/纳米二氧化钛复合材料的制备与表征

利用单螺杆挤出机和平板硫化机制备了聚苯乙烯/纳米二氧化钛(PS/纳米TiO₂)的共混物。研究了PS/纳米TiO₂(100/1.5)中聚苯乙烯接枝马来酸酐(PS-MAH)加入量对共混物的拉伸强度、冲击强度、微观结构的影响。结果表明:当PS-MAH加入PS/纳米TiO₂中20g时,共混物的拉伸强度达到最大值。紫外光照射实验结果表明,PS-MAH的加入可有效地提高PS/纳米TiO₂复合材料的抗老化性能,与PS/TiO₂复合材料相比拉伸强度提高30%。     

Microstructure, mechanical properties and aging behavior of Mg–5Li–3Al–2Zn–xAg

Mg–5Li–3Al–2Zn–xAg (x = 0, 0.1, 0.3, 0.6, 1.2) alloys were prepared by medium-frequency induction furnace under the ambient of pure argon. The effect of Ag addition on the microstructure, tensile properties, and aging behavior was investigated. Results show that the addition of Ag can restrain the decomposition from MgAlLi₂ to AlLi. With the addition of Ag, the over-aging point is retarded and the over-aging phenomenon is avoided in Mg–5Li–3Al–2Zn–1.2Ag. The solid solution of Ag in matrix phases and the restraining of the decomposition from MgAlLi₂ to AlLi are two aspects that strengthen the alloys.     

Effect of High‐Energy Ball Milling on Mechanical Properties of the Mg–Nb Composites Fabricated through Powder Metallurgy Process

New biocompatible and biodegradable Mg–Nb composites used as bone implant materials are fabricated through powder metallurgy process. Mg–Nb mixture powders are prepared through mechanical milling and manual mixing. Then, the Mg–Nb composites are fabricated through cold press and sintering processes. The effect of mechanical milling and Nb particles as reinforcements on the microstructures and mechanical properties of Mg–Nb composites are investigated. The mechanical milling process is found to be effective in reducing the size of Mg and Nb particles, distributing the Nb particles uniformly in the Mg matrix and obtaining Mg–Nb composite particles. The Mg–Nb composite particles can be bound together firmly during the sintering process, result in Mg–Nb composite structures with no intermetallic formation, lower porosity, and higher mechanical properties compared to composites prepared through manual mixing. Interestingly, the mechanical properties of manually mixed Mg–Nb composites appear to be even lower than that of pure Mg.

     

SiO2/TiO2复合气凝胶的孔道结构研究

为了在常压干燥下制备高比表面积且具有多级孔道结构的SiO2/TiO2复合气凝胶,以正硅酸乙酯、钛酸丁酯为原料,利用低聚体聚合将分相平行引入到溶胶凝胶过程中,获得SiO2/TiO2醇凝胶,并通过溶剂替换技术实现气凝胶的常压干燥制备.不同硅钛比气凝胶的内部结构研究表明:合成的气凝胶是由纳米SiO2和TiO2颗粒分散复合而成的介孔块体,其中Ti—O—Ti、Si—O—Si和Ti—O—Si键相互交织.气凝胶的结构变化是分相与溶胶凝胶过程相互竞争的结果.Si含量能显著改善气凝胶的结构,当n(Ti)∶n(Si)为3∶1时,比表面积高达712.2 m2/g,平均孔径为3.36 nm;当n(Ti)∶n(Si)为1.5∶1时,复合气凝胶具有明显双连续孔道,比表面积高,同时孔状结构清晰.     

Synthesis of in situ Al–TiB2 composites using stir cast route

When elemental Ti and B powders were added to molten Al at above 1000°C, fine in situ TiB₂ particulates were formed through Al–Ti–B exothermic reaction. By optimising the nucleation of TiB₂, the tensile and yield strengths of a synthesised Al–15V_f%TiB_s composite were twice that of matrix material. Modification of Al-matrix with 4.5 wt%Cu tripled the tensile and yield strengths at peak-aged condition. Owing to the co-presence of brittle Al₃Ti flakes with TiB₂ particles in the composites synthesised by the Al–Ti–B system, ductility was reduced to 68% and 84% in composites with Al- and Al–Cu matrices, respectively. When the (Ti + B) mixture was incorporated with 3 wt%C, TiB₂ and TiC reinforcing phases were simultaneously produced in the composite with Al–Cu matrix. Such an approach reduced Al₃Ti compound in the composite considerably. Although the presence of Cu in the composite was found to promote the formation of Al₃Ti, its effect on the fluidity caused the melt recovery to increase from 33% to 52%.     

Mechanical properties of in situ Al2O3 formed Al–Si composite coating via atmospheric plasma spraying

In this study, mechanically alloyed Al–12Si/SiO₂ composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The composite coating consisting of in situ formed Al₂O₃ reinforced hypereutectic Al–18Si matrix alloy was achieved. The produced coatings were extensively analyzed with respect to X-ray diffraction (XRD). The XRD patterns of the coatings include Al, Si and Al₂O₃ phase formation. Mechanical properties of layers were examined by Dynamic Ultra-micro hardness test machine for estimating Young’s modulus due to load–unload sensing analysis. The hardness and Young’s modulus of the composite coatings sprayed at different plasma current and the distance were measured under 200, 400, 600, 800 and 1000 mN of applied peak loads by indentation technique. The effects of spray distance and arc current on the hardness and Young’s modulus have been investigated. Additionally, it was observed that the arc current and spray distance strongly influence the mechanical properties of the coatings.     

Effect of Al2O3 particles on mechanical properties of directionally solidified intermetallic Ti–46Al–2W–0.5Si alloy

The effect of Al₂O₃ particles on microhardness and room-temperature compression properties of directionally solidified (DS) intermetallic Ti–46Al–2W–0.5Si (at.%) alloy was studied. The ingots with various volume fractions of Al₂O₃ particles and mean ₂–₂ interlamellar spacings were prepared by directional solidification at constant growth rates ranging from 2.78×10⁻⁶ to 1.18×10⁻⁴ ms⁻¹ in alumina moulds. The ingots with constant volume fraction of Al₂O₃ particles and various mean interlamellar spacings were prepared by directional solidification at a growth rate of 1.18×10⁻⁴ ms⁻¹ and subsequent solution annealing followed by cooling at constant rates varying between 0.078 and 1.889 K s⁻¹. The mean ₂–₂ interlamellar spacing λ for both DS and heat-treated (HT) ingots decreased with increasing cooling rate according to the relationship λ∝ ^−0.46. In DS ingots, microhardness, ultimate compression strength, yield strength and plastic deformation to fracture increased with increasing cooling rate. In HT ingots, microhardness and yield strength increased and ultimate compression strength and plastic deformation to fracture decreased with increasing cooling rate. The yield stress increased with decreasing interlamellar spacing and increasing volume fraction of Al₂O₃ particles. A linear relationship between the Vickers microhardness and yield stress was found for both DS and HT ingots. A simple model including the effect of interlamellar spacing and increasing volume fraction of Al₂O₃ particles was proposed for the prediction of the yield stress.     

玄武岩纤维/TiO2复合材料的制备及表征

TiO_2纳米粉体应用于光催化领域存在光吸收仅局限于紫外光区域、难以回收等缺点,因此,纳米TiO_2固定化和可见光改性成为光催化领域的两个研究热点.本文采用绿色环保的水热法,将TiO_2负载于玄武岩纤维载体上,在较低的温度下制备出一种新型的玄武岩纤维/TiO_2复合材料.使用XRD分析了复合材料的物相结构,采用SEM观测了复合材料的形貌,并对水热法合成其机理进行了分析.结果表明:150℃水热条件下、反应10 h合成的玄武岩纤维/TiO_2复合材料中,颗粒状的TiO_2涂层均匀包覆于玄武岩纤维表面,并没有改变玄武岩纤维结构,形成了一种具有核壳结构的新型玄武岩纤维/TiO_2复合材料,经过TiO_2修饰的玄武岩纤维对可见光有很好吸收.因此,玄武岩纤维/TiO_2复合材料是一种具有潜在应用价值的可见光催化材料.