Microstructure Size Research Articles

Failure Analysis of Burst Tube Caused by Corrosion Thinning of the Tube Wall of Boiler Economizer

Abstract A boiler economizer is in continuous operation during several burst pipes. Burst tubes are located near the elbow below the weld, and the weld on both sides of the tube wall is thinning seriously. There is a flue gas formation vortex in the furnace chamber; the outer wall of the tubes is thicker ash, and fins and tubes are corroded to varying degrees. This study employed meticulous macroscopic observation, precise chemical composition analysis, detailed metallography, advanced scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to determine the causes of the coal economizer tube burst and tube wall thinning, ensuring the accuracy of the findings. The chemical composition, microstructure, and grain size of the base material met the requirements of the relevant standards. The heat-affected zone and weld seam show the Widmannstatten structure, a superheated tissue caused by excessive heat input during welding. The outer wall of the pipe corrosion is more serious, resulting in serious wall thinning, and ultimately, the pipe bursts, unable to withstand the pressure inside the pipe. It was eventually determined that the cause of the pipe burst was that the operating temperature of the economizer was close to the dew point, and the flue gas contained sulfur dioxide, sulfur trioxide, and hydrogen chloride that met water vapor at that temperature to form acid. Acid on the outer wall of the pipe was caused by flue gas dew point corrosion, seriously causing the pipe wall to thin. When the pipe wall is thinned to a certain extent due to corrosion, it cannot withstand the pressure inside the pipe, and rupture will occur.

MAIN STAGES OF DESIGNING RESOURCE-SAVING TECHNOLOGIES FOR INGOT DEFORMATION ON HYDRAULIC PRESSES

Objective. To study the technological process of forging large ingots on hydraulic presses in order to identify and reduce resource consumption. Research methods. A finite element method that makes it possible to assess the stress-strain state of a workpiece, the possibility of levelling it, and homogenising it by controlling the factors that form the optimal forging method for a given workpiece. Results. A resource-saving technological process based on the optimal forging method has been developed, which allows to bring the quality of the designed products to a new level and leads to an increase in technical and economic indicators of production. By controlling the stress-strain state of the metal, high quality forged products can be achieved and resource-saving technologies for forging forgings of high-alloy steel grades and alloys can be created. Scientific novelty. The factors that form the rational resource-saving technological process of plastic deformation and the method of forging large forgings from alloyed, stainless steels and alloys on hydraulic presses, as well as the directions of their optimisation, have been formed. The finite element method allows us to predict the distribution fields of the workpiece’s stress-strain parameters, metal microstructure, and grain size. Practical value. Practically grounded recommendations for optimal modes of forging ingots from tool steel grades were developed. This will reduce energy consumption, save time in the production of forged products and generally intensify the process of plastic deformation. The proposed recommendations can be applied not only in the processes of forging tool steel grades but also in other types of hot plastic deformation of metals of a wide range.

Optimization of Magnetic Field-Assisted Laser Cladding Based on Hierarchical Analysis and Gray Correlation Method

Process parameters directly affect the quality of laser cladding. In this study, magnetic field-assisted laser cladding experiments were carried out on the surface of 300 M ultra-high-strength steel by setting laser energy density, magnetic field strength, and frequency as processing parameters. The optimization of laser cladding process parameters was investigated based on evaluating the quality of the laser cladding layer through hierarchical analysis and gray correlation analysis. Based on orthogonal test data, the correlation coefficients of the process parameters with the single objective function and the correlation degree of the multi-objective function were calculated by using the gray theory. Then the comprehensive objective optimization was carried out according to the gray correlation degree. The optimization problem with multiple process objectives was transformed into a single gray correlation degree optimization method to realize the optimization of process objectives and obtain the optimal combination of process parameters. The validation experiments indicate that the quality of the laser cladding layer can be greatly improved by employing optimal process parameters. The optimized laser cladding layer shows a reduced microstructure size and enhanced wear resistance, indicating the effectiveness of the optimization approach.

Numerical simulation of GTAW for ZW61 magnesium alloy thin plates: Coupling the finite element method with the cellular automata method

ZW61 magnesium alloy has a wide range of application prospects as a lightweight green engineering material. In this paper, the temperature field and microstructure of gas tungsten arc welding (GTAW) for ZW61 magnesium alloy are simulated by the finite element method and the cellular automata (CA) method. The results show that the microstructure in the center of the fusion zone (FZ) is all equiaxed grains affected by compositional supercooling. While at the edge of the molten pool, the crystals produced by associative crystallization evolve into columnar grains after undergoing competitive growth. Furthermore, the temperature field of the molten pool alters as the welding heat input increases. Especially, the temperature gradient behind the molten pool slows down. Thus, the cooling rate during solidification of the molten pool decreases, increasing the size of the weld microstructure. Meanwhile, solute concentration plays an essential role in the weld microstructure evolution. The rise in Zn content both refines the size of the equiaxed grains and inhibits the growth of the columnar crystals. Moreover, the experimental results of the thermal cycling curves and the FZ microstructure exhibit minimal error with the simulation results, verifying the reliability of the model.

The behaviour of micro-injection moulding inserts produced with material jetting technology

The increasing interest in additive manufacturing and advancements in precision and production quality have sparked attention to its use in industrial prototyping. High-performance polymer resins enhance flexibility in mass production processes like micro-injection moulding. This flexibility allows for reconfigurable moulds using resin inserts, enabling the transition of devices, such as microfluidics, from labs to large-scale production. Despite progress, limitations exist in additive manufacturing, including the minimum size of microstructures and the brittle behaviour of resin inserts during moulding cycles, impacting overall production capacity. This study focuses on using a micro-injection moulding machine to reproduce PMMA thin plates with single straight microchannels (250 μm) and with different side wall angles (0°, 15°, and 30°), investigating the best compromise between capability and insert resistance to moulding cycles. A careful study of the dynamics leading to the insert failure and the resin limits was carried out. The results showed that it is possible to produce about 15 micro-structured thin plates with good accuracy using a resin insert realised with Material Jetting technology.

Strain energy density maximization principle for material design and the reflection in trans-scale continuum theory

Traditional efforts in the design of damage-tolerant structural materials were largely exercises in optimizing the combination of strength and ductility. However, the simultaneous consideration of these two conflicting mechanical indices, improving one inevitably sacrifices the other, makes the design extremely complex and difficult, due to the dilemma of choosing between them. Here, physically guided by the energy variational expression in trans-scale continuum mechanics theory, we propose a general mechanics principle for material design that involving only one index: towards strong and tough material the strain energy density limit (w) should be maximized, i.e., strain energy density maximization principle, referred to as wmax principle. It aims to guide the attainment of exceptional comprehensive mechanical properties, while circumventing the dual-index dilemma by employing a singular index w. Extensive experimental data analyses prove that (i) the maximum wmax always exists, at a critical dimension of characteristic microstructure dc,micro, and (ii) w can effectively index strength-ductility synergy and the wmax is conjugated with both high strength and high ductility, verifying the validity of wmax principle. The universality, practicality and downward compatibility are also examined. The dc,micro approaches twice the span of strain gradient region around internal boundary, suggesting that the microstructure state with wmax is the critical state with strongest strain gradient. Importantly, the w improvement as a function of the characteristic size of either microstructure or deformation field can be well captured by strain gradient theory, confirming the consistence between the wmax principle, experimental results and trans-scale continuum theories. This principle opens up a new design concept for advanced structural materials from the perspective of microstructure-w-mechanical properties relationship.

Experimental simulation of the ancient production of gold granules

Granulation is an ancient and sophisticated decorative technique. The production of granules is a crucial part of this process but has rarely been studied. The present study employed three techniques—pouring method, heating method, and crucible method—to produce gold granules. The success ratio of granule formation, granule surface morphology, microstructure, and formation were analyzed to identify the techniques used in archaeological objects. The cooling medium significantly influenced small granule formation, microstructure, and grain size. Both heating and crucible methods could control the granule formation, but these methods produced distinct microstructures. Based on these experimental granules, the probable production methods of ancient gold balls were identified. The present study provided microscopic information for determining ancient gold granule production techniques.

Temperature gradient mechanism in the heterogeneous nucleation of inoculated alloy: A quantitative phase-field study

The grain size of solidification microstructure has a significant influence on the mechanical properties of castings. Generally, smaller grain size makes the strength of castings higher. Therefore, inoculation is an effective strategy to reduce grain size and improve casting performance. In this work, the phase-field method combined with the free growth model is employed to simulate the solidification of inoculated aluminum alloy with temperature gradient. The simulations indicate that a higher temperature gradient slows the progression of already nucleated grains into impingement growth and enhances the undercooling of the melt ahead of the solid-liquid interface. Hence, more inoculants have chance to get the corresponding nucleation undercooling, promoting grain nucleated sequentially along the gradient direction. These results are consistent with previous real-time observed experiments. This work may provide guidance on improvement of the theoretical models for predicting grain size of inoculated alloys and the optimization of casting process to obtain refined grains in inoculated ingots.

Microstructure, thermal, and mechanical properties of hierarchical porous silicon carbide made by direct ink writing

AbstractHierarchical porous silicon carbide (SiC) ceramics were fabricated by combining particle‐stabilized emulsions and three‐dimensional (3D) printing. Direct ink writing (DIW) was used as the 3D printing technique. The formulation for successful printing is discussed in relation to the rheology of the emulsions. The SiC emulsions were able to be printed with a lower storage modulus (G′) and apparent yield shear stress (τy) than previously reported SiC ink pastes. The printed and sintered porous SiC ceramics possess a total porosity of 73.7% with an average pore size within the filaments of 2.2 µm in diameter. A hierarchical pore structure that contains pore sizes of about 250 µm, around 1–10 µm and smaller than 0.5 µm can be observed in the microstructure and pore size distribution. The mechanical properties showed a good strength‐to‐density ratio, and the thermal conductivity was reduced to 4.9 W/m·K. This study provides a new reliable approach for fabricating hierarchical porous SiC ceramics with low thermal conductivity.

Thermal-induced crystallographic transformation in shells of Mytilus galloprovincialis Lamarck, 1819

Biominerals in hard parts are widely used as paleoenvironmental archives, employing proxies such as elemental and isotopic composition, microstructure, and crystallography. However, the effective selection and application of these proxies in fossil materials depends on their preservational potential. Here we evaluated the preservational potential of these proxies through controlled experiments on bivalves, one of the commonly used fossils in paleoenvironmental reconstructions. We utilized cultured Mytilus galloprovincialis specimens at five controlled temperatures to investigate the impact of elevated temperatures on various proxies extracted from both aragonitic and calcitic components of the same shell, including isotopic composition, microstructure and crystallography. Elevated temperatures first induced changes in the oxygen isotope composition (in both aragonite and calcite), followed by modification in aragonitic parts, such as changes in the aragonite phase, textures, nacre microstructure, and grain size of aragonite crystals. Despite aragonite's susceptibility to temperature, the microstructure and texture of calcite remained largely unaltered, demonstrating significantly higher resilience. Our findings emphasize the preservational potential of different shell proxies under heat exposure, ranging from oxygen isotopes to microstructure and texture. A ranking of preservation potential provides a practical guide for selecting well-preserved specimens, as textures and microstructures are not always reliable indicators. In distinguishing aragonite from calcite in fossils, our study pioneers a new avenue by proposing the analysis of high-angle boundary (HAB) content, including twin boundaries, as a reference for altered aragonite.

Enhancing the Performance of PNN-PHT Perovskite Ferroelectric via Configurational Entropy Strategy: Component Design, Electric Properties, and Mechanism Analysis

The traditional approach to designing ferroelectrics through phase boundaries has limitations in regulating polarization configuration and achieving significant performance enhancements. In contrast, the concept of high-entropy materials has emerged as a promising strategy for designing new materials with enhanced properties. Herein, by incorporating the high configurational entropy (Sconfig) strategy, the investigation explored the influence of Sconfig on the electrical properties of PNN-PHT piezoceramics. The results demonstrated that high Sconfig values were highly beneficial in improving the piezoelectric properties and significantly influenced the microstructure and grain size. The increase in Sconfig value was found to be positively correlated with the Rayleigh coefficient (α), dielectric loss (tanδ), and frequency dispersion (γ), while inversely correlated with the coercive electric field (Ec). By exploring the mechanism via Raman and simulation analyses, it was discovered that high Sconfig induces enhanced disorder, increased lattice distortion, and sharp volume changes. This ultimately resulted in a richer phase structure, reducing the potential energy barriers and leading to a lower activation energy (Ea) required for polarization switching. This finding provides novel strategies and directions for the development of high-voltage and high-coercive-field materials, holding promise for designing piezoelectric devices with enhanced power density and precision.

Internal hydrophobic treatment for mortar containing supplementary cementitious materials: thermal analysis of kinetics and products of hydration

AbstractThe presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped.

Effect of Initial Intergranular Ferrite Size on Induction Hardening Microstructure of Microalloyed Steel 38MnVS6

In this study, we investigated the effect of grain size of an initial microstructure (pearlite + ferrite) on a resulting microstructure of induction-hardened microalloyed steel 38MnVS6, which is one topical medium carbon vanadium microalloyed non-quenched and tempered steel used in manufacturing crankshafts for high-power engines. The results show that a coarse initial microstructure could contribute to the incomplete transformation of pearlite + ferrite into austenite in reaustenitization transformation by rapid heating, and the undissolved ferrite remains and locates between the neighboring prior austenite grains after the induction-hardening process. As the coarseness level of the initial microstructure increases from 102 μm to 156 μm, the morphology of undissolved ferrite varies as granule, film, semi-network, and network, in sequence. The undissolved ferrite structures have a thickness of 250–500 nm and appear dark under an optical metallographic view field. To achieve better engineering applications, it is not recommended to eliminate the undissolved ferrite by increasing much heating time for samples with coarser initial microstructures. It is better to achieve a fine original microstructure before the induction-hardening process. For example, microalloying addition of vanadium and titanium plays a role of metallurgical grain refinement via intragranular ferrite nucleation on more sites, and the heating temperature and time of the forging process should be strictly controlled to ensure the existence of fine prior austenite grains before subsequent isothermal phase transformation to pearlite + ferrite.

Automated Workflow for Phase‐Field Simulations: Unveiling the Impact of Heat‐Treatment Parameters on Bainitic Microstructure in Steel

Bainitic steels are extensively utilized across various sectors, such as the automotive and railway industries, owing to their impressive mechanical properties, including strength, hardness, and fatigue resistance. However, the pursuit of achieving the desired optimal mechanical properties presents considerable challenges due to the intricate bainitic microstructures consisting of multiple phases. To tackle these challenges, an automated workflow is used for extracting 2D and 3D microstructural features. The proposed method allows for a detailed examination of the correlations between microstructure characteristics and the processing parameters, specifically the holding temperature during transformation. In these findings, it is revealed that as the holding temperature decreases, there is a notable reduction in microstructural element size and carbon partitioning. Some of the observations are microstructural features such as area, perimeter, and thickness of the bainitic ferrite grains under two different holding temperatures. Phase‐field simulations results show that the microstructures at lower holding temperatures have finer grains. The distributions of grain areas and perimeters are uniform, with smaller grains dominating at low and high isothermal holding temperatures. While the grain thickness measurements from simulations and experiments at high temperature are qualitatively aligned, data from low temperatures show discrepancies.

Improvement of lactose digestion by highland barley (Hordeum vulgare var. coeleste L.) β-glucan: Activation of lactase under simulated gastric/small intestinal digestive conditions

β-Galactosidase (lactase) plays a crucial role as a dietary supplement in managing lactose intolerance. Here, the catalytic activity of lactase was successfully activated for the first time through complexation with water-extractable β-glucans from highland barley (WHBG). Under simulated gastric/small intestinal digestive conditions, WHBG and lactase spontaneously formed complexes, resulting in a remarkable increase in catalytic activity up to 172.6 %. Structural analyses revealed that the incorporation of WHBG caused partial unfolding of lactase, thereby exposing its hydrophobic regions with active sites, and the electrostatic and hydrophobic interactions between the two played pivotal roles. Meanwhile, according to microstructure and particle size analyses, the dissociation of aggregates and the re-distribution of lactase molecules were also observed. Consequently, the enzyme-substrate contact was promoted, and the hydrolysis efficiency of complexed lactase in the digestion of lactose in milk was superior to that of native lactase. Notably, among WHBG30/50/70 obtained by continuous fractionation of WHBG with 30 %/50 %/70 % ethanol, WHBG70 exhibited the lowest molecular weights and size, and the highest negative ζ-potential, potentially contributing to its superior activation abilities on lactase. These findings challenge the traditional view of polysaccharides as enzyme inhibitors and highlight their potential for diverse applications.

Microdeformation and strengthening mechanism of 3D printed TC4/TC11 gradient titanium alloy subjected to tensile loading

3D printing of heterogeneous alloys holds promising application potentials in industry, especially in the field of aerospace. However, the relationship between the microstructure and mechanical properties of heterogeneous gradient titanium alloys produced by this technique, especially the micromechanical properties and mechanisms within the gradient zones, remains largely unexplored. In this study, we investigated the tensile micromechanical properties and deformation mechanism of 3D printed TC4/TC11 titanium alloy using the digital image correlation method in combination with scanning electron microscopy. The results show that this heterogeneous gradient titanium alloy possesses superior tensile properties. Furthermore, we elucidated the influence of microstructure and grain size on the alloy’s mechanical properties. Notably, an increased presence of secondary α phases and refined grain size were found to reduce the likelihood of microcrack initiation and propagation. Interestingly, all samples fractured on the TC4 side, with the microcracks predominantly extending at a 45° angle to the tensile direction. This observation underscores the necessity for optimizing the fabrication process of the TC4 alloy. Additionally, the strengthening mechanism of the gradient-bonded region of the alloy was also explored. The heterogeneous deformation-induced strengthening was identified as a key factor enhancing the strength of the dual alloyed zone. Collectively, this study provides valuable insights for optimizing the 3D printing process of heterogeneous gradient titanium alloys. It also lays a solid foundation for future investigation in this burgeoning field.

Influence of spatial position of sound source on dual-frequency ultrasound-assisted preparation of magnesium alloy

In this work, a dual-frequency ultrasonic field was employed to improve the quality and mechanical properties of magnesium alloy ZW61 ingot. The effect of the spatial position of the sound source on the cavitation volume, microstructure size, and morphology was discussed in detail combined with numerical simulations and experiments. The mechanical properties were analyzed elaborately and the relationship between yield strength (YS), ultimate tensile strength (UTS), and average grain size (d) was established. The results showed that the dual-frequency ultrasonic field (DUF) had a larger cavitation range and superior grain refinement ability than the single-frequency ultrasonic field (SUF) at the same energy consumption, with the grain refining from 578 μm (untreated) and 395–433 μm (SUF) to 55.2 μm. The grain refining effect of DUF weakened with increasing sound source spacing, with d increasing from 55.2 μm to 163 μm. The radiating angle had little effect on the grain size. Too shallow or too deep inserting depth of the ultrasonic rods could seriously weaken the grain refinement. In this case, 30 mm source spacing, 60° radiating angle, and 30 mm inserting depth were the optimal process parameter combinations, and the ingot strength was increased from YS of 83 MPa and UTS of 151 MPa to 138 MPa and 241 MPa, respectively. YS and d for all conditions conformed to the Hall-Petch relationship, with σ0 and k values of 71.3 MPa and 503.9 MPa μm−1/2. The relationship between UTS and d could be expressed as UTS = 126.7 + 907.0 d−1/2.

Characterization, in vitro antioxidant activity and stability of cattle bone collagen peptides‑selenium chelate

In this study, cattle bone collagen peptides–selenium chelate (CCP-Se) was prepared and its structure, oxidation resistance and stability were characterized. The selenium binding capacity was 33.65 ± 0.13 mg/g by optimized preparation conditions. Structural analysis showed that selenium ions bound mainly to the amino nitrogen, carboxyl oxygen and hydroxyl oxygen atoms of the cattle bone collagen peptide (CCP). The microstructure and particle size analyses showed that the particle size of CCP-Se was increased and formed a regular and compact crystal structure compared with CCP. Additionally, CCP-Se exhibited excellent antioxidant activity. Stability analysis showed that CCP-Se was stable in thermal processing, simulated in vitro digestion and acid/alkali tolerance tests. The intestinal selenium permeability of CCP-Se was significantly better than sodium selenite (p < 0.05). This study provides reference for the high-value application of cattle bone and suggests the potential of CCP-Se as a new effective selenium supplement.

Exploring the impact of TiO2 microstructures fabricated via alcoholysis on the optical and electrical properties of α-quaterthiophene for photovoltaic applications

In this study, we investigate the optical, photovoltaic, and structural properties of TiO2 nanostructures produced by alcoholysis using various alcohols. An X-ray diffraction study highlights how the choice of alcohols affects the process by revealing variations and separation. The anatase phase is confirmed by Raman spectroscopy, which also sheds light on the effects of various alcohols. The granular nature of TiO2 microstructures is demonstrated using scanning electron microscopy. We demonstrate how the size and shape of microstructures influence the band gap using absorption spectroscopy. Using fluorescence spectroscopy and Franck-Condon analysis, we investigated the performance of the α-Quaterthiophene + 40 % TiO2 nanocomposite. Important parameters are then taken out of the analysis using the Franck-Condon technique. Studies on the photovoltaic performance of the α-Quaterthiophene + 40 % TiO2 nanocomposite active layer show significant improvements in both open-circuit voltage and short-circuit current when TiO2 nanostructures are incorporated. This demonstrates the enormous potential of TiO2 nanostructures to improve solar cell applications’ efficiency. Self-assembly fabrication of TiO2 microspheres via the alcolysis process and their effect on exciton dissociation in hybrid systems is a topic of interest in materials science and nanotechnology.

Microstructures and mechanical properties of laser-arc hybrid welded high-strength aluminum alloy through beam oscillation

High-frequency beam oscillation and synchronous wire-powder feeding were adopted for the laser-arc hybrid welding of a 2219-T6 high-strength aluminum alloy. Increasing the beam oscillation frequency from 0 to 250 Hz not only reduced the weld porosity from 2.64% to 0.16% but also promoted the transformation of columnar dendrites to fine equiaxed grains. In addition, the content of precipitated Al2CuMg increased with the refined size of the weld microstructure. The length of the columnar grains and the diameter of the equiaxed grains in the weld center were reduced by 40% and 50%, respectively. Owing to these improvements, the weld microhardness increased and became more uniform, and the variance decreased by 74%. The ultimate tensile strength and elongation of the welded joint reached 238.5 MPa and 4.3%, respectively, which were 26.5% and 105% higher than those of the non-oscillating hybrid weld, respectively. The weld tensile strength and the proportion of the area of the pore were negatively correlated. The porosity and microcracks of the welded joints were the main factors affecting the tensile strength of welded joints.