Higher Residual Strain Research Articles

Role of the thermal regime in the defect formation of zinc oxide nanostructures prepared by the thermal decomposition process

Abstract The intrinsic defect of ZnO depicts a crucial role in the charge transfer owing to the suppression of the exciton recombination, exhibiting superior semiconducting performance. In this study, the intrinsic defect of ZnO nanostructures prepared by direct thermal activation of 300–900 °C was investigated. X-ray diffraction (XRD) was employed to analyze phase, crystallite size, Zn–O bond length, and dislocation density. The relation of Williamson–Hall (W–H) was used to calculate crystallite size and micro-strain. The atomic coordination was approximated through the Rietveld method. Morphology and crystal growth investigation was carried on by scanning electron microscope (SEM) and tunneling electron microscope (TEM), exhibiting rod-like nanostructures transform to oval shape particle with high residual strain when increasing calcination temperature, exhibiting the crystal growth direction of (101). Specific surface and pore analysis reveals a significant value corresponding to SEM analysis. Fourier transform infrared spectroscopy (FT-IR) detected Zn–O stretching vibration bands, presenting a notable increase in the intensity when heat at 600 °C. Relating to the thermal regime, energy bandgap (Eg) was found to be 3.41–3.50 eV as increasing heat treatment temperatures. Photoluminescence (PL) was applied to determine intrinsic defects through emissive spectra. The surface charge was determined through the zeta potential measurement. The photo-induced dye degradation was measured to understand the effect of the defect in semiconductors. The X-ray photoelectron spectroscopy (XPS) confirms the wurtzite structure appearance, including the intrinsic defects. The observed intrinsic defects are discussed, associating with the structural constants, emissive spectra, cationic dye degradation, and binding energy.

Effects of coarse aggregate morphology on concrete mechanical properties

The morphology of coarse aggregate can significantly affect the mechanical performance of concrete. In this study, the correlation between the compressive properties of concrete and the coarse aggregate morphology was systematically explored. Three kinds of aggregates with significant morphology differences were selected: Spherical Aggregates, Flaky Aggregates, and Elongated Aggregates. Three-dimensional morphological information was obtained by 3D Structured-Light Scanner, and quantitative statistical analyses were conducted to assess the distribution of morphological characteristics for these three-types aggregates. It is found that the three-type aggregates with the same mesh size can be properly discriminated through the axis length, flatness, elongation, the product of flatness and elongation, and sphericality. The simplex-centroid design was used to build the correlation between aggregate morphology and the compressive strengths of concrete with different water-cement ratios. The concrete with 100% spherical aggregates owns the highest compressive strength, which is higher than that of concrete mixed with other two aggregates by 9.4%–36.2% and 5.2%–28.8% at the curing of 3-day and 28-day, respectively. When the ratio of spherical aggregates reaches above 50%, the strength loss caused by the elongated aggregates and flaky aggregates content is not obvious. Further, the failure mechanism of concrete with 100% spherical aggregates, 100% flaky aggregates, and 100% elongated aggregates under cyclic loadings were investigated by X-ray computed tomography scanning. It is found that the cracks inside spherical aggregates concrete mainly initiate from the edges and the core section remains almost intact before the destruction by a major oblique crack. Meanwhile, the high residual strain after cyclic loadings can originate from the generated vertical cracks under compression. The research findings in this study can serve as a solid base for the designing of concrete structures.

Influence of Cu content on microstructure, grain orientation and mechanical properties of Sn–xCu lead-free solders

The effect of Cu content on the microstructure, grain orientation and mechanical properties of Sn–xCu (x=0–4.0 wt.%) lead-free solder was studied. Results showed that added Cu induced the formation of intermetallic phases. Only the η-Cu6Sn5 and ɛ-Cu3Sn phases were present in the β-Sn matrix. For all contents, the strongly preferred orientation of the β-Sn phase was formed on the {001} plane. In Sn doped with 1.0 wt.% Cu, the η-Cu6Sn5 phase exhibited the preferred orientation of {0001} plane, whereas doping with 3.0 or 4.0 wt.% Cu transformed the preferred orientation to the {010} plane. In addition, only the {0001} and planes were present in the ɛ-Cu3Sn phase. The high Cu contents contributed to an increased number of low-angle boundaries, high residual strain, tensile strength and microhardness.

Flexural and fatigue properties of polyester disk material for milled resin clasps.

To evaluate the flexural and fatigue properties of a polyester disk material used in milled resin clasps of removable partial dentures, experimental polyester disk (mPE), injection-molded polyester (iPE), and polymethyl methacrylate disk (mPMMA) were examined by three-point bending tests and cyclic fatigue tests at 0.75 or 1.50 mm deflection. The mPE exhibited significantly higher flexural strength than the iPE (p<0.05). Meanwhile, the mPMMA displayed higher flexural modulus and strength than the polyesters. The mPE exhibited a significantly lower residual strain than the iPE at the cyclic 0.75 mm deflection (p<0.05); however, microcracks were observed in the mPE at the 1.50 mm deflection. The mPMMA showed a high residual strain at the 0.75 mm deflection and fractured within 1,000 cycles at the 1.5 mm deflection. The higher flexural strength and lower residual strain of the mPE compared with the iPE suggest the advantages of milled resin clasps within a limited deflection.

Anomalous Hall effect in antiferromagnetic Cr thin films

Bulk chromium is the simplest antiferromagnet in our general material database, which has been firmly believed to exhibit a collinear spin structure and a consequent vanishing anomalous Hall effect (AHE). In this work, we report an unexpected weak AHE in polycrystalline thin films of chromium. We attribute this phenomenon to the noncollinear spin textures induced by the local spin frustration and rearrangement in certain areas with high residual strain and defect densities. Moreover, a dominant underlying mechanism of intrinsic Berry phase is speculated. This could be a general feature for all the collinear antiferromagnetic thin-film materials with moderately high defect concentrations, making them promising candidates for emergent antiferromagnetic spintronics.

Facile Synthesis of Thermoplastic Polyamide Elastomers Based on Amorphous Polyetheramine with Damping Performance.

Novel thermoplastic polyamide elastomers (TPAEs) consisting of long-chain semicrystalline polyamide 1212 (PA1212) and amorphous polyetheramine were synthesized via one-pot melt polycondensation. The method provides accessible routes to prepare TPAEs with a high tolerance of compatibility between polyamide and polyether oligomers compared with the traditional two-step method. These TPAEs with 10 wt % to 76 wt % of soft content were obtained by reaction of dodecanedioic acid, 1,12-dodecanediamine, and poly(propylene glycol) (PPG) diamine. The structure–property relationships of TPAEs were systematically studied. The chemical structure and the morphologic analyses have revealed that microphase separation occurs in the amorphous region. The TPAEs that have long-chain PPG segments consist of a crystalline polyamide domain, amorphous polyamide-rich domain, and amorphous polyetheramine-rich domain, while the ones containing short-chain PPG segments comprise of a crystalline polyamide domain and miscible amorphous polyamide phase and amorphous polyetheramine phase due to the compatibility between short-chain polyetheramine and amorphous polyamide. These novel TPAEs show good damping performance at low temperature, especially the TPAEs that incorporated 76 wt % and 62 wt % of PPG diamine. The TPAEs exhibit high elastic properties and low residual strain at room temperature. They are lightweight with density between 1.01 and 1.03 g/cm3. The long-chain TPAEs have well-balanced properties of low density, high elastic return, and high shock-absorbing ability. This work provides a route to expand TPAEs to damping materials with special application for sports equipment used in extremely cold conditions such as ski boots.

High temperature tribological behavior of textured CSS-42L bearing steel filled with Sn-Ag-Cu-Ti3C2

To expand the applications of MXene-Ti3C2 in the field of high temperature tribology (450 °C), CSS-42L smooth surfaces (CSs), textured surfaces (TSs), textured surfaces with Sn-Ag-Cu (TSs-SAC) and textured surfaces with Sn-Ag-Cu-Ti3C2 (TSs-SACT) were prepared. The tribological behaviors under high temperature were investigated, and TSs-SACT showed excellent tribological properties at high temperatures. The amplitudes of friction force and coefficient could be reduced on TSs-SACT with the best antifriction performance. At high temperatures, the crystallinity, microhardness, residual strain and grain size on TSs-SACT are improved, which promotes the formation of enamel layers. The tribochemical reactions improve the wear resistance of enamel layers. TSs-SACT with uniform profiles has strong resistance to plastic deformations, prolonging the life of enamel layers.

Численное исследование термомеханических процессов при короткоимпульсном лазерном облучении полупространства.

Лазерное облучение металлических поверхностей интенсивными тепловыми источниками используется для генерации коротких зондирующих импульсов, которые распространяются внутрь тонких образцов и позволяют оценивать структуру и механические свойства последних в рамках классического акустического подхода. При кратковременном облучении поверхности конструкции источником энергии высокой плотности возникают большие тепловые напряжения и остаточные деформации. В данной статье численно исследуется осесимметричная задача о термомеханической нагрузке полупространства. При этом учитывается влияние объемных и неупругих характеристик отдельных фаз на остаточное напряженно деформированное состояние полупространства. Постановка задачи включает соотношение Коши, уравнение движения, уравнение теплопроводности, исходные условия, тепловые и механические граничные условия. Термомеханическое поведение изотропного материала описывается унифицированной моделью течения Боднера–Партома. Задача решается с помощью конечно-элементной методики. Численная реализация задачи проводится с помощью пошагового интегрирования по времени. Уравнения движения интегрируются методом Ньюмарка, а уравнение теплопроводности — неявным методом первого порядка. С помощью методики численного решения осесимметричной динамической задачи для полупространства при термомеханической нагрузке и модели течения описано остаточное напряженно-деформированное состояние. Установлено, что микроструктурные превращения, учитываемые через термотрансформационную деформацию, и зависимость неупругих характеристик материала от фазового состава существенно уменьшают остаточные неупругие деформации и способствуют появлению сжимающих напряжений. Получена трехзонная область формирования поля остаточных напряжений.

Mechanical properties and microstructural characteristics of rotary friction welded dissimilar joints of rolled homogeneous armor steel and medium carbon steel

Abstract Distinct materials are used for the construction of battle tanks used in defense sectors. The hull and turret of the battle tanks are made up of rolled homogeneous armor steel (also known as armor steel). The inner portions like the driver cabin and control room are covered with medium carbon steel. Hence, the dissimilar joint between these materials is unavoidable in the battle tank construction. Conventional fusion welding processes like manual metal arc welding, gas metal arc welding, and gas tungsten arc welding are preferred to join the dissimilar metals. However, the high heat input nature of these processes will create hydrogen induced cracking, high residual tensile strain, and HAZ softening, etc. To minimize these issues, solid state welding processes were adopted. In the present study, mechanical properties and microstructural characteristics of rotary friction welded dissimilar joint of armor steel and medium carbon steel was analyzed. The ultimate tensile strength of the dissimilar joint is around 775 MPa and the failure occurred at the medium carbon steel side. The impact toughness value of dissimilar joints is higher than medium carbon steel and lower than armor steel. The microstructure across the dissimilar joint has distinct features and a complex pattern was observed at the weld interface.

Effects of sintering temperature on structural, electrical and ferroelectric properties of La2Ti2O7 ceramics

Sintering characteristics of La2Ti2O7 prepared by solid state reaction method have been studied. Variations in the structural, electrical and ferroelectric properties are correlated with the changes in the physical and chemical microstructure occurring at different sintering temperatures. High sintering temperatures reduce the porosity; produce plate-like grain morphology with a large crystallite size, and a dense microstructure at 1600 °C with significant lattice strain. X-ray diffraction and vibrational spectroscopy confirm the formation of a well reacted La2Ti2O7 compound. Frequency dependent dielectric response ε'(f) in the range (10−2-106 Hz) shows significant dispersion for ceramics sintered at lower sintering temperatures (1200–1500 °C). Variations in the high frequency dielectric constant (ε') in the dispersion-free region at 1 MHz are found to correlate with the micro-structural changes occurring at different sintering temperatures. Ceramics sintered at 1600 °C exhibit high resistivity (~1014 Ω cm), low dielectric loss (tanδ ~ 10−2-10−3), and a stable dielectric constant (ε'~47) which remains dispersion-free in the entire frequency range (10−2-106 Hz). The high residual lattice strain in ceramics sintered at 1600 °C prevents reliable hysteresis loop measurements, whereas strain-free ceramics sintered at 1400–1500 °C exhibit hysteresis loops but the polarization values are low (0.34–0.37 μC/cm2), coercive fields are high (50–67 kV/cm) and the piezoelectric coefficient d33 = 1.0–1.5 pC/N is low.

Characteristics of hydrogen embrittlement in high-pH stress corrosion cracking of X100 pipeline steel in carbonate/ bicarbonate solution

Stress corrosion cracking (SCC) of X100 grade pipeline steel was researched in carbonate/bicarbonate solutions by using slow strain rate tensile (SSRT) tests, electrochemical testing, X-ray photoelectron spectroscopy (XPS), electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), the focused ion beam (FIB) lift-out technique and transmission electron microscopy (TEM). It is found that the X100 pipeline steel has low SCC sensitivity at the open circuit potential (OCP) and has high susceptible to SCC owing to the combined effect of anodic dissolution (AD) and hydrogen embrittlement (HE) at the applied cathodic potentials in carbonate/ bicarbonate solutions. At applied cathodic potentials less than about −950 mV, the SCC processes of X100 steel are dependent on AD and HE, while at more negative applied potentials, HE plays a more dominant role. The detailed SCC mechanism was studied by advanced detection methods. The results show that cracks propagated along the interface with low residual strain at various cathodic potentials, indicating that the low residual path is more active for both the anodic reaction and dislocation emission, and the high residual strain area may act as the cathodic zone. This phenomenon will be helpful to the design of high-SCC-resistant high-strength pipeline steel.

Effects of Cold-Work Degree on Stress Corrosion Cracking Behavior of Alloy 600 in Simulated Boiling Water Reactor (BWR) Water Environments

The growth behavior of stress corrosion cracking (SCC) of Alloy 600 with different cold-work levels was investigated in simulated boiling water reactors water environments. In addition, a correlation of cold-work levels, grain boundary characteristic, and the SCC growth behavior of Alloy 600 were studied. The results show that grains with high residual strain caused by cold work provide transgranular crack growth paths. The SCC growth rates of the specimens also increase with an increase in the degree of cold work and decrease remarkably after switching to the hydrogen water chemistry environment. Grain boundary character proves to be a factor more important than the localized strain concentration at the grain boundary in terms of its role in the intergranular crack growth rate of the Alloy 600 with a cold-work degree from 20% to 30%.

Characterization of Microstructure and Stress Corrosion Cracking Susceptibility in a Multi-pass Austenitic Stainless Steel Weld Joint by Narrow-Gap TIG

In the present study, correlation of the microstructure and stress corrosion cracking (SCC) susceptibility in the top, middle and root regions of a multi-pass austenitic stainless steel weld joint fabricated by narrow-gap tungsten inert gas welding (NG-TIG) was investigated by slow strain rate tests (SSRT) following a microstructure characterization. The results show that from the top to root regions in both the heat-affected zone (HAZ) and weld metal (WM), the dislocation density and length fraction of the Σ3 boundaries present a decreased trend, while the grain size, length fraction of LAB and residual strain all increase. By comparing the microstructure of WM with HAZ, δ-ferrite in WM is excessive and continuous while that in HAZ is island-shaped and discontinuous. In addition, larger grain size, lower dislocation density, higher residual strain, lower length fraction of Σ3 boundaries and higher length fraction of RGB are observed in WM. As a result, the SCC susceptibility in various regions of the weld joint follows the order of root regions > middle regions > top regions and WM > HAZ.

Ionically Conductive Hydrogel with Fast Self‐Recovery and Low Residual Strain as Strain and Pressure Sensors

Hydrogel-based sensors have attracted enormous interest due to their broad applications in wearable devices. However, existing hydrogel-based sensors cannot integrate satisfying mechanical performances with excellent conductivity to meet the requirements for practical application. Herein, an ionically conductive hydrogel with high strength, fast self-recovery, and low residual strain is constructed through a facile soaking strategy. The proposed ionically conductive double network hydrogel is achieved by combining chemically crosslinked polyacrylamide and physically crosslinked gelatin network followed by sodium citrate solution immersing. The obtained hydrogel has a tensile strength of 1.66 MPa and an elongation of 849%. The ionically conductive hydrogels can be utilized as both strain and pressure sensors with high sensitivity. Moreover, they can be used as ionic skin to monitor various human movements precisely, demonstrating their promising potential in wearable devices and flexible electronics.

The role of crystallographic orientations on heterogeneous deformation in a zirconium alloy: A combined experimental and modeling study

This study explores the effect of crystallographic orientations on the development of residual strains and local misorientations in a polycrystalline Zircaloy-4 during controlled tensile deformation. A combination of experiments (electron backscattered diffraction (EBSD), micro-Laue diffraction) and modeling (crystal plasticity finite element (CPFE)) are used. Data from two sets of grain orientations are analyzed and modeled: orientations within 5° of the exact (0002) basal pole (‘near basal’) and those within 5° of the exact (101‾0) prism pole (‘near prism’). In order to maintain similitude with experiments, the actual experimental microstructures (along with their crystallographic orientations) are used as an input for the CPFE simulations. Minor differences are observed for different measures of local misorientation developments. However, the ‘near basal’ grains show higher spread of grain reference orientation deviation, both in experiments and in CPFE simulations, and correlate with the intergranular strain heterogeneity predicted from CPFE simulations. Simulated trends of residual strains also compare favorably with the micro-Laue measurements. The ‘near basal’ grains have higher residual strains as compared to the ‘near prism’ grains. This observed behavior appears to originate from the elastic anisotropy of the hcp crystals and not from differences in the plastic deformation on the different family of slip systems.

Mechanical properties of graphene oxide: The impact of functional groups

In the current study, mechanical characteristics of graphene oxide (GO) as a promising substitute of graphene are systematically studied through molecular dynamics simulation. For this purpose, several GO samples having different concentrations of epoxide and hydroxyl functional groups are considered. The results reveal that increasing the epoxide coverage causes a noticeable deterioration in the mechanical characteristics of GO systems. This change is correlated with the increase of the formation of ripples in the structure upon increasing the epoxide coverage. Moreover, investigating the bond lengths in the system, it is concluded that the higher epoxide percentage leads to an increase in the length of single and hybrid resonance bonds leading to an overall deterioration of the mechanical properties of GO samples. Additionally, our results demonstrate that high concentration of functional groups can lead to a negative Poisson’s ratio. Increasing the amount of hydroxyl groups shows the same declining effect on the Young’s modulus. In a graphene system containing both epoxide and hydroxyl groups, it is deduced that a higher percentage of the former can result in a higher residual strain because of the formation of more ripples within the system.

Understanding the strain effect on coercivity enhancement in L10-Mn56Ga42 alloy via low-energy mechanical cryomilling

Varying degrees of strain were observed in L10-Mn56Ga42 powders via low-energy mechanical cryomilling, and the relationship between coercivity and strain was analyzed in detail. With increasing milling time, the powders do not show obvious variations in grain size and cell parameters, but a large strain is induced into the powders, leading to a remarkable enhancement in coercivity. A maximum coercivity of up to 6.7 kOe was accomplished for 20 h milled powders, with a high residual strain of about 0.96%. The initial magnetization curve indicates that the coercivity mechanism is mainly governed by the domain-wall pinning process where strain-induced defects act as pinning centers. Studies on heat treatments show that the strain-induced coercivity contributes to over 50% of the total coercivity, and a moderate annealing can eliminate the strain, changing the coercivity mechanism to a nucleation process.

Self-repairing flexible strain sensors based on nanocomposite hydrogels for whole-body monitoring

Flexible strain sensors based on extensible hydrogels are extensively investigated for human motion monitoring, but the performances of such strain sensors are limited by failure or high residual strain of hydrogels. Herein, self-repairing flexible strain sensors are fabricated with poly(AA-co-SMA)/c-CNF/Fe3+ nanocomposite hydrogels (AA: acrylic acid, SMA: stearyl methacrylate, c-CNF: carboxylate modified cellulose nanofibril). Because the nanocomposite hydrogels are fully supramolecularly cross-linked by hydrophobic association and ionic interaction, the flexible strain sensors can repair themselves upon damage and recover their sensing ability. Compared with other hydrogel-based self-repairing sensors, the flexible strain sensors in this work have intrinsically reversible sensing ability based on the improved resilience of the nanocomposite hydrogel by introducing c-CNF. In addition, such sensors also have integrated large sensing range (0∼800 %), low response time (0.25 s), high sensitivity (strain 0∼300 %, gauge factor = 1.9; strain 400 %∼800 %, gauge factor = 4.4) and excellent durability (∼1000 cycles) for guaranteeing their potential applications in whole-body monitoring.

Stress Corrosion Cracking of the Fusion Boundary for 304L/82 Dissimilar Metal Weld Joint in Simulated Primary Water

The stress corrosion cracking behavior of the fusion boundary for 304L/82 dissimilar metal weld joint was studied in simulated primary water. Analytical electron microscopy was utilized to characterize the cracking features. Results demonstrated that the heat-affected zone in Type 304L has a higher stress corrosion cracking susceptibility and the crack propagated from weld region to Type 304L heat-affected zone in the form of intergranular cracking. The electron back-scattered diffraction and transmission electron microscopy–electron dispersive x-ray spectroscopy results showed that the intergranular cracking in the heat-affected zone of Type 304L was caused by the high residual strain rather than grain boundary Cr-depletion in front of the crack tip. The suppressed crack growth rate in hydrogenated water was attributed to the stable Cr-rich oxide formed at crack tip.

Dilation Behavior of Thermal Spray Coatings

The thermal expansion of a thermally sprayed coating material is an important design-relevant property from both processing and application service points of view. High thermal stresses and residual strains can arise during deposition, and thermal exposure in service. The linkage to process conditions which can impact both physical and chemical attributes of the microstructure and consequently its expansion behavior is of great importance. The observed dilation response of various coatings is discussed based on the processing effects that induce differences in microstructural features and the impact of residual strain and annealing of defects on the dilation behavior during first thermal exposure. The coefficient of thermal expansion (CTE) of coatings was found to approach the bulk when the material is not sensitive to oxidation in-flight. For those materials sensitive to oxidation, mathematical models used to describe effective properties of composite materials were adopted to describe the CTE property. A large irreversible dilation change was found in the first heating cycle due to defect annealing (referred to as thermal shakedown). Several reasons are hypothesized for the magnitude of such dilation change. Together, the paper presents a comprehensive analysis of thermal expansion behavior of a diversity of thermal spray processed materials.