Effect Of Microstructural Changes Research Articles

Effects of polytetrafluoroethylene treatment and compression on gas diffusion layer microstructure using high-resolution X-ray computed tomography

The microstructure of a TGP-H-120 Toray paper gas diffusion layer (GDL) was investigated using high resolution X-ray computed tomography (CT) technique, with a resolution of 1.8 μm and a field of view (FOV) of ∼1.8 × 1.8 mm. The images obtained from the tomography scans were further post processed, and image thresholding and binarization methodologies are presented. The validity of Otsu's thresholding method was examined. Detailed information on bulk porosity and porosity distribution of the GDL at various Polytetrafluoroethylene (PTFE) treatments and uniform/non-uniform compression pressures was provided. A sample holder was designed to investigate the effects of non-uniform compression pressure, which enabled regulating compression pressure between 0, and 3 MPa at a gas channel/current collector rib configuration. The results show the heterogeneous and anisotropic microstructure of the GDL, non-uniform distribution of PTFE, and significant microstructural change under uniform/non-uniform compression. These findings provide useful inputs for numerical models to include the effects of microstructural changes in the study of transport phenomena within the GDL and to increase the accuracy and predictability of cell performance.

미세구조 해석을 통한 고농축 복합화약 시뮬란트의 유변물성 예측

고분자 결합제로 vinyl acetate(VA) 함량이 각각 30, 60%인 poly(ethylene-co-vinyl acetate)(EVA)를 사용하여 고농축 복합화약 시뮬란트의 유변학적 특성을 연구하였다. 충전제로는 탄산칼슘 및 research department explosive (RDX)와 물리적 특성이 유사한 Dechlorane을 사용하였다. 회분식 용융 혼련기를 사용하여 농축 현탁계를 혼련하였는데 최대 75 v%까지 충전이 가능하였다. 동적 기계적 물성 변화를 측정한 결과 Dechlorane이 탄산칼슘보다 결합제수지와 더 높은 상호작용을 보였다. 일정 전단속도 방식과 일정 전단응력 방식의 평판-평판 레오미터를 사용하여 현탁계의 미세구조의 변화가 유변물성에 미치는 영향을 조사하였고, Krieger-Dougherty 식을 사용하여 최대 충전 부피분율 및 고유점도를 구하였다. EVA31/Dechlorane 현탁계의 최대 충전 부피분율은 약 70 v%이고, 혼련시 전단응력이 약 2000 Pa 정도 부가되는 것이 적절함을 알 수 있었다. The rheological properties of highly concentrated polymer bonded explosive simulant were studied by using poly(ethylene-co-vinyl acetate) with 30 and 60% vinyl acetate (VA) content as a binder, respectively. Calcium carbonate and Dechlorane, whose physical properties are similar to resarch department explosive (RDX)'s, were used as fillers. The suspensions were mixed in a batch melt mixer and it was possible to fill 75 v% at maximum. From dynamic mechanical analysis, Dechlorane showed higher interaction with binder resins than that with calcium carbonate fillers. The effects of microstructural change on the rheological properties of the suspensions were investigated by a plate-plate rheometer with constant shear rate and constant shear stress modes, respectively. The theoretical maximum packing fraction of EVA31/Dechlorane suspension obtained from Krieger-Dougherty equation was 70 v% and it was thought that 2000 Pa was proper shear stress condition for this melt processing.

Influence of Sintering Temperature on the Translucency of Sintered Zirconia by Cold Isostatic Pressing

Zirconia-based ceramics exhibit excellent mechanical properties and biocompatibility in dental applications. However, the production of translucent zirconia that offers resemblance to real teeth remains a challenge. This study aims to fabricate zirconia compacts by cold isostatic pressing (CIP) and investigate the influence of sintering temperature on translucency, microstructure, hardness, and density of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). Zirconia stabilized with 3 mol% yttria (3Y-TZP) was pressed by uniaxial pressing and later by CIP to produce green bodies in pellet form. Subsequently, the green bodies were sintered at different temperatures (1100 °C to 1300 °C). The specimens were then investigated in terms of translucency, density, and hardness. X-ray diffraction was also performed and the microstructure of the specimens was observed under a scanning electron microscope (SEM). Density and light transmittance tests results showed that zirconia sintered at 1200 °C exhibits the highest density (5.957 g/cm3) and light transmittance intensity. Vickers hardness test showed that higher sintering temperatures result in higher hardness of the sintered zirconia. SEM micrographs illustrate the effect of microstructural changes on the translucency of zirconia. A temperature of 1200 °C is found to be the recommended sintering temperature at which zirconia exhibiting optimum translucency and mechanical properties is produced. CIP is found to be a suitable consolidation method to produce high-density translucent zirconia.

Instability in wear mechanism and its relevance to microstructural features in cryotreated T42

This paper investigates effect of microstructural changes in AISI T42 that occurred due to cryogenic treatment on the material properties such as wear behaviour, hardness and impact energy. Specimens of T42 were hardened in the salt bath at 1215°C, tempered four times in salt bath at 550°C followed by air cooling. All specimens were cryotreated at −185°C for varying length of cryosoaking periods followed by soft tempering at 100°C. Samples characterised for residual stress, carbide density, hardness, impact energy and wear volume. An optimum cryosoaking period of 8 h was established with appreciable combination of carbide density, hardness and dramatic reduction in wear rate by 58%. Morphology of carbides and merging of ultramicroscopic W rich and V rich carbides at higher cryosoaking period on material properties was analysed. Microstructural changes at subsurface has been correlated in light of prevailing the wear mechanism and operative wear modes.

The effects of microstructural changes on montmorillonite–microbial interactions

Clay minerals are important natural adsorbents of soil organic matter (SOM) and therefore are natural modulators of soil-atmospheric carbon fluxes. Although such effects have been reported, little is known about the spatial distribution of organic matter (OM) on the surfaces of soil minerals and even less is known about the effects of microstructural changes on clay–organo interactions. Here we employ acid hydrolysis to induce varying degrees of microstructural changes to montmorillonite clay mineral as a function of time and combine IR spectroscopy, X-ray diffraction, and SEM-EDX as primary techniques to independently provide molecular-level information on the effects these changes on microbial interactions with the mineral. We observed that progressive dissolution of octahedral cations and the simultaneous enrichment of amorphous silica are prominent structural changes induced by hydrolysis, and that the adsorption of microbial-derived components (in particular lipids) on the surfaces of acid-treated clay decreases with increasing acid dissolution time. Although the precise mechanism(s) of interactions remains unclear, we speculate that this adsorption behavior is most likely due to spatial co-variation of microbial-derived OM with octahedral cations in the mineral, acid erosion of biochemically active binding sites, and/or a progressive increase in the hydrophilicity of the mineral surfaces by acid attack over time.

Effects of microstructure changes on the superplasticity of 2205 duplex stainless steel

The high temperature deformation behavior of 2205 duplex stainless steel under different conditions had been studied by tensile tests. The whole tensile test was conducted at a constant temperature 950°C with an initial strain rate 1.5×10−3/s. Some tests were interrupted purposely and then the samples were quenched using water. Elongations of the fractured specimens were calculated. Microstructure changes just before and during the deformation were observed. Phase ratio of σ precipitate was analyzed. The results showed that the superplasticity of 2205 duplex stainless steel was directly affected by the microstructure before the deformation. The recrystallization phenomenon was distinct along with the homogenizing time and the grains became equiaxed and stable. Meanwhile, the quantity of σ phase increased when prolonged the homogenizing time. After homogenized for 7min before the tensile test, the σ phase ratio was about 4.8% and the grain size was about 998nm, the maximum elongation value 1260% was obtained. During the deformation progress, dynamic recrystallization was observed and quantity of σ phase increased with the increasing of deformation strain. The σ phase restricted the grain growth and kept the equiaxed duplex structure stable with a grain size of about 1μm.

Corrosion Behavior of Ultra Fine Grain Copper Produced by Accumulative Roll Bonding Process

In this study the effect of microstructure changes on the corrosion behavior of pure tough pitch copper in 3.5 % NaCl solution with pH = 5.5 at ambient temperature was studied. Accumulative roll bonding process as severe plastic deformation was applied up to 8 cycles to produce the ultrafine grain copper. For corrosion resistance investigations, the polarization and electrochemical impedance spectroscopy was used. Corrosion morphologies analyzed by FE-SEM microscopy after polarization and immersion tests. Results show the minimum corrosion resistance for cycle 2 and maximum corrosion resistance for cycle 8. Corrosion rate of copper decreased after it was rolled for forth time. The corrosion degradation in cycle 8 was uniform and it was intergranular for sample of cycle 2 and unrolled counterpart. The higher corrosion rate in cycle 2 was attributed to unstable microstructure and the uniform corrosion of cycle 8 was due to ultra fine grain formation.

3527/4343 알루미늄 클래드재의 인장 및 침식특성에 미치는 미세조직 제어의 영향

Aluminum clad sheets for brazing materials in the automotive heat exchangers are required to exhibit both high strength and excellent erosion resistance. In this study, the effects of microstructural changes on the property of clad sheets due to thermomechanical treatment were investigated. The clad sheets were fabricated by roll bonding of twin-roll-cast AA3527 and AA4343 alloys followed by cold rolling down to a thickness of 0.22mm. Partial or full annealing was conducted at the final thickness in order to improved the erosion resistance while keeping the proper strength. Since full annealing was achieved for a temperature of <TEX>$400^{\circ}C$</TEX>, annealing treatments were performed at 360, 380, and <TEX>$400^{\circ}C$</TEX>, respectively. The tensile strength of 3527/4343 clad material was found to be inversely proportional to the annealing temperature before the brazing heat treatment. After this latter treatment, however, the tensile strength of the clad material was about 195~200MPa regardless of the annealing temperature. The erosion depth ratio of the clad annealed at <TEX>$400^{\circ}C$</TEX> was 8.8% (the lowest), while that of the clad annealed at <TEX>$380^{\circ}C$</TEX> was 17% (the highest). The effect of annealing temperature on the tensile and erosion properties of 3527/4343 aluminum clad sheets was elucidated by means of microstructural analyses.

Mechanical, Metallurgical Characteristics and Corrosion Properties of Equal Channel Angular Pressing of Duplex Stainless Steel

Duplex Stainless Steel (DSS) is well known for their higher mechanical strength and better corrosion resistance. DSS is commonly used for marine construction, petrochemical and chemical industries. DSS (2205) is having equal amount of α and γ phases.The present study was conducted on12mm diameter rod of the UNS S32205 duplex stainless steel subjected to equal channel angular pressing (ECAP). The refinement of original grains was observed. Effect of microstructure change on the corrosion behavior of equal channel angular pressed (ECAP) UNS S32205 duplex stainless steel was investigated. After single pass ECAP process and study about the pitting corrosion resistance. The mechanical properties of UNS S3 2205 duplex stainless steelwere evaluated. The amount of ferrite after ECAP and before ECAP for the two different conditions was investigated. Also observed percentage of ferrite content reduces 3.32% after ECAP.

Relationship analysis of processing parameters with micro and macro structure of silica aerogel dried at ambient pressure

In the present study, tetraethoxysilane (TEOS) aerogel was produced by a two-step catalytic process at ambient pressure drying under different synthesis conditions. The relationship of the key processing parameters such as EtOH/TEOS, H2O/EtOH molar ratios and synthesis temperature with micro and macro structures of the synthesized aerogel has been analyzed. The effectiveness degree of each key processing parameter in the microstructure and then the effects of microstructure changes on the morphology and physical properties including the density and porosity were also evaluated.The results apparently showed that the processing temperature presented the highest effectiveness on the pore structure, porosity and density of the synthesized aerogels. Synthesizing at the temperature of 30°C gave rise to a dense structure with very small pore size (3nm) and porosity of 59% which exhibited a type-I adsorption–desorption isotherm. Other processing parameters affected the micro and macro structure but their effects were less significant compared to the temperature effect.

Dynamics of complex fluid-fluid interfaces

EXTENDED ABSTRACT Surface rheological properties like surface shear viscosities, or surface dilatational moduli often play an important role in the stability and dynamic behavior of emulsions, foam, biological fluids, liquid jets, coatings flows, or immiscible polymer blends [1]. This is particularly true when the interfaces in these systems have a complex microstructure, for example, when the surface active components stabilizing the interface form a 2d gel phase, a 2d glass phase, or 2d (liquid) crystalline phase. Such 2d mesophases are typically formed when interfaces are stabilized by colloidal particles, proteins, protein aggregates, proteinpolymer complexes, or amphiphilic polymers [1]. Applied deformations induce changes in the microstructure of the interface, and the resulting changes in surface rheological properties (such as surface shear thinning, shear thickening, or thixotropic behavior) affect the behavior of the multiphase system on a macroscopic scale. Most currently available constitutive models for the surface extra stress tensor either do not account for the strain (rate) dependence of surface rheological properties, or are appropriate only for infinitesimally small rates, where departures from linear behavior are very small [1]. In this paper we will discuss recent advances in the development of nonlinear constitutive equations for the stress-deformation behavior of fluidfluid interfaces in the framework of nonequilibrium thermodynamics. We will focus on two frameworks: the classical irreversible thermodynamics (CIT) framework, and the general-equation-for-the-nonequilibrium-reversible-irreversiblecoupling (GENERIC) framework. We will illustrate the construction of surface rheological constitutive equations within these two frameworks for a specific example: interfaces stabilized by anisotropic colloidal particles, in the dilute particle concentration regime. In both frameworks we construct models describing the effect of microstructural changes on the nonlinear response of an interface to a deformation through a dependence of the surface stress tensor on a set of scalar and a tensorial structural variables. We present the time evolution equations for these structural variables, and evaluate the ability of these types of models to describe the shear thinning behavior typically observed experimentally for such interfaces. We compare the models in both simple and oscillatory shear. We find that both frameworks allow us to construct nonlinear expressions for the surface extra stress tensor capable of describing shear thinning behavior, but the CIT model gives realistic predictions only for small departures from equilibrium, whereas the GENERIC framework allows us to create models valid also far from equilibrium. Besides giving more accurate predictions for the shear thinning behavior the GENERIC model also predicts the existence of in-plane normal stresses (normal to the direction of flow), and effect of which its existence has been hypothesized, but that has so far not been observed experimentally. These results show that microstructural models developed using nonequilibrium thermodynamic frameworks provide a valuable tool for the analysis of the highly nonlinear dynamics of multiphase systems with complex liquid-liquid interfaces.

Deposition Behavior and Microstructural Features of Vacuum Kinetic Sprayed Aluminum Nitride

The vacuum kinetic spray (VKS) method is a relatively advanced technology by which thin and dense ceramic coatings can be fabricated via the high-speed impact of submicron-sized particles at room temperature. However, the actual bonding mechanism associated with the VKS process has not yet been elucidated. In this study, AlN powders were pretreated through ball-milling and heat-treatment processes in order to investigate the effects of microstructural changes on the deposition behavior. It was found that ball-milled and heat-treated powder with polycrystals formed by partially aligned dislocations showed considerably higher deposition rates when compared to only ball-milled powder with tangled dislocations. Therefore, in the VKS process, the deposition behavior is shown to be affected by not only the particle size and defect density, but also the microstructure of the feedstock powder.

Investigation of Portevin–Le Chatelier Effect in Al-2.5 pct Mg Alloy with Different Microstructure

An experimental study is presented on the effect of microstructure change on the Portevin–Le Chatelier (PLC) effect of Al-2.5 pct Mg alloy. Tensile tests are performed on as-received and heat-treated [at 673 K (400 °C) for 16 hours] samples for a wide range of strain rates. The serrations observed in the stress–time curves are investigated on statistical analysis point of view. The microstructures of the samples are characterized by optical metallography, X-ray diffraction, and electrical resistivity measurements. It is found that the excess vacancies generated due to heat treatment have an effect on the PLC phenomenon, which leads to a decrease in the strain rate sensitivity and an increase in the number of stress drop occurrences per unit time. The microstructural parameters like domain size and dislocation density have no appreciable effect on the PLC effect as far as the statistical behaviors of the serrations are considered.

Effect of microstructure changes on magnetic properties of spark plasma sintered Nd-Fe-B powders

In this study the SPS method was applied for low RE content (8,5% at.) and high RE content (13,5 % at.) MQ powders. The powders were sintered in a wide range of temperature, for 5 min., under pressure of 35 MPa. The low RE content grade, densified reluctantly and gained the density close to the theoretical value only for 850 °C. The coercivity decreased gradually with increasing sintering temperature. On the other hand, the densification of the higher RE content grade powder occurred much easier and the coercivity, close to the theoretical value, was achieved already at 650 °C. The coercivity of this material also decreased with increasing sintering temperature. Microstructural studies revealed that the SPS sintering process leads to partial decomposition of the Nd2Fe14B phase. The proportion of the RE-rich and iron phases increases parallel to the increasing sintering temperature. On the basis of the current results one can conclude that fabrication of high density MQ powders based magnets by the SPS method is possible, however the powders having higher RE content should be used for this purpose and the sintering temperature as low as possible, related to density, should be kept.

Micro-structural changes of Zn–Al alloy influencing micro-topographical surface in micro-cutting

This study investigates the effects of micro-structural changes of Zn–Al alloy induced by ultra-precision diamond turning under various depth of cut on surface topography, using the X-ray diffraction technique, back-scan electron microscopy, and surface measurement instrument. It is found that as micro-structural changes of the machined surfaces occurred, depth of cut promotes the micro-structural changes that simultaneously ensue and enhance uncertainty and fluctuation of surface topography relating to material swelling, recovery and pile-up, and surface roughness. The surface material property changes significantly contribute to surface micro-topography.

Effects of Microstructural Changes by Injection Velocity Variations on Conductivity in Polyaniline-Based Polymer Blends

Polyaniline doped with dodecylbenzenesulfonic acid (PANI-DBSA)/high-impact polystyrene (HIPS) blends were injection molded with increasing velocity, in order to understand how shear stress-induced microstructural changes influence polymer conductivity. The results showed the changes in the chain conformation from a compact coil to an expanded coil in PANI, increased degree of polymer orientation along the flow direction, and increase in the degree of crystallinity on the skin, but not on the core with increasing injection velocity. The blends, in which the microstructure is anisotropic, exhibited anisotropic conductivity between the skin and core (σskin/σcore).

Investigation of the age hardening and operative deformation mechanism of 7075 aluminum alloy under creep forming

Creep forming is a process where plastic deformation is applied at the material's ageing temperature. In order to study the effect of microstructure changes on the hardening and creep deformation behavior of 7075 aluminum alloys, creep forming experiments have been performed at temperatures of 150°C and 190°C for 6–72h. Results indicated that with increasing of forming time and temperature the size of globular shaped phase (known as GP zones) increased and transformed into η′ precipitates. Meanwhile, the η-MgZn2 phase with almost the same size formed along the grain boundaries with quite narrow precipitate free zones. Further increasing of forming time, led to a decrease in the number of η′ precipitates and an increase in precipitate spacing, where the large equilibrium η phase formed and the precipitate free zones became wider. Moreover and creep curves can be divided into two stages. During the first stage, higher creep rate occurred, which increased with temperature but decreased with forming time. While during the second stage, the creep rate reached its lowest value and kept constant. The variations of hardness and creep strain have been discussed in detail by taking account of the evolution of precipitate microstructure.

Microstructural characterization of non-equilibrated 4D carbon/carbon composites in ultrahigh temperature environment

A comparative study has been carried out on microstructure, ultrahigh temperature tensile properties, and erosion behavior of non-equilibrated four-directional reinforced carbon/carbon composites, prepared using polyacrylonitrile based carbon fibers as the reinforcement and coal-tar pitch as the matrix, to assess the effect of microstructural changes on the properties of the composites in an ultrahigh temperature environment. X-ray diffraction and scanning electron microscopic analyses suggest that the carbon matrix is highly graphitized, which is composed of mosaic and domain structures. The composites retain superior tensile properties with a visco-plastic behavior at ultrahigh temperature, which is consistent with the observation of mixed microstructural changes, crack propagation, and deflection as well as fiber debonding. The ablation behavior of non-equilibrated four-directional reinforced carbon/carbon composites is mainly dominated by thermo-chemical ablation and mechanical erosion, and different microstructures exhibit distinguished erosion mechanisms.

The Effect of Microstructural Changes Induced by Annealing on Mechanical Properties of FeCoCrMoCBY Bulk Glassy Alloy

Bulk metallic glasses have interesting mechanical properties, such as high strength up to 5 GPa, high elastic strain and many other additional desirable properties. However, BMGs beyond the elastic region fail catastrophically on one dominant shear band and show little macroscopic plasticity in an apparently brittle manner. Nano-crystallized BMGs have been found to possess better ductility comparing with brittle parent BMGs. Annealing treatment of glassy alloys is a useful method to prepare bulk nano-crystalline alloys. In the present study, the crystallization trend of the FeCoCrMoCBY alloy which is claimed to have the best glass forming ability was studied in various times in temperature ranges of a) between Tg (glassy temp.) and Tx1 (first crystallization temp.), and b) between Tx1 and Tx2 (second crystallization temp.). The influences of different annealing time and temperatures on the microstructure and microhardness of Fe41Co7Cr15Mo14Y2C15B6 BMG are reported in this paper.

Effect of Microstructure Change on the Mechanical Properties in Hot-Forged Ultra High Carbon Steel

Effect of Microstructure Change on the Mechanical Properties in Hot-Forged Ultra High Carbon Steel