Effect Of Microstructural Changes Research Articles

Study of polarization behavior in BaTiO<sub>3</sub>-based multilayer ceramic capacitors using AC- and Uni-poling treatment ∼ Part 1: Effects of microstructural changes

To obtain guidelines for the microstructure design of BaTiO3-based multilayer ceramic capacitors from the viewpoint of polarization behavior, the effects of AC- and Uni-poling treatments were examined using intentionally grain-growth samples. For purposes of comparison, the DC-aging characteristics of each sample were also examined. From the results of the polarization behavior induced by AC- and Uni-poling treatments, it was confirmed that changes in the core–shell structure, grain size, and oxygen vacancy concentration of the dielectrics strongly affected the domain wall pinning. In comparison with DC-aging characteristics, AC- and Uni-poling treatments are also expected to be effective tools for clarifying the relationships among more detailed microstructure and polarization behaviors of dielectrics.

Correlation Analysis of the Change Law of Index Gas and Active Functional Groups in the Process of High-Temperature Spontaneous Combustion of Minerals in the Fushun West Mine.

The spontaneous combustion of underground minerals causes huge property losses and ecological damage. Coal and oil shale are co-associated minerals in the Fushun West Mine, and both have the ability to undergo oxidative spontaneous combustion. To study the effect of microstructure changes on the macroscopic gas product concentration during the mineral oxidation spontaneous combustion process in the Fushun West Mine, this study used a high-temperature temperature-programmed test to obtain the change trend of gas product concentration in different oxidation stages of minerals. Using Fourier transform infrared spectroscopy technology, the changes in active functional groups of surface molecules during the process of mineral oxidation and spontaneous combustion were identified. Finally, using the gray correlation degree, correlation analysis between the concentration of gas products and the concentration of active functional groups in different oxidation stages was carried out. The key reactive functional groups affecting mineral spontaneous combustion were identified. The essential reason for the change in the gas product was revealed.

Effects of micro-structural changes on properties of aged bamboo paper

我国大量的竹纸文物面临严重的老化糟朽问题，为进一步探讨竹纸的老化行为，对采集的传统手工竹纸进行人工加速老化处理，结合傅立叶变换红外（FTIR）、X射线衍射（XRD）、扫描电子显微镜（SEM）、抗张强度测试、热重分析（TG）以及动态水分吸附（DVS）等多种方法研究老化竹纸的微观结构变化对纸张性质的影响。结果表明，竹纸老化后内部－OH、C－O－C等基团的红外吸收峰强度下降，纤维分子链降解断裂产生了C=O等新基团；老化过程中竹纸的纤维结构受损使纤维素结晶度指数CrI呈现先升后降的趋势，与纤维素结晶区与无定形区对老化作用的敏感差异有关；SEM显示竹纸老化后出现纤维断裂、粉化等微观形貌变化是纤维结构遭受破坏的直观表现。由于老化竹纸的纤维分子链降解断裂使纤维的自身强度降低，纸张的力学强度下降；纤维素结晶区受损使纸张的热稳定性变差，表现为老化竹纸的热解特征温度T0.05、T0.5及Tmax整体降低；毛细结构受损、羟基等亲水基团的含量降低是老化竹纸吸湿性下降的主要原因。老化竹纸的性质劣化与其微观结构的改变密切相关，在科学制定纸质文物的保护方案以及评估保护效果时需注重检测纸张的内部结构，有助于在古籍文物的修复实践中达到最佳保护效果。

Comparison of the microstructure, corrosion resistance, and hardness of 321 and 310s austenitic stainless steels after thermo-mechanical processing

In this study, the effects of microstructural changes after thermo-mechanical processing (TMP) on the corrosion resistance and hardness of 321 and 310 s austenitic stainless steels (ASS) were investigated and the corrosion behavior of these two alloys were compared. First, the as-received sample was subjected to 90% thickness reduction through cryo-rolling at liquid nitrogen temperature (-196 °C), and then, annealing treatment was performed at 850 °C for 5 and 15 min. To evaluate the corrosion properties of the samples, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were performed. The microstructure of the as-received samples consisted of equiaxed grains, annealing twins, and a small amount of delta ferrite. Due to annealing for 5 min after cryo-rolling, a combination of fine and ultrafine grains was observed. By increasing the annealing time to 15 min, grain growth and secondary recrystallization (abnormal grain growth) occurred in 310 s and 321 ASS, respectively. The results of potentiodynamic polarization and EIS tests confirmed each other and both indicated an improvement in the corrosion resistance of cryo-rolled and annealed specimens compared with as-received samples. It is postulated that the development of fine-grained and ultrafine-grained structures in TMP specimens leads to the reinforcement of the passive layer of chromium and improvement of re-passivation. Moreover, optical microscope images before and after the corrosion test showed pitting corrosion. The differences in the corrosion behavior of 321 and 310 s ASS were also discussed. The results of the hardness test showed hardness amplification in TMP specimens which were confirmed by the Hall-Petch relationship.

Investigation of microstructural changes of Pt-Al-7% YSZ coating during high-temperature hot corrosion and its effect on tensile properties of coated Rene-80 superalloy at 950 °C

In the present study, the microstructural changes in Pt-Al-7%YSZ coating on Rene-80 superalloy after 10, 20, and 40 cycles of hot corrosion and the effect of hot corroded coating on the tensile properties of Rene-80 substrate at 950 °C were investigated. For this purpose, the cross-section and fracture surface of the coating, substrate, and coating/substrate interface, were studied and the correlation between tensile behavior and microstructural changes of substrate and coating was evaluated. It was found that the effect of coating's microstructural changes on the tensile properties is less than the effect of microstructural changes on the substrate. As the cycles of hot corrosion increased, yield strength and tensile strength changed. This event was attributed to the γ' precipitates and volume fraction and the average size of voids in the substrate. The intergranular cracks were nucleated in the substrate from micro-voids in the adjacent areas to MC carbides, grew, and coalesced. However, the most influential factors in the coating on the tensile properties of coated samples were thermally grown oxide (TGO) stresses and thermal stresses due to the difference in thermal expansion coefficients between the coating layers and substrate and increasing the release rates of these stresses. The strain energy release rate (GC) was highest in TGO/Pt-Al, and coating degradation occurred through nucleation of delamination and longitudinal cracks in the TGO/Pt-Al interface and propagation of some of these cracks to the substrate.

Analysis of the binding selectivity and inhibiting mechanism of chlorogenic acid isomers and their interaction with grass carp endogenous lipase using multi-spectroscopic, inhibition kinetics and modeling methods

Polyphenols are inhibitors for lipase, but the binding selectivity and mechanism of polyphenol isomers and how they interact with lipase are not clear. Here, chlorogenic acid (CGA) isomers, neochlorogenic acid (NCGA) and cryptochlorogenic acid (CCGA) were used to explore the binding selectivity and mechanism of lipase. An inhibition assay indicated that both CGA isomers had dose-dependent inhibitory effects on lipase; however, the inhibitory effect of NCGA was better (IC50: 0.647 mg/mL) than that of CCGA (IC50: 0.677 mg/mL). NCGA and CCGA formed complexes with lipase at a molar ratio of 1:1, and the electrostatic interaction force plays a major role in the lipase–CCGA system. Molecular dynamics studies demonstrated that NCGA had a greater impact on the structure of lipase. The multi-spectroscopic and modeling results explained the effects of micro-structural changes on the binding site, the interaction force and the inhibition rate of the isomers when they combined with lipase.

Implantation of heat treatment Ti6al4v alloys in femoral bone of Wistar rats

Two heat treatments were carried out at below (Ti6Al4V800) and above (Ti6Al4V1050) the beta-phase transformation temperature (TTRANSUS = 980 °C), to study the effect of microstructural changes on osseointegration. The alloys were implanted in the femurs of hind legs of Wistar rats for 15, 30, and 60 days. Histology of the femur sections obtained for the first 15 days showed inflammatory tissue surrounding the implants and tissue contraction, which prevented osseointegration in early stages. After 30 days, trabecular bone, reduction of inflammatory tissue around the implants, and osseointegration were observed in Ti6Al4V as received and Ti6Al4V1050 alloys, while osseointegration was detected for the three alloys after 60 days. These results were supported through morphometric studies based on the analysis of Bone Implant Contact (BIC), where there was a larger bone contact after 60 days for the Ti6Al4V1050 alloy; indicating that microstructural features of the Ti6Al4V alloys influence their osseointegration, with the lamellar microstructure (Ti6Al4V1050), being the most responsive.Graphical abstract

Mechanical responses of Semi-crystalline thermoplastic polymers at various temperatures

This study examines the mechanical responses of three semi-crystalline POM polymers under uniaxial tension and compression loadings with various loading histories and at different temperatures. The studied POM polymers show variations in their molecular weight and degree of crystallinity with insignificant differences in the lamella thickness. Experimental results indicate that mechanical loadings, even at relatively low strain levels, cause permanent deformations and hysteretic responses, which are attributed to changes in the microstructures of polymers. Tensile and compressive loadings lead to different microstructural changes and elevated temperatures accelerate the changes. The POM polymers also show pronounced viscoelastic responses. A new mathematical model, based on a multi-network approach, is formulated to describe the macroscopic thermo-mechanical response of viscoelastic POM polymers incorporating the net effect of microstructural changes. The model assumes that the polymer has different stress-free configurations associated with different microstructures and the microstructural changes are governed by the deformations of the polymers. The model is shown capable of describing mechanical responses of POM polymers under various loading conditions, loading histories, and temperatures.

Sensitivity to hydrogen induced cracking, and corrosion performance of an API X65 pipeline steel in H2S containing environment: influence of heat treatment and its subsequent microstructural changes

In this investigation, the effect of microstructural changes and phase equilibria on corrosion behavior and hydrogen induced cracking (HIC) sensitivity of an API X65 pipeline steel was studied. For this purpose, heat treatment was performed at 850 °C, 950 °C, 1050 °C and 1150 °C to engineer the desired microstructure of this pipeline steel. Then, the microstructural evolution was performed by optical microscopy, and Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Corrosion properties were evaluated in H2S environment by open circuit potential (OCP), Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). As well, HIC sensitivity of the API X65 pipeline steel was assessed by hydrogen charging of the cathode and immediately conducting the tensile test. Microscopy analyses showed that the microstructure of the steel is ferritic-pearlitic together with the islands of martensite/austenite constituents. Increasing the heat treatment temperature reduced the amount of pearlite and increased ferrite grain size. It also stabilized the ferrite content. Corrosion results indicated that no active layer was formed on the surface of this pipeline steel. Also, increasing the heat treatment temperature increased the corrosion resistance and reduced sensitivity to micro-galvanic localized corrosion. As well, results suggested that the sensitivity to HIC in the API X65 pipeline was substantially increased with increasing the amount of pearlite and reducing the amount of ferrite; i.e. at lower heat treatment temperature.

Assessing Battery Cell Performance Through 3D Microstructure Simulations

Understanding the effect of microstructural changes on battery cell performance is critical to robust cell design for automotive applications. Mathematical modeling at multiple scales can be utilized to evaluate the relative effect of design changes on the performance of battery cells. These performance metrics can include cell power, instantaneous resistance, propensity towards aging, and lithium plating. Electrochemical modeling of the three-dimensional microstructure of battery cell electrodes also offers the ability to study the effect of active material particle size distribution on the porosity, tortuosity, and transport performance. Volume change in the active material can also be quantified using a microstructure model allowing for comparison to continuum models as well as determination of localized stress-strain effects on mechanical fatigue.In this work we will discuss the performance of a battery cell for automotive applications through the use of microstructure modeling and compare the performance of this microstructure model to that of a typical porous electrode model. Finally, we will evaluate the volume change seen in the microstructure model and compare it to previously published volume change seen in a pouch cell for automotive applications. The governing equations, boundary conditions, and setup of the microstructure model will be discussed, along with considerations for electrode design and the ability of microstructure modeling to discriminate between various cell designs.

Lactation alters fluid flow and solute transport in maternal skeleton: A multiscale modeling study on the effects of microstructural changes and loading frequency.

The female skeleton undergoes significant material and ultrastructural changes to meet high calcium demands during reproduction and lactation. Through the peri-lacunar/canalicular remodeling (PLR), osteocytes actively resorb surrounding matrix and enlarge their lacunae and canaliculi during lactation, which are quickly reversed after weaning. How these changes alter the physicochemical environment of osteocytes, the most abundant and primary mechanosensing cells in bone, are not well understood. In this study, we developed a multiscale poroelastic modeling technique to investigate lactation-induced changes in stress, fluid pressurization, fluid flow, and solute transport across multiple length scales (whole bone, porous midshaft cortex, lacunar-canalicular pore system (LCS), and pericellular matrix (PCM) around osteocytes) in murine tibiae subjected to axial compression at 3N peak load (~320με) at 0.5, 2, or 4Hz. Based on previously reported skeletal anatomical measurements from lactating and nulliparous mice, our models demonstrated that loading frequency, LCS porosity, and PCM density were major determinants of fluid and solute flows responsible for osteocyte mechanosensing, cell-cell signaling, and metabolism. When loaded at 0.5Hz, lactation-induced LCS expansion and potential PCM reduction promoted solute transport and osteocyte mechanosensing via primary cilia, but suppressed mechanosensing via fluid shear and/or drag force on the cell membrane. Interestingly, loading at 2 or 4Hz was found to overcome the mechanosensing deficits observed at 0.5Hz and these counter effects became more pronounced at 4Hz and with sparser PCM in the lactating bone. Synergistically, higher loading frequency (2, 4Hz) and sparser PCM enhanced flow-mediated mechanosensing and diffusion/convection of nutrients and signaling molecules for osteocytes. In summary, lactation-induced structural changes alter the local environment of osteocytes in ways that favor metabolism, mechanosensing, and post-weaning recovery of maternal bone. Thus, osteocytes play a role in balancing the metabolic and mechanical functions of female skeleton during reproduction and lactation.

Thermo-elastic properties in short fibre reinforced ultra-high temperature ceramic matrix composites: Characterisation and numerical assessment

The thermo-elastic properties of a novel class of ceramic composites based on an ultra-refractory matrix and containing short carbon fibre to provide failure tolerance and thermal shock resistance were experimentally characterised and numerically simulated. The composites samples were fabricated with fibre volume fractions ranging from 5 to 60 vol% and were featured by homogeneous dispersion of fibre along the basal plane due to the processing route. A random sequential adsorption algorithm was implemented to generate Representative Volume Elements (RVEs), following which finite element (FE) analyses were conducted to determine the elastic modulus and the coefficient of thermal expansion of the composites . Comparison of the experimental and modelling results showed good agreement for the modulus at low fibre volume fractions, and for CTE at higher volume fractions. Discrepancies are attributed to significant evolution of the composite microstructure upon processing at high temperatures, as revealed by microscopic analysis. The observations emphasise the need to account for the effects of microstructural changes on the constituent properties in the modelling of the thermo-mechanical properties in sintered ceramic composites.

Young’s modulus evolution during sintering and thermal cycling of pure tin oxide ceramics

Pure tin oxide (SnO2) ceramics is well known for its bad sinterability, more precisely for the difficulty to densify without additives by conventional pressureless sintering. This is related to the fact that the sintering mechanisms in pure tin oxide ceramics are non-densifying (surface diffusion at low temperature and evaporation-condensation at high temperature). On the other hand, for the same reason, pure tin oxide ceramics is a very unusual model system that can be used to demonstrate the effects of microstructural changes on effective properties without the otherwise dominating effect of changes in porosity. In this paper we show that pure tin oxide ceramics uniaxially pressed at 50 MPa, pre-sintered at 500 °C and re-sintered at 1000, 1200 and 1400 °C exhibit relative Young’s modulus increases of 30, 70 and 120 % while the porosity remains essentially constant at a value of 51.6 ± 0.7 %.

Interfacial reactions and microstructure related properties of explosively welded tantalum and steel sheets with copper interlayer

This paper presents a comprehensive study of the microstructure-property relationships in Ta and stainless or carbon steel composites, fabricated by explosive welding using Cu interlayer. Employing scanning (SEM) and transmission (TEM) electron microscopy and X-ray synchrotron diffraction, a complex microstructure of interfacial layers was examined. Particular attention was placed on the description of the phase transformation mechanisms in the reaction regions, and the competition between the strain-hardening and softening processes in parent sheets. SEM and TEM analyses showed that Cu and Ta nanoparticles, and small dendrites, dominated the reaction regions near the Ta/Cu interfaces, whereas the nano-grained phases having more complex chemical compositions were identified near the Cu/steel interfaces. SEM orientation mapping revealed that the interfacial layers of the parent sheets underwent severe plastic deformation as a result of dislocation slip, twinning, and shear banding. Such heavily deformed areas can easily undergo recovery and recrystallization already during clad processing. In consistence with these findings, the micro-hardness values of the welded sheets increased as the joining interface approached, except for the layers directly adhering to large reaction regions, where a decrease in micro-hardness was observed. However, the solidified melt regions were essentially softer than the strain-hardened layers of both steels. Based on experimental results a new explanation for the reaction region formation was proposed and a significant modification of the description of the interfacial microstructure of parent sheets was done. Finally, the effect of microstructural changes on the clads properties was discussed.

Experimental and numerical investigation of the effect of microstructural changes on the vibrational characteristics of ck35 steel

This study aims to identify the microstructural changes of metal by measuring its natural frequency and damping loss factor. For this purpose, six CK35 steel specimens with ferritic-pearlitic structure were prepared and then, four specimens were spheroidized to significantly change microstructures. Subsequently, the modal testing was applied to determine the vibrational characteristics of specimens with ferrite-pearlite and spheroidized structures, which were identical in terms of size and weight. Experimental results indicated that the dispersion of spheroidized carbides in the ferritic matrix could increase natural frequencies and damping loss factors, such that changing the microstructure of specimens increased the natural frequency and damping loss factor of the first vibration mode by 0.4 (from 3732 to 3747 Hz) and 15%, respectively. Finally, a microstructure-based finite element model was developed to interpret experimental results. The representative volume element (RVE) was modeled using image processing and writing scripts in ABAQUS/CAE 2016. The statistical analysis of stresses calculated by finite element analysis confirmed the results obtained by experimental tests. The numerical results showed that changing microstructures led to considerable changes in stress statistical dispersion, although the mean stress value did not change. Ultimately, the approximate formula of stress-damping could explain significant changes in the damping loss factor.

Grain boundary blocking effects in Sm/Yb-doped AlN ceramics

The effect of microstructural changes on the electrical and thermal properties of AlN ceramics is studied in terms of cation size and nature of sintering aids (i.e. Sm2O3 and Yb2O3) in AlN ceramics. It is revealed that the addition of Yb2O3 to Sm-bearing AlN ceramics results in 80 % reduction of thermal conductivity with an increase of the grain boundary resistivity that is one order of magnitude larger than for the sample without Yb2O3. Additionally, the grain boundary/grain resistivity ratio is significantly increased, when the Sm2O3 sintering aid is employed instead of Yb2O3, for which the secondary phases at the grain boundaries and the triple junctions are responsible for the increase in the electrical resistivity. The microstructural investigations confirm the tendency of the secondary phase to segregate at the triple junctions in Sm-containing AlN ceramics while it is grain boundaries that are favored as segregation site in the case of Yb.

Effect of microstructural change on cutting force fluctuation

Machining of aerospace and biomedical grade titanium alloys such as Ti6Al4V is always a challenge due to their low thermal conductivity and elastic modulus. Formation of localized shear bands during machining of Ti6Al4V alloy results in chip segmentation, which causes force variation on the cutting tool. An unconventional way is followed to study the effect of microstructural changes on cutting forces while machining Ti6Al4V alloy. Microstructure of the material was altered using static annealing and laser heat treatment. For static annealed material the study was focused on the effect of microstructure on machinability of Ti6Al4V alloys at different cutting speeds. The variation in force was observed to be smallest in the case of lower grain size samples subjected to machining.

The Effect of Microstructural Changes on Mechanical and Electrochemical Corrosion Properties of Duplex Stainless Steel Aged for Short Periods.

This work reports the effects of Microstructural changes due to the secondary phases, in particular sigma (σ), on the mechanical properties and electrochemical behavior of thermally aged duplex stainless steel (DSS). Structural, morphological, mechanical, and electrochemical characterizations were performed. Sigma phase content increased with increasing aging treatment time. It had a net-like shape, as observed by electron backscatter diffractometry (EBSD). Its presence directly damaged mechanical properties. The corrosion assessment included electrochemical impedance spectroscopy (EIS) in 1 M NaCl solution at temperatures of 25, 40, and 65 °C. EIS results demonstrate that an increase in the σ phase content decreased the corrosion resistance (21.1–0.8, 3.5–0.3, and 3.1–0.2 kΩ cm2 at 25, 40, and 60 °C, respectively).

Effect of microstructure change on resistance of spherical LiCoO2 to electrode degradation for proton intercalation

Lithium cobalt oxide (LCO) with layered crystal structure suffers the structural proton intercalation in aqueous electrolytes of low pH values, little information is available about the effect of microstructure change on the cycling stability of LCO in response to the proton intercalation. In this work, electrochemical properties of three kinds of LCO spheres with different microstructures are studied in neutral aqueous 0.5 M Li2SO4 solution. The investigated materials were obtained by calcining the spherical LCO precursors at various temperatures, which were synthesized via a modified solid phase method for lithiation of spherical Co3O4. Structure and morphology of materials were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The spherical LCO prepared at lower temperature shows more superior electrochemical stability. Herein, the resistance of spherical LCO with a particular microstructure to the electrode degradation for the proton intercalation can be measured by the frequency of occurrences of greater-than-100% coulombic efficiencies during cycling. Meanwhile, the capability of retaining the capacity contribution from the order-to-disorder transformation of lithium ions on the hexagonal lattice of host site after the first-order phase transition was proposed to compare and investigate the cyclability of the three kinds of spherical LCO with different microstructures.

Abnormal Evolution of Pitting Behavior of Warmly Pre-Strained Austenitic Stainless Steels

The effect of warm pre-strain on the corrosion behavior of 304 and 316 steels in 3.5% NaCl solution was first explored by electrochemical tests, passive film characterization, and structural analysis. The pitting corrosion resistance of 304 steel decreases with the increase of strain level below 20% and increases with the strain at a higher strain level, while the pitting corrosion resistance of 316 steel increases slightly with the increase of strain level below 20% and decreases with the strain at a higher strain level. The random grain boundaries in 304 steel are interrupted with the increase of strain level higher than 20%; this does not occur in 316 steel, which exhibits more dislocations. The coupling effect of microstructure changes induced by warm pre-strain affects the oxide content of the passive film, especially for the chromium oxide, which results in abnormal corrosion behavior. Knowing the corrosion mechanism is of value for academic research and enables the design of advanced stainless steel with high strength and corrosion resistance.