Effect Of Microstructure Research Articles

Multiscale modeling of microstructural and hygrothermal effects on vibrations of CNT-enhanced fiber-reinforced polymer composites

This work presents a multi-scale analytical and computational approach designed to predict the hygro-thermo-mechanical vibrational response of laminated composite structures reinforced with multi-walled carbon nanotubes (MWCNTs). Employing the modified Halpin-Tsai model, this study estimates the elastic properties of the MWCNT-enhanced epoxy matrix, incorporating the impacts of MWCNT agglomeration, orientation, waviness, and size-dependent characteristics. Additionally, the Chamis micromechanical model is utilized to ascertain the independent elastic constants of the nanocomposite lamina, considering environmental variables such as temperature and humidity. Subsequent analysis involves the determination of natural frequencies for both pristine and MWCNT-integrated laminated composite structures via the Finite Element Method (FEM), addressing various design-related parameters. This investigation further explores the macroscopic influences of MWCNT incorporation, boundary condition and layup scheme, along with the temperature, moisture content, and the nanoscopic impact of MWCNTs on the natural frequencies of laminated composite plates. The obtained results of the proposed multiscale modeling are compared with experimental and theoretical observations. It has been demonstrated that while the incorporation of carbon nanotubes (CNTs) can enhance the mechanical properties of nanocomposite laminae, the natural frequencies of these nanocomposite plates are adversely affected by variations in temperature and moisture content. Furthermore, the findings indicate that the microstructural characteristics of CNTs play a crucial role in determining the efficacy of the reinforcement phenomenon. The developed multi-scale methodological framework offers significant potential for the design and optimization of MWCNT-based composite structures across diverse industries, including automotive and aerospace sectors.

Influence of Process Parameters on Selected Properties of Ti6Al4V Manufacturing via L-PBF Process.

This study investigates the microstructural effects of process parameters on Ti6Al4V alloy produced via powder bed fusion (PBF) using laser beam melting (LB/M) technology. The research focuses on how variations in laser power, exposure velocity, and hatching distance influence the final material's porosity, microhardness, and microstructure. To better understand the relationships between process parameters, energy density, and porosity, a simple mathematical model was developed. The microstructure of the alloy was analyzed in the YZ plane using a confocal microscope. The study identified optimal parameters-302.5 W laser power, 990 mm/s exposure velocity, and 0.14 mm hatching distance-yielding the lowest porosity index of 0.005%. The material's average hardness was measured at 434 ± 18 HV0.5. These findings offer valuable insights for optimizing printing parameters to produce high-quality Ti6Al4V components using PBF-LB/M technology, shedding light on the critical relationship between process parameters and the resulting microstructure.

Effect of microstructure on hydrogen uptake in SA 210 grade A1 steel studied using cyclic voltammetry and hydrogen permeation method

Effect of microstructure on hydrogen uptake in SA 210 grade A1 steel studied using cyclic voltammetry and hydrogen permeation method

Study of the fatigue fractography of dual phase low carbon steel used in automotive industry

Fatigue properties play a crucial role as they are vital to ensuring the durability and integrity of components subjected to repeated loading conditions over long periods. The main objective of this work is to investigate the fatigue behavior of dual-phase low-carbon steels used in automotive applications using a rotating bending fatigue machine. Heat treatments were carried out to analyze the microstructure's effect on the fatigue properties, including quenching low-carbon steel samples at 800 °C and 900 °C. Hardness and tensile tests were performed, and the microstructure was inspected to examine the constitute phases. With the assistance of a scanning electron microscope, fractographic analyses were carried out to reveal the fracture features of the samples at different lifetime ranges. The results show that various failure mechanisms occur depending on the stress levels. Additionally, the specimens quenched at 900 °C exhibited higher fatigue strength.

Multifunctional Si3N4-skeleton-reinforced graphite flake composites with preferred orientation integrate excellent mechanical, thermophysical, and electromagnetic shielding properties

Si3N4-skeleton-reinforced graphite flake (GF/Si3N4) composites with preferred orientation were fabricated using a combination of vacuum infiltration and plasma-activated sintering to produce highly oriented graphite-based composites with excellent strength, favorable thermal conductivity, low thermal expansion, and effective electromagnetic shielding properties. The impact of Si3N4 content on the microstructure, bending strength, thermophysical properties, and electromagnetic shielding effectiveness of the composites was systematically examined. The composites exhibited reasonable anisotropy (Lotgering factor f > 93 %), endowing them with high thermal conductivity in the basal plane direction of the GF. The formation of SiC at the Si3N4/GF interface increased the interfacial bonding and effectively suppressed the thermal expansion of GF perpendicular to the basal plane from ∼28 × 10−6/K to ∼8 × 10−6/K. The composite with 21 vol.% Si3N4 exhibited the optimal properties, including a satisfactory bending strength of 128 MPa, good thermal conductivity of 247 W/m/K, a suitable thermal expansion of 9.4 × 10−6/K, and good electromagnetic interference shielding effectiveness of 30 dB. Hence, the fabricated GF/Si3N4 composites demonstrate significant potential as high-orientation graphite-based composites for multifunctional thermal management.

Effect of microstructure rafting on deformation behaviour and crack mechanism during high-temperature low-cycle fatigue of a Ni-based single crystal superalloy

The low cycle fatigue behaviours of a microstructure rafting Ni-based single crystal superalloy have been experimentally investigated at 980 ℃. Deformation of γ/γ’ phases and the corresponding dislocation configurations were investigated, highlighting rafting γ/γ’ morphology that contributes to crack initiation and propagation, as well as macro-scale accumulated plastic strain. Unlike the discrete slip lines of a virgin superalloy, intense slips developed along the parallel {111} slip plane result in crossed slip bands in the rafting superalloy. The decreased resistance of widened γ channels to dislocation movement, along with the prevention of dislocation cutting through γ’ precipitates in pre-existing dense dislocation networks, facilitates crack propagation in the γ channel in the slightly rafting superalloy. As the rafting state increases, the dislocation network loses its protective effect by reducing coherency stress and acting as a superdislocation source, which facilitates crack propagation along the γ/γ’ interface. Finally, a microstructure-based fatigue model is developed considering the reduction of deformation resistance induced by rafting. The fatigue loading control mode effect is introduced by a combination of resolved shear stress and tensile stress effects on crack initiation. The LCF life of rafting Ni-based superalloys significantly decreases under stress-controlled conditions compared to strain-controlled conditions due to the increase in cumulative plastic strain. However, the insignificant impact of the initial surface oxide layer on LCF life is revealed.

Exploring the impact of microstructure refinement on high temperature steam oxidation behavior of FeCrAl alloy

Microstructure refinement is an effective way to improve the mechanical properties and radiation resistance of FeCrAl alloy, which may also increase the susceptibility to high temperature steam oxidation (HTSO) due to the increased surface chemical activity. To investigate the microstructural effects on the HTSO behavior, a FeCrAl alloy was subjected to controlled annealing strategies to produce three types of microstructures: “fine sub-grains + fine precipitates”, “coarse grains + fine precipitates” and “coarse grains + coarse precipitates”. The three alloys were exposed to high temperature steam during a heating and holding procedure. Large oxide nodules and rough multilayer-structured oxide films were formed during heating, which subsequently evolved into a single α-Al2O3 layer during the isothermal oxidation. Microstructure refinement can promote the oxidation and slightly increase the weight gain. However, the variation of isothermal oxidation parabolic rate constants brought by the microstructure refinement is 1-2 orders of magnitude lower than that brought by alloying. Microstructure refinement can improve other service performance of FeCrAl alloy without significantly deteriorating the HTSO resistance, indicating its advantages for engineering applications.

Microstructure effect of mechanical and cracking behaviors on brittle rocks using image-based fast Fourier transform method

Microstructure effect of mechanical and cracking behaviors on brittle rocks using image-based fast Fourier transform method

Effect of plastic deformability and fracture behaviour on interfacial toughening mechanism at Fe/Ni interfaces

Fracture at interface causes plastic deformation in the vicinity region. Conventional plastic energy dissipation theory indicates that ductile vicinity toughens the interface by absorbing plastic deformation energy. However, the microstructure in the vicinity directly affects local plastic deformability and fracture behaviour, implying a more complicated toughening mechanism. In this study, the effect of microstructure and hardness on fracture behaviour of Fe/Ni interface was investigated. By experimental approach, interfaces with and without dynamic recrystallization (DRX) were fabricated by controlling the bonding conditions. It showed that compression-induced plastic deformation is the main source of the hardening behaviour in the vicinity. Moreover, the interfaces with hardened DRX vicinities exhibited improved fracture toughness, which is inconsistent with the plastic energy dissipation theory. To clarify this observation, the crystal plasticity finite element method (CPFEM) approach was employed to distinguish the effects of plastic deformation and interfacial microstructure. The result showed that although higher plastic deformability in the vicinity absorbs more dissipated plastic energy, severe stress concentration at the interface leads to early fracture and poor toughness. On the other hand, the interfacial hardened DRXed grains disperse interfacial stress distribution and provide potential sub-crack sites. A combined result of uniform plastic deformation and fracture energy dissipation is responsible for the improved toughness at interfaces with DRXed grains.

Microstructural Effects on the Mechanical Properties of Ti-6Al-4V Fabricated by Direct Energy Deposition

Microstructural Effects on the Mechanical Properties of Ti-6Al-4V Fabricated by Direct Energy Deposition

Research Progress on Laser Powder Bed Fusion Additive Manufacturing of Zinc Alloys.

Zinc, along with magnesium and iron, is considered one of the most promising biodegradable metals. Compared with magnesium and iron, pure Zn exhibits poor mechanical properties, despite its mild biological corrosion behavior and beneficial biocompatibility. Laser powder bed fusion (LPBF), unlike traditional manufacturing techniques, has the capability to rapidly manufacture near-net-shape components. At present, although the combination of LPBF and Zn has made great progress, it is still in its infancy. Element loss and porosity are common processing problems for LPBF Zn, mainly due to evaporation during melting under a high-energy beam. The formation quality and properties of the final material are closely related to the alloy composition, design and processing. This work reviews the state of research and future perspective on LPBF zinc from comprehensive assessments such as powder characteristics, alloy composition, processing, formation quality, microstructure, and properties. The effects of powder characteristics, process parameters and evaporation on formation quality are introduced. The mechanical, corrosion, and biocompatibility properties of LPBF Zn and their test methodologies are introduced. The effects of microstructure on mechanical properties and corrosion properties are analyzed in detail. The practical medical application of Zn is introduced. Finally, current research status is summarized together with suggested directions for advancing knowledge about LPBF Zn.

Effects of Different Microstructure on Strengthening Mechanism and Hardening Mechanism in Peak-Aged Mg–14Gd–0.2Sn Alloy

Effects of Different Microstructure on Strengthening Mechanism and Hardening Mechanism in Peak-Aged Mg–14Gd–0.2Sn Alloy

Effect of heterogeneous microstructure on the mechanical and corrosion properties of FeCoCrNiMn-(N, Si) high entropy alloy

Effect of heterogeneous microstructure on the mechanical and corrosion properties of FeCoCrNiMn-(N, Si) high entropy alloy

The Effect of Microstructure on Spontaneous Imbibition of Water in Coals

The Effect of Microstructure on Spontaneous Imbibition of Water in Coals

Tailorable piezoelectric and flexoelectric output of a polymer-particle composite

Materials with different combinations of piezoelectric and flexoelectric properties offer multifunctionality and versatility in terms of modes of operation in sensing, actuation, and energy harvesting. We explore a microscopic mechanism for tailoring the macroscopic quasi-static mechanoelectrical output of polymer-particle composites by taking advantage of heterogeneity-induced enhancement of the stress fields and strain gradient fields. The idea focuses on using microscopic inclusions, such as embedded particles and voids, to manipulate the activation and relative contributions of the piezoelectric and flexoelectric effects under different modes of mechanical excitation, such as uniaxial compression and flexural bending. The material system studied is a composite of poly(vinylidene fluoride-co-trifluoroethylene [P(VDF-TrFE)] polymer and nanoaluminum (nAl) particles, or P(VDF-TrFE)/nAl. This system is interesting because P(VDF-TrFE) exhibits both piezoelectric and flexoelectric behaviors and nAl particles have significantly higher elastic stiffness than the polymer. A range of piezoelectric and flexoelectric properties of P(VDF-TrFE) and the stiffness of the particles are considered. Significant microstructural effects are found to enable tailoring of the mechanoelectrical response through microstructure variation. The responses of the composite are quantified using the effective piezoelectric constant (d33,effo) and the effective flexoelectric coefficient (μTR,effo). It is found that the effective macroscopic piezoelectric and flexoelectric behaviors can be changed either independently or simultaneously through different combinations of microstructure attribute changes. The mechanism revealed points out avenues for developing materials with tunable mechanoelectrical behaviors and multifunctionality.

Effect of coating-substrate microstructure on nucleation and growth of surface microcracks in a PtAl-coated Ni-based SX superalloy with sheet specimens during HCF at 900 °C

The fatigue crack initiation process accounts for the main portion of the high-cycle fatigue (HCF) life. Although coated superalloys are well-known to be prone to surface microcracks, the influence of the coating-substrate microstructure on the damage mechanism during HCF of the coated single crystal (SX) superalloys remains unclear. In the current study, HCF failure and interrupted tests were conducted at 900 °C under a low applied maximum stress on a PtAl-coated third-generation SX superalloy using sheet specimens. The HCF crack initiation was investigated by analyzing the evolution of surface microcracks and coating-substrate microstructure. The results show that the surface microcracks nucleation and growth are controlled by the initial microstructure of the coating-substrate region and the oxidation process during the HCF crack initiation stage. The rapid nucleation and growth of the surface microcracks are promoted by grain boundaries (GBs) in the coating and the interdiffusion zone (IDZ). Comparatively, the surface microcracks are blunted by oxidation in the SX substrate due to the loss of GBs, leading to a slower microcrack growth. However, the surface microcracks can gradually grow further into the substrate by repeating the processes as follows: oxidation at the crack tip, formation of γ′-depleted region due to oxidation, recrystallization at the γ′-depleted region and cracking along the GBs in the recrystallized γ′-depleted region. Subsequently, the surface microcracks, which reach the critical size, propagate along the slip bands during the progressive propagation stage. This study will contribute to improve the HCF durability of the PtAl-coated SX superalloy.

Effects of Ti and Nb Additions on Microstructure and Shape Memory Effect of Fe-10Mn-6Si-4Ni-7Cr-0.3C Shape Memory Alloy

Effects of Ti and Nb Additions on Microstructure and Shape Memory Effect of Fe-10Mn-6Si-4Ni-7Cr-0.3C Shape Memory Alloy

Severely weakened extrusion strengthening effect in porthole die extrusion of Al-Mg-Si alloy miniature complex hollow profile under an ultra-large extrusion ratio

Ultra-large extrusion ratio is hardly inevitable during porthole die extrusion of miniature complex hollow profile on industrial horizontal extruders. Although batch extrusion of miniature complex hollow profile has been achieved at ultra-large extrusion ratio, their microstructure and mechanical properties are still unclear. To this end, under the extrusion temperature ranging from 400 ℃ to 480 ℃, a 4×4 mm Al-Mg-Si alloy micro heat pipe profile was extruded at an ultra-large extrusion ratio of 137. The grain size and crystal orientation of the profile were obtained by metallographic and electron backscattered diffraction (EBSD) techniques, and further exploration of the microhardness, tensile properties and pressure-resisting performance were conducted. Interestingly, severely weakened extrusion strengthening effect and low sensitivity of microstructure and mechanical properties to extrusion temperature were observed. Compared to the as-cast extrusion billet, the profile exhibits slight grain refinement and improvement in mechanical performance, and the extrusion temperature does not significantly affect the microstructure and mechanical properties. Instead, as the extrusion temperature increases, the recrystallization fraction generally decreases. These abnormal phenomena are inferred from the fact that even at lower extrusion temperatures, an ultra-large extrusion ratio leads to premature dynamic recrystallization (DRX), and more abnormal growth grains are formed in the profile, weakening the mechanical properties. The higher the extrusion temperature, the earlier DRX occurs, generally forming more abnormal growth and dynamic recovery grains.

Microstructure effects on high velocity microparticle impacts of copper

Constitutive models can fail to predict high-rate deformation behavior due to their inability to account for microstructural effects. In part, this is because of a dearth of experimental benchmarking data in the high strain-rate, low pressure regime, since many high-rate experiments also probe a region of strong shockwaves, at which point microstructure effects no longer play a primary role. This work uses laser-induced particle impact testing to quantitatively study high velocity impacts of small, rigid alumina microspheres on flat copper substrates with varying amounts of initial cold work in the weak shock regime, but at very high strain rates up to ∼107s−1. Through paired experiments and numerical simulations, this work shows that the initial microstructure condition can have significant influence on dynamical mechanical properties in this range. Specifically, prior work hardening of the copper substrate leads to increased rebounding of the microparticles (i.e., less plastic dissipation in the impact) as well as smaller craters. Each of these experimental measurables can be converted into a strength measure, i.e., the dynamic yield strength or dynamic hardness, respectively, neither of which is well predicted consistently by existing constitutive laws. The general trend of hardening can be captured by such models by incorporating an existing “pre-strain,” suggesting that future calibration of the materials parameters may yield a good fit over a broader range of conditions. Our results emphasize the importance of reporting the microstructural condition in dynamic studies, as well as the necessity of accounting for these factors when formulating and optimizing constitutive models.

Effect of prior microstructure on carbide precipitation in a Cr-Mo-V pressure vessel steel at 650 °C

Cr-Mo-V steels are key materials used for constructing thick reactor pressure vessels (RPV) owing to an impressive combination of their mechanical properties and weldability. Conventionally, these steels are subjected to a quality heat treatment that comprises austenitization, quenching and tempering. Owing to its large thickness, an RPV experiences widely different cooling rates across its thickness during quenching, leading to considerable variation in the microstructure from the surface to the centre of the vessel. In this study, a Cr-Mo-V steel was austenitized at 950 °C for 1 h and cooled at two rates (water quenching and 10 °C/min), representative of the cooling rates at the surface and centre of a typical RPV, to study the effect of prior microstructure on the carbide precipitation during tempering of the steel at 650 °C. Electron microscopy of the as-cooled samples revealed the presence of martensitic microstructure in water quenched sample and predominantly granular bainitic microstructure in slow cooled sample. Synchrotron studies revealed the presence of retained austenite containing ∼0.8% carbon in the slow-cooled sample. Tempering of the steel at 650 °C for 200 h precipitated M7C3 and MC (VC) carbides in the water-quenched sample, while the slow cooled samples precipitated M23C6 as an additional constituent. This difference in the carbide precipitation in the two samples has been attributed to the excess carbon in the martensite/austenite (M/A) regions in slow cooled samples and explained on the basis of carbide precipitation sequence predicted using Thermo-kinetic simulations. This analysis has shown that M23C6 and M7C3 carbides in the slow cooled sample precipitate simultaneously as critical radii of their nucleation as well as their incubation time become comparable when the matrix contains more than 0.25% C. The present study has demonstrated that the microstructure prior to tempering may significantly affect the precipitation sequence of carbides during tempering.