Effect Of Microstructural Parameters Research Articles

Microstructure-dependent mechanical properties of an electron beam welded Ni-Co based superalloy

The microstructure gradient of electron beam welded Ni-Co based superalloy was investigated. In-situ tensile test and micro-hardness measurement were performed to analyze the microstructure-dependent mechanical properties. The temperature gradient during welding process resulted in obvious changes in grain size, γ' volume fraction and dislocation density at the weld joint. The mechanical properties were influenced by the microstructure evolution, while the effects of microstructure evolution on micro-hardness and Young's modulus were different. Effects of microstructure parameters on the strengthening mechanisms and mechanical properties were analyzed in detail.

Effect of Microstructure Parameters on Mechanical Properties of Cold-Rolled, Niobium-Microalloyed Steels after Continuous Annealing

Effect of Microstructure Parameters on Mechanical Properties of Cold-Rolled, Niobium-Microalloyed Steels after Continuous Annealing

The effects of microstructural parameters on the tension-compression mechanical behavior of extruded Mg-XY rods using crystal plasticity finite element modeling

In the present study, the effects of rare earth element Y, texture intensity, and grain size on the tension-compression mechanical behavior of extruded Mg-XY(X = 0–3, wt pct) rods were investigated using improved phenomenological crystal plasticity. To this end, finite element modeling of a three-dimensional representative volume element (3D-RVE) was employed to consider the effects of microstructural parameters. Subsequently, the computational modeling approach was validated with the experimental data to assess the reliability of predictions of the responses of a polycrystalline aggregate. Afterward, the validated computational modeling was employed to predict the mechanical behaviors of extruded Mg-XY (X = 0–3, wt pct) by considering the role of slip/twinning activities during deformation. The results showed that the Y addition significantly improved the yield strength, ultimate strength, and ductility. Examination of the deformation modes activities indicated that the basal slip activity of extruded Mg-XY (X = 1–3, wt pct) is higher than that of extruded pure Mg due to the formation of non-basal texture components, which hindered the twinning activation. Increasing the Y content further reduced the suppression of tensile twinning activity. Therefore, the weak tension–compression yield asymmetry of extruded Mg-XY (X = 1–3, wt pct) was mainly attributed to the reduced tensile twinning activity. The simulated stress-strain curves illustrated that texture weakening, and grain refining improved the mechanical behavior and reduced tension-compression yield asymmetry.

Effect of Microstructural Parameters on Channel-Type Segregation Formation in DC Casting of Al–Mg Billet

Effect of Microstructural Parameters on Channel-Type Segregation Formation in DC Casting of Al–Mg Billet

Achieving High Strength-plasticity of Nanoscale Lamellar Grain Extracted from Gradient Lamellar Nickel

Traditional metallic materials usually face a dilemma between high strength and poor strain hardening capacity. However, heterogeneous structured metallic materials have been found to obviously overcome the trade-off. Herein, gradient lamellar structure was fabricated through ultrasound-aided deep rolling technique in pure Ni with high stacking fault energy after heat treatment. The gradient lamellar Ni was successively divided into the four regions. In-situ micropillar compression tests were conducted in different regions to reveal the corresponding microscopic mechanical properties. Microscopic characterization techniques were performed to explore underlying deformation mechanisms and the effects of microstructural parameters on deformation behaviors. This work demonstrates that the micropillar with near nanoscale lamellar thickness possesses excellent strength and plasticity. On one hand, the reason for high strength of near nanoscale micropillar is that the strength of micropillar increases with the decrease of lamellar thickness according to the Hall-Petch effect. On the other hand, numerous lamellar grain boundaries perpendicular to the loading direction is found to hinder the motion of slip bands, resulting in great strain hardening capacity in the near nanoscale lamellar micropillar.

Crack Initiation and Propagation in Dual-phase Steels Through Crystal Plasticity and Cohesive Zone Frameworks

Ferrite-martensite dual-phase (DP) steels have become popular in weight-reduced automotive components due to their straightforward thermomechanical processing and excellent mechanical properties. Even though it has been a popular and productive area of research, there are still many open questions related to their interesting microstructure. Being composed of brittle martensitic clusters dispersed in a ductile ferrite matrix, DP steels benefit from the properties of both phases, which induce interesting failure mechanisms at the same time. The microstructural parameters such as martensite volume fraction, grain size, carbon content, martensite/ferrite morphology, ferrite grain size, and texture, as well as micro and mesoscale segregation, make them difficult to analyze. However these aspects have to be studied in order to link the underlying microstructural influence to macroscopic behaviour. Therefore, the modelling techniques at the microstructure scale should be utilized for physical understanding. In this work, a multi scale modeling strategy is followed for the analysis of plastic deformation and failure in DP steels. A rate-dependent crystal plasticity framework and the isotropic J2 plasticity model are employed for the simulation of the plastic deformation in ductile ferrite phase and in the hard martensite phase respectively at the RVE scale. Moreover, the intergranular cracking is studied by the incorporation of a cohesive zone model at the ferrite-martensite grain boundaries and the failure in martensite phase is addressed through a ductile failure model. The effect of microstructural parameters on both plastic and fracture behaviour is analyzed under axial loading conditions.

Numerical Study of Thermal Shock Damage Mechanism of Polycrystalline Ceramics

A dual-scale model is proposed to study the effect of microstructure parameters (grain size and grain boundary fracture energy) on the thermal shock damage mechanism on an example of alumina. At microscale, representative volume element (RVE) models generated by Voronoi tessellation are simulated to obtain the mechanical parameters for macro models. At macroscale, a coupled thermomechanical model based on the finite–discrete element method (FDEM) is applied to simulate the crack nucleation and propagation. Energy dissipation (ALLDMD) is introduced to investigate the thermal shock cracking mechanism by combining crack patterns and crack density, which indicates that decreasing grain size and increasing grain boundary fracture energy have a positive effect on thermal shock resistance. The proposed models not only predict the critical stress temperature which is well consistent to the theoretical thermal shock resistance factor, but also quantify the two previously unconsidered stages (crack nucleation and crack instability stage). Our models suggest the crack nucleation and instability will not occur immediately when the model reaches critical stress, but the models can sustain for higher temperature difference. The thermal shock damage mechanism and the influence of microstructural parameters on thermal shock resistance have also been discussed in detail.

Factors influencing mobility in ITO thin films and the consequent effects on optical and NIR surface plasmon resonance properties

Metal oxide-based plasmonics is an emergent field for which indium tin oxide (ITO) is a promising material. Improving the performance of ITO-based surface plasmon resonance (SPR) sensors requires a deeper knowledge of their optical and electrical properties. The effects of microstructural parameters and defects on mobility, which strongly influences SPR in the near-IR regime was explored. The proposed model incorporates different scattering mechanisms and non-parabolic conduction bands to obtain realistic values of mobility. The results show that larger grain sizes and higher carrier concentrations in ITO thin films improve SPR performance at near-IR wavelengths as low as 1300 nm

Thermoelastic wave and thermal shock based on dipolar gradient elasticity and fractional-order generalized thermoelasticity

In the current work, the thermoelastic wave propagation and the thermal shock problems are studied based on the dipolar gradient elasticity and fractional order generalized thermoelasticity in order to take into account the microstructure effect and the thermal effect at a small scale. First, the fractional-order governing equations for coupled thermoelastic wave propagation are derived and the effects of microstructure parameters and fractional order on the dispersion and the attenuation are discussed; next, the transient problems by the thermal shock and the mechanical shock on the surface of half-space are studied. The Laplace transformation method and the state transfer equation method are used to solve this problem. The numerical results for the temperature, the displacement, the stress and the high order stress distributions are provided and shown graphically. The effects of the fractional order and the microstructure parameter on the thermoelastic behavior are investigated. Some interesting phenomenons and conclusions are presented at last.

The effects of microstructural parameters on the electrochemical properties of LSM-LSCF composite cathode by the particle-based discrete element method

In this paper, the particle packing-based discrete element method is applied to study the correlations between the microstructural parameters and electrochemical performances of LSM-LSCF composite electrodes. Firstly, through the verification of domain size independence and the comparison with the percolation theory, the computational domain size and effectiveness of the particle packing are determined. Then, the changes of the electrochemical reaction sites in the composite electrode with the LSM volume fraction under two different ratios of particle radius are investigated, including the LSM-LSCF-pore three-phase boundaries (TPBs) per electrode volume, TPBs per electrolyte surface, and percolated LSCF-pore double phase boundaries (DPBs). The distribution characteristics of the LSM-LSCF-pore TPBs within and outside the threshold volume fraction zone at different particle size ratio cases are obtained. When the particles are of equal radius, the formation of both percolated e−, O2−, and O2 transport paths is in the LSM volume fraction range of 0 to 0.7, due to the electronic conducting path is fully connected. The distribution characteristics of the LSCF-pore DPBs within the electrode in the percolation area and outside the percolation area are obtained respectively. This work is of great significance for the follow-up study of the physical and electrochemical processes within porous composite electrodes based on large-scale complex morphology.

A crystal plasticity based finite element framework for RVE calculations of two-phase materials: Void nucleation in dual-phase steels

A crystal plasticity based finite element (CPFE) framework is developed for performing representative volume element (RVE) calculations on two-phase materials. The present paper investigates the mechanical response and the evolution of microstructure of dual-phase (DP) steels under uniaxial tensile loading, with a special focus on void nucleation. The spatial distribution and morphology of the ferrite and martensite grains in DP steels are explicitly accounted for by generating three-dimensional RVEs with Voronoi tessellations. The effects of microstructural parameters—the volume fraction, morphology and spatial distribution of the martensite phase, and the grain size and orientation distribution of the ferrite phase—on the initiation and spread of localized plastic deformation (leading to void nucleation) are investigated in detail. The soft ferrite phase is modelled by a local crystal plasticity theory with anisotropic elasticity, and the hard martensite phase by the J2 flow theory with isotropic elasticity. The developed CPFE framework successfully predicts both the overall and the local mechanical response, and is perfectly capable of distinguishing between different void nucleation mechanisms experimentally observed for DP steels.

Substitution of Ni with NiB prevents shape distortion of liquid phase sintered 90W–6Ni–2Fe–2Co heavy alloys

The shape distortion of liquid phase sintered tungsten heavy alloys (WHAs) depends on different factors. Here, the effect of partial and full substitution of Ni with its monoboride (NiB) on distortion characteristics of 90W–6Ni–2Fe–2Co (wt.%) heavy alloy is investigated systematically without changing wt. fraction of W. The phase and microstructural evolution during sintering and effect of microstructural parameters on the distortion is studied. In order to understand the phase and microstructure evolution of the matrix phase of sintered samples, free-standing samples were prepared using the composition of the matrix phase under similar sintering conditions. XRD patterns of sintered sample show characteristic W-peaks along with austenitic matrix phase, whereas, in the case of free-standing samples majority of reflections corresponding to matrix phase (fcc, lattice parameter = 0.360 nm) eliciting a peak shift to slightly higher 2θ values as opposed to those of sintered samples. The FESEM micrographs of free-standing samples reveal microstructure resembling a hypoeutectic system with decreasing inter-lamellar and proeutectic spacing with the extent of NiB substitution. In the sintered 90W–6Ni–2Fe–2Co system, shape distortion resulted in elephant-foot formation (distortion parameter: 22.9). Owing to the partial and full substitution of Ni with NiB, the shape distortion is restricted by formation of uniformly contiguous microstructure, inherent microstructural changes of the matrix phase, increase in dihedral angle, and grain connectivity in partially (90W–3Ni–3NiB–2Fe–2Co) and fully (90W–6NiB–2Fe–2Co) NiB substituted samples, respectively. As a result, the distortion parameter reduces from 22.9 to 9.3 and to 3.7 for partially and fully substituted NiB samples.

The Influence of Microstructural Characteristics on Austenite Formation Kinetics in a Plain Carbon Steel

Since the condition of austenite phase formed during intercritical annealing treatment has a crucial impact on the final microstructure and mechanical properties of dual-phase (DP) steels, detailed investigations with regard to austenite formation in this heat treatment process need to be done. In this study, the effects of different microstructural features, such as ferrite grain size, cementite particle size, and pearlite morphology, on austenite formation in a plain carbon steel (0.165 wt pct C, 1.15 wt pct Mn) during isothermal intercritical annealing treatment have been evaluated. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model was used for modeling the kinetics of austenite formation in this steel during isothermal annealing treatment. The volume fraction of austenite (martensite at room temperature) at different intercritical annealing holding times was calculated by this model using the corresponding results obtained from the experiments. It was found that the starting steel microstructure from which austenite phase is formed has a significant effect on both austenite nucleation and growth. The effect of microstructural parameters on the kinetics of austenite formation in ferrite-cementite steel microstructures was more significant than that in ferrite-pearlite (F-P) steels. An increase in the average cementite particle size or ferrite grain size in ferrite-cementite steels caused a significant decrease in the rate of austenite formation. In F-P steels, on the other hand, pearlite morphology exhibited a small effect on the kinetics of austenite formation while ferrite grain size had a pronounced effect on the rate of austenite formation at the later stage of intercritical annealing, i.e., ferrite to austenite transformation stage.

THE EFFECT OF MICROFRACTURING IN GABBRO-DOLERITES ON THEIR PHYSICAL PROPERTIES

Simple and cheap methods for the study of building stone deposits for the production of blocks of commercial size can be used to make geological work more efficient. However, physical processes in a massif are hard to understand when doing geophysical research, and the effect of microstructural parameters, mainly the microfracturing of rocks, on geophysical field indices is poorly understood.
 The authors have studied the impact of microfracturing on the physico-mechanical properties on coarse- to giant-grained rapakivi granites from the Salmi massif, Fennoscandian Shield. The goal of the present study is to assess the physical and physico-mechanical parameters in fine- and medium-grained quartz-free rocks.
 The authors have studied the various physical and physico-mechanical indices of gabbro-dolerites from the Ropruchei sill (Fennoscandian Shield, within the deposit prospected and revealed the effect of microfracturing indices on them.
 The study of these properties have shown that microfracturing in gabbro-dolerites is an essential factor which forms the physical parameters of a rock. The testing of this rock type has shown the rate of travel of an elastic wave is clearly related to the microfracturing of samples.
 The magnetic properties of gabbro-dolerite are due to high concentrations of titanomagnetite, the mineral grains of which formed upon the crystallization of magma during its interstratal intrusion. The distribution of titanomagnetite, based on size and concentration in the rock, depends on liquation conditions in the active stress field. The dependence of the microfracturing of gabbro-dolerites on their iron concentration (FeO+Fe2O3) shows that these «damages» appeared at a ‘brittle” stage in the evolution of the massif in the form of microfractures, the structural parameters of which have inherited the parameters of the stress and deformation field which existed in the massif at that time and which accumulated iron.
 As a result, microfracturing has a considerable effect on the parameters of the electromagnetic indices of the massif by accumulating iron oxides in the pores, and the higher the index, the higher the geophysical medium indices.
 Understanding of the physical problem, which accompanies the formation of a gabbro-dolerite complex, helps conduct the geophysical study of a massif, interpret data more objectively and more accurately delineate massive zones in the medium that could be used as high-quality building materials.

Modeling Microstructure Effect on Thermal Conductivity of Aerogel-Based Vacuum Insulation Panels

Understanding the effects of microstructural parameters on the heat transfer through an aerogel-based vacuum insulation panel (VIP) is important for the design and development of thermal insulation materials. The present work first prepared the aerogel-based VIP and characterize its microstructure through scanning electron microscopy and nitrogen gas adsorption analysis. A theoretical model for the thermal conductivity of the aerogel-based VIP was then presented and validated with experimental results. Based on the model, the effects of microstructural parameters, i.e. particle diameter and pore diameter, on the thermal conductivity of the aerogel-based VIP were explored. The results indicated an extremely low thermal conductivity with approximately 1.7 × 10−3 W·m−1·K−1 can be achieved as the particle diameter and pore diameter are 1 and 10–15 nm, respectively. Furthermore, the microstructure effect under various service time of the aerogel-based VIP was considered for practical heat transfer engineering. It was found that the increase rate of the thermal conductivity decreases with a decreased particle diameter or an increased pore diameter. The microstructure effect modeling of the aerogel-based VIP could be of great advantage to heat transfer engineering applications aiming to reducing heat loss and saving energy.

Thermal conductivity of unidirectional composites consisting of randomly dispersed glass fibers and temperature-dependent polyethylene matrix

Abstract This extensive study investigated the influence of microstructure on the effective transverse thermal conductivity of unidirectional glass fiber reinforced composites, in which the fibers are randomly dispersed and the thermal conductivity of polyethylene matrix is a function of test temperature. The microstructure is characterized by parameters such as the number of fibers, fiber volume fraction, fiber size, fiber arrangement and thermal property contrast. Firstly, a simple algorithm is developed to automatically generate closest-to-real random array of fibers in unit cell to reconstruct the composite microstructure. Then, the established two-dimensional random two-component composite unit cell is solved using finite element simulation and the obtained effective thermal conductivities are compared with the theoretical predictions and the experimental results. Subsequently, the effects of microstructure parameters and test temperature are investigated, respectively. It is found that the finite element predicted properties are in very good agreement with the experimental predictions, while they are always lower than the analytically predicted properties. These results can find applications in the design of composite materials taking into account the fiber distribution morphology.

Microstructural engineering and strength-impact toughness prediction in ultra-low carbon bainitic steel

ABSTRACTThe strength–toughness combination of an ultra-low carbon, low alloyed ‘air-cooled’ steel has been enhanced by developing and refining the granular bainite (GB) structure. Suitable alloy design and thermo-mechanical treatment involving forging, austenitisation (950–1150°C) and air-cooling resulted in the formation of GB matrix along with small islands of martensite–austenite constituents and allotriomorphic ferrite grains. Microstructural characterisation and phase transformation behaviour were studied by scanning electron microscopy and electron backscattered diffraction analysis. The effect of microstructural parameters on the strength-impact toughness combination was investigated. The steel showed an exceptionally low yield ratio, which is beneficial for seismic resistance application.

Correlation between microstructure and electrical properties of A-site substituted YAlO3 ceramics

The effect of microstructural parameters on the electrical properties of Y1−xCaxAlO3−δ (x = 0.10, 0.20) synthesized by Pechini and solid state routes was studied. A study on the phases formed was conducted using the X-ray diffraction method. Microstructural analyses were performed by scanning electron microscopy coupled energy dispersive X-ray spectroscopy and electron backscatter diffraction techniques. Electrochemical impedance spectroscopy over the temperature range 200–800 °C and frequency range 5 Hz–15 MHz was used to separate the grain interior and grain boundary contributions of the total conductivity. Brick layer model was used to interpret the impedance data. A correlation between the microstructural features and the impedance measurements was attempted to understand the effect of preparation route on the electrical conductivity. The role played by microstructural elements such as grain size, grain boundary area, grain orientation and grain boundary thickness on the electrical behaviour of doped YAlO3 ceramics was investigated.

Microstructural characterization of deformation-induced martensite in an ultrafine-grained medium Mn advanced high strength steel

Microstructural characterization of deformation-induced martensite in its early stage of formation has been performed in an ultrafine-grained (UFG) medium Mn advanced high strength steel (AHSS). By using field emission scanning electron microscope (FESEM) and electron backscattered diffraction (EBSD), the nucleation site of deformation-induced martensite has been studied. Grain sizes, Schmid factors and aspect ratios of the parent austenite grains of deformation-induced martensite were measured in order to know their influence on the formation of deformation-induced martensite. Orientation relationship between deformation-induced martensite and its parent austenite has also been analyzed. Discussion on the effect of microstructural parameters on the formation of deformation-induced martensite in AHSS is given.

Microstructure Optimization of Dual-Phase Steels Using a Representative Volume Element and a Response Surface Method: Parametric Study

Dual-phase (DP) steels have received widespread attention for their low density and high strength. This low density is of value to the automotive industry for the weight reduction it offers and the attendant fuel savings and emission reductions. Recent studies on developing DP steels showed that the combination of strength/ductility could be significantly improved when changing the volume fraction and grain size of phases in the microstructure depending on microstructure properties. Consequently, DP steel manufacturers are interested in predicting microstructure properties and in optimizing microstructure design. In this work, a microstructure-based approach using representative volume elements (RVEs) was developed. The approach examined the flow behavior of DP steels using virtual tension tests with an RVE to identify specific mechanical properties. Microstructures with varied martensite and ferrite grain sizes, martensite volume fractions, carbon content, and morphologies were studied in 3D RVE approaches. The effect of these microstructure parameters on a combination of strength/ductility of DP steels was examined numerically using the finite element method by implementing a dislocation density-based elastic-plastic constitutive model, and a Response surface methodology to determine the optimum conditions for a required combination of strength/ductility. The results from the numerical simulations are compared with experimental results found in the literature. The developed methodology proves to be a powerful tool for studying the effect and interaction of key microstructural parameters on strength and ductility and thus can be used to identify optimum microstructural conditions.