Microstructure Control Research Articles

Workability optimization and microstructure regulation for a multi-angular extrusion process of AZ80 magnesium alloy

Engineering stability control of microstructure evolution and precision forming is a key technical issue for the high-performance manufacturing of magnesium alloy components. In this paper, a fine-grain processing window was proposed for the workability optimization and microstructure control of AZ80 magnesium alloy. The hot activation energy map (AEM) and processing map (PM) were established to analyze the hot-working properties and microstructural mechanisms, respectively. The internal state variable (ISV) based finite element (FE) model was introduced to predict the evolutions of grain size and microstructure homogeneity with processing parameters during multi-angular extrusion process. The fine-grain processing window was used to form a magnesium alloy plate. Fine microstructure and good forming performance were obtained with the optimized processing parameters at the complete DRX domain. Forming at the processing instability domain exhibited flow defects and microstructure heterogeneity. The above research can be applied to the processing parameter optimization and microstructure regulation during hot forming processes of magnesium alloy.

Microstructure Control of Directionally-solidified Mg/LPSO Two-phase Alloys

Microstructure Control of Directionally-solidified Mg/LPSO Two-phase Alloys

Controlled Crystallographic Texture Orientation in Structural Materials Using the Laser Powder Bed Fusion Process—A Review

Advantages of the laser powder bed fusion (LPBF) process over conventional processing methods include microstructural control capability and complex geometry parts fabrication. For most alloys, the microstructure–property relationship typically guides the LPBF process toward achieving application‐specific properties. Nonetheless, the LPBF process produces a high degree of anisotropy, primarily from the epitaxial preferred grain growth mechanisms during solidification and the consequent highly textured microstructures produced. The crystallographic texture‐controlled build concept through the LPBF process is a material design and processing approach gaining a lot of interest because of the promising unique and superior properties offered by the anisotropy accompanying the LPBF process. The numerous attempts at intentional texture‐controlled building or parts fabrication from structural materials using the LPBF process warrant an up‐to‐date review. Thus, this review presents solidification mechanisms that influence texture evolution during the LPBF process such as the melting mode, melt pool shape, influence of thermal gradient, and solidification rate. Furthermore, this review delves into the influence of LPBF process parameters on texture, accompanying microstructural evolution, and the intentional control of texture effects on properties such as mechanical, corrosion, and oxidation resistance.

A machine learning method to quantitatively predict alpha phase morphology in additively manufactured Ti-6Al-4V

sQuantitatively defining the relationship between laser powder bed fusion (LPBF) process parameters and the resultant microstructures for LPBF fabricated alloys is one of main research challenges. To date, achieving the desired microstructures and mechanical properties for LPBF alloys is generally done by time-consuming and costly trial-and-error experiments that are guided by human experience. Here, we develop an approach whereby an image-driven conditional generative adversarial network (cGAN) machine learning model is used to reconstruct and quantitatively predict the key microstructural features (e.g., the morphology of martensite and the size of primary and secondary martensite) for LPBF fabricated Ti-6Al-4V. The results demonstrate that the developed image-driven machine learning model can effectively and efficiently reconstruct micrographs of the microstructures within the training dataset and predict the microstructural features beyond the training dataset fabricated by different LPBF parameters (i.e., laser power and laser scan speed). This study opens an opportunity to establish and quantify the relationship between processing parameters and microstructure in LPBF Ti-6Al-4V using a GAN machine learning-based model, which can be readily extended to other metal alloy systems, thus offering great potential in applications related to process optimisation, material design, and microstructure control in the additive manufacturing field.

Flexible control of bigel microstructure for enhanced stability and flavor release during oral consumption

Edible delivery systems such as emulsions and gels that possess flexible oral flavor sensation and comprehensive stability under freeze–thaw processing are highly demanded in the frozen food industry. Bigels were fabricated via emulsification of stearic acid based oleogel with konjac glucomannan (KGM)-gelatin (G) based binary hydrogel. By varing the KGM/G mass ratio (γ) and oleogel/hydrogel volume ratio (φ) of bigels, modulation over the micromorphology, tribology, flavor sensation and cheese stick imitating capacity were achieved. Notably, as φ increased from O4:W6 to O5:W5, the microstructural transformation from oleogel-in-hydrogel to bicontinuous morphology emerged as a remarkable feature. The influence of γ was evident in bicontinuous bigels, significantly enhancing water holding capacity (WHC) by 3.38-fold as γ transitioned from 1KGM:5G to 6KGM:5G during freeze–thaw cycles. φ and γ both played pivotal roles in altering the microstructure and rheological properties of the bigels, enabling customizable release of bioactive components and flavor perception. Oleogel-in-hydrogel bigels effectively prevented bioactive compound leakage during freeze–thaw conditions, while bicontinuous bigels demonstrated sustained flavor release during oral mastication. Release behaviors were dual-controlled by φ and γ, reducing oil-soluble flavor release with increased φ and lowering hydrophilic volatile release with elevated γ. Moreover, bigel-based cheese sticks showcased lower viscosity, higher creep recovery rates, and enhanced mouthfeel during minimal oral chewing, suggesting their potential in mimicking the properties of commercial counterparts. These findings extend insights into bigel design for tailored flavor release and bioactive preservation in food products.

Preparation of microstructure controllable Al/WO3/F2603 MICs by droplet microfluidic technology to improve combustion performance

The microstructure of metastable intermolecular composites (MICs) is crucial for their energy release and combustion performance. In this paper, Al/WO3/F2603 composites with controllable microstructure were prepared by droplet microfluidic technology. The microstructure control method of composite materials based on droplet microfluidic technology (DMT) was studied. Particles with controllable size, shape, composition, structure and function were prepared by droplet template, and the formation mechanism of particle microstructure was introduced. The Al/W/F-2 composites with high-quality spherical encapsulation have excellent flow properties and wettability. The ignition delay, combustion time and pressure output of the composites were monitored by a combustion and pressure test system. Compared with the physically mixed samples, the Al/W/F-x composites prepared by DMT have shorter ignition delay, shorter combustion duration, and higher pressurization rate. The analysis of combustion products showed that the encapsulated Al/W/F-x composites reduced the sintering and agglomeration of reactants and promoted the combustion efficiency. The results show that the characteristic structure design of the composite material can establish the interface synergy, enhance the thermal mass transfer between the components, and thus reduce the ignition delay and improve the combustion performance. DMT can realize the controllable preparation of composite microstructure, which provides a reference for the design and preparation of other composite materials.

Improvement of Fatigue Crack Propagation Property in Low Carbon Steel by Microstructural Control and an Investigation of its Practical Benefit

The fatigue crack propagation properties of newly-developed SM490 grade steels were investigated in comparison with a conventional steel of the same grade. The fatigue crack propagation rate of the developed steel in Region II of the da/dN-ΔK relationship was suppressed to about 1/2 that of the conventional steel, and its ΔKth value was more than twice as large as in the conventional steel. However, fatigue crack resistance for long crack propagation does not necessarily improve the fatigue life in a condition of increasing ΔK from a small defect, which is usually detected in practical fatigue damage in actual structures in service. The developed steels were subjected to surface crack propagation tests using specimens with artificial small defects to examine their potential under more practical conditions. The fatigue life of the developed steel was about three times longer than that of the conventional steel. A detailed analysis of the surface crack propagation revealed crack propagation below ΔKth only in the developed steels, which suggested the so-called "short crack regime" in a fatigue crack. The crack propagation from a surface defect that deviated from long crack behavior was convincingly explained by the corrected threshold using the R-curve model of a short crack proposed in the previous literature. Based on the experimental fatigue life improvement and its analytical estimation of the propagation resistance in the short crack regime, the effect of the ΔKth value for a long crack in the initial propagation stage just after fatigue crack initiation was discussed.

Microstructural control of additively manufactured Ti6Al4V via in-situ large-area laser annealing

Additively manufactured (AM) alloy Ti6Al4V often exhibits a distinctive α/α’ microstructure due to the high cooling rates associated with AM, which can lead to increased brittleness and necessitate costly post-processing and heat treatment. In this work, we explore the use of layer-by-layer large area surface annealing with a secondary diode laser to control the microstructure of Ti6Al4V during AM and site-specifically induce more ductile, dual-phase α/β Ti6Al4V. Annealing treatments were selected to target sub- and super-β-transus temperatures at annealed layers, leading to 13 % and 20 % reductions in hardness, respectively, in the 2 mm below the annealed surfaces. Components with rapid switching between annealed and unannealed microstructures were also produced. Temperature measurements at the built surface and base plate were combined with a thermal model to validate microstructural observations, setting the stage for development of full 3-D microstructure and property control using in-situ laser annealing.

Understanding structure-processing relationships in metal additive manufacturing via featurization of microstructural images

Understanding and predicting accurate property-structure-processing relationships for additively manufactured components is important for both forward and inverse design of robust, reliable parts and assemblies. While direct mapping of process parameters to properties is sometimes plausible, it is often rendered difficult due to poor microstructural control. Exploring the direct relationship between processing conditions and microstructural features can thus provide significant physical insights and aid the overall design process. Here, we develop an automated high-throughput framework to simulate an uncertainty-aware additive manufacturing (AM) process, characterize microstructural images, and extract meaningful features/descriptors. A kinetic Monte Carlo (KMC) based model of the AM process is used to simulate microstructural evolution for a diverse set of experimentally relevant processing conditions. We perform a parametric study to explore the relationship between microstructural features and processing conditions. Our results indicate that a many-to-one mapping can exist between processing conditions and typical descriptors; therefore, multiple descriptors are thus necessary to unambiguously represent microstructural images. Our work provides crucial quantitative and qualitative information that would aid in the selection of features for microstructural images. Featurized microstructures could then be utilized to build data-driven models for predictive control of microstructures and thereby properties of additively manufactured components.

Time-dependent multicolor evolution of photoluminescence and afterglow in lanthanide-doped gallate

The general stimulus-responsive color modulation method requires both strict control of microstructures and continuous adjustment of specific stimuli conditions to externally manipulate emission color for scientific research and applications. Herein, by hierarchically utilizing the energy transfer processes from traps to luminescent centers, a possible mechanism for the dynamic multicolor evolution in a single material is proposed. This mechanism explains the fundamental principle of the dynamic photochromic behavior and afterglow color variation. A series of Sr3Ga4O9:Ln3+ (SGO, Ln = Dy, Tb, Pr, Sm) phosphors with dynamic photoluminescence (PL) and afterglow color that change over time under a fixed stimulus were developed using the mechanism as a basis for experimental design. The PL dynamically transformed from orange, green or red to blue under 254 nm irradiation in seconds and reversed from blue to orange, green or red after the excitation source was removed. Finally, based on distinctive luminescence properties, their potential application in optical encryption and optical anticounterfeiting was also methodically investigated.

Enhancing mechanical properties and wear resistance of heavy-haul rail systems through complex microstructure control

This study delves into the formulation of an advanced microstructure in medium-carbon high-silicon spring steel through a series of engineered heat treatments. The microstructure, composed of lower bainite, proeutectoid ferrite, and pearlite, exhibits superior mechanical properties compared to traditional pearlitic steel. Specifically, the novel microstructure yields a strength of 870 MPa and an ultimate tensile strength of 1050 MPa, along with an enhanced total elongation of 9.75 %, while the pearlitic steel achieved a yield strength of 745 MPa, an ultimate tensile strength of 845 MPa, and a total elongation of 9.0 %. The steel's heightened strength is attributed to dislocation and precipitation strengthening, with the proeutectoid ferrite at grain boundaries contributing to the excellent elongation. The study thus establishes a groundbreaking and readily implementable heat treatment process that significantly boosts the performance and longevity of heavy-haul rail system, owing to the synergistic contribution of lower bainite, proeutectoid ferrite, and pearlite in the microstructure.

Review — Microstructure Control and Function Expression Using Metal 3D Additive Manufacturing in the Digital Age

Review — Microstructure Control and Function Expression Using Metal 3D Additive Manufacturing in the Digital Age

Recent advances in high value-added carbon materials prepared from carbon dioxide for energy storage applications

Since the industrial revolution, the consumption of fossil fuels has increased year by year, which has resulted in increasing greenhouse gas emissions. Carbon capture, utilization and storage technology has received extensive attention as a technology for converting atmospheric carbon dioxide into high value-added materials. Carbon materials, as ideal materials for various energy storage devices, have attracted extensive research. Therefore, the selective reduction of CO2 to carbon materials with high added value is a promising solution, which can not only effectively alleviate the greenhouse effect, but also promote the development of the energy storage field. This review introduces the research work of high-value conversion of carbon dioxide into carbon materials and its impact on the performance of energy storage devices in recent years. In particular, we emphasize the reaction processes during CO2 conversion, which can build an understanding of the science and technology involved in the control of interfacial properties, microstructure, and pore structure of CO2-converted carbon nanomaterials. We also summarized the basic design principles for the application of carbon nanomaterials in the field of energy storage. The effect of the microstructure and interface properties of carbon materials converted from CO2 on the energy storage performance are further analyzed. Finally, prospects and discussions are made on the challenges of future development.

Achieving remarkable enhancement of yield strength and high ductility in a fine-grained Mg-6Zn-0.2Ca alloy via rotated hard-plate rolling

Developing Mg alloys with high strength-ductility synergy presents a major challenge. In this work, a novel Mg-6Zn-0.2Ca alloy prepared via rotated hard-plate rolling (RHPR) exhibits a simultaneous high yield strength (YS) of ∼268 MPa and ductility of ∼22%. The RHPRed alloy features a fine-grained structure containing high-density low angle boundaries (LAGBs) and densely distributed nano-coherent precipitates, contributing to a remarkable improvement of YS (∼82 MPa) in comparison to the conventional rolling counterpart, while homogenizing tensile deformation. In the RHPRed alloy, the presence of ellipse-shape texture and grain-boundary disclinations adjacent to LAGBs promotes the activity of pyramidal <a> and <c + a> slip that governs the high ductility. The current work demonstrates the essential role played by high-density LAGBs and nano-coherent precipitates to the high strength-ductility synergy, which may provide insights into microstructural control strategy towards superior performance of Mg-Zn-Ca alloys.

Microstructure control of BN interface and its effect on mechanical behavior of SiCf/SiC composites

Chemical vapor infiltration (CVI) of BCl3 and NH3 at low temperature was used to synthesize the BN interface of SiCf/SiC composites. The structure of the BN interface was adjusted by changing the deposition pressure, and its effect on the mechanical properties of SiCf/SiC composites was studied. The BN interface showed a quasi-isotropic microstructure when the deposition pressure was low at 500 Pa. After increasing the deposition pressure to 1500Pa, the crystallinity of BN improves and some high-crystallized domains appear. The later tensile test illustrated that increasing the deposition pressure of BN interface could enhance the matrix cracking stress but decrease the fracture toughness, indicating that the BN interface deposited at high pressure has higher bonding strength. It can be attributed to that the high-crystallized BN layers vertical to the SiC fibers suffering in-plane shear stress, which impedes the deformation and cracking of the BN interface. Our research provides a deep insight into the relationship between the structure and performance of composites, and a guiding significance in the preparation of high-strength and high-toughness SiCf/SiC composites.

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair.

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

Thymol-loaded polylactic acid electrospun fibrous membranes with synergistic biocidal and anti-bacterial adhesion properties via morphology control

Antibiotic resistance is a growing challenge in modern medicine, highlighting the urgent need for alternative antimicrobial strategies. The combination of synergistic sterilization and inhibition of bacterial adhesion presents a promising approach for achieving a long-lasting antibacterial effect. Herein, we report the fabrication of thymol-loaded polylactic acid (Thy-PLA) porous fibrous membranes that exhibit both bacteria-killing and bacteria-repellent functions, accomplished through control of microstructure and morphology during the electrospinning process. Notably, we employed the breath figure method, a humidity-induced morphology control technique, which significantly increased the surface roughness of the Thy-PLA fibers and resulted in a nano-porous structure for bacterial repulsion. Additionally, this method facilitated the enhanced release of thymol, thereby enabling efficient sterilization. By simply modifying the morphology, we achieved bacterial reduction rates of up to 99.92 % and 99.87 % for Escherichia coli and Staphylococcus aureus, respectively, and robust mechanical properties (ultimate tensile stress of 20 MPa and elongation at break of 822.7 %). Furthermore, the fibrous membranes exhibited an impressive oil/water absorption capacity (∼36.7 g/g in 90 s) thanks to the interior and surface porosity. The porous fibrous membranes with synergistic antimicrobial efficiency and tunable mechanical properties demonstrate great potential for diverse applications, particularly in wound dressing and oil/water filtration.

Microstructure control and hot cracking behavior of the new Ni-Co based superalloy prepared by electron beam smelting layered solidification technology

The prevention of hot cracking formation is of utmost importance in the production of the new Ni-Co based superalloys through the utilization of the electron beam smelting layered solidification technique (EBSL), as it ensures exceptional homogeneity and dependable consistency of the specimens. In contrast to previous studies that focused on minimizing the liquid film and solidification range, our methodology adopts a distinct approach. In this research, a novel methodology was employed to mitigate internal stresses through the implementation of equiaxed grain layers via an alternately reduced cooling method. This ultimately resulted in the elimination of hot cracking. To be more specific, the transition from a columnar to an equiaxed structure was observed during the layer-by-layer construction process in the fabrication of the new Ni-Co based superalloy in EBSL. The EBSL-Ni-Co superalloy, when subjected to the alternating reduction cooling method, exhibited an internal stress of 49 MPa. This value represents a significant reduction of 83.8% compared to the internal stress observed when employing the linear reduction cooling method. Additionally, the solvus temperature of the γ-γ' eutectic phases in EBSL-Ni-Co superalloys produced by the alternating reduction cooling method is significantly higher. Intriguingly, the Nth layer of the EBSL-Ni-Co based superalloys produced by EBSL simultaneously heats treated with the preceding layers. And the low melting point phase gradually dissolved back into the matrix. The implementation of an alternating reduced cooling method successfully mitigated the formation of the liquid film in the γ-γ' eutectic phase and the buildup of internal stresses in the EBSL-Ni-Co superalloy during its manufacturing process. These discoveries open up a novel preparation procedure pathway for the manufacture of crack-free superalloys with superior mechanical characteristics using EBSL.

A Review of Recent Research Trends of Forming of Metallic Bondlines Using Core-Shell Particles and Bonding Properties According to Particle Type

With the increasing numbers of electric vehicles and the prevalence of high heat generating devices, recent studies have attempted to address the limitations of conventional solder materials, including their low durability at temperatures exceeding 200 ℃, insufficient mechanical properties in a joint, and low thermal conductivity. Transient liquid-phase (TLP) partial bonding using solders or Sn, and sinter bonding using Ag particles, are alternative bonding methods which involve a modification or change of the material. Advanced alternatives can significantly reduce bonding time or material cost. Various additional studies have investigated various core-cell particles that can be used to form an all-metallic bondline. This review summarizes reports of bonding studies using different core-cell particles. The particles were not only applied as a form of paste but also preform. In the TLP bonding using X(Cu, Ag, Ni)@Sn particles, the degree of voids generated in the formed bondline was dependent on the type of intermetallic compound formed. The preforms consisting of X@Sn particles provided relatively uniform microstructure and void distribution, compared to the pastes containing identical X@Sn particles, resulting in better long-term mechanical reliability. The addition of Zn@Sn particles contributed to the more practical control of microstructure and mechanical properties in the joint formed by pure Sn and Sn-58Bi solder alloys. Cu@Ag particles can be considered a promising low-cost material for compression-assisted sinter bonding, replacing pure Ag particles. The application of core-cell particles is expected to improve the processes used for forming metallic bondlines.

Photografting of Surface-assembled Hydrogel Prepolymers to Elastomeric Substrates for Production of Stimuli-Responsive Microlens Arrays.

Hydrogels have emerged as prototypical stimuli-responsive materials with potential applications in soft robotics, microfluidics, tissue engineering, and adaptive optics. To leverage the full potential of these materials, fabrication techniques capable of simultaneous control of microstructure, device architecture, and interfacial stability, i.e., adhesion of hydrogel components to support substrates, are needed. A universal strategy for the microfabrication of hydrogel-based devices with robust substrate adhesion amenable to use in liquid environments would enable numerous applications. This manuscript reports a general approach for the facile production of covalently attached, ordered arrays of microscale hydrogels (microgels) on silicone supports. Specifically, silicone-based templates were used to: i) drive mechanical assembly of prepolymer droplets into well-defined geometries and morphologies, and ii) present appropriate conjugation moieties to fix gels in place during photoinitiated crosslinking via a "graft from" polymerization scheme. Automated processing enabled rapid microgel array production for characterization, testing, and application. Furthermore, the stimuli-responsive microlensing properties of these arrays, via contractile modulated refractive index, were demonstrated. This process is directly applicable to the fabrication of adaptive optofluidic systems and can be further applied to advanced functional systems such as soft actuators and robotics and 3D cell culture technologies.