First preparation of optical quality films of nano/micro hollow spheres of polymers of aniline

In the present study, an experimental procedure used to prepare high-quality, transparent, uniform thin film of a new nano/micro material, a new type of polymer of aniline, is described. The method was used to prepare, for the first time, a solid-state thin film of nano/micro material for various types of studies, such as ultraviolet and visible spectroscopy (UV–vis), scanning electron microscopy (SEM) and electrochemistry. The UV–vis spectra showed that the as-prepared solid thin film of the nano/micro material was apparently not protonated when it was formed in an acidic solution of pH 3.0 since no change in the UV–vis spectrum was observed when it was treated with a deprotonating solution of 1.0 mol dm⁻³ of ammonium hydroxide. To our surprise, it was found that the UV–vis spectrum of a nano/micro material deposited on a glass slide was completely different from its solution UV–vis spectrum when the film was dissolved in NMP (N-methyl-2-pyrrolidinone). The SEM studies showed that the thin film consists of rod-like nanostructures as well as nano/micro spheres. The electrochemical studies showed that the thin film of the nano/micro material deposited on ITO surface presented only one redox process in the potential interval of −0.20 and +0.80 V (versus SCE) in the presence of 1.0 mol dm⁻³ hydrochloric acid.     

The coupling influence of size effects and strain rates on the formability of austenitic stainless steel 304 foil

In order to understand the coupling influence of size effects and strain rates on the formability of the austenitic stainless steel 304 foils in micro scale, a series of micro scale limited dome height (LDH) tests were designed and conducted in three different speeds without lubricant on the annealed and as-received austenitic stainless steel 304 foils. In this study, a technique was developed to coat a layer of pure chromium (≈0.3 μm thick) on the foils and by using the etching process to make the micro square grids (50 μm × 50 μm) on the foils. Then, the foils were annealed at different temperatures for obtaining different microstructures. A set of the forming limit curves (FLC) of the foils were obtained and they can be used by industry right away for product design, process design and development, die design, and simulations, etc. Besides, the coupling influence of the size effects and the strain rates on the formability of the austenitic stainless steel 304 foils has been studied, observed and understood.     

Micro fabrication by electrochemical process in citric acid electrolyte

This paper describes micro electrochemical machining of stainless steel in an environmentally friendly electrolyte of citric acid. Electrochemical dissolution region is minimized by applying a few hundred nanosecond duration pulses between the tungsten SPM tip and the work material. Electrochemical machining (ECM) characteristics according to citric acid concentration, feed speed and electric conditions such as pulse amplitude, pulse frequency, and tool electrode baseline potential are investigated through a series of experiments. Micro holes of 60 μm in diameter with the depth of 50 μm and 90 μm in diameter with the depth of 100 μm are perforated using citric acid electrolyte. Square and circular micro cavities are also fabricated by electrochemical milling. This research may contribute to the development of safe and eco-friendly micro manufacturing technology.     

New dual-focalization ferroelectret-based array for air-coupled ultrasonic inspection of textiles

This work presents a design methodology for half-curved airborne ultrasonic arrays based in cellular ferroelectret film. The geometry of the array proposed allows us focus naturally in the vertical plane and electronically in the horizontal one, obtaining similar spatial resolution in both directions. Theoretical predictions and simulated results were validated with a developed array prototype designed to operate at frequencies between 50 kHz and 300 kHz. The potential of the device is shown by inspecting different textile samples in transmission mode. This multitransducer design is a low cost alternative to the use of composite 2D arrays in noncontact ultrasonic inspections.     

Multi-coil focused EMAT for characterisation of surface-breaking defects of arbitrary orientation

Electromagnetic Acoustic Transducers (EMATs) are a useful ultrasonic tool for non-destructive evaluation in harsh environments due to their non-contact capabilities, and their ability to operate through certain coatings. This work presents a new Rayleigh wave EMAT transducer design, employing geometric focusing to improve the signal strength and detection precision of surface breaking defects. The design is robust and versatile, and can be used at frequencies centered around 1 MHz. Two coils are used in transmission mode, which allows the usage of frequency-based measurement of the defect depth. Using a 2 MHz driving signal, a focused beam spot with a width of 1.3±0.25 mm and a focal depth of 3.7±0.25 mm is measured, allowing for defect length measurements with an accuracy of±0.4 mm and detection of defects as small as 0.5 mm depth and 1 mm length. A set of four coils held under one magnet is used to find defects at orientations offset from normal to the ultrasound beam propagation direction. This EMAT has a range which allows detection of defects which propagate at angles from 16° to 170° relative to the propagation direction over the range of 0–180°, and the setup has the potential to be able to detect defects propagating at all angles relative to the wave propagation direction if two coils are alternately employed as generation coils.     

Cutting performance of TiCN–HSS cermet in dry machining

This work is focused on the cutting performance of a new cermet based on high-speed steel (HSS) matrix with hard phase TiCN. The processing route to manufacture the cermet M2 + 50 vol.% TiCN is described. Orthogonal cutting tests, carried out in a lathe showed the ability of the new cermet to achieve turning operations, showing reasonably wear resistance performing dry cutting operations. Tool life was significantly increased, when the cermet was compared with the reference material M2 without reinforcement and with commercial HSS M2. Evolution of flank wear and chipping wear, being the dominant wear patterns, were analysed.     

Grain-size effect on plastic flow in nanocrystalline cobalt by atomistic simulation

Molecular dynamics simulation is employed to investigate the plastic flows in nanocrystalline (nc) hexagonal close-packed cobalt under uniaxial tensile deformation. In nc-Co samples modeled by a semi-empirical tight-binding potential, different deformation behaviors such as nucleation and growth of disordered atom segments (DAS) inside grains, deformation-induced hexagonal close-packed to faced-centered cubic transformation, partial dislocation activities are identified at different grain sizes (4–12 nm). At high stresses (1.2–3.2 GPa) and low temperatures (77–470 K), growth of DAS and their interaction with stacking faults are found to dominate the deformation process, even when the grain size is as small as 4 nm. A model for plastic flow generated by DAS inside grains is proposed. The strain rates and the inverse Hall–Petch-like behaviors in nc-Co with sub-10 nm grain sizes can be well described by the DAS plastic-flow model.     

Effects of dispersants on dispersibility of titanium carbide aqueous suspension

In this study, the dispersing phenomenon of titanium carbide suspensions has been investigated using various dispersants. The effect of pH and dispersant concentration on the dispersibility of the powder has been studied via sedimentation and zeta potential test. To optimize the pH range for the best dispersibility, the sedimentation test has been carried out in various dispersant concentrations in wide pH range. The zeta potential of TiC suspensions, both with and without polyelectrolyte addition, is examined as a function of pH. Zeta potential studies show that the isoelectric point of TiC powder is at pH 3.1. The use of an anionic polyelectrolyte, tetramethylammonium hydroxide in the optimum concentration, significantly increased the stability of suspension. The maximum value of the zeta potential − 60 mV is obtained in 0.4 wt.% at pH 8. The addition of a cationic dispersant, polyethylenimine, significantly alters the isoelectric point and shifts to the basic pH. The maximum stability of suspension was achieved in 2 wt.% at pH 8. The result showed that nonionic dispersant polyethylene glycol 400 is not a good dispersant for TiC suspension. The surface charge and potential do not change in the presence of this dispersant.     

A study on the effects of silica particle size and milling time on synthesis of silicon carbide nanoparticles by carbothermic reduction

Silicon carbide nanoparticles were produced by a carbothermic reduction of nano and micro size silica with graphite at 1450 °C for 1 h. The SiC nanoparticles were characterized by XRD, SEM and TEM. The results showed that in the case of nano silica, milling up to 20 h could develop SiC particles of 5–25 nm with some residual SiO₂ particles. By extending milling time to 40 h, more energy was provided and produced Fe contamination, which could act as catalyst and increased SiC yield as well as Fe₂Si phase formation after heat treatment. Coarser particles of micro silica caused higher Fe erosion, more SiC formation with 20–70 nm size and presence of Fe₂Si phase at shorter milling times after heat treatment. Leaching treatment could purify SiC nanoparticles. Increase of milling from 20 to 40 h changed the morphology from polygonal shape to spherical with some reduction in the particle size.     

Texture evolution of high purity tantalum under different rolling paths

Deformation behavior and texture evolution of the material can be significantly affected by strain path change. For this reason, two rolling methods, unidirectional rolling (UR) and clock rolling (CR), were employed to manufacture tantalum plates. Texture evolution during unidirectional rolling and clock rolling was studied respectively by orientation distribution function (ODF). Related annealed microstructures were investigated by orientation image map (OIM). Usually, unidirectional rolling led to a strengthening of the main texture component with increasing strain, but for tantalum dominant texture component {0 0 1} θ-fiber was stable after 70% deformation, while minor texture component {1 1 1} γ-fiber was enhanced with increasing strain. In clock rolling, both of the two fibers were not stable any more for their intensity varied with rolling pass. After the final deformation, a similar texture was produced by the two rolling methods. However, recrystallization texture revealed a big difference. Such different texture development was contributed to microstructural change resulted from rolling path change.     

Micro cutting of V-shaped cylindrical grating template for roller nano-imprint

The roller nano-imprint technology is considered as efficient and low cost method for the large scale micro-pitch grating fabrication. The surface quality of the V-shaped grooves for roller grating template developed by diamond tool cutting process is investigated. The surface quality of the micro V-shaped grating is optimized with minimized burr formation by optimizing the cutting tool's shape design and the micro-cutting process, based on the chip morphology and non-free chip interference analyses. Burr shows different variation with the grating pitch of 10–20 μm and less than 2 μm. The burr formation mechanism for V-shaped micro-cutting is studied by material (H62 Copper) metallography and homogeneity analyses. Finally, high precision grating template with various pitches is successfully achieved.     

Influence of pretreatment and deposition parameters on the properties and cutting performance of NCD coated PCB micro drills

Nowadays, a broad growing market of printed circuit board (PCB) micro drills has been developed. In this study, nano- crystalline diamond (NCD) coated printed circuit broad (PCB) micro drills are fabricated by the hot filament chemical vapor deposition (HFCVD) technique. The main factors affecting their cutting performance are generally their breaking strength, film-substrate adhesion, continuity and smoothness of coatings, and coating thickness. Consequently, the corresponding pretreatment and deposition parameters including pretreatment zone, pretreatment time in Murakami's reagent, substrate temperature during the deposition process, as well as the deposition time are optimized. A novel pretreatment zone, only involving cutting zone of micro drill, is proposed by cantilever flexural tests. Then, the substrate temperature is optimized to be about 850 °C by temperature simulation and its verification tests. Furthermore, the pretreatment time in Murakami's reagent and the deposition time are determined to be 10 min and 2 h by high speed dry drilling of copper clad laminates (CCLs).     

Plastic deformation of wadsleyite: IV Dislocation core modelling based on the Peierls–Nabarro–Galerkin model

In this paper, we determine dislocation core structures and Peierls stresses of wadsleyite, a high-pressure mineral present in the Earth mantle. We use a Peierls–Nabarro model combined with a finite-element method in which we introduce two-dimensional generalized stacking fault energies. Several potential slip planes of wadsleyite are considered. The results show that dislocations in this mineral can exhibit complex dislocation cores with linear or non-collinear dissociation and even three-dimensional dislocation cores. The calculation of the Peierls stresses gives information on the potential activity of slip systems governing the plasticity of wadsleyite. Our study confirms experimental observations that ½〈1 1 1〉{1 0 1} is the easiest slip system in this structure at high-pressure and that [1 0 0](0 1 0) is the second easiest. Both these easily slip systems have dislocations that dissociate into collinear partial dislocations. In contrast [0 1 0] dislocations with very large Burgers vector (11.2 Å) are stabilized by complex dissociations involving four partial dislocations.     

Organic field-effect transistors with ultrathin gate insulator

We have used a commercially available Mylar film coated with a thin (≈60 nm) layer of aluminium and an ultrathin (≈3.5 nm) SiO₂ layer as flexible substrate for the manufacture of bottom-gate organic field-effect transistors (OFETs). We show that the SiO₂ layer has insulating properties with a breakdown voltage of 1.6 V and a capacitance of ≈1 μF/cm². We have manufactured organic field-effect transistors using this substrate, regioregular poly(3-hexylthiophene) (rrP3HT) as a p-type semiconductor, and gold source and drain contacts. This results in OFETs that operate with voltages on the order 1 V.     

Diagnostics of austenitic steels by coercivity mapping

In this paper a novel application of magneto-optical films is described. This method is capable of mapping the coercivity with resolution as high as 50 μm with the magnetic field sensitivity of 100 A/m. The results thus obtained demonstrate the potential of the magneto-optical method when applied to the indication of positions on the surface of the austenitic steel that are critically degraded.     

Production of carbon nanotubes by single-pulse discharge in air

The production of carbon nanotubes (CNTs) has various methods, such as arc discharge, laser ablation, chemical vapor deposition (CVD), template-directed synthesis. These methods generally require, besides catalyst particles, vacuum environment and special ambient gas to prevent carbon from high temperature oxidation. However in this paper, CNTs were successfully produced on selected locations under atmospheric environment and room temperature by micro electrodischarge method. The micro electrodischarge system was composed with transistor circuit to offer discharging time of microseconds and peak current of several ampere. The effect of peak current and discharging time on the production of CNTs was addressed. Experimental results show that the structure and quantity of CNTs is different with different processing parameters. Multi-wall CNTs with the outer diameter of 17 nm and inner diameter of 5 nm were produced using peak current of 2.5 A and discharging time of 1000 μs.     

A new 3D multiphase FE model for micro cutting ferritic–pearlitic carbon steels

A new three-dimensional multiphase finite element computation model is proposed for the simulation of micro drilling two-phase ferritic–pearlitic carbon steels in order to understand the cutting, ploughing, tribological and heat transfer mechanisms at the microscale. Based on the Split-Hopkinson-Pressure-Bar technique, a constitutive material law has been developed to model the thermo-mechanical material behaviour including the effect of the microstructure. Micro drilling tests using solid carbide twist drills with different diameters (d = 50 μm to 1 mm) were performed on ferrite–pearlite two-phase steel AISI 1045 for the verification of the developed 3D FE computation model regarding chip formation, feed force, and torque.     

Electrochemical etching model in aluminum foil for capacitor

A novel tunnel growth model is proposed to reveal how hydrogen is transported out of tunnels and explain the phenomena during etching process of aluminum foil for capacitor. Experimental results indicated that tunnel density increased and tunnel width decreased with temperature increasing at the temperature range of 70–80 °C. The pressure in electrolyte had an effect on the tunnel density. The tunnel density after etching at 0.2 atm was larger than that at 1 atm. A pulse electrochemical etching process is described according to the novel tunnel growth model. It considers that hydrogen bubble of nanometer dimension is absorbed on the tunnel’s walls surface during the pulse electrochemical etching process, and the saturated hydrogen at the end of the tunnel is accumulated to be a large bubble before hydrogen is transported out of the tunnel. The large bubble will emanate from the end of tunnel when the pressure in the bubble is equal to that outside. The wall surface passivation phenomena is explained by this model; the naturally corrugated texture with ripples of about 0.1 μm in tunnel’s walls surface is regarded to be produced by the potential periodical changes, which are caused by the large hydrogen bubble at the end of the tunnel. At the same time, the effect of temperature and pressure on the morphology of the tunnel is also investigated by use of the model. The pressure of the large hydrogen bubble in the tunnel is calculated according to the date in other references when the period of the pulse electrochemical etching is inferred to be 3 ms at their experimental conditions. The proposed process of pulse electrochemical etching could explain well the calculation results and the SEM images of etched tunnels under the same experimental conditions.     

Theory-guided bottom-up design of β-titanium alloys as biomaterials based on first principles calculations: Theory and experiments

In this study we present a new strategy for the theory-guided bottom up design of β-Ti alloys for biomedical applications using a quantum mechanical approach in conjunction with experiments. Parameter-free density functional theory calculations are used to provide theoretical guidance in selecting and optimizing Ti-based alloys with respect to three constraints: (i) the use of non-toxic alloy elements; (ii) the stabilization of the body centered cubic β-phase at room temperature; (iii) the reduction of the elastic stiffness compared to existing Ti-based alloys. Following the theoretical predictions, the alloys of interest are cast and characterized with respect to their crystallographic structure, microstructure, texture, and elastic stiffness. Due to the complexity of the ab initio calculations, the simulations have been focused on a set of binary systems of Ti with two different high melting body-centered cubic metals, namely, Nb and Mo. Various levels of model approximations to describe mechanical and thermodynamic properties are tested and critically evaluated. The experiments are conducted both, on some of the binary alloys and on two more complex engineering alloy variants, namely, Ti–35 wt.% Nb–7 wt.% Zr–5 wt.% Ta and Ti–20 wt.% Mo–7 wt.% Zr–5 wt.% Ta.     

A molecular dynamics simulation study of the velocities,mobility and activation energy of an austenite–ferrite interface in pure Fe

Molecular dynamics simulations have been used to obtain the mobility, in pure Fe, of a face-centered cubic (fcc)–body-centered cubic (bcc) interphase boundary with an orientation given by (1 1 0)_bcc//(7 7 6)_fcc and [0 0 1]_bcc//[?1 1 0]_fcc. The interface is best described by a 4.04° rotation, about an axis lying in the boundary plane, from the Nishiyama–Wasserman orientation and the boundary consists of a parallel array of steps (disconnections). An embedded atom method interatomic potential was employed to model Fe, and the free energy difference as a function of temperature between the fcc and bcc phases, which provided the driving force for boundary motion, was determined by a thermodynamic integration procedure. Although the boundary was found to be very mobile, the transformation did not proceed by a martensite mechanism. The boundary mobility was obtained for several temperatures in the range 600–1400 K and Arrhenius behavior was found with an activation energy of 16.5 ± 2.7 kJ mol^?1 and a pre-exponential factor equal to 7.8( ± 0.9) × 10^?3 mmol J^?1 s^?1. The activation energy is much lower than that extracted from experiments on the massive transformation in Fe alloys and possible reasons for the discrepancy are discussed.