Residual Microstrain Research Articles

Dual interface strategies enable efficient wide bandgap perovskite solar cells

High performance wide bandgap perovskite solar cells (WB-PSCs) have found widespread applications in tandem solar cells. In WB-PSCs, achieving a high conversion efficiency relies on the effective utilization of light absorption and minimization of electronic defects. In this work, electronic defects at the surface and grain boundaries of perovskite materials have been passivated by n-butylammonium bromide (BABr) to suppress carrier non-radiative recombination. Confirmed through x-ray powder diffraction and x-ray photoelectron spectroscopy spectra, ultra-thin two-dimensional (2D) perovskite layers were successfully generated on a perovskite surface. The BABr-treated devices exhibited an increased fill factor and open circuit voltage (VOC) compared to the references. Furthermore, a nanotextured electrode with a roughness of 22.98 nm was employed to trap light. The nanotextured buried interface not only promoted light utilization but also alleviated residual stress and micro-strain in the perovskite film compared to the smooth substrate. Finally, the champion WB-PSC achieved a power conversion efficiency of 20.46% in the reverse scan. These findings pave a promising path for the development of solution-processed perovskite films on nanotextured silicon substrates to improve the performance of monolithic tandem solar cells.

Evaluation of process parameter of friction stir processing of AA2024-T351 Alloy using RSM and GRA

A fundamental method for changing the characteristics of metals through localised severe plastic deformation is friction stir processing (FSP), which is both straightforward and efficient. Because of its high strength-to-mass ratio and resilience to fatigue, aluminium alloy 2024 is commonly utilised. The experiments were designed utilising the Box–Behnken method and the process parameters’ chosen range values. In this research, the impact of FSP process variables on the tensile, surface roughness, and hardness properties of AA2024 will be examined. These parameters include tool rotation speed, welding speed, and axial load. The base sample tensile strength, surface roughness and microhardness values were 325 MPa, 0.5125 μm, and 120 HV. The optimised sample’s maximum tensile strength, minimum surface roughness, and maximum microhardness values were 420 MPa, 0.4 μm, and 144 HV. The grey relational analysis (GRA) determines the ideal combination of process parameter values for the best values in all responses. XRD was used to assess residual stress, dislocation density and micro-strain. The optimal process parameters have been obtained at a rotational speed of 1000 rpm, traverse speed of 45 mm/min, and axial load of 10.25 kN.

Suppressing the Photoinduced Halide Segregation in Wide‐Bandgap Perovskite Solar Cells by Strain Relaxation

AbstractEfficient and stable wide bandgap (WBG) perovskite solar cells (PSCs) are imperative for fabricating superior tandem devices. However, small crystal grains and light‐induced phase segregation of WBG perovskite result in large open‐circuit voltage (VOC) deficits, critically impeding the development of the related devices. Herein, the effective functional groups of Lewis‐base trans‐Ferulic acid (t‐FA) are employed to release the residual microstrain in the perovskite lattice. Larger perovskite crystals are formed by strengthening the interaction between the perovskite solute and solution. The lattice structure is stabilized to suppress light‐induced halide segregation. Finally, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈1.77 eV is increased from 17.33% to 19.31% with the enhancement of VOC. Moreover, replacing a mixture of MeO‐2PACZ and Me‐4PACZ as the hole transporting layer (HTL), the PCE further lifts to 19.9% and VOC is 1.32 V, one of the highest performances reported for WBG PSCs, especially for devices prepared entirely by solution spin‐coating. Therefore, this study provides a practicable alternative for realizing efficient WBG PSCs, which can contribute to the growth of perovskite‐based tandem devices.

Homogenization of residual stress in the raceway of cold rolled M50 bearing ring via electromagnetic shocking treatment

The uneven residual stress caused by cold rolling on the raceway seriously affect the distortion and performance of bearing rings. Here, a novel strategy of electromagnetic shocking treatment (EST) was proposed to regulate the distribution of residual stress in the raceway of cold rolled M50 bearing ring. The results indicate that the distribution of residual stress and local micro-strain along the raceway of the cold rolled ring become more homogenized after EST, leading to the homogenization of hardness along the whole cross section. In addition, attributed to the ‘targeted’ regulation effect of EST without joule heat effect, the distribution of small angle grain boundaries and the texture also become uniform along the raceway.

Structure refinement, microstrains and crystallite sizes of Mg-Ni-phyllosilicate nanoscroll powders

The morphology and structure of (Ni x Mg1−x )3Si2O5(OH)4 synthetic phyllosilicate nanoscrolls have been studied by means of electron microscopy and X-ray powder diffraction. Scrolling of phyllosilicate layers originates from size differences between octahedral and tetrahedral sheets. This strain-energy-driven process raises a number of questions, including the preferred direction of scrolling (along the a or b axis) and the presence of residual microstrain. In order to clarify these points, the structure of (Ni x Mg1−x )3Si2O5(OH)4 phyllosilicates (x = 0, 0.33, 0.5, 0.67, 1) was first described by a monoclinic Cc (9) unit cell, whose parameters decrease with increasing Ni concentration. The Williamson–Hall plots constructed for x = 0 and 0.67 reveal the absence of microstrain, which suggests that scrolling is an effective means of stress relaxation. The sizes of the crystallites were determined by using Rietveld refinement with predefined needle-like models and fundamental parameter fitting with crystallites of arbitrary form. Both approaches show qualitative and quantitative correlation, in terms of aspect ratio, with electron microscopy data. At the same time, the phyllosilicates studied do not demonstrate one preferred direction of scrolling: instead, there might be a mixture of chirality vectors codirected with the a or b axis, with the proportion altering with Ni concentration.

Pre-Buried Additive for Cross-Layer Modification in Flexible Perovskite Solar Cells with Efficiency Exceeding 22.

Halide perovskites have shown superior potentials in flexible photovoltaics due to their soft and high power-to-weight nature. However, interfacial residual stress and lattice mismatch due to the large deformation of flexible substrates have greatly limited the performance of flexible perovskite solar cells (F-PSCs). Here, ammonium formate (HCOONH4 ) is used as a pre-buried additive in electron transport layer (ETL) to realize a bottom-up infiltration process for an in situ, integral modification of ETL, perovskite layer, and their interface. The HCOONH4 treatment leads to an enhanced electron extraction in ETL, relaxed residual strain and micro-strain in perovskite film, along with reduced defect densities within these layers. As a result, a top power conversion efficiency of 22.37% and a certified 21.9% on F-PSCs are achieved, representing the highest performance reported so far. This work links the critical connection between multilayer mechanics/defect profiles of ETL-perovskite structure and device performance, thus providing meaningful scientific direction to further narrowing the efficiency gap between F-PSCs and rigid-substrate counterparts.

Effects of sample bias on adhesion of magnetron sputtered Cr coatings on SiC

Swelling of SiC at 300 ∘C due to in-service neutron irradiation causes tensile residual stresses in coatings which are expected to adversely affect the performance of coated SiC composite fuel cladding for light water reactors. Matching the coating swelling with the substrate, a solution common for thermal expansion, is not practical in the case of neutron irradiation. Biasing samples during magnetron sputtering deposition induces compressive residual stress which may counteract this. In this study, chromium coatings were deposited on SiC by DC magnetron sputtering with no external heating at bias voltages of –50V, –75V, and –100V. The effects of the bias voltage on morphology, residual stress, microstrain, texture, and adhesion are shown. The low deposition temperature resulted in the coating microstructure evolution following an energetic particle bombardment dominated trend. At the two lower bias voltages knock-on implantation dominated increasing the residual stress and microstrain while at the highest bias voltage, thermal spike migration allowed for defect relaxation. When the knock-on induced compressive residual stress exceeded 0.8 GPa microcrack formation in the SiC substrate decreased coating adhesion. While no microcracks formed at the lowest bias voltage, insufficient atomic mobility during coating growth lead to voids forming in the coating. A balance is needed to form void-free coatings that have high compressive residual stress.

Structure and Microstructure of Advanced Materials Characterized by Neutron Diffraction

Characterization of advanced materials by neutron powder diffraction provides information not accessible by other techniques. Thanks to the low absorption of neutrons, the bulk of the material and large-grain samples can be investigated, moreover in situ at elevated temperatures. The neutron diffraction use is demonstrated on two types of technologically important materials: Ti-Zr alloy and Co-Re high temperature alloy. In Ti-Zr alloy, the residual stress relief and microstrain evolution after ECAP was established. Boron influence on TaC strengthening precipitates in Co-Re high temperature alloys was shown not to be significant at the foreseen alloy operation temperatures, although boron content has a strong influence on the matrix phase.

Subsurface grain refinement in electron beam-powder bed fusion of Alloy 718: Surface texture and oxidation performance

Subsurface grains of Alloy 718 additively manufactured via electron beam-powder bed fusion technique were refined using shot peening to improve the surface texture and oxidation performance. Oxidation of the specimens was performed at 650 and 800 °C in ambient air. Due to plastic deformation upon shot peening, compressive residual stress and high microstrain were generated in the subsurface region within a depth of approximately 50 μm. The shot-peened specimen exhibited lower surface roughness, finer subsurface grains, and higher hardness compared to the as-built specimen. Shot peening, coupled with hot isostatic pressing and heat treatment (HIP-HT), yielded superior oxidation performance with substantially low oxidation kinetics at 800 °C. The smooth surface, as well as dense and refined subsurface microstructure resulting from shot peening, facilitated the formation of a continuous, protective, and adherent Cr-rich oxide scale.

Visible light sensitive Cu doped ZnO: Facile synthesis, characterization and high photocatalytic response

The different concentrations of 0.0, 1.0, 2.5 and 5.0 wt% Cu-doped ZnO (Cu@ZnO) nanoparticles (NPs) have been synthesized for opto-photocatalytic applications by a facile and cost-effective route. The formation and structural analyses of Cu@ZnO NPs was recognized by X-ray diffraction (XRD), Fourier transform (FT)-Raman and Transmission electron microscopy (TEM). The average crystallite size of 28.9, 27.4 and 26.4 nm was calculated for (101) intense peak and found to be decreased with increasing the contents of Cu. The residual microstrain values are noted ~3.84 × 10−3, 4.03 × 10−3 and 4.19 × 10−3. The particle size of 170, 109, 127 and 175 nm is obtained for undoped and Cu doped ZnO NPs from FESEM. The optical band gap of Cu@ ZnO NPs were estimated through Kubelka-Munk theory and noted ~3.225, 3.150, 3.100 and 2.995 eV for 0.0, 1.0, 2.5 and 5.0 wt% Cu@ZnO NPs; this shows decreases with increasing the Cu contests in ZnO lattice. Photoluminescence (PL) spectra of Cu@ZnO NPs shows near band edge emission at 407–411 nm with emission band 565-572 nm correspond to intrinsic defects in ZnO lattice. The photocatalytic performance of Cu@ZnO NPs was assessed through decolourizing of methyl green beneath the visible light illumination (λ = 425–460 nm). Photocatalytic action of Cu@ZnO samples was 3.5 times greater to neat ZnO. Photocatalytic properties of Cu@ZnO NPs can be used for water purification in environmental applications.

Determination of residual stresses in fibre laser welded AA2024-T3 T-joints by numerical simulation and neutron diffraction

This paper presents an experimental and numerical study of residual stress states and deformation in fillet welded AA2024-T3 T-joints produced using a high-power fibre laser. Welded sheets with one and three stiffeners were prepared, respectively, to determine changes in microstructure, residual stress, distortion and micro-hardness. 3D sequentially coupled thermo-mechanical finite element models were developed to analyse welding temperature fields, and accurately simulate welding residual stresses and deformation. The simulated results were calibrated using the experimental database on weld pool geometry obtained from optical metallography and temperature fields measured using thermocouples. Residual stress measurements were made using neutron diffraction techniques and sheet distortions were measured using a coordinate measuring machine. The influence of various mechanical boundary conditions on angular and cambering sheet distortions was examined to optimise the restraint parameters. The application of element death and rebirth and dummy element techniques were studied and compared to incorporate the effect of filler metal deposition during welding. The level of residual microstrain was evaluated by diffraction peak width analysis, which indicated the maximal values in the weld metal. The effect of grain growth with respect to strength was of minor importance, whereas, considerable softening in the weld metal was observed.

Residual Microstrain in Root Dentin after Canal Instrumentation Measured with Digital Moiré Interferometry

IntroductionResidual microstrain influences the resistance to crack propagation in a biomaterial. This study evaluated the residual microstrain and microdefects formed in dentin after canal instrumentation in teeth maintained in hydrated and nonhydrated environments. MethodsCanals of 18 extracted human premolars with single-root canals were instrumented in accordance with 3 groups: the ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) group: ProTaper Universal (S1, S2, F1, and F2) used in rotation, the WaveOne Primary (Dentsply Maillefer) group: the WaveOne (Primary) used in reciprocal motion, and the control group: hand files. Half the specimens (3/group) were maintained in deionized water (hydrated) and half in ambient relative humidity conditions (22°C, 55% RH) for 72 hours (nonhydrated). Customized high-sensitivity digital moiré interferometry was used to qualitatively evaluate pre- and postinstrumentation dentinal microstrain. Subsequently, specimens were examined for dentinal microdefects with micro–computed tomographic imaging and polarized light microscopy. ResultsDigital moiré interferometry showed only minor changes in postinstrumentation microstrain in hydrated dentin in all groups, suggestive of a stress relaxation behavior. Nonhydrated dentin in all groups showed localized concentration of postinstrumentation microstrain, which appeared higher in the WaveOne group than in the other groups. No dentinal microdefects were detected by micro–computed tomographic imaging and polarized light microscopy in hydrated and nonhydrated specimens in all groups. ConclusionsThis study suggested that the biomechanical response of root dentin to instrumentation was influenced by hydration. Reciprocating, rotary, and hand instrumentation of well-hydrated roots did not cause an increase in residual microstrain or the formation of microdefects in root dentin.

Determination of the compressive yield strength for nano-grained YAG transparent ceramic by XRD analysis

Nano-grained ceramics have their unique mechanical characteristics that are not commonly found in their coarse-grained counterparts. In this study, nano-grained YAG transparent ceramics (NG-YAG) were prepared by low-temperature high-pressure technique (LTHP). The peak profile analysis of the X-ray diffraction was employed to investigate the compressive yield strength of NG-YAG. During the temperature at 450 °C, the residual micro-strain (RMS) increased with increasing loading pressure. However when the loading pressure was exceeded to 4.0 GPa the RMS exhibited a severe negative slop. The temperature effects on the compressive yield strength were also studied. It shows that the compressive yield strength of NG-YAG is 4.0 GPa and 5.0 GPa respectively at 450 °C and 350 °C. More importantly according to this investigation, a feasible technique to study the nano-grained ceramics is provided.

Variations in surface residual compressive stress and magnetic induction intensity of 304 stainless steel

This study proposed micromagnetic nondestructive detection technology to detect the surface residual compressive stress of 304 stainless steel specimens after annealing treatment and loading. X-ray diffraction was used to determine the changes in residual compressive stress, microstrain, and grain size to aid in verification. Variations in surface residual compressive stress and magnetic induction intensity were analyzed. When residual compressive stress changed markedly, the change in magnetic induction intensity reflected the change in residual compressive stress. With the increase in residual compressive stress, the surface magnetic induction intensity and residual compressive stress of the specimen exhibited an approximate linear relationship, manifesting an increasing trend. Therefore, residual compressive stress was analyzed by detecting the changes in the surface magnetic induction intensity of specimens. Micromagnetic nondestructive detection allows the effective detection of the surface residual compressive stress of 304 stainless steel.

Residual stress relaxation mechanism at low homologous temperature in nanocrystalline iron thin film deposited on Si (1 0 0) substrate

The effect of thermal stress and the role of defects in residual stress relaxation have been investigated in a nanocrystalline iron thin film coated on Si (1 0 0) substrate using glancing incidence x-ray diffraction (GIXRD) and depth resolved positron beam studies. The film has been annealed isothermally at a low homologous temperature of 400 K (~0.2Tm) for different time intervals. The change in residual stress, micro-strain and grain size as a function of annealing time has been deduced using GIXRD. The change in vacancy defects as a function of the annealing time has been investigated using defect-sensitive line shape S-parameter from depth-resolved positron beam studies. It is observed that the residual stress relaxes by the creation of defects at the film surface. A physical model has been proposed based on the atomic diffusion through the grain boundaries, which explains the observed results well. The proposed model confirms the residual stress relaxation by the transport of atoms and corresponding point defects between the free surface of the film and the grain boundaries indicating the stress relaxation is mediated by atomic diffusion.

Influence of annealing temperature on the properties of In2S3:Sn films deposited by spray pyrolysis

Tin-doped In2S3 films were grown by the chemical spray pyrolysis method using compressed air as a carrier gas. The films were annealed for 2 h at different temperatures (300, 400 and 500 °C) under nitrogen atmosphere. X-ray diffraction data show that In2S3:Sn films are polycrystalline with a cubic phase. The film grain size increases from 26 to 37 nm. The residual microstrain and dislocation network reach the values 3.08 × 10−3 and 0.73 × 1011 lines cm−2, respectively, at the annealing temperature of 500 °C. Transmittance decreases with increasing temperature. It varies in the range of 65–85 % in visible and infrared regions. The optical band gap is found to vary in the range 2.4–2.85 eV for direct transitions. The best surface state is obtained at 400 °C. The RMS roughness was estimated to be 39.4–19.8 nm. Electrical measurements at room temperature show that the sheet resistance decreases down to 130 Ω at 500 °C. The conductance and capacitance characterization at ambient temperature are also investigated and give interesting physical properties for photovoltaic applications.

Application of neutron stress diffractometry for the study of residual stress and texture in industrial metal products processed in various ways

Residual stress and texture in industrial metal products, processed in different ways, are investigated by means of high-resolution neutron diffraction. The samples are pipe sections made of 30KhN2MFA steel, which are parts of precision machinery and operate under complex loading conditions. The products are manufactured using various methods of plastic deformation, namely, rotary forging and drawing on a mandrel. The results of comparative analysis of the distributions of residual stress and microstrain throughout the wall thickness for all samples are presented. Additionally, neutron texture experiments are performed; based on their results, pole figures are calculated and the crystallographic texture characteristics are evaluated.

Microstructure and Direct Measured Micro-Strain by TEM of Hot Iso-Static Pressed Alumina-Titanium Carbide (Al<sub>2</sub>O<sub>3</sub>-TiC) Composite

Alumina-titanium carbide composite (Al2O3-TiC) is one of advance ceramic matrix composites (CMC) that have been used in machining tool and tribology application because of its excellent mechanical properties. Powder processing is often a chosen method to produce this family of material, i.e. hot pressed (HP), hot iso-static pressed (HIP), and pressure-less sintering (PS). These manufacturing techniques convert sub-micron powder into dense bulk component. Al2O3-TiC composite has been prepared by HIP process, containing 65%vol Al2O3and 35%vol TiC. The powders were pressured and sintered at temperature between 1250˚C - 1650˚C. Thermal residual stress from Al2O3-TiC manufacturing process is conventionally unavoidable. The aim of this study is to investigate the microstructure of HIPped Al2O3-TiC composite and its residual micro-strain using transmission electron microscopy (TEM) with selected area electron diffraction pattern (SADP) analysis. The Al2O3-TiC composite was prepared by high-precision machining/grinding processes then focus ion beam milling process was used to section the TEM lamella. Microstructures, grain size and phases were determined by TEM and X-ray diffractometry (XRD). Micro-strains of {200}TiC, {111}TiC , {220}TiC and {012}Al2O3were investigated by SADP (Selected Area Diffraction Pattern). Our result revealed there is approximately 0.01 compressive strains distributed in Al2O3-TiC composite.

Effect of Annealing on Microwave-absorption Properties of Fe/Al2O3 Nanocomposite Prepared by Ball-milling

An Fe/Al2O3 nanocomposite was prepared by high energy ball milling method, and which then annealed at 700C for 0.5 h in Ar atmosphere. The effect of annealing on the microstructure, magnetism and microwaveabsorption properties of Fe/Al2O3 nanocomposite has been investigated. It follows that the annealing resulted in increasing grain size, decreasing lattice defects and releasing the residual microstrain; meanwhile, decreasing the intensity of photoluminescence peaks of Al2O3 significantly, therewith the peaks at 398 nm and 484 nm exhibit a blue shift. An optimal reflection loss of -11.4 dB at 15.5 GHz was measured for a 7.7 mm thick layer of as-milled composite powder mixture with paraffin. However, the annealing treatment could remarkably enhance the dielectric loss, magnetic loss and microwave absorption performance of the composite, leading to an optimal reflection loss of -35.5 dB at 17 GHz for a layer thickness of 6.4 mm for the annealed composite.

Synthesis of manganese–zinc ferrite nanopowders prepared by a microwave-assisted auto-combustion method: Influence of sol–gel chemistry on microstructure

Based on the quantitative analysis and optimization of the complexing conditions for the sol–gel process, single phase Mn–Zn ferrite (Mn0.745Zn0.173Fe2.082O4) nanopowders with high saturation magnetization (MS=75.42emu/g) were one-step synthesized via a microwave-assisted sol–gel auto-combustion approach. The microstructures and magnetic property of the resulting powders were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy and magnetic measurement of M×H curves. The XRD patterns indicated that the low value of CA/M⁎ (the reduced molar ratio of citric acid to metal ions) and inadequate microwave irradiation are easy to result in the formation of impurity phases. Furthermore, the poor chelating of metal ions can be effectively improved by adding the ethylene glycol, which also acts as fuel to increase the reaction temperatures during the auto-combustions when oxidation degree Q (the relative amount of the oxidant) is high enough. The influences of the gel׳s chemistry, defined by the gel-parameters: CA/M⁎, oxidation degree Q and gross calorific value H (the total heat potentially produced by the complete oxidation of hydrocarbons), on the formation of single phase Mn–Zn ferrite nanopowders and their microstructures were investigated with the help of the orthogonal testing method. The microstructure of single phase Mn–Zn ferrite nanopowders is closely associated with the gel׳s chemistry. Moreover, the average grain size is more sensitively impacted by the gel-parameters than the residual microstrain and, relatively, the influences on the cell parameter are the smallest, with the impacting sequences of the gel-parameters: oxidation degree Q>gross calorific value H>CA/M⁎ for the grain size, oxidation degree Q>CA/M⁎>gross calorific value H for the microstrain and gross calorific value H>CA/M⁎ >oxidation degree Q for the crystal lattice parameter.