Mismatch Stress Research Articles

Water vapor corrosion behaviours of nanostructured Yb2O3-Yb2SiO5/mullite/Si environmental barrier coatings

In this work, the nanostructured Yb2O3-Yb2SiO5/mullite/Si environmental barrier coatings (EBCs) were designed and prepared by atmospheric plasma spraying. The water vapor corrosion behavior of coatings was investigated at a temperature of 1350 °C for durations ranging from 100 to 500 hours, and the influence of phase compositions, microstructure on this behavior was systematically investigated. The results indicate that phase transformation occurs during the water vapor corrosion process, and severe corrosion takes place at the Yb2O3-Yb2SiO5 top coating and the mullite intermediate layer. Obvious diffusion reaction between Yb2O3-Yb2SiO5 and mullite layers occurred without water vapor, while the diffusion reaction cannot be observed under water vapor. The water vapor corrosion mechanism of EBCs is mainly attributed to residual thermal mismatch stresses, phase transformation resulting from sintering of Yb2O3-Yb2SiO5, as well as the formation of TGO by oxidation.

Relevance of Prosodic Focus and Lexical Stress for Discourse Comprehension in Turkish: Evidence from Psychometric and Electrophysiological Data.

Prosody underpins various linguistic domains ranging from semantics and syntax to discourse. For instance, prosodic information in the form of lexical stress modifies meanings and, as such, syntactic contexts of words as in Turkish kaz-má "pickaxe" (noun) versus káz-ma "do not dig" (imperative). Likewise, prosody indicates the focused constituent of an utterance as the noun phrase filling the wh-spot in a dialogue like What did you eat? I ate----. In the present study, we investigated the relevance of such prosodic variations for discourse comprehension in Turkish. We aimed at answering how lexical stress and prosodic focus mismatches on critical noun phrases-resulting in grammatical anomalies involving both semantics and syntax and discourse-level anomalies, respectively-affect the perceived correctness of an answer to a question in a given context. To that end, 80 native speakers of Turkish, 40 participating in a psychometric experiment and 40 participating in an EEG experiment, were asked to judge the acceptability of prosodic mismatches that occur either separately or concurrently. Psychometric results indicated that lexical stress mismatch led to a lower correctness score than prosodic focus mismatch, and combined mismatch received the lowest score. Consistent with the psychometric data, EEG results revealed an N400 effect to combined mismatch, and this effect was followed by a P600 response to lexical stress mismatch. Conjointly, these results suggest that every source of prosodic information is immediately available and codetermines the interpretation of an utterance; however, semantically and syntactically relevant lexical stress information is assigned more significance by the language comprehension system compared with prosodic focus information.

Improved strategy of oxygen-assist heat treatment to prepare the antioxidant coating for carbon/carbon composites

In this study, a feasible slurry sintering strategy with the oxygen-assist heat treatment was developed to realize one-step full densification of high-temperature ceramic coating. The results show the stable oxidation resistance of the SiC/Si-B-Zr-Cr/SiC coating, which exhibits an overall mass loss of only 2.28 % after 1400 °C/300 h oxidation and high fracture toughness of 2.13–2.54 MPa·m1/2. The protection/failure mechanisms reveal that the formation of ZrSiO4@ZrO2 alleviates stress mismatch in the coating, competing with the contribution of coating failure arising from the increasing tensile stress. The liquid-phase convection inside the coating can reconstruct its structure and composition, thereby improving the thermal performance.

Structure and tribological behavior of a polyetherimide/polytetrafluoroethylene matrix filled with negative thermal expansion zirconium tungstate particles

Thermal expansion mismatch stresses may be a reason for premature failure of sealing and bearing components made of polymer composites that are rubbed against metallic surfaces at elevated temperatures. It is of particular importance for polymer matrix composites loaded with anti-friction inclusions of polytetrafluoroethylene (PTFE) that possesses high coefficient of thermal expansion. In this regard, a study was undertaken to elucidate the effect of the thermal mismatch on wear and friction of amorphous polyetherimide (PEI) matrix loaded with either polytetrafluoroethylene (PTFE) particles (i) or PTFE particles covered with negative thermal expansion zirconium tungstate (ZT) α-ZrW2O8 (ii) at temperatures 23 °C, 120 °C and 180 °C. The ball-on-disk testing scheme was used according to standard with AISI 52100 steel balls rubbed against a polymer composite disks at normal force P = 5 N and sliding velocity V = 0.3 m/s. The PEI/PTFE/ZT composite demonstrated a tendency for wear rate (WR) reduction in sliding at 120 °C and 180 °C as compared to corresponding WR enhancement on the PEI/PTFE. The rationale is provided that the ZT additive effectively reduced thermal expansion of the PTFE in the PEI matrix and thus improved wear resistance of the composite. New thermal expansion-controlled wear and friction instability mechanism has been proposed and discussed.

High-temperature creep mechanism of Ti-Ta-Nb-Mo-Zr refractory high-entropy alloys prepared by laser powder bed fusion technology

Creep resistance, which is one of the most important deformation modes, is rarely reported for refractory high entropy alloys (RHEAs). The experiment investigated the high-temperature creep mechanism of Ti-Ta-Nb-Mo-Zr RHEA prepared by laser powder bed fusion (LPBF) technology. The high cooling rate of LPBF suppresses most of the elemental segregation, but there are still over-solidified precipitates and a few continuous precipitates (CP). In the range of 923–1023 K, the stress exponent and activation energy were determined to be 3.2–3.4 and 261.5 ± 19.5 kJ/mol, respectively. Compared with other conventional alloys and HEAs, a large reduction of the minimum creep rate is found in the LPBF-built Ti1.5Ta0.5NbZrMo0.5 RHEA, indicating a significant improvement in high-temperature properties. The dislocation tangles at the interface is formed during the creep process and new Zr-rich CP phases are generated in the dislocation tangles region. The interfacial dislocation tangles is the result of the interaction between dislocations and two-phase mismatch stresses. The dislocation tangles prevents dislocations from further cutting the matrix phase, which is very favorable to the high-temperature creep performance. At the same time, the formation of this dislocation tangles greatly accelerates the nucleation process and growth rate of the new CP phase. The present work provides a pathway to design novel HEAs with improved high-temperature creep resistance.

Hybrid Piezoresistive 2D MoS2/PEGDA/PANI Covalent Hydrogels for Wearable Strain Sensors

The continuous research on electronics, biocompatible materials and nanomaterials has led to the design of a new generation of wearable devices that can be employed in direct contact with the body of the user, which is attractive for real-time, non-invasive health monitoring1. For the satisfaction of such requirements, hydrogel-based conductive devices are often proposed as promising candidates for these applications, thanks to their softness, flexibility, and biocompatibility.Here we report the synthesis of conductive hybrid hydrogels containing two-dimensional (2D) MoS2. The nanoflakes are integrated in the polymeric matrix creating an anisotropic structure, which helps to generate mismatch stress for a strain sensing under a certain stimulus2, thus allowing the gel to give an electrical response to pressure. 2D MoS2 nanoflakes were produced via top-down chemical exfoliation3 and were incorporated in the hydrogel through a covalent grafting to the polymeric building blocks by exploiting the prior surface functionalization of the flakes4. The conductivity of the hydrogels was increased with the further incorporation of in-situ polyaniline (PANI), which is a widely used material in biomedical applications as a biocompatible conductive polymer5. The as-obtained hydrogels are characterized through a combination of techniques, whereas their electromechanical properties are investigated via a home-made setup to prove that compression causes an increase in current due to the piezoresistive properties introduced with the incorporation of 2D MoS2 and PANI.[1] Xie, J. et al. J Electrochem Soc 2020,167, 037541.[2] Zhang, D. et al. J Mater Chem B 2020, 8, 3171–3191.[3] Acerce, M. et al. Nat Nanotechnol 2015, 10, 313–318.[4] Knirsch, K. C. et al. ACS Nano 2015, 9, 6018–6030.[5] Humpolicek, P. et al. J. Synth Met 2012, 162, 722–727.

Investigation on improving soldering reliability of large-scale LCCC devices with high-lead solder ball materials

Abstract Leadless Ceramic Chip Carrier (LCCC) is commonly used in high-density electronic packaging PCB boards. Due to the different thermal expansion of materials, the solder joints of LCCC devices are prone to stress and cracking after assembly, which leads to the failure of LCCC devices’ electrical performance. In this paper, the advantages and disadvantages of four solutions were analysed, and comprehensively considered the use of ball planting to alleviate thermal mismatch stress. After experimental verification, the thermal mismatch between the LCCC devices and PCB results in a lifespan of less than 200 cycles for direct assembly of the LCCC devices. Planting balls at the bottom of LCCC devices and soldering can effectively increase the lifespan of solder joints and improve product reliability. By analysing the SMT process, the bottom high-lead ball placement of LCCC devices was implemented, and environmental testing was conducted using temperature shock testing to demonstrate that bottom ball placement can extend solder joint life and improve reliability. This study provides a reliable soldering method for large-scale LCCC devices and provides a basis for improving LCCC reliability.

Prediction of internal stress in alumina laminates induced by shrinkage mismatch based on elastic model modification

AbstractCracks induced by internal stresses compromise the structural integrity of ceramic laminates. Such stresses can be classified into thermal stress derived from thermal expansion mismatch and shrinkage stress derived from shrinkage mismatch. Analytical models have been proposed for the former, whereas only numerical predictions have been explored for the latter. In this study, an equation is constructed to predict the shrinkage stress by modifying an elastic solution proposed in previous studies. We fabricated laminates with three‐layer sandwiched structures using only alumina specimens with high and low densities to control the shrinkage and avoid thermal mismatch. Surface cracks were initiated when the shrinkage stress exceeded the flexural strength of the surface layer. Although the original strength of the surface layer was 308.8 MPa, the laminates’ flexural strength was lower than that because of shrinkage constraint. Our results demonstrate that the shrinkage stress was successfully estimated analytically using a few material properties measured in an ordinary environment. This study will ensure the structural integrity of ceramic laminates in laminate designs.

Enhancing the Efficiency and Stability of Inverted Formamidinium-Cesium Lead-Triiodide Perovskite Solar Cells through Lewis Base Pretreatment of Buried Interfaces.

Mixed components of formamidinium(FA) and cesium (Cs)-based perovskite solar cells are the most hopeful for commercialization owing to their excellent operational and phase stabilities, especially for devices with inverted structure. The nonradiative recombination of carriers can be effectively suppressed through interface optimization, therefore, the performance of devices can be improved. Notably, the buried interface emerges as critical aspects such as charge transport, charge recombination kinetics, and morphology of perovskite films. This study focuses on a straightforward yet effective approach to overcome buried interface challenges between organic polymers (poly(-triarylamine) (PTAA) and FACs-based perovskite films. The PTAA substrate is pretreated with a Lewis base known as 2-butynoic acid (BA) with a C═O functional group. First, it can be an interfacial buffering layer, harmonizing stress mismatch between the perovskite and PTAA layers, consequently optimizing crystallization and improving perovskite film quality. Second, Pb2+ defect can be passivated at the buried interface of the perovskite film through binding with the C═O group of the BA molecule. This dual-function strategy leads to a substantial enhancement in both photoelectric conversion efficiency (PCE) and stability of devices. Finally, the PCE of the device-modified buried interface with BA reaches an impressive 23.33%. Furthermore, unencapsulated devices with BA treatment maintain approximately 94% of their initial efficiency after aging at maximum power point tracking for 1000 h.

Electromechanically Reconfigurable Terahertz Stereo Metasurfaces.

Dynamic terahertz devices are vital for the next generation of wireless communication, sensing, and non-destructive imaging technologies. Metasurfaces have emerged as a paradigm-shifting platform, offering varied functionalities, miniaturization, and simplified fabrication compared to their 3D counterparts. However, the presence of in-plane mirror symmetry and reduced degree of freedom impose fundamental limitations on achieving advanced chiral response, beamforming, and reconfiguration capabilities. In this work, a platform composed of electrically actuated resonators that can be colossally reconfigured between planar and 3D geometries is demonstrated. To illustrate the platform, metadevices with 3D Split Ring Resonators are fabricated, wherein two counteracting driving forces are combined: i) folding induced by stress mismatch, which enables non-volatile state design and ii) unfolding triggered by the strain associated with insulator-to-metal transition in VO2, which facilitates volatile structural reconfiguration. This large structural reconfiguration space allows for resonance mode switching, widely tunable magnetic and electric polarizabilities, and increased frequency agility. Moreover, the unique properties of VO2, such as the hysteretic nature of its phase transition is harnessed to demonstrate a multi-state memory. Therefore, these VO2 integrated metadevices are highly attractive for the realization of 6G communication devices such as reconfigurable intelligent surfaces, holographic beam formers, and spatial light modulators.

High-performance zero thermal expansion in Al metal matrix composites

Zero thermal expansion (ZTE) composites reinforced by negative thermal expansion (NTE) compounds exhibiting superior dimensional stability and high thermal conductivities, are urgently needed in the modern industrial field. Unfortunately, conventional strategies for achieving ZTE composites often compromise thermal conductivity by incorporating high-content NTE particles. This study reports an overlooked factor enhancing NTE: the in-situ thermal mismatch stresses within the composites, which provide a significant driving force for lattice distortion. The 50 vol.% Cu2P2O7/Al-Si composite achieves isotropic ZTE, low density, and high thermal conductivity due to pressure-enhanced NTE and a tight interface structure. Synchrotron X-ray diffraction and Density Functional Theory (DFT) calculations have revealed the key mechanism of in-situ residual thermal stress in the composite contributing to the enhancement of NTE in Cu2P2O7. This work proposes a novel design approach for high-performance ZTE materials.

Crystal Quality and Efficiency Engineering of InGaN‐Based Red Light‐Emitting Diodes

This article is aimed at understanding of the complex design of metalorganic chemical vapour deposition ‐grown InGaN‐based red light‐emitting diode (LED) structure. The contribution of different elements of red LED structure to the stress distribution and threading dislocation density (TDD) evolution is theoretically investigated. For this purpose a self‐consistent modeling of the structure growth process is used, taking into account stress‐modulated indium incorporation, mismatch stress relaxation by threading dislocations and V‐pits, and nucleation of new threading dislocations. The simulation results, consisting of composition, stress, and TDD profiles, are then utilized for modeling of device operation, which allows to analyze contribution of different elements to the heterostructure operation.

On the effect of stiffness discontinuities on the reeling of pipelines using FEM and machine learning strategy

ABSTRACT Under current DNV specifications, pipeline design for reeling installation involves extensive FE simulations considering wall thickness and yield stress mismatch. This process is laborious, requiring multiple setups and trial-and-error calculations, with each simulation taking several hours. This paper proposes a machine learning strategy to study the mismatch design during the reeling process. Four machine learning models—Gaussian Process regression, Multilayer Perceptron, Support Vector Machine, and Random Forest—are used. Parameters that may affect failure, including yield strength, wall thickness, hardening coefficient, back tension, reel diameter, and pipe diameter are considered as input features. FE analyses simulate the reeling process, extracting output parameters such as maximum ovality, peak strain, local curvature, and lift-off for training. Based on careful calibration, it is shown to form an accurate and efficient regression framework, which only takes less than one minute to finish, exhibiting significant advantages over the conventional process.

A novel approach for brazing MgF2 ceramic to TA15 alloy using AgCu/GH4169/Bi2O3[sbnd]B2O3[sbnd]ZnO composite braze fillers

A two-step brazing process was successfully employed to join MgF2 ceramic and TA15 alloy using eutectic Ag28% (in mass fraction) Cu alloy and Bi2O3B2O3ZnO (BBZ) glass as fillers, by introducing a 100 μm thick GH4169 interlayer. Multiscale characterization revealed that interdiffusion and reaction occurred at the joint interfaces. As a result, a reliable joint system consisting of TA15/TiCu/TiCu2Al/Ag(s,s) + Cu(s,s)/TiCu2Al/TiCu Ni + Ag-rich layer/GH4169/nano-oxide layer/glass/Mg3(BO3)F3+MgO + MgF2 reaction layer/MgF2 was formed. The GH4169-interlayer exhibited adaptive compatibility though its interaction with AgCu and BBZ glass fillers, effectively accommodating strong interface bonding and thermal mismatch stress between TA15 and MgF2 substrates. It shows an excellent shear strength (32 MPa, at room temperature) as well as thermal cycling stability without any cracking or spallation observed after the 20 thermal shock cycles between room temperature and 300 °C. It provides valuable insights into designing highly reliable ceramic/metal joints that demonstrate superior stability and adaptability in specific applications.

Heterojunctions of Mercury Selenide Quantum Dots and Halide Perovskites with High Lattice Matching and Their Photodetection Properties.

Heterojunction semiconductors have been extensively applied in various optoelectronic devices due to their unique carrier transport characteristics. However, it is still a challenge to construct heterojunctions based on colloidal quantum dots (CQDs) due to stress and lattice mismatch. Herein, HgSe/CsPbBrxI3-x heterojunctions with type I band alignment are acquired that are derived from minor lattice mismatch (~1.5%) via tuning the ratio of Br and I in halide perovskite. Meanwhile, HgSe CQDs with oleylamine ligands can been exchanged with a halide perovskite precursor, acquiring a smooth and compact quantum dot film. The photoconductive detector based on HgSe/CsPbBrxI3-x heterojunction presents a distinct photoelectric response under an incident light of 630 nm. The work provides a promising strategy to construct CQD-based heterojunctions, simultaneously achieving inorganic ligand exchange, which paves the way to obtain high-performance photodetectors based on CQD heterojunction films.

Separation of wafer bonding interface from heterogenous mismatched interface achieved high quality bonded Ge-Si heterojunction

In the realm of optoelectronic integration, silicon-based Ge bonding has attracted great attention due to its advantages in short-wave infrared response and low cost. However, owing to the inherent lattice mismatch and thermal mismatch between Ge and Si, the bonded Ge-Si heterogenous interfaces encountered problems of thermal instability and high interface states. Herein, an approach of separating the bonding interface from the heterogenous interface is proposed through inserting a Ge epitaxial layer (GeEL) between the Si substrate and Ge film. This separation modifies the bonding interface to a homogenous one, alleviating the massive mismatch stress and achieving film relaxation, enhancing bonding stability in all aspects. Moreover, during 850 °C annealing, GeEL is doped via diffusion hence realizes electric filed modulation, inhibiting the carrier recombination leakage current and trap assisted tunneling in this defect-rich layer. A Ge-Si heterogenous PIN diode prepared by this bonding method has achieved a remarkable low dark current density (1.33 mA/cm2), a low ideality factor (1.11), and a high on–off ratio (106), confirming the outstanding quality of the bonded heterojunction. This work provides great prospects for higher performance, larger scale and multi-functional Si-based heterogenous material device applications.

Ultra-Strong Janus Covalent Organic Framework Membrane with Smart Response to Organic Vapor.

Vapor-driven smart Janus materials have made significant advancements in intelligent monitoring, control, and interaction, etc. Nevertheless, the development of ultrafast response single-layer Janus membrane, along with a deep exploration of the smart response mechanisms, remains a long-term endeavor. Here, the successful synthesis of a high-crystallinity single-layer Covalent organic framework (COF) Janus membrane is reported by morphology control. This kind of membrane displays superior mechanical properties and specific surface area, along with excellent responsiveness to CH2Cl2 vapor. The analysis of the underlying mechanisms reveals that the vapor-induced breathing effect of the COF and the stress mismatch of the Janus structure play a crucial role in its smart deformation performance. It is believed that this COF Janus membrane holds promise for complex tasks in various fields.

Biodegradable suture development-based albumin composites for tissue engineering applications

Recent advancements in the field of biomedical engineering have underscored the pivotal role of biodegradable materials in addressing the challenges associated with tissue regeneration therapies. The spectrum of biodegradable materials presently encompasses ceramics, polymers, metals, and composites, each offering distinct advantages for the replacement or repair of compromised human tissues. Despite their utility, these biomaterials are not devoid of limitations, with issues such as suboptimal tissue integration, potential cytotoxicity, and mechanical mismatch (stress shielding) emerging as significant concerns. To mitigate these drawbacks, our research collective has embarked on the development of protein-based composite materials, showcasing enhanced biodegradability and biocompatibility. This study is dedicated to the elaboration and characterization of an innovative suture fabricated from human serum albumin through an extrusion methodology. Employing a suite of analytical techniques—namely tensile testing, scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA)—we endeavored to elucidate the physicochemical attributes of the engineered suture. Additionally, the investigation extends to assessing the influence of integrating biodegradable organic modifiers on the suture's mechanical performance. Preliminary tensile testing has delineated the mechanical profile of the Filament Suture (FS), delineating tensile strengths spanning 1.3 to 9.616 MPa and elongation at break percentages ranging from 11.5 to 146.64%. These findings illuminate the mechanical versatility of the suture, hinting at its applicability across a broad spectrum of medical interventions. Subsequent analyses via SEM and TGA are anticipated to further delineate the suture’s morphological features and thermal resilience, thereby enriching our comprehension of its overall performance characteristics. Moreover, the investigation delves into the ramifications of incorporating biodegradable organic constituents on the suture's mechanical integrity. Collectively, the study not only sheds light on the mechanical and thermal dynamics of a novel suture material derived from human serum albumin but also explores the prospective enhancements afforded by the amalgamation of biodegradable organic compounds, thereby broadening the horizon for future biomedical applications.

Understanding the effect of bondcoat surface treatment on enhanced lifetime of suspension plasma sprayed thermal barrier coatings

Thermal barrier coatings (TBCs) are extensively used in gas turbine engines in power generation and aerospace applications. Improvements in TBC performance and lifetime are continuously pursued by the gas turbine industry. Suspension plasma spraying (SPS) has shown promising results in recent years as it could produce a porous columnar TBC microstructure exhibiting low thermal conductivity and high durability. Further improvements in lifetime and fundamental understanding of failure mechanisms would lead to their wider application.Lifetime of a TBC system is dependent not only on the topcoat microstructure and chemistry, but also on topcoat-bondcoat interface and bondcoat characteristics as they influence the growth rate of thermally grown oxide (TGO) layer as well as the mismatch stresses generated in the topcoat during operation. Moreover, in SPS TBCs, the column density and porosity in the topcoat are also affected by the bondcoat surface roughness which in turn affects TBC lifetime. In previous work, it was shown that bondcoat surface treatment by shot peening followed by light grit blasting can significantly enhance the cyclic lifetime of SPS TBCs.The objective of this work was to gain further insight into the lifetime improvements due to surface treatment of bondcoat. Commercial NiCoCrAlY powder was deposited by high velocity air fuel (HVAF) and high velocity oxy fuel (HVOF) spraying while SPS was used to deposit yttria stabilised zirconia topcoat. Before spraying the topcoat, the bondcoat samples were subjected to vacuum heat treatment, shot peening, and/or grit blasting. Residual stress measurements were performed by X-ray diffraction on samples with different variants of bondcoat treatments and compared with Almen strip tests. The lifetime was examined by thermal cyclic fatigue testing. The relationships between changes in bondcoat surface roughness, residual stress state and microstructure due to surface treatments, and resultant topcoat microstructure and lifetime were studied and discussed.

Study on moisture absorption characteristics of glass fibre‐reinforced epoxy resin material for composite insulators based on the 3D‐Fick model

AbstractLong‐term exposure to moisture leads to a gradual deterioration of performance and reduced service life of glass fibre‐reinforced epoxy resin (GFRP) material in composite insulators. Therefore, it is necessary to analyse the moisture absorption characteristics of GFRP material and the evolution of damage to their internal interface properties. Moisture absorption tests on GFRP rod material used in composite insulators to obtain their three‐dimensional diffusion coefficients are conducted. Atomic force microscopy was then employed to obtain the composite material system's fibre/matrix interfacial phase parameters. Furthermore, a finite element model incorporating representative volume elements with interfacial phases and a mesoscale transient moisture absorption finite element model for the composite material was established. Finally, the moisture absorption characteristics of GFRP material and the evolution of damage to the interfacial phase under thermal‐humidity cycling conditions were investigated. The results showed that the diffusion coefficient along the fibre direction in GFRP material was higher than that in the perpendicular direction. The moisture diffusion finite element model, incorporating an anisotropic interfacial phase, fitted the anisotropic diffusion coefficients of GFRP material more accurately. As moisture invaded the GFRP material, the mismatch stresses continuously increased during the moisture absorption. Moreover, the non‐uniform arrangement of fibres resulted in uneven distribution of moisture‐induced stresses inside the material, leading to higher mismatch stresses in areas with dense fibre arrangements in the matrix. Prolonged high and low humidity cycles led to the development of micro‐cracks, micro‐porosity, and interface debonding along the fibre direction at the GFRP material interfaces, thereby affecting the anisotropic moisture absorption characteristics of the material. The findings of this study provide valuable insights into the mechanisms underlying the deterioration of GFRP material in composite insulator rods due to moisture degradation.