TEM study of the FSW nugget in AA2195-T81

During friction stir welding (FSW) the material being joined is subjected to a thermal-mechanical process in which the temperature, strain and strain rates are not completely understood. To produce a defect free weld, process parameters for the weld and tool pin design must be chosen carefully. The ability to select the weld parameters based on the thermal processing requirements of the material, would allow optimization of mechanical properties in the weld region. In this study, an attempt is made to correlate the microstructure with the variation in thermal history the material experiences during the FSW process.     

Thermogravimetric study of rare earth manganites AMnO3 (A=Sm,Dy,Y,Er,Yb) at 1200°C

The free energy changes of formation of SmMnO₃, DyMnO₃, YMnO₃, ErMnO₃ and YbMnO₃ were determined to be ?14.3, ?11.1, ?11.4, ?11.2 and ?10.5kcal/mol, respectively, at 1200°C on the basis of the equilibria. Simultaneously, the nonstoichiometry was also investigated in the oxygen partial pressure below logP_O2[atm]=0. The free energy change and the width of nonstoichiometry in these ternary oxides were revealed to be dependent on the radius of rare earth ion. YbMnO₃ showed no deviation from stoichiometry in contrast with LaMnO₃.     

A TEM study and non-isothermal crystallization kinetic of tellurite glass-ceramics

The glass transition temperature was studied via differential thermal analysis of glasses in the system (100 − x)TeO₂–5Bi₂O₃–xZnO and (100 − x)TeO₂–10Bi₂O₃–xZnO where x = 15, 20, 25 in mol%. The crystallization behavior and microstructure development of the 0.7TeO₂/0.1Bi₂O₃/0.2ZnO glass during annealing were investigated by non-isothermal differential thermal analysis (DTA), X-ray diffractometry, and transmission electron microscopy. The glass transition temperature, crystallization temperature, and the nature of crystalline phases formed were determined. From the heating rate dependence of the glass transition temperature, the glass transition activation energy was derived. From variation of DTA peak maximum temperature with heating rate, the activation energies of crystallization were calculated to be 305.8 and 197 kJ mol⁻¹ for first and second crystallization exotherms, respectively. Moreover, synthesized crystalline Bi_3.2Te_0.8O_6.4, Bi₂Te₄O₁₁, and Zn₂Te₃O₈ were investigated. In addition, the change in particle size with increasing annealing time was observed by high-polarized optical microscope.     

A TEM study on the microstructure of rapidly solidified Cu-Y alloys

The microstructure of rapidly solidified copper-yttrium alloys was studied by TEM. For the near-eutectic alloys, the following observations were made: melt-spun Cu-12.5 wt% Y whiskers showed a very fine eutectic of f.c.c. copper and hexagonal Cu₅Y plus isolated areas of a new metastable orthorhombic phase, Cu₉Y; melt-spun Cu-51.1 wt% Y whiskers contained an amorphous matrix plus precipitates of the equilibrium phase orthorhombic Cu₂Y. For far-from-eutectic alloys, glass formation was detected in the melt-spun whiskers of Cu-25.0 wt% Y alloy, while the melt-spun Cu-18.9 wt% Y whiskers showed a fine-grained single phase Cu₅Y, an easily formed metastable phase, and melt-spun Cu-41.6 wt% Y showed an ultrafine single phase Cu₂Y, an equilibrium orthorhombic phase.     

A TEM study of functionalized magnetic nanoparticles targeting breast cancer cells

In this paper, a transmission electron microscopy (TEM) study was carried out to investigate the ability of magnetic nanoparticles (MNPs) to target breast cancer cells in mice. MNPs were functionalized using Luteinizing Hormone Releasing Hormone (LHRH), whose receptors are expressed in most types of breast cancer cells. LHRH conjugated MNPs (LHRH-MNPs) were injected intravenously into female nude mice bearing MDA-MB-435S.luc tumors for thirty days. These mice were sacrificed 20 h after MNP injection. Tumors and periphery organs including livers, lungs and kidneys were collected for analysis. A dedicated transmission electron microscopy (TEM) study was then carried out to investigate the distribution of nanoparticles in cells. We found that dispersive LHRH-MNPs were distributed in tumor cells and cells in lungs and livers. No LHRH-MNPs were observed in kidney cells. Furthermore, LHRH-MNPs tend to aggregate and form clusters in tumor cells and cells in lungs where metastases were developed. These suggest that MNPs functionalized using LHRH can be used to target both primary cancer cells and the metastatic cells. The study also indicates that TEM is a useful tool to study the sub-cellular distribution of functionalized magnetic nanoparticles in mice bearing breast cancers.     

A study of precipitation and recrystallization behaviour of aluminium alloy AA1235

The recrystallization behaviour of 92% cold rolled commercial pure aluminium has been studied. Annealing was done at different conditions to evaluate the effect of recrystallization temperature and time on the microstructure and texture of the alloy along with a study of subsequent precipitation. Variation of orientation between grains has been studied by the orientation imaging microscopy (OIM). During precipitation, cube component {001}<100> has dropped and rolling texture component has increased comparatively. Recrystallization texture is the combination of cube, rolling and random texture. However, during grain growth strong cube grains have formed. A significant number of dislocations are present during grain growth owing to the pinning effect of Al₃Fe particles.     

A study on the re-solution heat treatment of AA 2618 aluminum alloy

In the present study, the effects of re-solution treatment of AA2618 aluminum alloy has been investigated. Solution heat treatments of 520–640 °C for 14–24 h were applied followed by artificial aging. Characterization studies that were carried out by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques showed that recrystallisation was not observed by solution treatment at 530 °C whereas it did occur as the solution treatment and the duration time were increased above 530 °C. Increasing the solution treatment temperature further coarsened both the grains and the precipitates, resulting in significant reduction in hardness. Al₉FeNi-type intermetallics are not completely dissolved by these solution treatments.     

A TEM study of precipitation and related microstructures in friction-stir-welded 6061 aluminium

Residual microstructures, including dynamic recrystallization and grain growth structures and a wide range of precipitation phenomena associated with a friction-stir-weld in a thin 6061-T6 aluminium plate have been systematically investigated utilizing light metallography and transmission electron microscopy. In this rather remarkable process, a hard steel head pin rotating at 400 r.p.m. was advanced into a solid 6061-aluminium plate at a traverse velocity of approximately 2 mm s–1 to produce a solid-phase weld in its trailing side. Maximum work-piece temperatures did not exceed 425°C and there was no melt evidence. Dynamic recrystallization associated with the solid-state plastic flow therefore seems to provide the process mechanism. Weld zone hardnesses averaged roughly 55 Vickers hardness number (VHN) in contrast to the base plate or work-piece hardness of 110 VHN. Precipitation microstructures ranged from continuous to discontinuous coherent zones (2 nm thick) coincident with {1 0 0} planes, semicoherent and non-coherent needles and plates characteristic of Widmanstatten structures coincident with {1 1 0} planes, and a range of homogeneous precipitate particles often intermixed with these microstructures in the effective heat-affected zone (HAZ) connecting the friction-stir-weld zone with the unaltered work piece microstructures. © 1998 Chapman & Hall     

A new approach of using Lorentz force to study single-asperity friction inside TEM

Taking advantage of the magnetic field inside transmission electron microscope(TEM),a unique Lorentz-force-actuated method for quantitative friction tests was developed via a commercial electromechanical holder.With this approach,a submicron-sized silver asperity sliding on a tungsten flat punch was actu-ated by Lorentz force due to electrical current through the punch,with the normal force imposed by the built-in transducer of the holder.The friction force was determined by tracking the elastic deflec-tion of the fabricated cantilever from in situ video.Through correlating the friction behavior with the microstructural evolution near the silver-tungsten interface,we revealed that even when the relative motion commenced with the plastic deformation of the silver asperity,the interface can still sustain the further increasing static friction force.Exactly following the arrival of the maximum static friction force,the sliding occurred at the interface,indicating the transition from static to dynamic friction.This work enriches our understanding of the underlying physics of the dynamic friction process for metallic friction behavior.     

Identification of the pin offset effect on the friction stir welding (FSW) via Taguchi – Grey relational analysis: A Case study for AA 7075 – AA 6013 alloys

The aim of this work is to present a case study relating to the dissimilar friction stir welding (FSW) ability of AA 7075‐T651 and AA 6013‐T6 by applying pin offset technique. An orthogonal array L18 was conducted to perform the overlapped weld seams using three different values of pin offset, welding speed and tool rotational speed along with two different pin profiles determine the impact of welding parameters on the tensile properties of friction stir welded joints. The nugget zone for each of overlapped weld seams exhibited a complex structure and also, the pin offset and profile also were found to have a great impact on the microstructural evolution of the nugget zone. The ultimate tensile strength, elongation at the rapture and bending strength of welded joints were measured in the ranges of 194–215 MPa, 1.79–3.34 % and 203–352 MPa. From the Taguchi based Grey relational analysis, the optimum welding condition was determined for the welded joint performed using a single fluted pin profile with the zero pin offset, tool rotational speed of 630 min^?1 and welding speed of 63 mm/min. Microstructural and macro‐structural observations revealed that welded joints exhibiting lower tensile strength are consistent of various types of defects (e. g. cracks, tunnels and cavities). The fracture location of welded joints was found to be on the heat affected zone and between the heat affected zone and AA 6013‐base metal. The tool and pin wear was not observed during the welding applications     

A differential scanning calorimetry study of recrystallization and its interaction with precipitation in Al-Fe-Si commercial alloys (AA1145 and AA8011)

Differential scanning calorimetry (DSC) was used to study several aspects of recrystallization in cold-rolled Al-Fe-Si commercial alloys. Two commercial alloys (AA1145 and AA8011) with different contents of Fe + Si and continuously cast in a twin roll machine, were used. It is shown that DSC allows a direct study of the interaction between the precipitation of alloying elements and recrystallization. The kinetics of recrystallization in the two alloys was also analysed, showing that the experimental data can be satisfactorily fitted with the Johnson-Mehl-Avrami equation with an exponentn = 2.5. The same kinetic parameters can be also used to fit the isothermal data obtained in the same DSC apparatus. The change in stored energy as a function of true strain is also considered.     

Reduction and adsorption of Pb in aqueous solution by nano-zero-valent iron—A SEM, TEM and XPS study

This study reports the synthesis, characterisation and application of nano-zero-valent iron (nZVI). The nZVI was produced by a reduction method and compared with commercial available ZVI powder for Pb²⁺ removal from aqueous phase. Comparing with commercial ZVI, the laboratory made nZVI powder has a much higher specific surface area. XRD patterns have revealed zero-valent iron phases in two ZVI materials. Different morphologies have been observed using SEM and TEM techniques. EDX spectrums revealed even distribution of Pb on surface after reaction. The XPS analysis has confirmed that immobilized lead was present in its zero-valent and bivalent forms. ‘Core-shell’ structure of prepared ZVI was revealed based on combination of XRD and XPS characterisations. In addition, comparing with Fluka ZVI, this lab made nZVI has much higher reactivity towards Pb²⁺ and within just 15 min 99.9% removal can be reached. This synthesized nano-ZVI material has shown great potential for heavy metal immobilization from wastewater.     

RBS, XPS, and TEM study of metal and polymer interface modified by plasma treatment

We performed a study of the diffusion of Ag and Au atoms in polyethyleneterephtalate (PET). Thin metal layers were deposited using a diode-sputtering technique on polymer foils at room temperature. Simultaneous post-deposition annealing and plasma treatments were used to induce metal-polymer intermixing. Rutherford back-scattering spectrometry and X-ray photoelectron spectroscopy were used to determine the integral amount of metal and chemical structure in the surface layer. After plasma treatment Ag thin films exhibit dramatic changes of chemical composition and an integral amount of metal compared to Au thin films. Transmission Electron Microscopy shows the differences in the size and the depth distribution of metal particles, depending on the annealing temperature at the metal-polymer interface.     

A TEM and SEM-cathodoluminescence study of oval defects in graded InGaAs/GaAs buffer layers

The nature of oval defects in compositionally graded InGaAs/GaAs buffer layers has been investigated by means of Transmission electron microscopy (TEM) and Cathodoluminescence (CL). CL spectra show that emissions from within the defects have energies lower than that from the defect-free regions, thus demonstrating that the defects are richer in In than the surrounding matrix. No In particles have been detected within the defect core. TEM investigations reveal that the defects form in the topmost strained regions close to the surface and originate from stacking faults.     

Li在石墨烯、BC_3及C_3N表面吸附与迁移的第一性原理研究

基于密度泛函理论的第一性原理方法,研究了Li在本征石墨烯及BC3、C3N表面的吸附和迁移行为。与本征石墨烯相比,硼掺杂浓度为25%(原子分数)时提高了Li的吸附能,而氮掺杂浓度为25%(原子分数)时减弱了Li的吸附能,这归因于掺杂物种具有不同的电子结构。通过NEB方法计算了Li在本征石墨烯、BC3、C3N表面的迁移,结果表明,相比于本征石墨烯,硼掺杂浓度为25%(原子分数)的石墨烯减弱了Li的扩散,而氮掺杂浓度为25%(原子分数)的石墨烯促进了Li的扩散。