Eddy current analysis for ECT by BEM utilizing induced currents at 90° edge

In this paper, we study a method to analyze eddy current testing (ECT) by using surface integral equations. When the skin depth is small, the surface integral equations with surface electric and magnetic currents, J_s and K_s, as unknowns give accurate solutions. However, the equations are singular at the sharp edge and so, we can’t expect accurate solutions. In ECT, the skin depth is thick, and so the electromagnetic fields are affected strongly by those around the edge. Some edges and corners of the crack are so close that it is difficult to get accurate solutions, moreover, as the width of the crack becomes narrower compared with its depth, the surface integral equations become ill conditioned and so it is more difficult to get accurate results. In order to overcome these problems and get accurate solutions for studying how to get better ECT system, we utilize electromagnetic fields produced by eddy currents at 90° edge in formulating the eddy current. It is assured that the magnetic field is formulated by the surface integral equation for J_s even at the edge and corner. To meet boundary condition for K_s at the edge, a semi-linear edge element and a loop magnetic current are introduced in discretization of the surface integral equation. So as to check adequacy of the proposed method, we have solved a typical eddy current problem and confirmed that eddy current problems with a narrow crack can be solved accurately.     

Conservation law of surface roughness in single point diamond turning

In this work, a comprehensive model is established to predict the surface roughness achieved by single point diamond turning. In addition to the calculation of the roughness components in relation to the kinematics and minimum undeformed chip thickness, the newly developed model also takes the effects of plastic side flow and elastic recovery of materials as machined into account. Moreover, the ‘size effect’ has also been successfully integrated into the model, i.e. an inflection point appears in the trend line of predicted surface roughness as the ratio of maximal undeformed chip thickness to cutting edge radius (h_Dmax/r_n) is equal to one unit. Face turning experiments validate that the maximal prediction error is only 13.35%. As the ratio of h_Dmax/r_n is higher than one unit, both the prediction and experiments reveal that a conservation law exists in diamond turned surface roughness, owing to the competitive effects of kinematics, minimum undeformed chip thickness, plastic side flow and elastic recovery of materials on surface formation. Under the conservation law, the freedom control for an invariable surface roughness can be fulfilled in response to a quantitative ratio of h_Dmax/r_n, either through an accurate configuration of feed rate and depth of cut with fixed tool nose radius and cutting edge radius, or by a reasonable selection of tool nose radius and controlled cutting edge radius with designed feed rate and depth of cut.     

An investigation of the effects of the tool path on the removal of material in polishing

Uniformity of removal affects the finishing, and in some cases, the form accuracy of the polished surface. Tool paths are required for the automation of surface polishing. How the tool path may affect the removal of material in polishing is investigated in this paper. An analysis of how removal at a location due to polishing along adjacent path lines is presented. Four tool paths reportedly used in polishing are covered: scanning, bi-scanning, Hilbert and Peano paths. Removal in the inner surface as well as near the edges of surfaces is examined through simulations and analysis. The results show that, for the same path pitch, the peak-to-valley height (h_pv) in the inner part of the removal map is the same for scanning, bi-scanning and Peano, while the texture of the removal maps can be quite different. The h_pv values of Hilbert are more than double those of Peano, although both are fractal paths. Removal near the edges is particularly severe for scanning-type tool paths. The ratio of the edge peak height to the inner peak height is about 1.6 on average for scanning. The uniformity of removal further deteriorates as the ellipticity of the tool contact increases. When the contact direction is closely aligned with the path line direction, that ratio goes up to about 2.9 for contact ellipticity of 2. Polishing experiments have also been conducted. Both experiments and simulations point to the presence of edge effects in scanning paths and its absence in Peano paths. It is further proposed that, for more uniform removal of material: (1) changes in the tool path direction should be well distributed and (2) the direction of the path lines should be well balanced over the entire surface.     

Electrochemical characterization of sintered magnetite electrode in LiOH solution

In relation to the mitigation of flow assisted corrosion (FAC) occurring at the carbon steel materials at power plants, magnetite powder was sintered into pellets and used to construct electrodes for electrochemical property measurements in LiOH solutions at ambient conditions. Measurements indicated adsorption of hydroxide ions on the magnetite surface. Slow cathodic scanning removed the adsorbed OH⁻ and returned the electrode surface to its original state. It is proposed that the cause of cyclic voltammetric (CV) peaks is the reduction of H₂O involving the conduction band edge (E_C) and valence band edge (E_V) of the magnetite. Negative polarization by the CV produced hydrogen atoms and injected them into the magnetite body; these were oxidized when the sweep was reversed and then dissipated at the magnetite surface by contact with OH⁻ ions. Results support the interaction of magnetite energy levels with adsorbed species, rather than the dissolution of magnetite.     

Hydrogen damage and delayed fracture in bulk metallic glass

Initiation, propagation, arresting and breaking of hydrogen blistering and hydrogen-induced delayed fracture (HIDF) under sustained load in a bulk metallic glass of Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 have been investigated. Results show that when the current density, i, is smaller than 20 mA/cm² corresponding to total hydrogen concentration of 3310 wppm, there are no hydrogen blistering and microcrack on the surface of the specimen without loading, but HIDF under sustained load can occur, and the threshold stress intensity factor for a single edge notched sample, K_IH, is 0.63 times of the notched toughness, K_Q, which is 62.2 MPa m^1/2. When i is equal to or larger than 20 mA/cm², hydrogen blistering or blistering plus microcrack appears on the surface of specimen without loading, as well as K_IH is 0.26 times of K_Q and independent upon i. The relative losses of the notched toughness induced by both atomic hydrogen and the blistering are all 37%. The critical pressure necessary for a stable blister formation, P_i, is 3.6 GPa, and that for cracking of the blister, P_C, is 3.9 GPa. The blister cracking will arrest after propagating for 20-30 μm, and the arrested crack will propagate again because of entering of hydrogen atoms. At last, the blister with cracking will break and leave local cleavage fracture surface with arrested lines on the sample surface without loading.     

Surface damage of a TiAl-based alloy during high temperature annealing

The near surface stability of a Ti–45Al–2Mn–2Nb alloy has been investigated. Samples of the alloy were annealed at two different temperatures, 1200 and 1000°C for various periods of time. It was found by detailed SEM and TEM investigation that a significant loss of aluminum occurred from the surface of the specimens during annealing, resulting in the formation of Al-depleted damaged layer near the surface of the specimens. The microstructure of the damaged layer was found to be considerably different from that of the bulk. The damaged layer was found to consist of α₂ phase near the interface between the damaged layer and the undamaged bulk, and α₂ phase and B2 phase with ω-type phase precipitates near the outer edge of the specimen. It was also observed that the thickness of the damaged layer increased with the annealing time and also with the annealing temperature. The thickness of the damaged layer exhibited a parabolic relationship with annealing time for both the temperatures.     

Forming process of cross-connected finned micro-grooves in copper strips

Using ploughing-extrusion method, a cross-connected finned micro-grooves structure was formed on the surface of copper strips with thickness of 0.4 mm. The structure was fabricated by making ‘V’-grooves in copper strips and perpendicular ‘V’-grooves on the opposite side that intersect the first set of grooves. Micro pores appear at the intersection of these cross-connected grooves, and micro fins appear on the groove fringes. So it can be defined as ‘pore-groove-fin’ structure. The preferable ‘pore-groove-fin’ structure can be obtained under the condition that the tool edge inclination angle (χγ) is 45°, both the major extrusion angle (γo) and the minor extrusion angle (γ 0′ ) are 30°, both the major formation angle (β) and the minor formation angle (β′) are 10°, the ploughing-extrusion depth (fd) is 0.32 mm and the groove pitch is 0.4 mm on surfaces A and B. The formed included angle of groove A is 70°, and the groove depth is 0.3 mm, while the included angle of opposite perpendicular groove B is 20° with the groove depth of 0.35 mm. The obtained fin height is 0.15 mm, the elliptical pore length is 0.2 mm and the width is 0.05 mm. Experiments show that fd has the greatest influence on the formation of micro pores. Bulges appear on the opposite surface B when the ploughing-extrusion depth on surface A (fdA) reaches a critical value. The ploughing-extrusion depth on surface B (fdB) has great influence on the re-growth of fin structure.     

Excited state dynamics in conjugated molecules

Using an equation of motion theory, optical absorption lineshapes are calculated for cis and trans-(CH)_x and are used to probe intramolecular and vibrational relaxation in these systems. We conclude that the broad edge in trans is due to a large-amplitude multiphonon relaxation consistent with the notion of soliton photogeneration, while the cis edge describes a weaker relaxation attributed to kink confinement in the excited state.     

Computer simulation of carbon diffusion near b/2[010](001) dislocation in cementite

Partial contributions U _i to the activation energy for the diffusion of carbon atoms in the Fe₃C lattice have been calculated. The U _i values have been compared upon the migration of carbon atoms in the ideal lattice, near the stacking-fault plane, and near the core of a partial edge dislocation with a Burgers vector b/2[010]. The most preferable ways of the migration of carbon atoms near the studied structural defects in the (001) cementite plane have been revealed. The values of the stacking-fault energy in this plane have been calculated. The possibility of splitting the dislocation with a Burgers vector b/2[010] into two partial dislocations has been shown.     

Energetic evaluation of possible insertion sites of Cu into BaSi2 using first principle calculations

Electronic energy calculations of Cu-doped BaSi₂, an expected solar-energy material, have been performed by a density-functional theory assuming several possible insertion sites of Cu into the BaSi₂ lattice. The 4c sites, which are surrounded by three Si atoms, one of which is at a peak of one Si-tetrahedron and other two of which are composing an edge of the other Si-tetrahedron, will be the most favorably inserted by Cu atoms. This insertion reaction is energetically more favorable than the substitution reactions of Ba or Si by Cu. Insertion of Cu into BaSi₂ will cause the n-type behavior of semiconducting BaSi₂. This prediction is consistent with the observed facts.     

A comparative study of the cutting forces in high speed machining of Ti–6Al–4V and Inconel 718 with a round cutting edge tool

Titanium alloy Ti–6Al–4V and nickel-based superalloy Inconel 718 have been widely employed in modern manufacturing. The published literature on high speed machining (HSM) of the two materials often involves different machining set-up, which makes it difficult to directly apply the research findings from one material to the other to select the most appropriate tool geometry and cutting conditions. A comparative experimental study of HSM of Ti–6Al–4V and Inconel 718 is conducted in this paper using the same machining set-up. The scope of this study is limited in high speed finish machining, where the tool edge geometry plays a significant role. The experimental set-up and the methods of measuring the cutting forces and the tool edge radius are introduced. A total of 40 orthogonal high speed tube-cutting tests were performed, involving five levels of cutting speeds and four levels of feed rates. Based on extensive experimental data, the similarities and differences between HSM of Ti–6Al–4V and Inconel 718 are quantitatively compared and qualitatively explained in terms of four quantities: (1) the cutting force F_c, (2) the thrust force F_t, (3) the resultant force R, and (4) the force ratio F_c/F_t. A total of 12 empirical regression relationships are obtained.     

Segmented polyacetylene, (CHDy)x: Electrochemical n-doping studies

Defects involving sp³ hybridized carbon atoms in the form of (HCD) units have been controllably introduced into trans-(CH)_x by chemical methods to produce polymers of the type trans-(CHD_y)_x, i.e., [(CH)_1-y⁻ (HCD)_y]_x (y = 0, 0.15 and 0.17), in order to study the nature of these defects and their effect on the electronic and magnetic properties of trans-(CH)_x. The effects of these defects on the electrochemical reduction (n-doping) of trans-(CHD_y)_x up to 4.0 mol % reduction levels have been studied. The results are consistent with optical and Raman spectra of trans-(CHD_y)_x species and are interpreted as showing that: (i) the band gap in trans-(CHD_y)_x is essentially unchanged from that in trans-(CH)_x because of a small but significant amount of long conjugated sequences remaining in the deuterated polymer; (ii) the maximum density of states near the conduction band edge has moved upwards from the band edge; and (iii) the (HCD) defects are clustered rather than randomly spaced in a given (CHD_y)_x chain.     

Sol-gel derived Li-Mg co-doped ZnO films: Preparation and characterization via XRD, XPS, FESEM

Li-Mg co-doped ZnO films have been deposited onto glass substrates by sol-gel spin coating method. The structural and morphological properties of the films were characterized by X-ray diffractometer (XRD), X-ray photo-electron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). The XRD spectra indicated that the films have polycrystalline nature. The crystallite size values decreased with the increasing Mg content. The chemical composition of the Li-Mg co-doped ZnO films were confirmed by XPS. Additionally, XPS results clearly showed the existence of Mg as a doping element into ZnO crystal lattice. The surface morphology of the films was found to depend on the concentration of Mg in the ZnO:Li. The absorption band edge values of the films were calculated and these values of the films increased with increasing Mg concentration. The refractive index dispersion curves of the films obeyed the single-oscillator model. The dispersion parameters such as E_o (single-oscillator energy) and E_d (dispersive energy) of the films were determined and increase with Mg content.     

Induced antibacterial capability of TiO2 coatings in visible light via nitrogen ion implantation

In order to enhance the antibacterial ability of titanium components, an antibacterial coating was fabricated on Ti surface by micro-arc oxidation (MAO) and further nitrogen plasma immersion ion implantation (N-PIII). The XPS spectra demonstrated that nitrogen was incorporated into TiO₂ coatings by N-PIII and the nitrogen content on the surface of TiO₂ coatings increased as the N-PIII time increased. Nitrogen-incorporated samples exhibited remarkably increased absorbance in the visible region and the light absorption edge of nitrogen-incorporated samples showed a redshift compared to MAO samples. Escherichia coli and Staphylococcus aureus were seeded on the samples to assess their antibacterial ability. The bacterial experiment demonstrated that nitrogen-incorporated TiO₂ could effectively reduce the bacterial viability in visible light. Thus, the antibacterial TiO₂ coatings fabricated by MAO and further N-PIII might have large potential in the medical and marine fields.     

Development of micro milling tool made of single crystalline diamond for ceramic cutting

In order to machine micro aspheric ceramic molds precisely and efficiently, micro milling tools made of single crystalline diamond (SCD) are developed. Many cutting edges are fabricated 3-dimensionally on the edge of a cylindrical SCD by a laser beam. Flat binderless tungsten carbide mold was cut with the developed tool to evaluate the tool wear rate and its life. Some micro aspheric molds of tungsten carbide were cut with the tool at a rotational speed of 50,000 min⁻¹. The molds were cut in the ductile mode. The form accuracy obtained was about 100 nm P–V and the surface roughness 12 nm R_z.     

AISI430铁素体不锈钢表面制备MnCo2O4涂层特性及内应力研究

为了探究MnCo₂O₄尖晶石涂层作为固体氧化物燃料电池的金属连接体表面涂层的性能,使用溶胶-凝胶法制备出纯净的前驱体粉末,再使用电泳沉积方法制备出致密的MnCo₂O₄尖晶石涂层,利用SEM、EDS和XRD等表征手段观察分析MnCo₂O₄尖晶石涂层的相结构和微观组织形貌。采用“四探针法”测量MnCo₂O₄尖晶石涂层800℃氧化200h前后的面比电阻使用拉拔法完成不同界面粗糙度下的涂层结合强度测试,并用有限元仿真加以验证。结果显示,MnCo₂O₄尖晶石涂层结构均匀,致密度较好。相较于AISI430不锈钢基体来说,在800℃空气中氧化200h,抗氧化性提高了接近3倍。且中温面比电阻小于SOFC金属连接体规定的极限值。此外,基体表面粗糙度可以有效的增加涂层与基体的机械咬合作用,但同时也会导致应力集中,出现缺陷,从而降低了结合强度。     

Theoretical analysis of silicon surface roughness induced by plasma etching

A theoretical study of single-crystal silicon surface roughness induced by SF₆ plasma has been carried out by means of atomic force microscopy. Plasma which contains the velocity shear instability has been used to study the relation between the plasma parameters and subsequent surface roughness. The surface roughness has been examined in the dependence on experimental parameters. The results obtained by theoretical calculations are identical to the experimental ones. The present paper has quantified the influence of a DC electric field values on plasma parameters such as the ratio of ion flux to the neutral reactant flux (J ⁺/J _F), exposure time, DC electric field, magnetic field and inhomogeneity. Theoretical investigation shows that the roughness of silicon surface increases with the increase of the values of J ⁺/J _F, exposure time, of magnetic field, of inhomogeneity in a DC electric field and decreases through increasing the value of a DC electric field.     

Thermoelectric properties and electronic structure of p-type Mg2Si and Mg2Si0.6Ge0.4 compounds doped with Ga

Mg₂Si:Ga_x and Mg₂Si_0.6Ge_0.4:Ga_x (x = 0.4% and 0.8%) solid solutions have been synthesized by direct melting in tantalum crucibles and hot pressing. The effect of Ga doping on the thermoelectric properties has also been investigated by measurements of thermopower, electrical resistivity, Hall coefficient and thermal conductivity in temperature range from 300 to 850 K. All samples exhibit a p-type conductivity evidenced by positive sign of both thermopower and Hall coefficient in the investigated temperatures. The maximum value of the dimensionless figure of merit ZT was reached for the Mg₂Si_0.6Ge_0.4:Ga(0.8%) compound at 625 K (ZT ∼ 0.36). The p-type character of thermoelectric behaviours of Ga-doped Mg₂Si and Mg₂Si_0.6Ge_0.4 compounds well corroborates with the results of electronic structure calculations performed by the Korringa-Kohn-Rostoker method and the coherent potential approximation (KKR-CPA), since Ga diluted in Mg₂Si and Mg₂Si_0.6Ge_0.4 (on Si/Ge site) behaves as hole donor due to the Fermi level shifted to the valence band edge. The onset of large peak of DOS from Ga impurity at the valence band edge, well corroborates with high Seebeck coefficient measured in Ga-doped samples.     

Effect of surface anisotropy on the dynamic properties of Néel domain walls in the films with planar anisotropy

This work is devoted to the investigation into the effect of surface magnetic anisotropy on the motion of domain walls in magnetic uniaxial films with an in-plane anisotropy in the range of thicknesses corresponding to the stability of one-dimensional Néel walls. It has been established that the surface anisotropy with a constant K _s > 0 (K _s < 0) increases (decreases) the velocity of both stationary and nonstationary motion of the domain wall, as well as the period of oscillations of the velocity of nonstationary motion. The magnitude of the critical field as a function of K _s has been determined. Effect of surface anisotropy with K _s < 0 on the scenario of the dynamic transformation of the domain-wall structure has been revealed.