Reduction Of Internal Stress Research Articles

Composite electroforming of precision Ni-P-PTFE mold inserts with low internal stress and self-lubricating properties

An electrolyte solution incorporating sodium saccharin and an alkynyl compound was provided to electroform Ni-P-PTFE mold inserts with both low internal stress and good self-lubricating properties. The results showed that with 5 g·L−1 sodium saccharin and 1 mL·L−1 alkynyl compound, the internal stress reached a minimum of −114 MPa, an 82 % reduction from the −646 MPa observed without additives. The presence of sodium saccharin and alkynyl compound in the electrolyte solution reduced the hydrogen evolution reaction current from 15.2 to 12.9 mA at the operating cathode potential of −1 V and decreased the RTC(111) from 100 % to 90 %. The reduction of internal stress in the electrodeposited Ni-P-PTFE composites was attributed to the decreased hydrogenation strain, diminished Ni (111) texture intensity, and the partial incorporation of alkynyl compound reaction products into the cathode surface, which weakened the connections between crystallites. Finally, 5 g·L−1 sodium saccharin and 1 mL·L−1 alkynyl compound was applied to electroform Ni-P-PTFE mold insert with micro features. Only slightly pile-up defects at the corner of grooves were observed on the polymer chips demolded from Ni-P-PTFE mold insert, demonstrating its good self-lubricating property.

Effect of annealing on layer intermixing in nanoscale Cr/Ti multilayers depending on the period value

The effect of annealing on the intermixing of thin Ti and Cr layers and their crystallinity in multilayer structures was studied using XPS, TEM, XRR and XRD methods. Multilayer structures with varios period values (sum thickness of the Ti and Cr layers) in the range from 1.4 nm to 4.3 nm were considered. The analysis revealed the formation of TiCrx at the interfaces of the layers. The contribution of the formed chromide relative to the base layers increases with decreasing period of the structure. The layers in the structure with thinnest period were found to be X-ray amorphous, while the structure with a thicker period exhibited the appearance of large crystallites of chromium and titanium. Annealing of the multilayer structures induced additional intermixing, leading to an increase in the extension of the chromide regions. Additionally, it resulted in a reduction of internal stresses within the structures. When the multilayer structures were annealed at a temperature of 700 °C, complete degradation occurred, with all layers intermixing with each other and with the Si substrate.

Static mechanical properties and failure behaviors of self-piercing riveted joints in aluminum alloy 5A06 after aging

This paper conducts an investigation on the static mechanical properties and failure behavior of self-piercing riveted joints in aluminum alloy 5A06 after being subjected to the aging process. The study involves three distinct categories of joint specimens: original specimens, 1-year aged specimens and 1-year aged specimens that have been additionally heat-treated at 200 °C. The research findings affirm that strain aging is responsible for a reduction in the peak strength of the joints. Furthermore, the weakest failure chain within the self-piercing riveted joint shifts towards the upper sheet due to a more significant reduction in internal stress experienced by the upper plate. This leads to a failure model characterized by upper sheet pull-off. Through Weibull distribution analysis, it has been established that the 5 % lower limit value for the strength of the SPR joint experiences an 86 % decline following 1-year aging. In practical terms, this means that for a vehicle structure with 7000 riveting points will lose an overall structural strength equivalent to the initial strength of 1000 riveting points within one year.

Suppression of cracking in drying colloidal suspensions with chain-like particles.

The prevention of drying-induced cracking is crucial in maintaining the mechanical integrity and functionality of colloidal deposits and coatings. Despite exploring various approaches, controlling drying-induced cracking remains a subject of great scientific interest and practical importance. By introducing chain-like particles composed of the same material and with comparable size into commonly used colloidal suspensions of spherical silica nanoparticles, we can significantly reduce the cracks formed in dried particle deposits and achieve a fivefold increase in the critical cracking thickness of colloidal silica coatings. The mechanism underlying the crack suppression is attributed to the increased porosity and pore sizes in dried particle deposits containing chain-like particle, which essentially leads to reduction in internal stresses developed during the drying process. Meanwhile, the nanoindentation measurements reveal that colloidal deposits with chain-like particles exhibit a smaller reduction in hardness compared to those reported using other cracking suppression approaches. This work demonstrates a promising technique for preparing colloidal coatings with enhanced crack resistance while maintaining desirable mechanical properties.

Understanding the Room Temperature Recovery Behavior in a Ti–24Nb–4Zr–8Sn Superelastic Alloy

Metastable β Ti–Nb‐based superelastic alloys have potential uses in the biomedical and aerospace industries due to an attractive combination of properties. However, their mechanical response can be seen to vary with cycling, limiting their uptake. Furthermore, recent studies have also highlighted changes in properties under no applied stress at room temperature, with the reasons for these changes poorly understood. To investigate potential mechanisms for these changes, the superelastic behavior of Ti–2448 is studied during mechanical cycling both pre‐ and post‐room temperature (RT) aging treatments. On cycling, there is a reduction in both σSIM and hysteresis area, consistent with behavior commonly seen in the literature. However, during RT aging, there is a rapid, time‐dependent process leading to a partial recovery. In situ diffraction data indicated that this recovery is coincident with a reduction in internal stresses, the potential mechanisms for which are discussed.

Reduction of internal stress in InGaZnO (IGZO) thin film transistors by ultra-thin metal oxide layer

In this study, the modification of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) with an ultrathin metal oxide layer successfully reduces internal film stress. The introduction of an Al2O3 metal oxide layer effectively diminishes defects within the film and minimizes distortion in the film densification process. A low-temperature annealing process at 200 °C was employed to mitigate thermal expansion differences between the film and the substrate, thus reducing internal stress within the device. Furthermore, we have discovered that this structural modification holds the potential to enhance mechanical stress resistance. This paper offers a novel perspective and an experimental foundation for the stress analysis of flexible TFTs.

Thermal Stability of Electrodeposited Fe-55wt%Ni Alloy and Effect of Low-Temperature Heat Treatment on Magnetic Properties

Electrodeposited nanocrystalline soft magnetic materials have emerged as one of the hottest research topics in the field of magnetic materials due to they are easy to implement in miniaturization, lightweight, and energy-saving of electronic devices. The thermal stability and grain growth process of electrodeposited Fe-55wt%Ni alloy were investigated. Results indicated that the grain growth was rapid at a temperature of about 678 K, while the exothermic peak appeared in DSC with an exothermic heat of about 12 ± 1 J g−1. The activation energy for grain growth was obtained through the optimized Kissinger equation and isothermal kinetics calculations, and the growth mechanism was evaluated based on the calculation results. Below 678 K, the activation energy required for grain growth was low, which implied the growth mechanism was the rearrangement of atoms at the grain boundary; Above 678 K, the growth mechanism was grain boundary diffusion. After the low-temperature heat treatment, the coercivity (H c) decreased and the saturation magnetization (M s) increased slightly, which was attributed to the reduction of internal stress and the ultra-fine nanocrystalline structure. The optimal heat treatment process was 573 K heat treatment for 5 h, where M s and H c of 160 emu g−1 and below 1 Oe, respectively.

Surface stress release in AlCrN coatings determined by synchrotron radiation multi-reflection grazing-incidence X-ray diffraction

In this work, the residual stress distribution of c. 3.8 μm arc-evaporated AlCrN coatings was investigated by the synchrotron radiation multi-reflection grazing-incidence X-ray diffraction method. Ar ion bombardment post-treatment was also used to tune the stresses in the AlCrN coating to elucidate the evolution of stress therein. The result showed that the as-deposited AlCrN coating showed large surface stress of −1500 MPa, this sharply decreased in magnitude to −800 MPa in the internal coating. Ar ion bombardment (post-treatment) could significantly reduce the surface stresses by around −1000 MPa and the interior stresses by around −400 MPa for an AlCrN coating, the “shot peening” effect arising therefrom could promote migration and diffusion of the adatoms, which contributed to the reduction of the micro-strain and interior stress. Furthermore, Ar ion bombardment also promoted the growth of surface grains, which also contributed to the stress reduction in the near-surface region of the AlCrN coating. In addition, Ar ion bombardment could increase the substrate stresses from −32 MPa to −210 MPa. The results suggested that internal stress reduction could be achieved by promoting the migration and diffusion of adatoms.

Quenched Residual Stress Reduction in Pentagon-Curved Aluminum Alloy Forgings Using the Bulging Process.

Quenched residual stress in pentagon-curved forgings (PCGs) often leads to severe deformation during subsequent machining operations. This study aims to mitigate the quenched residual stress in PCGs through the implementation of the bulging method. The edge distance ratio (e/D), a geometric characteristic of PCGs, is defined and considered in the established thermo-mechanical model, which incorporates the effects of quenched residual stress. Increasing e/D resulted in amplified maximum internal stresses and surface stresses. To address this issue, a bulging finite element (FE) model was developed to effectively alleviate the quenched residual stress. The stress reduction in surface stress and internal stress was qualified using average stress reduction (Ra) and peak stress reduction (Rp), respectively. Notably, stress reduction exhibited an inverse relationship with e/D, indicating that decreasing e/D yields greater stress reduction. Furthermore, an overall stress reduction assessment was conducted for different bulging ratios, revealing that the stress reduction increased as the bulging ratio increased. A comprehensive comparison of different bulging ratios highlighted 2% as the most optimal bulging ratio for stress reduction in PCGs. X-ray diffraction measurement and the contour method were employed to determine surface stress and internal stress, respectively. The experimental results were in agreement with the simulation outcomes, validating the high accuracy of the FE model.

Quantitative and qualitative characterization of the damage, deformation mechanisms, and failure modes of a nickel-based GH3536 alloy prepared via laser powder bed fusion after various heat treatments

Nickel-based alloys prepared via laser powder bed fusion (LPBF) exhibit high strength and low elongation during tensile testing at room temperature. To optimize the performance, hot isostatic pressing (HIP) and HIP with heat treatment (HT), that is, HIP + HT were applied to the deposited GH3536 samples. The plasticity and elongation of the post-treated Ni-based alloy are clearly improved; this can be attributed to the change in micromorphology from columnar grains to equiaxed grains, as well as to the reduction in defects and internal stresses. It is experimentally confirmed that the characteristic grains and defects formed during the LPBF process caused the porosity of the deposited samples to change considerably during tensile testing. The increment is up to 12.3%, and the grain deformation rate of the deposited samples is minimal. The porosity increased by 1.4% for the HIP-ed GH3536 (i.e., after hot isostatic treatment) samples and by 5.4% for the (HIP + HT)-ed GH3536 (i.e., after hot isostatic pressing and heat treatment) samples during tensile testing. The results of electron backscatter diffraction characterization and grain statistics revealed that the average grain diameter of the HIP-treated samples increased the most (>25 μm) during the tensile process, and the samples exhibited the best deformation ability. Microstructural characterization showed that the (HIP + HT)-ed samples contained a large number of “small equiaxed grains” (i.e., grains with the grain size are always less than 50 μm in the whole process of deformation). According to the grain deformation behavior analysis, these small equiaxed grains coordinated the deformation process, resulting in the (HIP + HT)-ed samples exhibiting the best deformation coordination ability and deformation mechanism.

Microstructure- Assisted Changes in the Magnetic Barkhausen Emission of a Mild Steel Under the Influence of Various Mechanical and Environmental Loading Factors; a Semiquantitative Analysis

The aim of the present work is to introduce some novel possible ways for the semiquantitative analytical characterization of ferromagnetic steels. The characterization attempt focuses on microstructural changes occurring under the combined influence of certain mechanical loading as well as physico – chemical degradation factors such as applied stressstrain, tempering processing and salt water – induced electrochemical corrosion. In this direction, various conveniently simple developed functional modelling approaches are used to be able to analyse and estimate related experimental results obtained by means of micromagnetic Barkhausen emission measurements. The approaches are correlated to macroscaling as well as microscaling parameters such as stress-strain, dislocation – controlled cell size and pinning spacing – strength as well as internal cell flow stress. The needed correlations and estimations are made on the basis of an adopted specific micromagnetic activity parameter by which the obtained experimental data are compared and analysed. In this manner the opposite effects of internal flow stress and cell size reduction on the micromagnetic activity can reasonably be demonstrated where the first tends to stimulate an increase while the second a decrease in the specific micromagnetic parameter with progressive plastic deformation. One can further demonstrate that various physico-chemical degradation factors may markedly influence the microstructural as well as micromagnetic behaviour. For instance, hydrogen produced by corrosion of steel in NaCl – water solution and tempering processing lead to appreciable mechanical embrittlement as well as magnetic hardening of steel, expressed by an associated decrease in the specific micromagnetic parameter. With respect to this the tempering processing leads to a higher magnetic hardening compared to the corrosion process of steel.

Post-forming, electro-plastic effect internal stress reduction in AA5754 aluminium alloy

Aluminium alloys are one of the most efficient materials for weight reduction in the car industry. However, the favourable performance of alloys conflicts with the difficulties of transforming these materials through plastic deformation processes such as stamping. Among the different issues, they are characterised by a high springback effect. Numerous authors have explored the use of the electro-plastic effect (EPE) to mitigate internal stresses and the resultant springback. However, up-scaling existing laboratory solutions to an industrial framework is a critical challenge. Therefore, in this work, the post-forming electro-plastic effect (PFEPE) is explored in AA5754 material. Stress-relaxation + PFEPE experiments were conducted using different electric pulse charge passing though the sample, and, apart from the impact on residual stresses, the potential occurrence of recrystallisation was evaluated. The results indicate that a range of pulses exists (>2000 A·ms/mm2 and <4500 A ms/mm2) in which a 10–30% reduction in stresses can be achieved without critically impacting the material's mechanical performance.

Effects of processing parameters and heat treatment on the microstructure and magnetic properties of the in-situ synthesized Fe-Ni permalloy produced using direct energy deposition

The present work investigated the correlations between heat treatment and the microstructure and magnetic properties of the in situ alloyed Fe-50%Ni samples manufactured using laser-based direct energy deposition under different production conditions. The samples with high relative density were directly synthesized from the pure Fe and Ni elemental powders. In addition, a fine FCC microstructure with relatively elongated grains in the building direction was observed in the as-print samples. After applying short-time heat treatment, the grain morphology remained unchanged, while the grain size and microhardness were slightly increased and decreased, respectively. This also caused the reduction in internal residual stresses and, subsequently, partial stress relaxation in the microstructure. According to the electron probe microanalysis results, the simultaneous Fe and Ni depletion/enrichment formed during the in-situ alloying was practically decreased after applying short time heat-treatment, resulting in the significant improvement of magnetic properties, as compared to the as-built ones. The maximum magnetization, coercivity, and curie temperature of ~170 emg/g, 1.8 Oe, and 530 °C, respectively, were obtained in the optimum processed sample, which were significantly higher than those of other soft magnetic permalloys produced by additive manufacturing methods.

Understanding the effect of hygroscopic cycling on the internal stress and stiffness of natural fibre biocomposites

This article investigates the development and the evolution of hygroscopic stresses within flax/ Polypropylene + Maleic Anhydride grafted Polypropylene (PP + MAPP) asymmetric biocomposites when exposed to various hygroscopic cycles that simulate a wide range of outdoor applications with large Relative Humidity (RH) variation (from 11 to 50% RH, 50–99% RH, 11–99% RH) and with various cycling periods (1-week and 24-hour cycles between 50 and around 90% RH). The transversal and longitudinal tensile properties of biocomposite laminates are characterised, and the weight and curvature of the asymmetric samples are tracked throughout the cycles. The study shows that the hygroscopic cycles entail a reduction of internal stress due to damage development and a relaxation mechanism that are illustrated by permanent hygroscopic deformations. Two parameters have been identified to play a role on the damage development: the magnitude of the RH level and the duration of the cycles.

Evaluation of the effect of heat treatment on the structure parameters and cold resistance of metals produced by additive electric arc growth

In this work, we studied the influence of the type and mode of heat treatment on the structure and parameters of cold resistance of 09Mn2Si and 07Cr25Ni13 steels obtained by additive electric arc growth. It is shown that, under optimal printing conditions, a relatively uniform and fine-grained material structure is observed in 09Mn2Si steel, while a dendritic structure is observed in the 07Cr25Ni13 alloy. Heat treatment of the investigated alloys leads to a more uniform distribution of structural components in metals, and in steel 07Cr25Ni13 the dendrites are destroyed, which leads to a decrease in the anisotropy of material properties. Also, heat treatment leads to a significant reduction in internal residual stresses in the material. The results of the study of impact strength in a wide range of low temperatures show that in the initial state after surfacing, the investigated alloys have a significant anisotropy of impact strength (up to 8 and 25% for alloy 09Mn2Si and 07Cr25Ni13, respectively). Heat treatment significantly reduces the anisotropy of the properties of the studied alloys and increases the values ​​of impact strength. So for steel 09Mn2Si after heat treatment, an increase in impact strength by more than 1.5 times is observed over the entire temperature range. The studies carried out made it possible to identify the temperature range of the ductile-brittle transition and the impact strength of 09Mn2Si and 07Cr25Ni13 alloys, which is of great practical importance in the manufacture of parts and structural elements of the Northern version.

Effect of Cryogenic Treatment on Internal Residual Stresses of Hydrogen-Resistant Steel.

To reduce the influence of internal residual stress on the processing deformation of thin-walled hydrogen-resistant steel components, combined aging cryogenic and high-temperature treatment was used to eliminate the residual stress, and the effect of cryogenic process parameters on the initial residual stress of the specimens was compared and analyzed based on the contour method. X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy were used to research the mechanism of the effect of cryogenic treatment on the internal residual stress of the specimen. After forging, the internal residual stress distribution of the hydrogen-resistant steel specimens without aging was characterized by tensile stress on the core and compressive stress on both sides, with a stress amplitude of −350–270 MPa. After compound treatment of −130 °C for 10 h and 350 °C for 2 h, the internal residual stress distribution remained unchanged, and the stresses decreased to −150–100 MPa. The internal residual stresses were reduced by 57–63% compared with the untreated specimens. The cryogenic treatment did not cause phase transformation and carbide precipitation of the hydrogen-resistant steel material. Instead, grain refinement and dislocation density depletion were the main reasons for the reduction in internal residual stresses in the specimens.

Preparation of PLA with High Impact‐Toughness and Reduced Internal Stress via Formation of Laminated, Bimodal Structure with Micro/Nanocells

AbstractThe pressure‐induced‐flow (PIF) processing method is used to fabricate oriented, self‐toughening poly(lactic acid) (PIF‐PLA) with excellent mechanical properties. However, residual internal stress in PIF‐PLA may lead to their deformation and cracking. Hence, to eliminate internal stress, solid‐state supercritical carbon dioxide foaming (sc‐CO2 foaming) is applied to PIF‐PLA, with the resultant structure being called FOAM‐PLA. The microstructure and mechanical properties of the PLAs are characterized pre‐ and post‐foaming. Scanning electron microscopy results show PIF‐PLA to exhibit oriented texture structures composed of staggered microfibers. Following sc‐CO2 foaming, the PIF‐PLA is converted into a bimodal cellular structure consisting of micro and nano‐cells. According to the 2D wide‐angle X‐ray diffraction and Raman spectra results, this structure of the FOAM‐PLA can, through a marginal reduction of orientation, release significant amounts of internal stress. Moreover, the impact strength of FOAM‐PLA is found to be 32.7 kJ m−2, which is 10.2 times higher than that of crystalline PLA. This paper depicts the evolution of the PLA microstructure through the stages of PIF‐processing and the subsequent solid‐state sc‐CO2 foaming. Meanwhile, the mechanism of the internal stress reduction is promoted.

Effect of heat treatment on property and residual stress of cold drawn tube

The change of strength, toughness and residual stress of Q690 cold-drawn tube were studied under (400˜;600)°C and heat preservation (1-3)h heat treatment. With the increase of temperature and the extension of the holding time, the strength and residual stress of the cold drawn tube gradually decreased, and the impact toughness increased first and then decreased. When holding at 550 °C for 2 hours, the impact toughness reached the highest 34.6J;the mechanical properties of cold drawn tubes were mainly affected by the reduction of internal stress and grain deformation caused by heat treatment.

The Preliminary Analysis of the Effect of Low-Energy Plasma Treatment on Internal Stresses in a Welded Plate of Steel S355

The articles presents a pilot study aimed to provide preliminary assessment concerning the effect of the low-energy plasma treatment on the level of internal stresses in welded plates. In addition, the article discusses the similarity of a stress relief mechanism based on annealing and that based on low-energy plasma treatment. The extensormetric measurements of internal stresses involving steel S355 after welding and after treatment in the plasma chamber revealed the low-energy plasma treatment-induced reduction of internal stresses.

Thickness regulates the ferroelectric and resistance switching properties of BiFeO3 (Nia/Nib) superlattice films

Bi0.89Ho0.08Sr0.03Fe0.97-aMn0.03NiaO3/Bi0.89Ho0.08Sr0.03Fe0.97-bMn0.03NibO3 (Nia/Nib) superlattice films were prepared by the sol–gel successfully. The influence of the change of the thickness of the superlattice films on the multiferroic and resistance switching properties were studied. It shows that due to the reduction of internal stress, the thin Nia/Nib superlattice films make the layer interface effect enhance to get more the interface charges, which improves the efficiency of the interaction between the interface charges, thereby obtaining good resistance switching (RS) performances. However, the thick Nia/Nib superlattice films improved the ferroelectricity due to the smaller layer interface effect. It indicates that changing the thickness of the single layer of the superlattice film is beneficial to the regulation of the properties of the films. Eventually, the different applications of BiFeO3 film in modern microelectronic devices can be realized by adjusting the thickness of the superlattice film.