Search

Herein, the Co‐free, low‐cost dual‐phase AlCrCuFeNi3 high‐entropy alloy (HEA) is successfully developed by in situ alloying induced by selective laser melting (SLM) technique from an initial mixture of Ni and AlCrCuFeNi alloy powders. The effect of process parameters on the microstructure and strength of the SLMed AlCrCuFeNi3 HEA is investigated. It is found that the degree of in situ alloying strongly depends on the laser power. Low laser power leads to insufficient in situ alloying, and a large amount of incompletely diffused Ni and body‐centered cubic (BCC) AlCrCuFeNi alloy powder blocks remain, forming the eutectic structure with alternating face‐centered cubic and BCC phases. With the increase in laser power, the degree of in situ alloying increases, resulting in a decrease in the number of BCC phases as well as the yield strength of the SLMed AlCrCuFeNi3 HEA. The highest yield strength of the SLMed AlCrCuFeNi3 HEA is obtained at low laser power (200 W–600 mm s−1), reaching 689.02 ± 17.54 MPa. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and mechanism of Ti65 alloy with a bimodal microstructure were investigated by isothermal compression experiments conducted on the Thermecmastor-Z simulator equipment at temperatures ranging from 950 to 1110 °C and strain rates ranging from 0.01 to 10.0 s−1. The Arrhenius constitutive model, based on strain compensation, and Grey Wolf optimization-neural network with back propagation model (GWO–BP), were both established. The differences between the experimental and predicted value of flow stress were compared and analyzed using the two models. The results show that the prediction accuracy of GWO–BP in the two-phase region is higher than that of Arrhenius model. In the single-phase region, both methods demonstrated high prediction accuracy. Compared to the single-phase region, the flow stress of Ti65 alloy shows a higher degree of softening in the two-phase region. During deformation in the two-phase region, the initial lamellar α phase transformed from a kinked and elongated morphology to a globularized topography as the strain rate decreased. Boundary-splitting was the primary mechanism leading to the spheroidization process. The degree of recrystallization increased with the increase in strain rate during the deformation in the single-phase region, while dynamic recovery and strain-induced grain boundary migration were the main deformation mechanisms at a lower strain rate. Discontinuous dynamic recrystallization may be the dominant recrystallization mechanism under a high strain rate of 10 s−1. [ABSTRACT FROM AUTHOR]

A sub-eutectic high-entropy alloy composed of CoCrFeNiNb0.25 was prepared using a combination of mechanical powder mixing and selective laser melting (SLM). The mechanical properties of the alloy were enhanced by employing an interlayer laser remelting process. This study demonstrates the feasibility of using mechanical mixing and SLM to form an CoCrFeNiNb0.25 alloy. The interlayer laser remelting process can effectively promote the melting of Nb particles introduced by mechanical mixing, release the stresses near the unfused Nb particles, and reduce their degradation of the specimen properties. The results indicate that the CoCrFeNiNb0.25 alloy, prepared using the interlayer laser remelting process, had an average microhardness of 376 HV, a tensile strength of 974 MPa, and an elongation at break of 10.51%. This process offers a viable approach for rapidly adjusting the composition of high-entropy alloys for SLM forming. [ABSTRACT FROM AUTHOR]

Traditional multi-pass friction stir processing (FSP) can homogenize the microstructure and enhance the mechanical properties of magnesium alloy, but the thermal cycle between adjacent passes will lead to a large heat-affected zone (HAZ), which will cause the inability to create large high-performance areas. In this paper, magnesium alloy with ultrafine grains was correctly prepared by multi-pass submerged FSP (SFSP), and a large number of fine tensile twins were introduced into the stirring zone (SZ). The microstructure and properties of the SZ under different processing conditions were characterized by scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The effects of microstructure and substructure on mechanical properties were systematically studied. The results show that the thermal cycle was seriously weakened and the HAZ was significantly reduced compared with air-cooling FSP (AFSP). In addition, SFSP led to more uniform distribution of second-phase particles and introduced high-density dislocations, while the dislocation density decreased after AFSP. Although the high dislocation density tended to lead to plasticity loss, this unique microstructure allows the material to achieve satisfactory mechanical properties. [ABSTRACT FROM AUTHOR]

Recently, there has been an increasing interest in liquid rubbers (LRs), which can work as reactive processing aids to replace conventional plasticizers and are used as prepolymers to synthesize novel block copolymers. However, the understanding of effects of their microstructures on the properties of materials is still not sufficient. In this study, liquid 1,4‐polyisoprene (L1,4‐IR) and liquid 3,4‐polyisoprene (L3,4‐IR) with similar molecular weight were selected and mixed with styrene–butadiene rubber (SBR)/butadiene rubber (BR). The effects of microstructures of the LRs on the properties of materials were investigated. L1,4‐IR has more 1,4‐units and fewer 3,4‐units than L3,4‐IR. This gives L1,4‐IR a lower glass transition temperature and much more flexible polymer chains. Vulcanizates containing L1,4‐IR had advantages over samples containing L3,4‐IR, including lower Mooney viscosities, smaller ΔG′ value from 0.3% to 43% of strain, fewer sol fractions, better abrasion resistance and lower values of tan δ at 60 °C. In contrast, high contents of 3,4‐units endow L3,4‐IR with low unsaturation in polymer backbones and high glass transition temperature. Samples containing L3,4‐IR showed higher values of tan δ at 0 °C, better thermal stabilities and excellent DIN abrasion resistance after aging compared to samples with L1,4‐IR. Furthermore, there were no big differences in the mechanical properties of SBR/BR compounds containing L1,4‐IR or L3,4‐IR. The results of this study are of great importance to the practical application of liquid polyisoprene in the rubber industry. © 2023 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

The design and exploration of novel structures in engineering, where unique structures can produce significant improvements in performance, has always been an important multidisciplinary research area. Unlike traditional manufacturing, the unique manufacturing concept of additive manufacturing (AM) enables the construction of complex structures with ease. Therefore, the exploration of novel structures by means of additive manufacturing has become a hot point of research in this field, taking full use of the advantages of AM. In this paper, we design a ribbed honeycomb structure based on the bionic principle and construct and study it by selective laser melting (SLM). The hardness, relative density, and structure are characterized at different combinations of scanning speed and laser power, and the best structure and properties are found at 1200 mm/s and 400 W. On the basis of these printing parameters, several groups of specimens with different structures were constructed again to investigate the deformation process and mechanical properties during the out-of-plane compression. It was found that the platform stress of the honeycomb could be increased by up to 19.0% after the addition of ribs, and the honeycomb with 10° rib inclination showed a rib-dominated deformation mode during the deformation process, in which the compression curve showed extremely regular and periodic fluctuations with a large range. [ABSTRACT FROM AUTHOR]

This study employed polyaluminium chloride (PAC) and polyaluminium ferric chloride (PAFC) for the phosphorus removal released during the hydration of phosphogypsum-based excess-sulphate slag cement (PESSC), as well as microstructure modification. The results indicated that the PESSC samples presented shorter setting times and bleeding rates with further modifier addition due to the effective phosphorus removal and rapid establishment of the flocculated structure. Compressive and flexural strengths were also significantly enhanced in modified samples at each age, where they exceeded 58 MPa and 13 MPa at 180 d, respectively, when PAC and PAFC supplements were within 1.0%. Furthermore, the distinctions in the effect mechanism of two functional compositions (Keggin-Al 13 and iron phase) in modifiers have also been studied. In contrast to affecting the microstructure of C-(A)-S-H gel, the released Al (OH) 4 ‐ and Fe (OH) 4 ‐ during hydrolysis often acted with sulphate and portlandite, leading to a higher level of ettringite formation, as well as hydration degree. Comparatively, the introduction of the iron phase adversely impacted pH value development of pore solution and retarded the activation process of slag at early age, while also promoting continuous hydration at later age. The optimisation in the microstructure of PESSC also contributed to impurities solidification, presenting the lower leaching concentration in an acid environment. Overall observations suggested that adding 0.5%–1.0% PAC or PAFC in the PESSC are capable of enhancing not only its engineering properties but also promoting its sustainability. [Display omitted] • Incorporating PAC and PAFC shows an excellent solidification of phosphorus at each age, as well as decline in setting time, bleeding rate and toxic leaching of PESSC. • Incorporating PAC and PAFC promotes hydration degree of PESSC, leading to excellent strength development. [ABSTRACT FROM AUTHOR]

The use of a high volume of industrial solid waste mineral admixture and hybrid fiber can greatly reduce the amount of cement in mortar or concrete, improve its performance, ensure the service properties of mortar or concrete, and reuse industrial solid waste to reduce the environmental burden, which has significant research significance. In this paper, the mechanical properties, wear resistance and microstructure of hybrid fiber-reinforced mortar (HFRM) with a high content of industrial solid waste mineral admixture were systematically studied under different water/binder ratios. Mineral admixtures include fly ash, silica fume and granulated blast furnace slag (slag). The total content of hybrid glass fiber (GF) and polypropylene fiber (PPF) was 2% by volume fractions, and six different water/binder ratios ranging from 0.27 to 0.62 were used. The following conclusions were drawn: fibers have a significant negative effect on the properties of mortars with a low water/binder ratio (w/b = 0.27) and high content of mineral admixtures. In general, the effect of adding hybrid fiber on improving the wear resistance of mortar is more obvious. The average residual weight of hybrid fiber-reinforced mortar is the highest after the wear resistance test. Comprehensively considering the compressive strength, flexural strength, wear resistance and microstructure of the mortar samples, G8PP2-0.40 is the optimal mix ratio. At this time, the replacement rates of fly ash, silica fume and slag are: 20%, 5% and 30%, the water/binder ratio is 0.40, and the content of GF and PPF is 1.6% and 0.4%, respectively. [ABSTRACT FROM AUTHOR]

Dissimilar AZ31B/2024-T4 T-lap-joint was successfully fabricated by friction stir welding (FSW) with the rotation speed of 600r/min and the welding speed of 65 mm/min. The microstructure characteristics were observed and analyzed with optical microscope (OM) and the forming mechanisms were discussed by energy spectrometer (EDS) and X-ray diffractometer (XRD). In addition, the effect of microstructure on mechanical properties was analyzed. The results showed that the metal of the skin and stringer are fully mixed at the original connection surface under the action of stirring and friction of the pin. The welded joint formed a mixed region of magnesium and aluminum (Mg–Al MR). A multiphase structure composed of α-Al, α-Mg, and Al12Mg17 was formed in Mg–Al MR, which also contained a small amount of Al3Mg2. The microhardness values were W-shaped and N-shaped along the skin and stringer directions, respectively. The microhardness values in MR rose rapidly and the broken Mg matrix in the skin was evenly distributed in the MR. The tensile results showed that the skin have excellent failure strength, which was 85.2% of the base metal. The fracture morphology of skin and stringer was mixed fracture and brittle fracture, respectively. [ABSTRACT FROM AUTHOR]

While curved surface microstructures have wide applications in optical components and devices, how to achieve high machining accuracy of the microstructures is crucial for their applications. In the present work, we fabricate sinusoidal modulation microstructures on a curved copper surface by ultra-precision diamond cutting, with the combination of a rotary B-axis and a fast tool servo system. Specifically, tool path planning, together with the consideration of a curved, sinusoidal surface meshing and tool tip arc segmentation compensation, is carried out. Preliminary cutting experiments are firstly carried out on a homemade four-axis ultra-precision lathe, which demonstrates the advantages of additionally applying the rotary B-axis in suppressing burr formations and over-cutting phenomenon over the sole utilization of the fast tool servo system. Subsequent experiments are carried out to evaluate the effects of feed rate and the number of sampling points on the machining accuracy of the microstructures under the combination of a rotary B-axis and a fast tool servo system. With the optimized machining parameters, sinusoidal modulation microstructures, which have a wavelength of 700.6 μm, a peak-to-valley of 18.7 μm, a surface roughness of 18.9 nm and a deviation of profile tolerance of 4.326 μm, are successfully fabricated on a curved copper surface with a face radius of 10 mm and a curvature radius of 500 mm. [ABSTRACT FROM AUTHOR]

Subzero liquid submerged friction stir welding (SFSW) on Magnesium alloy is an investigate limited in the past. As an important lightweight alloy with enhanced yield strength and heat resistance, ME20M Mg alloy has potential value to be researched. In this paper, numerical and experimental subzero SFSW were carried out to systematically investigate the thermal histories, the microstructures and the mechanical properties. The solution of dry ice and ethanol was employed to be the cooling liquid, and different cooling temperatures were employed on low-temperature SFSW of ME20M Mg alloy. The results show that the simulated temperature curves and the experimental temperature curves are closed and within 5% error; as the increasing of the heat input, the precipitations reduced and grew up, the tensile strength of the joints first increased and then decreased, the microhardness of the weld joint decreased. The largest tensile strength is 165.8 MPa, about 69.08% of the base metal. The highest hardness was the peak hardness of the smallest ω/v in WNZ, the lowest hardness located at HAZ of the AS of the largest ω/v, and the values were 57.1 HV0.1 and 44.1 HV0.1, respectively. [ABSTRACT FROM AUTHOR]

Ti65 alloy has extensive potential applications in manufacturing high-temperature components in the aerospace industry. During thermomechanical processing in the α+β phase region, complicated microstructure and texture evolution occurs. In this work, isothermal hot compression experiments were conducted to comprehensively investigate the substructure and texture evolution of Ti65 alloy with bimodal microstructure via the electron backscatter diffraction (EBSD) technique, and the influence of processing parameters on the evolution of substructure and texture was systematically analyzed. The experimental results showed that the distribution of grain boundaries and the transformation of low-angle boundaries (LABs) to high-angle boundaries (HABs) exhibited sensitivity to temperature and strain rate. The fraction of sub-grain boundaries decreased, while the fraction of HABs increased with the increasing of strain rate or temperature due to the spheroidization of the lamellar α phase accompanied by the wedging of the β phase during deformation and the relative misorientation angle distribution between different α variants precipitated from β phase. Temperature rising at a high strain rate resulting from adiabatic heat promoted atomic activity, caused dislocations to be absorbed by sub-grain boundaries or HABs, and finally reduced the dislocation density in both α p and α s phases. Dynamic spheroidization was the main mechanism with increasing temperature, and coarsening of the lamellar α phase was the main mechanism with increasing strain rate. With the increase of temperature or decrease of strain rate, the texture of the α p phase became stronger and the basal and pyramidal slip could be activated. For the α s phase, spheroidization and variant selection together influence the orientation distribution. As a result, the texture evolution showed a complicated tendency. • Substructure evolution of a novel near-α Ti65 alloy were studied. • Texture evolution of α p and α s under different conditions was discussed. • Deformation mechanisms were discussed based on the experiments results. • The slip systems activated under different parameters were analyzed. [ABSTRACT FROM AUTHOR]

In order to prepare high-performance tungsten alloys, surface modification of tungsten nanopowders prepared by a wet chemical method was carried out by acid pickling at room temperature. The low-temperature sintering characteristics of tungsten nanpowders before and after pickling was compared and analysed. The surface modification was carried out by pickling with a solution of hydrofluoric acid, concentrated nitric acid and ammonium fluoride at room temperature. After this surface treatment, uniformly distributed step-shaped defects formed on the surface of the tungsten nanopowders. After low-temperature sintering, the grain size of the tungsten alloy corresponding to the surface-modified powder precursor was reduced by 20% compared to the alloy using untreated powder as precursor. In addition, the step-shaped defects also increase the sintering activity of the pickled tungsten powder and promote its sintering densification, making the final density of pure tungsten sintered at 1600°C as high as 96.7%, and its hardness greatly increased to 521 HV0.2. The results show that room-temperature pickling and subsequent low-temperature sintering is a promising method for preparing high-performance nanotungsten alloys. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) of ME20M magnesium alloy without and with preheating in different temperatures is carried out. The thermal histories of different preheating temperatures are investigated; the microstructure and mechanical properties of the weld joints are studied. The results show that by increasing the preheating temperature, the peak temperature, the grain size as well as the precipitate size are increased, and the precipitation is reduced. After FSW, the preferred orientation of the ⟨ 0001 ⟩ crystal direction changes not to parallel but to normal direction, and the texture intensity improves. The microhardness and the tensile strength of the joints first increase and then decrease with the increase of the preheating temperature. [ABSTRACT FROM AUTHOR]

Reinsurance is the primary source of interconnectedness in the insurance industry. As such, reinsurance connectivity provides a transmission mechanism for financial shocks and potentially exposes insurers to contagion and systemic risk. In this article, connectivity within the U.S. property–casualty (P/C) reinsurance market is modeled as a network. We model the network of all primary insurers and reinsurers in the market. We analyze all bilateral reinsurance counterparty relationships (domestic and foreign) of U.S. P/C insurers, and we model both intra‐ and intergroup transactions. We extend the prior literature by providing a detailed examination of the reinsurance network structure, including network density, network components, centrality of individual insurers, and sub‐network analysis for top insurers. Our analysis of contagion and insolvency risk reveals that even the failure of the top 10 in‐degree or in‐strength insurers with 100 percent loss given default would not lead to widespread insolvencies in the U.S. P/C insurance industry. [ABSTRACT FROM AUTHOR]

• Novel method to preserve both chemical & microstructural properties of kerogen. • Combines closed-system acid-demineralization & critical point drying procedures. • Method enables study of oil & gas storage and transport in kerogen-hosted porosity. Hydrocarbon storage and transport in unconventional shale resources occurs predominantly within pores hosted by kerogen (solid and insoluble organic matter in sedimentary rocks). Kerogen-hosted pores are small, so physiochemical interactions between pore fluids and pore surfaces (e.g., adsorption) are particularly important in shale. The understanding and prediction of hydrocarbon storage and transport in shale is dependent, therefore, upon the correct understanding of both chemical composition and pore geometry of kerogen. Several recent studies have attempted to construct molecular models of kerogen physical and/or chemical structure. Developing these models is challenging, in part because of the lack of laboratory samples of kerogen for experimental characterization that preserve both its chemical and microstructural properties representative of those in the subsurface. This study presents an integrated kerogen-isolation procedure that combines closed-system chemical demineralization with pyrite removal and critical point drying. The method produces a kerogen that is not only high in chemical purity but more representative of kerogen microstructure that occurs in the subsurface. Characterization of kerogen microstructure, which can be performed by direct measurement of the isolate obtained by this procedure, is essential to better understand and predict the storage, transport, and production hydrocarbons from unconventional resources. [ABSTRACT FROM AUTHOR]

Magnetic pulse welding (MPW) has attracted widespread attention due to its advantages on joining dissimilar metals. This paper mainly focused on the effect of surface treatment on the weldability and mechanical properties of Al-Fe joints. Two kinds of surface grinding directions, including parallel to welding direction (P2W) and vertical to welding direction (V2W), were designed to prepare MPW joints. Mechanical properties and interface microstructures were systematically analyzed to establish the corresponding relationship between the two. Results showed V2W welded joints presented a wavy-shape interface and had better mechanical properties. The P2W specimens only showed a straight interface, and the element diffusion in the zone of the wave interface was better than that in the zone of the straight interface. The discharge energies affected mechanical properties by changing the interfacial morphology. In addition, the formed jets could be trapped and led to the formation of interfacial waves when the scratch direction did not coincide with the welding direction, contributing to the formation mechanism of wave interface. [ABSTRACT FROM AUTHOR]

The high‐speed synchrotron X‐ray imaging technique was synchronized with a custom‐built laser‐melting setup to capture the dynamics of laser powder‐bed fusion processes in situ. Various significant phenomena, including vapor‐depression and melt‐pool dynamics and powder‐spatter ejection, were captured with high spatial and temporal resolution. Imaging frame rates of up to 10 MHz were used to capture the rapid changes in these highly dynamic phenomena. At the same time, relatively slow frame rates were employed to capture large‐scale changes during the process. This experimental platform will be vital in the further understanding of laser additive manufacturing processes and will be particularly helpful in guiding efforts to reduce or eliminate microstructural defects in additively manufactured parts. [ABSTRACT FROM AUTHOR]

Twins and fine microstructure can improve the surface properties of magnesium alloys. However, most of the current grain refinement and twinning technologies are costly or complex. In contrast, submerged friction stir processing (SFSP) is a cost-effective process. In this work, Mg-Al-Zn alloys with a fine and uniform twin structure were prepared by multi-pass SFSP with flowing water as coolant. The macro/micro-structure and properties of the surface layer under different processing conditions were characterized. The correlation between microstructure, tribology and corrosion behaviors was systematically studied. The results display that SFSP led to finer grains and created a large number of ultra-fine tensile twins and high-density dislocations in the processed zones compared with air-cooled FSP (AFSP). This unique microstructure resulted in synergistic enhancement of wear and corrosion resistance of Mg-Al-Zn alloy at room temperature. • Twin remanufacturing of Mg-Al-Zn alloy is achieved by submerging FSP. • Fine twinned grains were formed on the surface of Mg-Al-Zn alloy by underwater friction stir processing. • The microstructure evolution mechanism of Mg-Al-Zn alloy was systematically clarified. • The simultaneous improvement of wear resistance and corrosion resistance is related to the fine and uniform twins. [ABSTRACT FROM AUTHOR]

Al 1.8 CrCuFeNi 2 /WC composite coatings – prepared on Ti-6Al-4 V alloy by laser cladding of a high entropy alloy (HEA) Al 1.8 CrCuFeNi 2 powder with the addition of either 0, 10, 20, 30, 50, or 70 wt% WC – were studied in detail for their structure, morphology, phase composition, mechanical and tribological properties. The WC-free Al 1.8 CrCuFeNi 2 coating is composed of a dendritic-shaped bcc matrix phase with ∼14.6 vol% fcc phases between these dendrites. With increasing WC addition, the fcc phase-fraction decreases and several carbide phases are formed leading to the formation of a more complex microstructure. For example, the HEA/WC composite coating prepared with the addition of 30 wt% WC to the HEA powder is composed of an Al-Ti-Ni-rich bcc phase, eutectic, equiaxed Ti-rich carbides, W-rich carbides, and fishbone-like Ti-rich carbides. This coating exhibits a very high hardness of 1372.6 HV 0.2 across the outermost 1.1 mm of the 1.5 mm coating thickness and allows for the highest hardness values among the coatings studied within the initial 0.4 mm directly at the interface to the substrate. This coating further provides the lowest mean-coefficient of friction of 0.49 and lowest wear rate, which is with 6.52·10−7 mm3/Nm only 7% of that provided by the WC-free HEA coating. Thus, by the addition of WC to the HEA powder and the thereby initiated formation of various carbides during the laser cladding process of the Ti-6Al-4 V alloy, composite coatings are accessible, which easily outperform those prepared without WC. [Display omitted] • Various Al 1.8 CrCuFeNi 2 /WC composite coatings were fabricated by laser cladding onto Ti-6Al-4 V. • With increasing WC powder content, the bcc phase fraction of the laser cladded coating increases • Intermixing between HEA/WC powder and Ti-6Al-4 V during LC causes the formation of various carbides, especially TiC. • The coating containing 30 wt% WC provides lowest friction coefficient and lowest wear rate. [ABSTRACT FROM AUTHOR]

Cr-doped ZnO thin films were deposited onto glass substrates by radio frequency magnetron sputtering technique. The effects of annealing temperature and annealing time on the structural and optical properties of the Cr-doped ZnO films were comprehensively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible (UV) and photoluminescence (PL) measurements. XRD studies reveal that the Cr-doped ZnO films are highly oriented along (002) direction. The intensity of ZnO (002) peak firstly increases and then decreases with increasing annealing temperature and annealing time. SEM analysis show that the grain size increases and the surface of films becomes rougher as the annealing temperature increases to 700 °C. The optical transmittance spectra indicate that the average transmittance in the range of the visible region is approximately 80%, and the band gaps of the films decrease with increasing annealing temperature. Two peaks of UV emission and green emission are observed in the PL spectra. The UV emission increases first and then decreases with increasing annealing temperature, which show that the increasing defect concentration in the films leads to the poor crystallinity. The green emission greatly increases with increasing annealing temperature, which could be attributed to the increase of oxygen vacancies and increased nonradiative process. [ABSTRACT FROM AUTHOR]

• The carbonation mechanism of phosphogypsum-based supersulfated cement paste and its effect on microstructure were studied. • The impact of three different CO 2 concentrations (atmospheric, 5% and 20%) on the microstructure was evaluated. • The CO 2 concentration less than 5% is recommended due to the similar microstructure with that of natural carbonation. This study investigates mechanisms of carbonation on the microstructure of phosphogypsum-based supersulfated cement (PSSC) paste at different CO 2 concentrations (atmospheric, 5% and 20%). The products was characterized using XRD, TGA, FTIR and 27Al MAS NMR. It is observed that the main hydration products of PSSC are ettringite, C-A-S-H gels and third aluminate hydrate (TAH), and the carbonation products are calcium carbonate (mainly vaterite and calcite), secondary gypsum, and C-A-S-H gels and separate TAH with varying degrees of decalcification. The quantitative analysis of BSEM images shows that the volume change of products occurring on carbonation significantly increases porosity and pore size of the PSSC paste. Results indicate that the carbonation of PSSC at different CO 2 concentrations results in a progressive carbonation degree, 5% CO 2 supports the accelerated carbonation experiment in PSSC to simulate the natural carbonation process due to the same phase composition and similar microstructure with atmospheric CO 2 and 20% CO 2 further loosens the microstructure of PSSC for the complete decomposition of ettringite and the severe decalcification of gel products. [ABSTRACT FROM AUTHOR]

The delamination toughness of Z-pins reinforced laminates could be improved significantly and in-plane mechanical properties of the laminates were degraded with a few of Z-pins inserted in the through-thickness direction. The influence of Z-pin inserted parameters and moisture absorption condition on the tensile properties of the laminates was experimentally studied. The results showed that Z-pins can change microstructure and the original stress-strain state of the Z-pinned laminates, and the tensile strength and modulus of the laminates were obviously influenced. The tensile modulus of the Z-pinned laminates decreased with the increasing of Z-pins' diameter and volume content, while it increased with that of Z-pins' angle. The moisture absorption rate and balanced moisture content of Z-pinned laminates increased due to Z-pin inserted, which eventually resulted in accelerating degradation of performance of composites laminates. [ABSTRACT FROM AUTHOR]

• PCBAs with the phosphogypsum content up to 80 % were qualified lightweight aggregates. • As the phosphogypsum content increased, hydration products in the aggregates diminished and proportion of harmful pores (greater than200 nm) increased. • A reduced concentration of phosphorus and heavy metals in the leachate of PCBAs compared to the leaching of the original phosphogypsum. While traditional disposal of phosphogypsum either occupies excessive amounts of land or causes serious pollution, novel recycling of phosphogypsum is desirable. Making phosphogypsum-based cold-bonded aggregates (PCBAs) through granulation technology is a potential recycling strategy. In this study, the quality of the recycled PCBAs is assessed, considering physical properties, mechanical strength, impurity stabilization ability, and microstructure. With the increase of phosphogypsum content from 60% to 90%, 28-day bulk density of the PCBAs decreased from 1080 to 950 kg/m3, cylinder compressive strength in over dry (OD) condition decreased from 16.5 MPa to 3.9 MPa, and water absorption increased from 5.9% to 13.6%. SEM, XRD, and MIP analyses showed that as the phosphogypsum content increased, hydration products in the aggregates diminished and proportion of harmful pores (greater than200 nm) increased. Leaching test on 28-day PCBAs showed a reduced concentration of phosphorus and heavy metals in the leachate compared to the leaching of the original phosphogypsum. The study concluded that the PCBAs with the phosphogypsum content up to 80 % are qualified lightweight aggregates (LWAs) for concrete. [ABSTRACT FROM AUTHOR]

Abstract: The effects of MO (Ma) on the crystallization of B2O3–Al2O3–SiO2 glass-ceramics were investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and dilatometer. MO can effectively facilitate the formation of B2O3–Al2O3–SiO2 glass which is influenced by the ratio of B2O3/SiO2, and the crystallization capacity of the glass turns to weaker with the decreasing of B2O3/SiO2 ratio. The main crystal phase is Al4B2O9 when the glass is heat-treated at 800°C, and Al4B2O9 phase could transfer into Al18B4O33 with the heat-treated temperature increasing to 1100°C. The calculation of crystallization activation energy (E) shows that crystallinity follows the order of CaO

Abstract: Pristine and Pd-doped nanoporous SnO x thin films were fabricated via a sol–gel route. The Pd-doped film exhibited enhanced H2 gas-sensing performance, in terms of higher sensitivity and shorter response time. Structural characterization was performed to investigate the effect of Pd doping on the microstructure evolution of the films. The grain and pore size of Pd-doped film, as measured using transmission electron microscopy and grazing-incidence small-angle X-ray scattering (GISAXS), are both smaller than those of undoped film. In particular, the pore size evolution of the films during annealing was quantitatively monitored in situ using synchrotron-based GISAXS. Knudsen gas diffusion and depletion layer models were employed to evaluate the microstructure influence on the gas sensitivity semi-quantitatively. The results suggest that the microstructure of the Pd-doped film is critical for improving the gas sensitivity but cannot account for the total sensitivity enhancement, implying other mechanisms could play a more important role. [Copyright &y& Elsevier]

Interstitial free steels with various grain sizes and textures were prepared by cold-rolling followed by an annealing process. The effect of grain size, crystallographic orientations and stored energy on corrosion behavior of interstitial free steel was investigated. It was found that the deformed microstructure and dislocation boundaries were consumed by recrystallizing grains during annealing. The average grain size increase ranging from 0.61 μm to 11 μm and the volume fraction of recrystallized grains was about 96% after annealing for 64 h; meanwhile, the γ fiber was the dominated recrystallized texture component. The stored energy gradually decreased due to the reduction in dislocation density by annealing. The potentiodynamic polarization and Nyquist plots show that the corrosion potential exhibits a more positive shift and depressed capacitive semicircle radius increase with rising annealing time. The 64 h annealed specimens had the biggest depressed semicircle in the Nyquist plots and the highest positive corrosion potential, which indicates the enhancement of corrosion resistance. Such an improvement of corrosion resistance is attributed to the increase in the volume fraction of the γ fiber and decrease in the stored energy. [ABSTRACT FROM AUTHOR]

Magnetic micromachines as wireless end-effectors have been widely applied for drug discovery and regenerative medicine. Yet, the magnetic assembly of arbitrarily shaped cellular microstructures with high efficiency and flexibility still remains a big challenge. Here, a novel clamp-shape micromachine using magnetic nanoparticles was developed for the indirect untethered bioassembly. With a multi-layer template, the nickel nanoparticles were mixed with polydimethylsiloxane (PDMS) for mold replication of the micromachine with a high-resolution and permeability. To actuate the micromachine with a high flexibility and large scalable operation range, a multi-pole electromagnetic system was set up to generate a three-dimensional magnetic field in a large workspace. Through designing a series of flexible translations and rotations with a velocity of 15mm/s and 3 Hz, the micromachine realized the propel-and-throw strategy to overcome the inevitable adhesion during bioassembly. The hydrogel microstructures loaded with different types of cells or the bioactive materials were effectively assembled into microtissues with reconfigurable shape and composition. The results indicate that indirect magnetic manipulation can perform an efficient and versatile bioassembly of cellular micromodules, which is promising for drug trials and modular tissue engineering. [ABSTRACT FROM AUTHOR]

This study explores the effects of metakaolin (MK) and silica fume (SF) on rheological behaviors and microstructure of self-compacting concrete (SCC). The rheology, slump flow, V-funnel, segregation degree (SA), and compressive strength of SCC are investigated. Microstructure characteristics, including hydration product and pore structure, are also studied. The results show that adding MK and SF instead of 4%, 6% and 8% fly ash (FA) reduces flowability of SCC; this is due to the fact that the specific surface area of MK and SF is larger than FA, and the total water demand increases as a result. However, the flowability increases when replacement ratio is 2%, as the small MK and SF particles will fill in the interstitial space of mixture and more free water is released. The fluidity, slump flow, and SA decrease linearly with the increase of yield stress. The total amount of SF and MK should be no more than 6% to meet the requirement of self-compacting. Adding MK or SF to SCC results in more hydration products, less Ca(OH)2 and refinement of pore structure, leading to obvious strength and durability improvements. When the total dosage of MK and SF admixture is 6%, these beneficial effects on workability, mechanical performance, and microstructure are more significant when SF and MK are applied together. [ABSTRACT FROM AUTHOR]

Highlights • The effects of seawater and SCMs on the durability of LAC were evaluated. • Seawater was more efficient than tap water on improvement of early strength development of LAC. • Synergetic reaction of SCMs and seawater improved durability and microstructure further. • ITZ was improved through internal curing and pozzolanic reaction. Abstract This study is investigated the mechanical properties and durability of lightweight aggregate concrete (LAC) incorporating of metakaolin (MK) and ground granulated blast furnace slag (GGBFS) mixed with artificial seawater. The compressive strength, chloride penetration, drying shrinkage and hydration products of LAC are analyzed. In addition, the micro-hardness of interface transition zone (ITZ) and microstructure development of LAC are characterized by different analytical techniques. The results indicate that the compressive strength of LAC containing 10 wt% GGBFS and 10 wt% MK with seawater mixing exceeds 50 MPa at 28 days. The resistance to chloride ion penetration and drying shrinkage of LAC are improved significantly by the addition of MK and GGBFS, and seawater mixing cannot deteriorate its chloride permeability due to the formation of Friedel's salt (Fs). The combinations of pozzolanic reaction of MK and GGBFS, internal curing of lightweight aggregate and accelerated cement hydration by seawater result in denser hydration products and reduction of Ca/Si ratio in ITZ, which have a great beneficial impact on the durability properties of LAC. [ABSTRACT FROM AUTHOR]

This paper was investigated the durability performances of coral sand concrete (CSC) production by using porous coral sand aggregate and supplementary cementitious materials (SCMs) compared to river sand concrete (RSC). The durability properties of CSC were evaluated in terms of chloride penetration, water absorption, drying shrinkage, accelerated carbonation, and sulfate drying-wetting cycle. The results indicated that the CSC exhibited higher drying shrinkage, capillary water absorption, carbonation depths, and a slightly lower later compressive strength compared with RSC. However, porous coral aggregate provided a more rapid early age strength, better resistance to chloride ion penetration, and sulfate drying-wetting cycle than the RSC due to its internal curing. Additionally, the combinations of internal curing and pozzolanic reaction contributed to the microstructure improvement of CSC, which conformed good durability properties of CSC containing SCMs. Moreover, the ecological evaluation demonstrated that the CSC incorporation of SCMs resulted in a significant reduction of CO 2 emission. [ABSTRACT FROM AUTHOR]

Synchrotron X-rays are integrated with a modified Kolsky tension bar to conduct in situ characterization of the grain refinement mechanism operating during the dynamic deformation of metals. Copper with an initial average grain size of 36 μm is refined to 6.3 μm when loaded at a constant high strain rate of 1200 s −1 . Synchrotron measurements revealed the temporal evolution of the grain refinement mechanism in terms of the initiation and rate of refinement throughout the loading test. A multiscale finite element based recrystallization model has been developed to predict the grain size evolution occurring during the dynamic deformation process. The model accurately predicts the initiation and temporal evolution of the refinement phenomenon with a predicted final average grain size of 2.4 μm. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcined gangue within 20% can be used as an substitution of slag for the preparation of phosphogypsum-based sulphate cementitious materials contained 45% phosphogypsum (PESCM). • Preparing PESCM by wet co-milling presents greater fresh and hardening properties, including stability, rheology, strength and heavy metal solidification. • Hydration phase assemblage and microstructure evolution of PESCM contained 0–20% calcined gangue with/without wet co-milling were characterized. • Effect mechanism of calcined gangue and wet co-milling on the hydration of PESCM was investigated. • Advantages and applicability of wet co-milling and adding calcined gangue on the PESCM preparation were assessed. This paper presents an experimental study on the effects of calcined gangue and wet co-milling on the properties of phosphogypsum-based excess-sulphate cementitious materials (PESCMs), including setting time, rheology, heavy metal solidification and strength development. For PESCMs containing 0%-50% calcined gangue, with and without wet co-milling, we examined hydration and microstructural evolution. Results indicate that the addition of calcined gangue shortens the initial and final setting time of fresh PESCM pastes, and impairs stability, fluidity and strength development. After wet co-milling, the rheological and mechanical properties of PESCM pastes are improved, where the binders with 10–20% calcined gangue show a 40% increase in 28-d compressive strength. Hydration of calcined gangue is rapid and weakens the retarding effect of impurities, providing more active aluminates and silicates for further hydration. Wet co-milling promotes physical dispersion, chemical dissolution and thus hydration, which helps refine microstructure for a better development of strength and heavy metal solidification capability. [ABSTRACT FROM AUTHOR]

Landfilled phosphogypsum would cause severe environmental issues, but the waste can be recycled for preparing excess-sulphate cement, an eco-friendly alternative to conventional cement. This paper investigates the effect of metakaolin (0–50%) on early hydration, phase assemblages and mechanical properties of the excess-sulphate phosphogypsum cementitious materials (ESPCMs). Results indicate that metakaolin is related to a new exothermic peak and significantly shortens the induction period. Setting time of ESPCM pastes is reduced by 13%–38% with 10%–50% dosage of metakaolin. More ettringite and highly disordered C-(A)-S-H gel are characterised when metakaolin dosage is below 20%, leading to 70% increase in 28-d compressive strength. With above 20% metakaolin dosage, portlandite consumption at early stage is promoted and hydration degree at late state is reduced. It turns out that within 20% metakaolin dosage is efficient to optimise setting time and strength development of ESPCMs, where slag and metakaolin synergistically promote the formation of ettringite and C-(A)-S-H gel to bind the unhydrated cement particles effectively. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of phosphogypsum (PG) on the hydration and retardation mechanism of phosphogypsum-based excess-sulfate slag cement (PESC) was mainly investigated. Based on the natural characteristics of PG, such as low pH value and the presence of soluble phosphorus impurities, the content of PG passing the 4.75 mm standard sieve was used as a variable to study the retardation mechanism of PG on PESC. It can be inferred from the heat flow and cumulative heat flow that the induction period is significantly prolonged with the content of PG, which is also reflected in the increase of the setting time of PESC. In the early period of hydration, as the content of PG increases, the soluble phosphorus concentration increases, and the pH value decreases. The changes in soluble phosphorus concentration and pH value affect the microstructure and amount of hydrates. Combined with experimental results, it has been demonstrated that the delay in the hydration of PESC by PG content is mainly due to: the excessive dissolution of Ca2+ and SO 4 2- promotes the recrystallization of dihydrate gypsum; the dissolution of soluble phosphorus reduces the pH value in the pore solution and forms precipitates of calcium phosphate and hydroxyapatite; in the initial reaction period, a large amount of ettringite and C-S-H gel precipitate to form a protective film; the decrease in pH value leads to a decrease in carbonization resistance, and CO 2 in the air is more likely to attack the PESC paste, react with alkaline substances in PESC, or degrade hydrated C-S-H and ettringite. The above factors all lead to a decrease in exchangeable ions during the hydration, thereby prolonging the setting of PESC. • Using phosphogypsum-based excess-sulfate cement (PESC) for the preparation of super retarding materials. • PESC can achieve initial setting for 86 hours and final setting for 134 hours without additional retarders, and its 28d-compressive strength is 24.9 MPa. • The retardation mechanisms of phosphogypsum in PESC has been explored. • The microstructure and amount development of hydrates in PESC were analyzed. [ABSTRACT FROM AUTHOR]