Electrografting of 3-methyl thiophene and carbazole random copolymer onto carbon fiber: characterization by FTIR-ATR, SEM, EDX

Electrografting of poly(3-methylthiophene-co-carbazole) onto high tenacity (TENAX HTA 5000) carbon fiber was carried out under preparative constant-current electrolysis conditions by electropolymerizing in non-aqueous media. The surface morphology of the electrografted carbon fibers was determined by scanning electron microscopy (SEM). For characterization of the chemical composition of the random copolymer, FTIR reflectance measurements (FTIR-ATR) were performed. The efficiency of the electrocopolymerization on carbon fiber surfaces under preparative constant-current electrolysis conditions as a function of the experimental conditions was evaluated (effect on thickness and morphology).     

Structural, morphological and electrical properties of spray deposited nano-crystalline CeO2 thin films

Nanocrystalline, uniform, dense, and adherent cerium oxide (CeO₂) thin films have been successfully deposited by a simple and cost effective spray pyrolysis technique. CeO₂ films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. Films were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy; two probe resistivity method and impedance spectroscopy. X-ray diffraction analysis revealed the formation of single phase, well crystalline thin films with cubic fluorite structure. Crystallite size was found to be in the range of 10-15 nm. AFM showed formation of smooth films with morphological grain size 27 nm. Films were found to be highly resistive with room temperature resistivity of the order of 10⁷ Ω cm. Activation energy was calculated and found to be 0.78 eV. The deposited film showed high oxygen ion conductivity of 5.94 × 10⁻³ S cm⁻¹ at 350 °C. Thus, the deposited material shows a potential application in intermediate temperature solid oxide fuel cells (IT-SOFC) and might be useful for μ-SOFC and industrial catalyst applications.     

SEM and TEM characterization of magnesium hydride catalyzed with Ni nano-particle or Nb2O5

The microstructures of MgH₂ catalyzed with Ni nano-particle or Nb₂O₅ mesoporous powders are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. For MgH₂ catalyzed with Ni, the Ni particles with the diameter smaller than 1 μm were detected on the MgH₂ particles with the diameter smaller than 5 μm by the back scattering electron (BSE) microscopy. In details, the TEM micrograph indicates that the Ni particles distribute 20 nm in diameter on MgH₂ uniformly, which was the same size as the additive doped in MgH₂ before milling. On the other hand, for MgH₂ catalyzed with Nb₂O₅, the additive particles could not be found anywhere in the BSE image. Even in the TEM micrograph by much larger magnification than the SEM micrograph, the particles corresponding to the additive cannot be observed at all. Furthermore, an energy dispersive X-ray (EDX) analysis in spots with a diameter of 20 nm indicated that the existing ratio of Mg to Nb was evaluated to 98:2, being the same as the starting ratio before milling. Therefore, the metal oxide Nb₂O₅ becomes extremely small particle that could not be observed by the present work after milling compared to metal Ni^nano.     

Morphology and texture evolution of FeCrAlTi-Y2O3 foil fabricated by EBPVD

An electron beam physical vapor deposition method was used to fabricate freestanding Y₂O₃ dispersive strengthened FeCrAlTi foils for high-temperature applications. The vapor incidence mode was found to have great impact on the morphology and crystallographic orientation of the foils. Under symmetric vapor incidence mode, an out-of-plane < 100> fiber texture was formed. While under asymmetric vapor incidence mode, both out-of-plane preference of < 111> direction and several in-plane preferences were developed. As the deposition proceeded, the extent of in-plane orientation increased, and the preferred out-of-plane orientation increasingly deviated from the surface normal. The vapor incidence mode played a role on the growth rate of < 100> direction and < 110> direction, by which the morphology and crystallographic orientation of grains were modified.     

The effect of heat treatment on thermal stability of Ti matrix composite

The microstructures of in situ synthesized (TiB + La₂O₃)/Ti composite after β and TRIPLEX heat treatment are investigated. The room temperature tensile properties of the titanium matrix composites (TMCs) are tested, and thermal stability is carried out at 600, 650 and 700 °C for 100 h, respectively. The results show that the microstructure of specimen after β heat treatment is widmanstätten, while it is similar to basketweave after TRIPLEX heat treatment. Room tensile properties of specimen after TRIPLEX heat treatment are better than those of β heat treatment. After thermal exposure, the strength of specimens treated by β and TRIPLEX heat treatment increases, while the ductility decreases sharply, this is attributed to the precipitation of Ti₃Al and silicides. The thermal stability of specimen after TRIPLEX heat treatment is better than that after β heat treatment.     

Preparation of epitaxial and polycrystalline bismuth titanate thin films on single crystal (100) MgO by chemical solution deposition

Epitaxial and polycrystalline Bi₄Ti₃O₁₂ thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi₄Ti₃O₁₂ may be suppressed by the formation of a titanium-rich phase such as Bi₂Ti₂O₇ owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C.     

Study on the microstructure and mechanical properties of Nd:YAG pulsed laser beam weld of UNS-C17200 copper beryllium alloy

In this study, the microstructure of Nd:YAG pulsed laser welding of copper beryllium sheet has been investigated by tensile and hardness tests, optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images reveals three distinct solidified structures due to various thermal gradients occurred in the fusion zone. The XRD patterns show that the preferred solidification directions are like other FCC materials. Tensile strength of the weld metal is lower than that of the base metal since the CuBe phase precipitates during solidification. The effects of pulsed laser parameters on the weld pool dimensions were also studied. The results show that by applying constant pulse energy, focused beam diameter should be kept as low as possible to obtain the weld pool with the highest penetration and the least width. Moreover, the effect of passive layer on the reflectivity of surface by incident beam was investigated. It was found that weld pool increases when the laser energy is high due to multiple internal reflections.     

Investigating the microstructure and composition of cold gas-dynamic spray (CGDS) Ti powder deposited on Al 6063 substrate

The compositional variation, morphology and microstructure of cold gas-dynamic spray are of great importance for its proper application. This study investigates titanium powder deposition on an Al 6063 substrate using light optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition was examined using energy dispersive X-ray spectroscopy (EDX), X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF SIMS). Optical and electron microscopy revealed heavily deformed Ti powder particles penetrating 10 to 30 μm into the Al substrate. Examination using TEM did not reveal any evidence of second phases at the interface suggesting a sharp transition between the two metals. The presence of nanocrystals and grain refinement of both the coating and the substrate suggest the formation of a partial hetero-epitaxy condition near the interface. EDX results from a dedicated high-resolution scanning transmission electron microscope showed a sharp compositional change with a maximum inter-diffusion region of about 5 nm. Bonding of the coating to the substrate is therefore thought to be achieved by the particle/substrate interlocking and direct metal to metal bonding. However, it is most likely that the refine crystalline structure near the interface will be beneficial to the adhesion of the coating. XPS and ToF SIMS provided evidence of nitrogen pick-up during the spray process in the form of N and TiN even when utilizing Helium as the gas carrier. The presence of TiN suggests reaction of the Ti with the entrained air during spraying which explains the occurrence of flashing jet outside the nozzle. Investigation of the material properties using nanoindentation showed reasonably consistent hardness and elastic modulus values throughout the titanium coating and at the transition region. The hardness was slightly higher than typical commercially available bulk Ti.     

Microstructure and surface mechanical properties of electrodeposited Ni coating on Al 2014 alloy

The surface of Al 2014 was modified by electrochemical deposition of Ni with an aim to improve the surface mechanical properties of the alloy. The deposition was performed at various values of DC current, potential and time using standard Watt's bath. The samples were heat treated to improve the adhesion and hardness of Ni coatings. Material characterization was performed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction. Microhardness, nanohardness, microscratch and coefficient of friction measurements were undertaken to determine the surface mechanical properties of the electrodeposited Ni coating. Experimental results indicate that electrochemical deposition combined with heat treatment can be used to improve the surface properties of Al alloys.     

粉土pH对X70钢早期电化学腐蚀行为的影响

采用电化学阻抗(EIS)、极化曲线和扫描电子显微镜观察(SEM)等方法,通过室内模拟试验研究了X70钢在不同pH粉土中的早期电化学腐蚀行为。结果表明:X70钢在酸性(H_2SO_4)、碱性(NaOH)以及中性粉土中的腐蚀差异较明显。在模拟酸性粉土中,X70钢在pH为5的粉土中腐蚀龄期达21d时的自腐蚀电位明显高于在其他环境中的,且X70钢的腐蚀速率随着pH的增大(4~5),呈现出降低的趋势。在模拟碱性粉土中,液相介质中的OH-对X70钢的腐蚀行为有较大的影响,且X70钢的腐蚀速率随着pH的增大(9~11),呈现出升高的趋势。     

Effect of carbon source on the carbothermal reduction nitridation for synthesis of (Ti, W, Mo, V)(C, N) nanocrystalline powders

The effect of carbon source on the carbothermal reduction-nitridation during synthesizing (Ti, W, Mo, V)(C, N) nanocrystalline powders was investigated. For a systematic comparison, activated carbon, graphite and two kinds of carbon black powder were used as reducing agents in this study. Ultrafine (Ti, W, Mo, V)(C, N) powders with a particle size of ~ 200-500 nm have been produced at 1450 °C for 2 h by using nanosized carbon black source with small particle size. The presence of phases in the reaction products was characterized with X-ray diffraction (XRD) and the microstructure of carbon source powders and final products was studied by scanning electron microscopy (SEM). The results show that the formation of the Ti(C, N) phase is strongly dependent on the particle size of carbon source powders, and the synthesizing temperature of the Ti(C, N) phase decreases significantly from 1750 °C to 1300 °C by using nanosized carbon black, as compared with micron graphite. In addition, activated carbon with a particle size of 5-50 μm does not favor the dissolution of tungsten or molybdenum carbides into Ti(C, N) despite its large specific surface area.     

等离子喷涂NiCr合金基复合梯度润滑涂层的组织与力学性能研究

选取了具有优异的高温性能和一定的自润滑性能的高温镍基合金,作为复合涂层基体材料,润滑相则分别从高、中、低温固体润滑剂中选取了Ag、CaF2、石墨(C)、MoS2、BN为基本润滑组元;耐磨相则选用了在高温下具有良好的抗氧化性能及耐磨损性能的碳化铬(Cr3C2)硬质粒子,采用等离子喷涂技术制备了具有极佳相容性的高温润滑涂层.涂层的结合强度测定、硬度测定和扫描电镜分析均显示出涂层的梯度结构优于单层结构.梯度结构缓和了涂层内部的物理性能差异,不仅使涂层的硬度得到平缓过渡,而且使涂层的结合强度大大提高,有效改善了涂层的性能.     

Corrosion properties of thermally annealed and co-sputtered nickel silicide thin films

The corrosion properties of nickel silicide thin films are addressed by means of polarisation experiments in combination with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterisation before and after the polarisation runs. The thin films studied included two pairs of nickel silicide of different compositions fabricated on Si wafer by means of ion-beam sputter deposition technique. For one pair, thin films were prepared by co-sputtering Si and Ni targets. To achieve higher crystallinity, the other pair was prepared by Ni sputter deposition followed by subsequent thermal annealing at 280 °C and 480 °C to develop single silicide phase of Ni₂Si and NiSi in individual film, respectively. The variation of the binding energy (BE) of Ni 2p_3/2 core-level peak in the XPS measurement in accordance with the Si content for this binary system follows a Boltzmann's relationship. The electrochemical polarisation tests conducted in 1.00 M HCl solution showed almost the same behaviour for the tested specimens irrespective of structure or film composition, still, the SEM and XPS studies together with optical microscopy showed that the Ni₂Si, leaner in Si, experienced thin film corrosion, whilst the NiSi appeared to be more resistant. Clearly, composition is found to be a more important design factor to tailor the corrosion properties than the structure for this binary silicide system.     

Investigation on carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water

The carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water is studied by potentiodynamic curve and electrochemical impedance spectroscopy (EIS); the micro-structure and composition of the corrosion scale formed at high-temperature and high-pressure are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that 13Cr stainless steel is in passive state in the stratum water, the passive current density increases and the passive potential region decreases with increasing temperature. The corrosion scale formed at high-temperature and high-pressure is mainly composed of iron/chromium oxides and a little amount of FeCO₃.     

Preparation by gravity casting and hydrogen-storage properties of Mg–23.5 wt.%Ni–(5, 10 and 15 wt.%)La

Mg–23.5 wt.%Ni–(5, 10 and 15 wt.%)La alloys were prepared by gravity casting and their hydrogen-storage properties were examined after pulverizing. The gravity cast Mg–23.5Ni–(5, 10 and 15)La alloys consist of α-Mg, Mg₂Ni and Mg₁₇La₂ phases. The activated Mg–23.5Ni–10La alloy has the highest hydrogen-storage capacity of 4.96 wt.%H (from P–C–T curve) and the highest initial hydriding rate (hydrogen content 3.83 wt.%H at 10 min) with an initial hydrogen pressure in the channel of 11 bar H₂ at 573 K. This is attributed to its containing the largest amount of the Mg₁₇La₂ phase, which is easily dissociable during the hydriding reaction.     

Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg-(Ti + n-Al2O3) composites

In this study, composites containing pure magnesium and hybrid reinforcements (5.6 wt.% titanium (Ti) particulates and 2.5 wt.% nanoscale alumina (n-Al₂O₃) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃)_BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg-(5.6Ti + 2.5n-Al₂O₃) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg-(5.6Ti + 2.5n-Al₂O₃)_BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness.     

Finishing characteristics of brittle materials by ELID-lap grinding using metal-resin bonded wheels

ELID-lap grinding is a method of constant pressure grinding which utilizes an electrically conductive wheel and the electrolytic in-process dressing (ELID) method. This method has the advantage of using micro grain-wheels above #10 000 and also, through simple modification, can be used on existing lap machines. To find the characteristics of metal-resin bonded wheels developed for ELID-lap grinding, experiments on the grinding of brittle materials were performed using wheels with a variety of grain diameters. The wheels used in the experiments were #8000, #120 000 and #3 000 000 metal-resin bonded diamond wheels (#8000 MRB-D, #120 000 MRB-D and #3 000 000 MRB-D wheels). The workpieces were silicon and glass. The results of the experiments showed that stable grinding can be achieved with the #8000 to #3 000 000 MRB-D wheels. With the #3 000 000 MRB-D wheel, very smooth surface finishes were obtained for both silicon (PV 2.8 nm) and glass (PV 2.5 nm). Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) observations indicated these surfaces to be very smooth in the order of several nanometers, obtained by mechanical removal using an ultrafine wheel.     

Effect of N, C and B interstitial atoms on local bonding structure in mechanically activated TiH2/h-BN, TiH2/C, and TiH2/B mixtures

Mechanically activated TiH₂/h-BN, TiH₂/C and TiH₂/B mixtures was studied by temperature-programmed desorption, X-ray diffraction, transmission electron microscopy and X-ray emission spectroscopy. Ball milling in the presence of additives results in a modification of hydrogen occupation sites. Additional Ti-N, Ti-C or Ti-B bonds from chemical bonding of Ti with interstitial N, C and B atoms, are formed in TiH₂ due to contact of TiH₂ nanoparticles with the respective additive matrix materials. Mixed configurations around Ti atoms with proportional combination of local Ti-H and Ti-N, Ti-C or Ti-B bonds significantly decrease the thermal stability of TiH₂. The effect is most pronounced when boron is the additive.