Layer Removal Technique Research Articles

Potassium hydroxide treatment of layered WSe2 with enhanced electronic performances.

2D WSe2-based electronic devices have received much research interest. However, it is still a challenge to achieve high electronic performance in WSe2-based devices. In this work, we report greatly enhanced performances of different thickness WSe2 ambipolar transistors and demonstrate homogeneous WSe2 inverter devices, which are obtained by using a semiconductor processing-compatible layer removal technique via chemical removal of the surface top WOx layer formed by O2 plasma treatment. Importantly, monolayer WSe2 was realised after several consecutive removal processes, demonstrating that the single layer removal is accurate and reliable. After subsequent removal of the top layer WOx by KOH, the fabricated WSe2 field-effect transistors exhibit greatly enhanced electronic performance along with the high electron and hole mobilities of 40 and 85 cm2 V-1 s-1, respectively. Our work demonstrates that the layer removal technique is an efficient route to fabricate high performance 2D material-based electronic devices.

Numerical Stress Analysis of Creep-Feed Grinding Through Finite Element Method in Inconel Alloy X-750

The present study developed a 2D finite element model for simulation of creep-feed grinding process. Fully-coupled mechanical-thermal analysis was used to predict the residual stresses distribution. As in the creep-feed grinding the thermal damages are considerable, so the best and worst cooling condition i.e. flood and dry grindings were studied. Convection heat transfer coefficient was utilized to shows the effect of coolant. The results show the maximum temperature of specimen has reduced by about 52% compared to non-use of coolant. The dominate residual stresses are tensile near the surface that a steep decline in stresses was observed in flood grinding. Also, by using the electro polishing layer removal technique the non-uniform residual stresses were measured to validate the model. The results demonstrated the presented model provides good congruency with the experiments

Comparative analysis of smear layer removal techniques in the treatment of dental caries

The purpose of this systematic literature analysis is to review the application features of various types of acids and to determine the most effective etching technique to achieve maximum elimination of the smear layer. Materials and methods: the analysis of up-to-date Russian and English literature was carried out in Google Scholar and PubMed electronic databases. The analysis identified the features of various etching techniques using phosphoric, maleic and polyacrylic acids to achieve maximum elimination of the smear layer. Results: during the analysis, 67 articles were examined. After analyzing the literature on the inclusion criteria, the total number of publications amounted 31. Conclusion: smear layer should be removed using phosphoric or maleic acids according types of tissues: phosphoric acid application used on the enamel, maleic acid is applied on the dentine due to ensure a high-quality adhesive protocol, taking into account the sparing effect on the structural and functional units of tissues. Recommended exposure: applied to the enamel for 15-30 seconds, taking into consideration the type and the molecular weight of the acid. The exposure time of acid on dentin is recommended from 10-15 seconds, but an increase in the exposure time of maleic acid on dentin did not lead to negative changes in the structure of dentin, which significantly distinguishes the use of orthophosphoric acid. Also, static batching is not enough for high-quality treatment, because, in case of static etching, only the internal areas consisting of enamel prisms can be fully etched. Consequently, the use of dynamic etching is recommended. All authors contributed equally to the writing of the article.

Experimental and numerical study on effect of constrained groove pressing on mechanical behaviour and morphology of aluminium and copper

The constraint groove pressing (CGP) is a severe plastic deformation (SPD) method for producing ultra-fine grained sheet metals. Firstly, the present study reports the effect of CGP on mico-hardness, tensile strength, and grain size in the multi-pass CGP of aluminium and copper. The aluminium and copper sheets are processed up to two passes. The improvement in tensile strength and hardness after every pass due to grain size reduction is reported. Further, an empirical model that correlates residual stresses and grain size is established. The residual stresses were measured by X-ray diffraction (XRD) and layer removal technique along the thickness of the samples. Moreover, the effect of residual stress nature on mechanical properties is investigated. It is found that the micro-hardness of the sheet depends on the nature of residual stress. Finally, a finite element (FE) model is constituted to predict the stresses, deformation, and residual stresses after every pass. This FE model can be used for exploring possibilities of improving the process capability of CGP by examining conditions not evaluated during experiments. The residual stress, Von Mises stress, deformation were decreased with the decrease in grain size up to two passes.

Residual stresses in Stellite 6 layers cladded on AISI 420 steel plates with a Nd:YAG laser

Clad tracks/layers with good geometry, desirable dilution, and hardness can be produced using optimal process parameters. However, cracking and deformation can occur in the laser cladded products. The tensile residual stress is mainly responsible for the failure of the cladded products. Therefore, different residual stresses’ control strategies during laser cladding were investigated, such as preheating the substrate, using an intermediate layer, and using different energy inputs. The residual stresses in clad layers were measured with layer removal and hole drilling techniques. The depth residual stress distributions obtained from both techniques show a good agreement. The residual stresses acting along the cladding direction σx and the maximum residual stresses within the clad layer were analyzed. The cooling rate and thermal gradient were simulated from our previously developed 2D thermal model. The relationships among the cooling rates, thermal gradients, maximum residual stresses, and absorbed energy were investigated and the results are discussed. Thermal gradients, cooling rates, and the maximum residual stresses decrease with energy input. The decay factors between maximum residual stress and absorbed energy and between the cooling rate and absorbed energy are close to each other indicating that a correlation between the maximum residual stress and cooling rate exists. An empirical relation is used to describe such a correlation.

Effects of solution and quenching treatment on the residual stress in extruded ZK60 magnesium alloy

The quench induced residual stress in extruded ZK60 magnesium alloy is investigated. X-ray diffraction and layer removal technique are employed to determine the residual stress in extrusion and long transverse direction through the thickness of the extruded plate after solution and quenching treatment. FEM simulation is employed to clarify the origin of the stress state. The residual stress is not uniform through thickness, it is compressive on the surface and first decreases and then increases in absolute magnitude with increasing depth and becomes tensile in the center. Anisotropic residual stress can be detected, with larger stress in long transverse direction and smaller stress in extrusion direction. This is rationalized by the anisotropic flow stress caused by the tilted basal texture. Anisotropic residual stress can be replicated in simulation using an isotropic yield function at high temperature and an anisotropic yield function at low temperature during quenching, the smaller flow stress in extrusion direction facilitates plastic flow at low temperature and results in smaller compressive residual stress in extrusion direction. The fact that no twins can be found after quenching demonstrates that the asymmetric yield strength associated with twinning does not affect the residual stress.

Determination of ply level residual stresses in a laminated carbon fibre-reinforced epoxy composite using constant, linear and quadratic variations of the incremental slitting method

Measurement of residual stresses in FRP composites is by no means a trivial task and there are no commonly applied or standardised methods currently available. As a result, characterisation of residual stresses is often avoided, resulting in the use of conservative safety margins, which has consequently resulted in structures being overdesigned. In the work described here, the incremental slitting method has been demonstrated to be a technique suitable for measuring residual stress in thin (∼0.3mm) plies of a [0°2/90°2]4s carbon fibre-reinforced epoxy laminate. The stresses measured using a constant stress approximation approach provided the best agreement with measurements obtained using the layer removal technique and stresses predicted using a semi-coupled transient-thermal and structural model.

Investigation on residual stresses in a Al2024 deep drawn square cup

The mechanical properties and dimensional stability of aluminum alloy sheet parts are strongly influenced by residual stresses. However, few studies deal with residual stresses in aluminum alloy sheet parts processed by deep drawing at elevated temperature. In this work, the through-thickness residual stresses distribution in a 2024 aluminum alloy deep drawn square cup was determined by layer removal technique and X-ray diffraction. It is found that the distribution of the tangential residual stress in the bottom circular arc shows a different with the width direction residual stress. Both the width direction and axial residual stresses in the side wall show some dependence on the axial position and decrease from the mid wall towards the cup bottom. The calculation method based on a wide sheet bending theory is capable of describing the distribution features of residuals stress in the bottom circular arc of the square cup.

Development and Application of the Contour Method to Determine the Residual Stresses in Thin Laser-Peened Aluminium Alloy Plates

The contour method was applied to obtain residual stress fields in a laser-peened 2.0-mm-thick Al2024-T351 sample. In order to remove the effects of near-surface wire electro-discharge machining (EDM) cutting artefacts on the measured residual stresses, sacrificial blocks were attached to both surfaces of the thin sample with a polymer-based glue doped with silver particles. A data analysis routine based on bivariate spline smoothing was conducted to obtain a 2D residual stress map. The results were compared with incremental hole drilling, and X-ray diffraction and layer removal techniques. The results are in good agreement in terms of the magnitudes and the location of the peak stresses, with the exception of the contour method results. Owing to the low thickness of the samples, the data analysis is very sensitive to the parameters used in the spline fitting, leading to fluctuation in the results. It is concluded that the contour method can be applied to thin samples, however, extra attention is required. Since the uncertainty is higher compared to the conventional contour method results, it is good practice to compare the results with at least one other experimental method.

Extension of the layer removal technique for the measurement of residual stresses in layered anisotropic cylinders

An extension of the layer removal technique is presented that allows the residual stresses within multilayered anisotropic pipes of any wall thickness to be determined. The method inherently satisfies the self-equilibrium requirement and limits the effects of measurement errors to the region local to the error. The thickness of each layer that is removed need not be uniform and is entirely independent of the thickness of each ply of material. Four example problems are considered. The first three allow results to be compared between the present method and previous work. The fourth problem demonstrates the method on a thick walled anisotropic pipe built up of +45°/-45° plies for which no solution was previously available.

Investigation of through thickness residual stress distribution in equal channel angular rolled Al 5083 alloy by layer removal technique and X-ray diffraction

The layer removal technique and the X-ray diffraction method have been employed to evaluate the residual stresses through the thickness of aluminum alloy 5083 processed by equal channel angular rolling (ECAR). ECAR is a severe plastic deformation process that introduces shear deformation to sheet metals. The process has been completed on 2mm thick strips passed three times through die channels in a continuous manner. In this work, the profile of residual stresses was quantitatively determined. It was observed that after the ECAR process, the residual stress magnitudes were changed from approximately zero in annealed condition up to half of the yield strength value of ECARed samples. The distribution of the residual stresses was found to be non-uniform through the thickness and the ECARed sample was compressive at the top surface while it was tensile at the bottom surface.

On the Measurement of Residual Stress in Induction Hardened Parts

It is well known that induction surface heating followed by rapid quenching generally increases the fatigue life of steel components subjected to bending loads by significantly postponing the micro-crack nucleation and propagation processes. The phase transformation volume change combined with severe thermal gradients leave a hard surface layer under relatively high and deep compressive residual stresses. In this paper, residual stress measurements are done on induction hardened AMS6414 martensitic steel (aerospace grade of AISI4340) cylinders using two techniques: the so-called contour method and X-ray diffraction. For both methods, induction hardened parts raise many challenges. The contour method hardly describes high stress gradients near the surface while the diffraction technique accuracy appears limited considering the strong microstructural variation and the high depth of the stresses to be measured. For the contour method, a CMM and an optical pen using the confocal chromatic imaging principle were used to measure the surface after precision WEDM cutting. The effect of data filtering and smoothing on the calculated stresses are discussed. For X-ray analysis, the effect of stress relaxation during layer removal and analysis technique is explained. The difference between the residual stress measurements done with the two techniques is discussed with emphasis on both the surface and the in-depth measurements.

Neutron Surface Residual Stress Scanning Using Optimisation of a Si Bent Perfect Crystal Monochromator for Minimising Spurious Strains

For non destructive stress analysis of surface treated steel samples the application of laboratory X rays or high energy synchrotron radiation in reflection mode covers the region from some micrometers up to a depth of about 150 - 200 µm. To access depth regions deeper than 200 µm the incremental layer removal technique in combination with the repeated application of X‑ray stress analysis for the newly generated surfaces can be used. However, this procedure is destructive, laborious and furthermore, it has to be checked whether corrections have to be applied due to stress relaxation. By using neutron radiation penetration depths generally up to several millimetres can be achieved non destructively [1]. However neutron measurements are critical at the surface. When scanning a sample surface, aberration peak shifts caused by so called spurious strains arise due to the fact that the gauge volume defined by the primary and secondary optics is partially outside of the sample. These aberration peak shifts can be of the same order of magnitude as the peak shifts related to residual strains [2-6]. In this exemplary study it will be demonstrated that, by optimising the bending radius of a Si (400) monochromator, the spurious surface strains can be strongly reduced when compared to the values obtained with a traditional Ge (311) mosaic monochromator, even when the gauge volume is mainly out of the surface. The objective of the experiments is to find the optimal monochromator settings for the Si (400) monochromator at the STRESS-SPEC instrument at the research reactor FRM II, Munich, Germany. For the parametric studies a stress free steel sample of the fine grained construction steel, S690QL was used. The optimised conditions for the Si (400) monochromator that resulted from the systematic studies were applied to a shot peened plate of steel SAE 4140. The residual stress distribution is analysed by means of through surface strain scanning. The residual stress gradient obtained is in very good agreement with the well characterised residual stress depth profile obtained within a round robin test in the scope of the BRITE-EURAM-project ENSPED (European Network of Surface and Prestress Engineering and Design) [7]. The results indicated that surface residual stress profiles can be measured with neutrons up to 200 µm underneath the surface without time consuming and laborious surface effect corrections.

An Electrochemical Machining Device for Residual Stresses Measurement in PM Parts by Layer Removal Method

Residual stresses play an important role in the performance of materials and the components produced from them. All manufacturing processes introduce residual stresses. These stresses can have a positive effect, for example by increasing the fatigue limit in the case of compressive surface residual stresses. Layer removal by electrochemical machining (ECM) can be used for measurement of the residual stresses in the PM parts. The device removed the layers by aid of electrochemical machining for this purpose is designed and developed. The device setup for residual stress measurement is based to the changes on deformation quantity. Since ECM is a non-mechanical metal removal process, ECM is capable of machining any electrically-conductive material with attendant high removal rates, regardless of mechanical properties. In particular, the removal rate in ECM is independent of the hardness, the porosity and toughness of the PM parts being machined. The micro constituents in PM steels resulting from different processing routes exhibit different thermal and mechanical behavior. This will lead to the formation of residual stresses around these micro constituents. Here we give the results of the first work carried out on PM steels in relation to residual stress measurements by the electro-chemical layer removal technique. The device works as follows. As a layer of thickness is removed, a certain amount of stress is removed from the sample. Equilibrium is violated and the sample deforms elastically to compensate for the stress removed. This elastic deformation in the sample is measured by the linear displacement gauge. This gauge pushes on the end of sample and deformation is recorded by this gage. The linear gauge send a signal to a display and then to the data converter. As simultaneous, this signal sent to the computer from the data converter for further calculations by RS 232.

Effects of the machining conditions on the strain hardening and the residual stresses at the roots of screw threads

The strain hardening and the formation of the residual stresses at the roots of threaded joints produced by machining according to American Petroleum Institute (API) standards was investigated. Initially the problem is defined and then an experimental technique was developed for measuring the residual stresses at the roots of fine screw threads. The screw thread was cut on a tubular bar from chromium–nickel based alloyed steel. Residual stresses were measured by the electro-chemical layer removal technique. Experimental work showed that, sever strain hardening and the concentration of residual stresses at the roots of the screw threads took place depending on the machining conditions. Strain hardening in the range of 320–430 HV were found on the screw thread surfaces as compared to the base hardness of 260 HV. Residual stress ranging from 600 to 1450 MPa was developed as compared to the material tensile strength of 850 MPa. The depth for maximum residual stress is around 20 μm.

Measurement of the residual stress tensor on the surface of a specimen by layer removal and interferometry: uncertainty analysis

A new method for measuring the principal residual stresses on the surface of a thin metallic specimen is presented. The novelty of the method resides in a combination of the layer removal technique by chemical etching and of electronic speckle pattern interferometry to measure the ensuing deformation. It is shown that the loci of constant deflection with respect to the original plane surface are conic sections. An interferometer sensitive to out-of-plane displacements was used, yielding fringe patterns that reproduced those curves. Immediate visualization of the orientation and relative magnitude of the principal stresses within the removed layer was then possible. A fit of the measured deformation to the theoretical shape, together with knowledge of the initial and final thickness of the specimen and of the elastic properties of the material (a cold-rolled low-carbon steel sheet), allowed estimating the principal stresses. It is shown that the critical factor that determines the uncertainty of these estimates is the thickness of the removed layer.

Residual stresses determination in injection molded virgin and recycled HDPE blends: mechanical properties and morphology

AbstractAn experimental study of residual thermal stresses has been carried out in injection molded virgin and recycled high density polyethylene (HDPE) blends. Effects of blend concentrations on residual stresses were investigated under different injection conditions such as melt temperature, mold temperature and cooling time. Layer removal technique was used for measuring residual stresses. In order to determine the relation between the residual stresses and material characteristic of HDPE blends, mechanical and morphological properties of the blends were also investigated. Elastic modulus and impact strength were important key factors for determining the blend characteristics. As a result, it was found that HDPE blends gave higher residual stresses but lower impact strength with higher elastic modulus when recycled concentration was increased. Furthermore, it was seen that shape and size of the crystallites were also effective on residual stresses. Small and spherulitic crystallite structured blends such as 30 % recycled HDPE induced reduction in residual stresses due to easier relaxation with lower elastic modulus and higher impact strength while lamellar crystallite structured blends such as 50 % recycled HDPE gave higher elastic modulus but lower impact strength with higher residual stresses.

Recast layer removal after electrical discharge machining via Taguchi analysis: A feasibility study

This study explores the feasibility of removing the recast layer (RCL) using etching and mechanical grinding for Ni-based superalloy materials by means of electrical discharge machining (EDM). The EDM process is widely used for machining hard metals and performing specific tasks that cannot be achieved using conventional techniques. The sparks produced during the EDM process melt the metal's surface, which then undergo ultra rapid quenching. A layer forms on the workpiece surface defined as a recast layer after solidification. Molds and dies desire to remove the RCL even though it is hard and has good matrix adherence. This experiment is divided into three stages. The first stage acquires a thick recast layer by using EDM with a larger discharging energy. A thick recast layer is essential for verification of the EDM technique for observing the recast process. Thus, this work applies the Taguchi L 18 analytical method to acquire the thick recast layer. The second stage optimizes the recast layer removal technique. Therefore, the thick recast layer is intentionally made in the first stage. This work determines the second stage setting using Taguchi's recommendation. Thus, the L 9 orthogonal array sets up the etching and mechanical grinding parameters and observes the recast layer removal quantity analysis. Finally, an experiment studies the surface characteristics of Ni-based superalloys, such as composition and micro-hardness after removing the recast layer.

Stress evolution of cold-drawn pearlitic steel wire subjected to uniaxial tension

The aim of this paper is to investigate the effect of uniaxial tension on the residual stress of cold-drawn pearlitic steel wire through X-ray diffraction in combination with layer removal technique. It is found that an extra 0.9% plastic strain is introduced to the steel wire due to the uniaxial tension using a universal electronic tensile machine. The XRD results indicate that uniaxial tension after drawing has dominate influence on the decrease of surface tensile residual stress and the corresponding stress gradient in the drawn wires.

Rapid determination of residual stress profiles in ferrite phase of cold-drawn wire by XRD and layer removal technique

A cost effective and simple approach on residual stress evaluation of cold-drawn pearlitic steel wire was proposed, on a basis of the AST XSTRESS 3000 X-ray system and layer removal technique. The system could accomplish stress measurement with high accuracy in a shorter time than conventional laboratory X-ray diffractometer. The stress profiles in ferrite phase of cold-drawn wires were quantitatively determined by extending the layer removal technique to the whole section of wires. It was observed that the cold-drawn wires were in tension at the surface and were compressive at the center along the axial direction, while there was near-zero intensity of stress level in the rods before cold drawing.