Matrix Microstructure Research Articles

Study on the effect of ultrasonic treatment for fabricating nodular cast iron with improved mechanical properties

In this paper, a novel ultrasonic treatment technique was proposed in nodular cast iron melt with the aim of improving the microstructure and mechanical properties of nodular cast iron. The effects of ultrasound on the microstructures and properties were investigated by comparing experiments with and without ultrasound. The results showed that compared with the NO UT specimen, the mean equivalent diameter of graphite nodules was reduced by 46% in the UT 105 s specimen, while the mean roundness and nodule count per unit area were increased by 33.9% and 43.6%, respectively. In addition, the ultrasonic treatment of melt could increase the pearlite content, refine the matrix microstructure and reduce the pearlite interlamellar spacing from 392.7 nm to 231.3 nm. Compared with the NO UT specimen, the mechanical properties of the UT specimen were improved significantly, and could up to UTS of 739 MPa, YS of 579 MPa and El of 9.4% in the UT 105 s specimen. In this work, the mechanism of ultrasonic action on nodular cast iron also was discussed in detail.

Research on mechanical properties of concrete by nano-TiC-BF-fly ash.

Ultra-high-rise buildings require high concrete bearing capacity. Ordinary concrete often fails to meet the project requirements. Admixture of admixtures in concrete is a means of solution. Currently, studies on the incorporation of basalt fiber (BF) and fly ash (FA) in concrete are relatively mature. However, research on incorporating nano-Titanium Carbide (nano-TiC) in concrete is still relatively scarce, which has a lot of room for development. To further improve the mechanical properties of concrete, BF, and FA synergized with nano-TiC were incorporated into concrete to produce TBF concrete in this study. And Response Surface Methodology (RSM) was used to optimize the mechanical properties of concrete. The collapse and compressive deformation damage characteristics of concrete were analyzed. The microstructure of the cement matrix was analyzed by the SEM (Scanning Electron Microscope). An optimization model of the TBF concrete craving function was developed. Optimized ratios with compressive, split tensile, and flexural strengths as response objectives were obtained, and the accuracy of the optimized ratios was investigated using the same experimental conditions. The results of the study showed that FA increased the collapse of concrete, while nano-TiC and BF decreased the collapse of concrete. Under uniaxial compression, nano-TiC, FA, and BF together incorporated into concrete can improve its compressive damage state. Moderate amounts of nano-TiC, BF, and FA could improve the mechanical properties of concrete. Their optimal mixing ratio admixtures were 0.88%, 0.24%, and 5.49%, respectively. And the measured values under the same conditions were compared with the predicted values. The maximum difference in compressive strength was 6.09%. The maximum difference in split tensile strength was 7.14%. The maximum difference in flexural strength was 8.45%. This indicated that the accuracy of the RSM optimization model was good. A moderate amount of nano-TiC, FA, and BF could improve the densification of concrete.

Effect of Travel Speed on the Properties of 5087 Aluminum Alloy Walls Produced by Wire and Arc Additive Manufacturing

An innovative Wire and Arc Additive Manufacturing combines the well-studied process of arc welding with direct energy deposition. Effect of travel speed 5.0 and 7.5 mm/s on the microstructure and mechanical properties of 5087 aluminum alloy was investigated. Five thousand eighty-three aluminum alloy was used as a substrate material and 5087 aluminum alloy was utilized as a filler material for the walls fabrication. The presence of pores reducing the strength of the overlay weld metal was detected on both overlay welds. The lower welding speed (5 mm/s) resulted in the smaller amount of porosity in comparison to higher welding speed (7.5 mm/s). Average pore area of wall No. 1 was 0.66% and wall No. 2 was 1.13%. It was found that higher welding speed affected the wall width and overlay weld bead geometry. Increase in welding speed led to a narrowing of wall width from 10.23 to 8.44 mm. The microstructure of weld metal matrix consisted of a α-Al substitution solid solution. The tensile strength of parallel to welding direction removed samples exceeded the tensile strength of perpendicular removed samples. It is a result of the cohesion of the layers in the overlay welding direction compared to the non-uniformity of the layers in the perpendicular direction. Furthermore, the tensile strength was higher in the case of travel speed of 5 mm/s in comparison to that of 7.5 mm/s.

Influence of β-cyclodextrin modified PCE on fluidity and hydration behavior of cement paste

A series of β-cyclodextrin (β-CD) modified polycarboxylate (PCE) was prepared. β-CD was first grafted onto polyethylene oxide chain to produce β-CD-HPEG, and β-CD-HPEG was then adopted to replace part of HPEG to fabricate β-CD modified PCE. The adsorption-dispersing performance of PCEs and cement hydration properties were investigated. Results showed that the insertion of β-CD into the side chain led to impaired adsorption behavior of PCE polymer onto cement particle, but performed higher steric hindrance effect. The dispersing behavior of β-CD modified PCE varied with the insertion ratio of β-CD modified HPEG. β-CD modified PCE exhibited enhanced retardation effect on cement hydration, resulting in prolonged induction period, decreased hydrates at early age. But, due to the enhanced dispersing performance of β-CD modified PCE, the hydration degree was promoted at 28d, resulting in more hydrates formed in the matrix and denser microstructure.

Evaluation of the acid degradation properties of colloidal nanosilica‐based cement pastes

AbstractThe present study examined the effects of colloidal nanosilica on the performance of cement paste samples exposed to nitric acid for a continuous period of 28 days. Compressive strength and weight losses in paste samples as a result of this attack were determined to be 66% and 27%. The inclusion of nanosilica up to 6% by weight reduced these sample losses by densifying the microstructure with its pore filling and pozzolanic effects. The addition of nanosilica decreased the flow of cement paste by 30%, but improved compressive and flexural strengths at the end of 28 days by up to 45% and 118%. The acid attack on the cement sample resulted in the formation of a degraded layer surrounding the unaltered core material. X‐ray tomography images showed this zone formation, and the scanning electron microscopy images revealed the degraded microstructure. The results of the x‐ray diffraction and nanoindentation tests confirmed the complete decalcification of the main cement hydrates, including calcium silicate hydrate and portlandite, as a result of acid attack. The results obtained suggest that the incorporation of nanosilica strengthens the microstructure of the cement matrix, thus improving the service life of structural concrete operating in chemical environments.

Construction of Integral Decellularized Cartilage Using a Novel Hydrostatic Pressure Bioreactor.

The decellularized extracellular matrix (ECM) of cartilage is a widely used natural bioscaffold for constructing tissue-engineered cartilage due to its good biocompatibility and regeneration properties. However, current decellularization methods for accessing decellularized cartilaginous tissues require multiple steps and a relatively long duration to produce decellularized cartilage. In addition, most decellularization strategies lead to damage of the microstructure and loss of functional components of the cartilaginous matrix. In this study, a novel decellularization strategy based on a hydrostatic pressure (HP) bioreactor was introduced, which aimed to improve the efficiency of producing integral decellularized cartilage pieces by combining physical and chemical decellularization methods in a perfusing manner. Two types of cartilaginous tissues, auricular cartilage (AC) and nucleus pulposus (NP) fibrocartilage, were selected for comparison of the effects of ordinary, positive, and negative HP-based decellularization according to the cell clearance ratio, microstructural changes, ECM components, and mechanical properties. The results indicated that applying positive HP improved the efficiency of producing decellularized AC, but no significant differences in decellularization efficiency were found between the ordinary and negative HP-treated groups. However, compared with the ordinary HP treatment, the application of the positive or negative HP did not affect the efficiency of decellularized NP productions. Moreover, neither positive nor negative HP influenced the preservation of the microstructure and components of the AC matrix. However, applying negative HP disarranged the fibril distribution of the NP matrix and reduced glycosaminoglycans and collagen type II contents, two essential ECM components. In addition, the positive HP was beneficial for maintaining the mechanical properties of decellularized cartilage. The recellularization experiments also verified the good biocompatibility of the decellularized cartilage produced by the present bioreactor-based decellularization method under positive HP. Overall, applying positive HP-based decellularization resulted in a superior effect on the production of close-to-natural scaffolds for cartilage tissue engineering. Impact statement In this study, we successfully constructed a novel hydrostatic pressure (HP) bioreactor and used this equipment to produce decellularized cartilage by combining physical and chemical decellularization methods in a perfusing manner. We found that positive HP-based decellularization could improve the production efficiency of integral decellularized cartilage pieces and promote the maintenance of matrix components and mechanical properties. This new decellularization strategy exhibited a superior effect in the production of close-to-natural scaffolds and positively impacts cartilage tissue engineering.

Salt Effect Engineering Single Fe-N2P2-Cl Sites on Interlinked Porous Carbon Nanosheets for Superior Oxygen Reduction Reaction and Zn-Air Batteries.

Developing efficient metal-nitrogen-carbon (M-N-C) single-atom catalysts for oxygen reduction reaction (ORR) is significant for the widespread implementation of Zn-air batteries, while the synergic design of the matrix microstructure and coordination environment of metal centers remains challenges. Herein, a novel salt effect-induced strategy is proposed to engineer N and P coordinated atomically dispersed Fe atoms with extra-axial Cl on interlinked porous carbon nanosheets, achieving a superior single-atom Fe catalyst (denoted as Fe-NP-Cl-C) for ORR and Zn-air batteries. The hierarchical porous nanosheet architecture can provide rapid mass/electron transfer channels and facilitate the exposure of active sites. Experiments and density functional theory (DFT) calculations reveal the distinctive Fe-N2P2-Cl active sites afford significantly reduced energy barriers and promoted reaction kinetics for ORR. Consequently, the Fe-NP-Cl-C catalyst exhibits distinguished ORR performance with a half-wave potential (E1/2) of 0.92V and excellent stability. Remarkably, the assembled Zn-air battery based on Fe-NP-Cl-C delivers an extremely high peak power density of 260mWcm-2 and a large specific capacity of 812mAhg-1, outperforming the commercial Pt/C and most reported congeneric catalysts. This study offers a new perspective on structural optimization and coordination engineering of single-atom catalysts for efficient oxygen electrocatalysis and energy conversion devices.

PBF-LB fabrication of microgrooves for induction of osteogenic differentiation of human mesenchymal stem cells

Stem cell differentiation has important implications for biomedical device design and tissue engineering. Recently, inherent material properties, including surface chemistry, stiffness, and topography, have been found to influence stem cell fate. Among these, surface topography is a key regulator of stem cells in contact with materials. The most important aspect of ideal bone tissue engineering is to control the organization of the bone extracellular matrix with fully differentiated osteoblasts. Here, we found that laser powder bed fusion (PBF-LB)-fabricated grooved surface inspired by the microstructure of bone, which induced human mesenchymal stem cell (hMSC) differentiation into the osteogenic lineage without any differentiation supplements. The periodic grooved structure was fabricated by PBF-LB which induced cell elongation facilitated by cytoskeletal tension along the grooves. This resulted in the upregulation of osteogenesis via Runx2 expression. The aligned hMSCs successfully differentiated into osteoblasts and further organized the bone mimetic-oriented extracellular matrix microstructure. Our results indicate that metal additive manufacturing technology has a great advantage in controlling stem cell fate into the osteogenic lineage, and in the construction of bone-mimetic microstructural organization. Our findings on material-induced stem cell differentiation under standard cell culture conditions open new avenues for the development of medical devices that realize the desired tissue regeneration mediated by regulated stem cell functions.

Synergistic mechanism of strengthening and toughening of tissue regulation response to Mg/Al composite laminates by hard plate accumulative roll bonding

The significance of light alloy in realizing the national strategy of energy saving and emission reduction and promoting the upgrading of the manufacturing industry is self-evident. Mg/Al composite laminates combine the lightweight of magnesium alloy and the plasticity and corrosion resistance of aluminum alloy. Traditional accumulative roll bonding technology relies on the advantage of introducing large deformation. Although high strength is obtained, it is often accompanied by a large loss of ductility, and there is a problem that it is difficult to balance strength and ductility. To solve this problem and optimize the process conditions, a new hard-plate accumulative roll bonding process is proposed in this paper, which is used to prepare high-performance Mg/Al composite plates, and the influence of forming temperature on the microstructure and mechanical properties of Mg matrix is studied. The results show that when the forming temperature is 350 °C, the properties of composite laminates are the best, the tensile strength can reach 243 MPa, the elongation is 14.7 %, and there are a lot of tearing edges and dimples on the fracture surface. At the same time, complete recrystallization can be realized at this temperature, and the opening of non-base slip can coordinate deformation stress, promote the dislocation slip, and reduce the dislocation density, SEM images show that there are no defects such as delamination at the interface, and a firm metallurgical bonding is achieved. It provides a new approach to the forming and manufacturing of high-quality lightweight heterogeneous composite laminates.

Utilizing industrial byproducts for the manufacture of clay-cellulose nanocomposite cements with enhanced sustainability

This study investigates the influence of different nano clay contents (0, 1, 3, and 5 wt% of cement) on the microstructure and the mechanical properties of cement composites reinforced with varying Nano cellulose fiber contents (0, 0.5, 0.75, and 1 wt% of cement). Unlike previous research that employed sonication to improve dispersion in the cement matrix, this study explores the effects of unsonicated nano-cellulose addition and the combined incorporation of nano-cellulose and nano-clay. The results demonstrate that these additions significantly enhance the compressive strength, abrasion resistance, and water absorption ratios of the cement composites. Furthermore, the inclusion of nano-clay improves the microstructure of the cement matrix, strengthening the interfacial transition zone and reinforcing the bond between nano-cellulose and the cement matrix. The microstructural analysis using scanning electron microscopy (SEM) reveals the presence of a dense interconnected structure characterized by rod-like crystals. This research contributes to the development of sustainable construction materials by examining the effects of nano-cellulose and nano-clay on the properties and microstructure of cement composites. The utilization of industrial byproducts, such as wood sawdust, for the extraction of nano-cellulose offers an eco-friendly approach to enhance the performance of cement-based materials. The maximum compressive strength obtained, after 28 days, was at mix with 0.75% NCL + 5%NC with a gain of 53.5% than that of the control mix. In mixes containing only nano-clay (NCL), the increase in NCL content led to a higher rate of water absorption in the cement matrix, which reaches 4%. Confirming the results obtained from compressive strength and water absorption, mix with 0.75% NCL and 5% NC had obtained the optimum values with an improvement of 20% than that of the control mix.

Mechanical, microstructural, and textural evaluation of aluminum-MWCNT composites manufactured via accumulative roll bonding at ambient condition

In the present study, aluminum-matrix composites reinforced by multi-walled carbon nanotubes (MWCNTs) were manufactured using the accumulative roll bonding (ARB) process. In the first step, MWCNTs were dispersed between two pieces of Al sheets that were then stacked together and rolled. In the second step, the above procedure was repeated for up to 12 cycles without adding MWCNTs. The microstructure and fracture surface of the composites were studied during various ARB cycles using optical microscopy (OM) and scanning electron microscopy (SEM). Also, the mechanical properties of the composites were measured employing tensile and Vickers hardness tests. More uniform dispersion of MWCNTs was found in the microstructure of the aluminum matrix after 12 ARB cycles. With an increase in the number of ARB cycles, the hardness of the composites was enhanced. The results indicated that after 11 cycles, both the elongation and tensile strength improved and strong interfacial bonding formed between MWCNTs and the Al matrix. However, the development of micro-cracks in the composite resulted in a decrease in elongation and tensile strength at the final cycle. SEM investigations of fracture surfaces revealed that the fracture mode of the composites changed from ductile to brittle in the final ARB cycle, while that of monolithic aluminum remained ductile for all ARB cycles. Texture analysis, also confirmed a transition from the initial recrystallized (Cube and Goss) texture to the ideal rolling texture, mainly with Copper and Dillamore components.

Effects of different treatment processes on microstructure and tensile fracture behaviour of selected laser melting TC17 titanium alloy

It is essential to study the tensile fracture mechanism of additively manufactured materials and develop the effective process treatment techniques to improve their fracture resistance. In this paper, the effects of different treatment processes on the microstructure and tensile fracture properties of TC17 titanium alloy melted by laser selective zone melting were investigated. The static tensile fracture morphological characteristics were observed by combining SEM and EDS. The metallographic microstructure after chemical corrosion was observed optically. And the tensile fracture morphology of the three states of TC17 titanium alloy samples at room temperature conditions was investigated. The results show that the metallographic matrix microstructure of TC17 titanium alloy after HT, HIP and HIP-HT treatments was a bimodal structure with α+β phases, i.e., β phase was in the form of a net basket, and α phase was in the form of a coarse bar. The grain sizes of the samples treated by different processes were different, but the difference in grain size of the HT-treated tissues was small, and the difference in grain size of the HIP-HT-treated tissues was large. And the coarse α-phase segregation could be seen at the edge of the samples. The 3D-printed materials had complex changes in anisotropic properties affected by the printing structure and tissue. The printed tissues were brittle and had high internal stresses. These problems were partly improved at high temperatures, but they still existed. The HIP-HT-treated materials had a large α+β-phase bimodal structure. The HT-treated material had coarse grains and precipitation phases, poor room temperature plasticity, and improved high temperature plasticity. After HT treatment, the original printing microstructure changed, the strength and plasticity were significantly improved, but the macroscopic printing structure still had a slight influence on the fracture morphology. When HIP treatment temperature was higher, the influence of macroscopic printing structure basically disappeared, but the grain and microstructure grew up, and the strength and plasticity were slightly lower than that of the HT treatment. HIP process basically eliminated the unfused defects of the three-dimensional morphology, and the local weak bonding zone formed.

Thermo- mechanical and microstructural characterization of LECA and low carbon cement based lightweight mortar using box behnken design, and embodied energy analysis

Lightweight aggregate mortar (LWAM) containing different kinds of supplementary cementitious materials (SCMs) has gained significant attention as a sustainable construction material. However, the behavior of this type of mortar at elevated temperature conditions, such as those encountered in fire events, remains largely unexplored. In this study, the effect of different temperatures (i.e. at 27⁰C, 110⁰C and 850⁰C) on the Thermo-mechanical and microstructural properties of LWAM containing low grade limestone slurry (LgLS), class- F fly ash (FA), and lightweight expanded clay aggregate (LECA) is investigated. LgLS and FA were replaced with ordinary Portland cement (OPC) in the range of 0–20%, and 0–30% by weight. River sand was replaced with LECA, ranging from 0% to 50% with an increment of 25% in river sand fractions. Along with this, statistical modelling and parametric optimization were done using Box Behnken Design (BBD) of Response Surface Methodology (RSM). Advanced characterization techniques such as- Field Emission Scanning Electron Microscopy (FE-SEM) and X-ray Diffraction (XRD) were performed to investigate the effect of higher temperatures on the microstructure and hydration products of LWAM matrix. Embodied energy analysis was also carried out to investigate the environmental assessment along with cost analysis. It was concluded that as compared to the reference LWAM mix at 27 °C; CS at 28 days was increased by 15–25% at temperature of 110 °C for different mixes, while the same was drastically decreased by 60–64% at higher temperature i.e. 850 °C. Embodied energy analysis predicted that carbon emission can be minimized by about 25%, which is the need of the recent era to meet sustainable development goals.

Durability assessment of fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates against acid and sulfate attack

There is a constant drive to develop high-performance concrete with enhanced mechanical and durability characteristics while incorporating environment-friendly materials. The study investigates the synergistic effects of fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) on the durability characteristics of 100 % recycled aggregate (RA) based geopolymer concrete (GPC) against acid and sulfate attacks. Moreover, its relative performance compared to control samples of ordinary Portland cement (OPC) concrete with natural and recycled aggregates was also assessed. The acid and sulfate resistance were determined by submerging the concrete specimens in the 5 % sulphuric acid (H2SO4), 5 % sodium sulfate (Na2SO4), and 5 % magnesium sulfate (MgSO4) for up to 180 days of exposure duration. The specimens' resistance to chemical attack was assessed by visual observation, changes in weight, and the percentage of compressive strength loss at different time intervals. In addition, the changes in the mineralogical and microstructures of the GPC matrix were also examined using X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) tests. Results indicated that an increased proportion of GGBS and SF positively influenced the durability of GPC, as revealed by reduced mass loss and compressive strength degradation. In addition, the microstructural, mineralogical, and morphological properties depicted enhanced densification and compactness of the GPC matrix due to the formation of CSH, CASH, and NASH gels. GPC-MG15 (FA:GGBS:SF – 35:50:15) yielded the highest strength and durability performance, compensating for the trade-offs of using 100 % RAs in conventional OPC concrete. So, optimized use of these sustainable materials has depicted promising results in aggressive environments while reducing the need for conventional OPC and natural aggregates.

Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. This study focuses on the GAG molecules chondroitin sulfate (CS), dermatan sulfate (DS), and hyaluronic acid (HA). CS and DS are stereoisomers while HA is the only non-sulfated GAG. We characterized and decoupled the effects of these GAG molecules on the stiffness, transport, and matrix microarchitecture properties of type I collagen hydrogels using mechanical indentation testing, microfluidics, and confocal reflectance imaging, respectively. We complement these biophysical measurements with turbidity assays to profile collagen aggregate formation. Surprisingly, only HA enhanced the ECM indentation modulus, while all three GAGs had no effect on hydraulic permeability. Strikingly, we show that CS, DS, and HA differentially regulate the matrix microarchitecture of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs define key physical properties of the ECM, this work shows new ways in which stiffness measurements, microfluidics, microscopy, and turbidity kinetics can be used complementarily to reveal details of collagen self-assembly and structure. Statement of SignificanceCollagen and glycosaminoglycans (GAGs) are integral to the structure, function, and bioactivity of the extracellular matrix (ECM). Despite widespread interest in collagen-GAG composite hydrogels, there is a lack of quantitative understanding of how different GAGs alter the biophysical properties of the ECM across tissue, cellular, and subcellular length scales. Here we show using mechanical, microfluidic, microscopy, and analytical methods and measurements that the GAG molecules chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially regulate the mechanical, transport, and microstructural properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. As such, these results will inform improved design and utilization of collagen-based scaffolds of tailored composition, mechanical properties, molecular availability due to mass transport, and microarchitecture.

Surface modification of miscanthus fiber with hydrophobic silica aerogel for high performance bio-lightweight concrete

Bio-fiber reinforced cementitious material is now attracted widespread attention thanks to its low carbon footprint and its advantages in energy conservation in buildings. However, the main concerns of using large volume of bio-fibers in concrete is its high water absorption and the leaching of organic matter that is incompatible with cement. This study investigates a surface modification method of a bio-fiber (miscanthus) by using hydrophobic silica aerogel and further evaluates its mechanical and insulating performance in lightweight concrete and increase its compatibility with cement. X-ray diffraction, thermal gravimetry and calorimeter test were carried out to investigate the effect of hydrophobic miscanthus fibers on the microstructure of cement matrix. The results show silica aerogel modified miscanthus fiber enhances both the compressive and flexural strength, meanwhile significantly improving the insulating performance of concrete. The use of superhydrophobic aerogel particles reduces the sugar leached from miscanthus and the hydration heat peak is only slightly delayed with the incorporation of aerogel coated miscanthus fibers. The results of this study shed light on surface modifications of bio-fibers for applications in high performance construction materials.

Effects of nano-SiO2 additives on carbon fiber-reinforced fly ash–slag geopolymer composites performance: Workability, mechanical properties, and microstructure

Abstract Fly ash and slag are commonly used precursors in alkali-activated concrete. However, they suffer from high brittleness, poor toughness, and susceptibility to cracking. To address these limitations, this experimental study investigates the effects of different contents of nano-silica (SiO2) additives on the workability, mechanical properties, and microstructure of carbon fiber-reinforced fly ash–slag geopolymer composites (CFSGs). The results indicate that owing to its large specific surface area, nano-SiO2 significantly increases the water demand of the geopolymer, thereby considerably decreasing the fluidity and shortening the setting time of the geopolymer. However, nano-SiO2 improves the porosity, water absorption, and mechanical properties of the CFSG. The optimal mechanical strength is obtained by using 2% nano-SiO2. In addition, appropriate nanodoping can relatively improve the bearing capacity and fracture toughness of the specimen. Compared with that of undoped CFSG, the peak load, fracture toughness, unstable fracture toughness, and elastic modulus of the 2%-SiO2-doped CFSG increased by 8.78, 5.0, 9.6, and 9.8%, respectively. The incorporation of nano-SiO2 increases the shrinkage of the geopolymer, with a more significant impact on early shrinkage. Moreover, nano-SiO2 improves the microstructure of the cement matrix and interface through the filling, volcanic ash, and crystal nucleus effects as well as interface regulation. This increases the bonding force between the matrix and carbon fibers (CFs), which results in good bonding between the CFs and geopolymer matrix, accelerated geopolymerization reaction, and denser geopolymer paste, thus improving the mechanical strength of the CFSG.

Computational model to estimate chloride diffusivity by ternary random walk simulation on tomographic 3D microstructure of cement matrix

This study proposed a model to estimate the chloride diffusivity of the cement matrix by performing a ternary random walk simulation, which considers both connected and disconnected pores in tomographic 3D microstructure. Ternary structures of cement paste, consisting of pore, hydrate, and anhydrous phases, were obtained from X-ray micro-CT images by calculating each phase's representative linear attenuation coefficient based on the quantitative X-ray diffraction results. A novel random walk simulation introducing the concept of hydrate retention time upon ternary microstructures was applied to cement paste. From the developed ternary random walk simulation, the values of the hydrate retention time were determined considering multi-scale porosities and the experimental data of chloride diffusivity. The results showed that the hydrate retention time ranged from 325 to 108 as w/c increased from 0.3 to 0.7. Empirical formulas for estimating hydrate retention time according to the porosity of hydrate voxels and the hydration degree was established. Based on these formulas, the proposed model performing ternary random walk simulation on X-ray micro-CT images enables the estimation of chloride diffusivity of actual cement paste with only the initial w/c as input, making it a practical and accurate tool for durability characterization.

Phase field simulating grain refinement of magnesium alloy by thin strip second phase particles

The study has investigated the grain growth of AZ31 magnesium alloy matrix with fine strip second phase particles, by the phase field model in the real space and time, through introducing free energy equation, and compared with the simulated results containing spherical particles. The results showed that both the thin strip ellipsoidal particles and the cuboid particles have grain refinement effect on the microstructure, moreover, when the content of the second phase particles is the same, the refining effect of thin strip particles could be better than the spherical particles on the matrix microstructure. This study provides the real scale phase field models to research the grain refinement by second phase particles.

The Microstructure and Mechanical Properties of High Entropy Alloy CoCrFeNiMn Matrix with Cr3C2 Reinforcement and Ag, BaF2/CaF2 Solid Lubrication

A series of CoCrFeNiMn high-entropy alloy matrix self-lubricating composites were prepared by spark plasma sintering. The composites are composed of an FCC phase, Cr7C3, Ag, and eutectic fluoride BaF2/CaF2 phases. The microstructure of the composites is uniform. The additional phases distribute along the boundary of equiaxed grains of the FCC phase. The compressive yield strength and fracture toughness decrease with the increase of eutectic fluoride BaF2/CaF2. The composites are susceptible to brittle cleavage fracture.