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Workability and early-ages mechanical properties are important indicators of magnesium potassium phosphate cement (MKPC) as a repair material. The effect of metakaolin (MK) on the setting time, fluidity and early-ages strength of MKPC paste was studied, and its influence mechanism was analyzed through pore structure, microstructure and nanomechanical properties. The results show that 10% and 20% of MK prolong the setting time of MKPC paste, but excessive MK shortens the setting time of MKPC paste. Meanwhile, incorporating MK reduces the fluidity of MKPC paste, and the early-ages strength of MKPC specimens increases when the substitution ratio of MK is 10%. When 10% of MK is incorporated to the MKPC paste, the 30-d shrinkage of the sample is only 69% of the control group. Meanwhile, a proper amount of MK can improve the pore structure of the MKPC specimen and make its microstructure denser by generating amorphous aluminosilicate phosphate gel. It is observed from the nano-scale characteristics that incorporating 10% MK can reduce the content of pore phase and unreacted MgO phase, and increase the volume fraction of hydration products. [ABSTRACT FROM AUTHOR]

As a nontraditional processing technology, electrochemical discharge machining (ECDM) can process glass and engineering ceramics precisely. This technology has proven to be a potential process for glass 3D microstructure. However, the key to expanding the application of ECDM is how to improve machining accuracy. This research conducted micro-hole and microgroove machining. Power voltage and frequency influence on hole processing efficiency, hole entrance diameter, and hole limit depth was explored. We considered four factors affecting ECDM—the voltage and frequency of the pulse power supply, the tool electrode feed rate, and the rotation speed. We studied their influence on the roughness of the microgrooves. The results show that machining efficiency, entrance diameter, and limit depth of micro-holes increased with the increase in voltage but decreased with the increase in power frequency. The results show that the roughness of microgrooves has an apparent positive correlation with the power voltage. In contrast, it had an evident negative correlation with the power frequency and electrode speed. The bottom surface roughness of microgrooves can be as minor as 0.605 μm. Various complex 3D microstructures on the glass surface by layer-by-layer method proved the great potential of ECDM. [ABSTRACT FROM AUTHOR]

• Inspired by human skin, a novel dual spinosum microstructured sensor was fabricated. • The sensor demonstrated high pressure sensitivity and excellent cycle stability. • Our sensor has excellent capabilities in temperature and texture roughness detection. The bionic sensor imitates the function of biological perception of external stimuli, which have attracted tremendous attentions. However, it remains a great challenge to prepare wearable bioinspired sensor with highly sensitive at low pressure and with multifunctional sensory capabilities. Herein, inspired by the spinosum structure of human skin, a novel surface morphology with dual spinosum microstructure (DSM) sensor was constructed by using clay and sucrose double template method. Benefiting from the reconfigurable behavior of the DSM, the assembled piezoresistive sensor demonstrated high sensitivity (32.9 kPa−1), pressure detection limit of 11 Pa, short response time (＜400 ms), and excellent stability (loading/unloading test of 3000 cycles). In practical application, the sensor showed excellent sensing performance in differentiating tiny stress changes and monitoring human motion in all directions, such as respiration, pulse, bending motions and gestures. Additionally, the novel sensor can detect environmental temperatures and recognize textures, which showed promising applications in intelligent electronic skins and human health monitoring. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of high-speed train bearing are significantly influenced by the harsh service environment during the long-term service process, which is crucial for the safety and service life of bearing. In this paper, the outer ring of high-speed train bearing is taken as the research object. The microstructure of the outer ring under different service periods was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) combined with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The mechanical properties were measured by the MTS testing machine and microhardness tester. The evolution of microstructure and mechanical properties of the high-speed train bearing outer rings under different service periods was investigated by comparative analysis. The results show that, with the increase of the service period, the bainite in bearing outer ring become coarser, the number of acicular carbides increases, and size of microcracks increases. Moreover, the dislocation density and microhardness near the inner-surface of the outer ring increases slightly. However, both yield strength and ultimate strength decrease with the increase of the service period. [ABSTRACT FROM AUTHOR]

The fabrication of micro-holes in silicon substrates that have a proper taper, higher depth-to-diameter ratio, and better surface quality has been attracting intense interest for a long time due to its importance in the semiconductor and MEMS (Micro-Electro-Mechanical System) industry. In this paper, an experimental investigation of the machining performance of the direct and chemical-assisted picosecond laser trepanning of single crystalline silicon is conducted, with a view to assess the two machining methods. The relevant parameters affecting the trepanning process are considered, employing the orthogonal experimental design scheme. It is found that the direct laser trepanning results are associated with evident thermal defects, while the chemical-assisted method is capable of machining micro-holes with negligible thermal damage. Range analysis is then carried out, and the effects of the processing parameters on the hole characteristics are amply discussed to obtain the recommended parameters. Finally, the material removal mechanisms that are involved in the two machining methods are adequately analyzed. For the chemical-assisted trepanning case, the enhanced material removal rate may be attributed to the serious mechanical effects caused by the liquid-confined plasma and cavitation bubbles, and the chemical etching effect provided by NaOH solution. [ABSTRACT FROM AUTHOR]

The degradation of components resulted from wear is unavoidable in service, which could be partly solved by applying surface treatment technique. Stellite-6 cobalt-based alloy is considered as a potential cladding material to improve the wear resistance of base materials owing to its excellent hardness and strength. The microstructural evolution and local mechanical properties of Co-rich matrix and Cr-rich eutectic carbide of Stellite-6 cladding with different aging times at 900 °C are investigated by optical microscopy, field emission scanning electron microscope and nanoindentation testing. The tribological characteristics of the matrix and eutectic carbide itself are systematically investigated using the single-pass nano-scratch testing. In the matrix region, the carbide precipitations occur after 5 h and coarsens after 10 h aging. The nanoindentation results indicate that the hardness of the matrix regions is significantly increased due to the presence of dispersed carbide and fine stripe-like precipitations. The nano-scratch tests depict that the wear resistance is improved with higher matrix hardness to support eutectic carbide based on aging treatment. Potential improvement on tribological performance through the aging treatment procedure is proved based on the micromechanical and wear behaviors of matrix and eutectic carbide were identified. [ABSTRACT FROM AUTHOR]

In this study, a novel hybrid ultrasonic-electromagnetic (UEM) field was introduced into laser cladding (LC) to fabricate Inconel 718/60% tungsten carbide (WC) metal matrix composites (MMCs) coating on Inconel 718 substrate. Effects of hybrid UEM field on macrostructural, microstructure, phase composition, crack propagation and microhardness of MMCs coating were studied. Results show that under hybrid UEM field, the height of the MMCs coating increases, the cracks in MMCs coating can be effectively eliminated, the distribution of WC particles in the coating becomes more homogeneously, and the heat damage degree of WC particles is significantly decreased. Moreover, hybrid UEM field helps refine the microstructure and promote the transition of coarse carbide precipitates to the smaller spherical carbides. As a result, the microhardness of MMCs coating distributes more evenly in the coating under hybrid UEM field. [ABSTRACT FROM AUTHOR]

• Microstructure of bearing outer ring Characterized by various means. • Three crack nucleation sites appear after tensile unloading. • The initiation and propagation of crack was monitored by in-situ tension with the increasing of stress. • Bainite colony (Prior austenite) leads to quasi cleavage fracture as the weakest link. Bearing plays an important role in operation safety as the key component of high-speed train. The service life is affected by the fracture behavior of bearing during operation seriously. In this paper, the MTS universal testing machine was used to carry out tensile test and tension-unloading test on the sample of the bearing outer ring. On this basis, the fracture process was dynamically monitored by in-situ tensile test. The stress state of the sample during tensile process was calculated by the finite element software ABAQUS. The results show that the microstructure is composed of lower bainite, (Fe,Cr) 3 C carbides and a small amount of residual austenite. The ultimate strength of outer ring is 2.3GPa. Compared with the center of the sample, the stress triaxiality on the surface is low and the shear stress is high relatively, reinforcing the local plastic deformation. Microcracks are the main damage forms of bearing outer ring. The microcracks nucleate in the three sites, which are the boundary of bainite colony, between the bainite lamellae and around carbide. The bainite colony is the weakest link of the bearing. A large number of microcracks nucleate on the boundary of bainite colony. Under the action of tensile loading, the microcracks propagate along the boundary of bainite colony. With the increasing of load, the cracks propagate unsteadily and lead to the quasi-cleavage fracture of the sample. [ABSTRACT FROM AUTHOR]

This paper provides a convenient, efficient and repeatable method for the preparation of flexible PDMS superhydrophobic films. The stainless steel template was etched with picosecond laser to create textures, which was then filled with PDMS and thermally cured to produce PDMS superhydrophobic films featuring corresponding microstructures. By constructing computational models of the microstructures and exploring the influence of laser scanning spacing on contact angle, the process parameters were optimized to obtain superhydrophobic PDMS films while ensuring the stability of microstructures. The microstructures showed straight lines spaced 55 μm apart, with each line connected by regular truncated cone structures. These structures formed Cassie contacts with the droplets, exhibiting a contact angle of 152.1° and a sliding angle of 9°. In addition, this study demonstrates the reproducibility of the PDMS superhydrophobic film preparation method and its effectiveness in delaying icing. The results indicate that the templates can be used for more than twenty replications, and the obtained PDMS superhydrophobic films have a delayed icing time of 3.3 times. These findings suggest that the PDMS superhydrophobic films have excellent performance and repeatable characteristics, making them suitable for various applications. • Preparation of PDMS superhydrophobic films with repeatable demoulding function • A wettability calculation model for multiple types of microstructures • Excellent application of flexible surfaces and delayed icing performance [ABSTRACT FROM AUTHOR]

The microstructure of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] was regulated by the heat treatment of partial melt recrystallization method (PMRM) to improve its mechanical properties effectively. The structural changes and toughening mechanism of P(HB-co-HV) were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), scanning electron microscope (SEM) as well as dynamic mechanical analysis (DMA) experiments. The imperfect crystals of P(HB-co-HV) melted at 176 °C while the remaining perfect crystals recrystallized at the higher temperature (T c = 120–150 °C). The results demonstrated that the HV units were easily to be excluded from the PHB crystal lattice in the P (HB-co-HV) recrystallization process, which promoted the crystal perfection of P(HB-co-HV) and improved the tensile strength and melting temperature. Furthermore, the heat treatment of PMRM reduced the molecular chain density and entanglement in the amorphous region and made the distribution of the tensile degree of the molecular chains more uniform, which was conducive to the sliding of lamellar crystals along the impact tensile direction, inducing plastic deformation. In addition, the heat treatment of P(HB-co-HV) via PMRM produced a large number of micropores, which was conducive to dispersing stress and improving its macroscopic toughness during the subsequent stretching process. [Display omitted] • The heat treatment of PMRM makes the crystal structure of P(HB-co-HV) more uniform and perfect. • The tensile strength and heat resistance of P(HB-co-HV) are improved. • The heat treatment of PMRM can effectively improve the macroscopic toughness of P(HB-co-HV). [ABSTRACT FROM AUTHOR]

The modified cold metal transfer (CMT) heat sources by adjusting the characteristic processing parameters were conducted in wire-arc additive manufacturing (WAAM) of AZ31 magnesium alloy for thin-wall component. The processing, microstructure, and mechanical behaviour were investigated. The CMT characteristic deposited a wide and shallow weld bead coupled with good wettability and low equivalent heat input was selected for CMT-WAAM process. The microstructure of thin-wall component showed obvious layer characteristics, which consisted of the deposited layers with fine columnar dendrite grains and the HAZ interlayers with coarse equiaxed grains and some pores. The thin-wall component exhibited anisotropic tensile properties with lower yield strength, higher elongation, and higher ultimate tensile strength in the deposition direction than in the build direction. CMT-WAAM component of AZ31 magnesium alloy has an accepted mechanical property compared with the as-forged and as-cast components. To improve the component strength, minimizing the softening effect of the HAZ interlayers by preventing grain coarsening and suppressing porosity is essential. [ABSTRACT FROM AUTHOR]

Highly oriented magnetite (Fe3O4) thin films have been produced by reactive sputtering in a mixture of hydrogen and argon. While different phases can be achieved by varying the ratio between hydrogen and argon, single phase magnetite films can be achieved with hydrogen concentration γ=0.75%–1%. For the sample grown at γ=1.0%, a Verwey transition at about 111 K can be seen from the temperature dependence of the resistivity, which is confirmed in the magnetization measurements. Maximum magnetoresistance (MR) of about 13.8% is observed just about the Verwey transition at T=115 K. MR results also suggest strong coupling among Fe3O4 nanoparticles originated from the Ruderman-Kittel-Kasuya-Yosida exchange interaction and dipolar interaction, which requires high order terms of (M/Ms)2 to explain the MR behaviors. However, with the fields applied perpendicular to the plane, MR exhibits a distinct behavior. The MR values under the condition of low fields seem to show a linear relationship with |M/MS|. [ABSTRACT FROM AUTHOR]

A novel Fe Ni coating with refined grain size and alternated distribution of element content was designed via laser-assisted electrochemical deposition. The formation of this microstructure is attributed to a specific laser scanning strategy, forming the periodic current waveform. This novel coating is expected to enhance the microhardness and wear performance within the grain size range of the inverse Hall–Petch (HP) relationship. The critical size of the HP relationship was estimated at 13 nm based on the relationship between different grain sizes and microhardness. Compared to the coating prepared by electrochemical deposition, the average grain sizes decrease from 8.4 ± 1.4 nm to 4.5 ± 1.6 nm. In addition, the microhardness was enhanced by approximately 28 %; the wear rate was decreased by approximately 58 %. The main mechanisms include abrasive, fatigue, and slight oxidation wear. This unique structure may enhance the resistance to grain boundaries mediated plastic deformation. • The critical HP size of Fe Ni coating is approximately 13 nm. • Average grain size decreases from 8.4 ± 1.4 to 4.5 ± 1.6 nm. • The microhardness and the wear resistance are enhanced. • The wear mechanism includes abrasive, fatigue, and slight oxidation wear. • GBs mediation is the main plastic deformation mechanism. [ABSTRACT FROM AUTHOR]

This study developed a new electrodeposited Fe–Ni coatings using the laser-induced current waveform. This process refined grains accomponied with a mixed nanocrystalline size and alternate element content. The electrochemical and immersion corrosion performance at 3.5 wt% NaCl was improved, which is still pitting corrosion. The corrosion pits are more likely to spread around rather than in the depth direction. The enhancement mechanism is mainly attributed to the richer grain boundaries. This microstructure increases the interface transfer resistance and makes the corrosion more uniform. This study provides a potential process for preparing nanocrystalline coatings with better performance. [Display omitted] • Laser-induced current waveform refines grains with a mixed size. • The element content is distributed alternately along the cross-section. • The electrochemical and immersion corrosion properties are improved. • The enhance mechanism is mainly attributed to the rich grain boundaries. [ABSTRACT FROM AUTHOR]

This paper proposes an optimization procedure for spot-welded structures. The welded sheets are connected through continuous solid materials instead of traditional discrete elements, and a topology optimization with Solid Isotropic Microstructure with Penalization (SIMP) method is used to remove the redundant connecting material. The current optimization procedure is able to predict an optimal number and distribution of spot welds for spot-welded structures. Applications to the double-hat welded crossbeam and D pillar joint of a body-in-white (BIW) show that the proposed optimization procedure furnishes good guidelines to redistribute spot welds in the spot-welded structures. The spot welds optimization of BIW is carried out on a finite element model. In order to verify the model, finite element analysis (FEA) and rig test of torsional stiffness are performed on the BIW, where both the FEA and rig test are carried out under the same boundary conditions. A satisfactory agreement between the FEA and experiment demonstrates the capabilities and the effectiveness of the present method. [ABSTRACT FROM AUTHOR]

The effect of holding time on microstructure, hardness and mechanical properties of unequal thickness weld joints between low carbon steel and advanced high strength steel is investigated in the present work. The microstructures in the regions of weld nugget, heat affect zone and base metal are obviously different. The hardness of fusion zone both at low carbon steel and advanced high strength steel sides shows a slight variation and it is much higher than that of base metal. The peak load and failure mode of the weld joints are carried out via tensile shear test and finite element analysis. The test result demonstrates that the peak load and failure mode depend on the resistance force generated via the failure zone. For a given fusion size, the increase of holding time raises the hardness of fusion zone, and affects the peak load and failure mode of weld joints via enhancing the interfacial resistance capability. The increase of holding time reduces the welding efficiency, thus, a suggestion based on the test result is proposed that the holding time should be less than 15 cycles to ensure the manufacturing efficiency. A nonlinear finite element analysis is applied to simulate the tensile test procedure. The simulation demonstrates the necking phenomenon and failure process at interfacial or base metal around the weld nugget. [ABSTRACT FROM AUTHOR]

In the present work, vertically aligned ZnO nanorod arrays with tunable size are successfully synthesized on nonseeded ITO glass substrates by a simple electrodeposition method. The effect of growth conditions on the phase, morphology, and orientation of the products are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is observed that the as-prepared nanostructures exhibit a preferred orientation along c axis, and the size and density of the ZnO nanorod can be controlled by changing the concentration of ZnCl2. Field emission properties of the as-synthesized samples with different diameters are also studied, and the results show that the nanorod arrays with a smaller diameter and appropriate rod density exhibit better emission properties. The ZnO nanorod arrays show a potential application in field emitters. [ABSTRACT FROM AUTHOR]

Abstract: The effects of antimony (Sb) on the microstructures of as-cast Mg–8Zn–4Al (ZA84) magnesium alloy were investigated by using optical microscopy, SEM, EDX, and XRD, etc. The results indicated that the microstructures of as-cast alloys containing Sb consisted of solid solution α(Mg), ternary phases τ [Mg32(Al, Zn)49] and φ (Al2Mg5Zn2), eutectic mixture phase [α(Mg)+τ], a newly formed dual phase MgZn2, and a newly formed needle-like phase Mg3Sb2. After adding Sb, the morphologies of ternary phase on the grain boundaries have been changed from quasi-continuous-net shape to uniformly dispersed particles, and the sizes of grains were decreased from 120–130μm to 50–60μm. In this experiment conditions, the optimal addition amount of Sb was 0.3wt%. Meanwhile, the microhardness of the matrix of ZA84 magnesium alloy was found to increase with the increases of Sb additions. As the phase Mg3Sb2 with high melting point and the dual phase MgZn2 were formed, the high-temperature strength of ZA84 magnesium alloy was increased. [Copyright &y& Elsevier]

The microstructure evolution, tensile properties and work-hardening behavior of AA2219 alloy reinforced by in situ nanosized TiB2 particles were studied in this paper. The observation indicated an impeded recrystallization of the matrix alloy by nanosized TiB2 particles, and the hybrids of nanosized TiB2 particles and Al2Cu phases located at the grain boundary hindered the grain growth. Meanwhile, a large amount fiber textures of <111>//RD (Rolling direction), <110>//RD, <100>//RD <111>//ND (Normal direction), <110>//ND and <100>//ND were detected in nanosized TiB2/AA2219 composite. Tensile test results exhibited a combination of good strength and ductility of the present composite whose yield strength and tensile strength were 11.4% and 5.8% higher than those of the alloy, while its fracture strain increased slightly. Meanwhile, the correlation between this modified microstructure of nanosized TiB2 particles and comprehensive mechanical properties was established. This study provides a new insight into the fabrication and strengthening behaviors of Al matrix composites reinforced by in situ nanoparticles. [ABSTRACT FROM AUTHOR]

Magnetic core materials with low loss, high saturation magnetization, large permeability, and operating frequency above 1 MHz are in high demands for the next generation of miniaturized power electronics. Amorphous FeHfB ribbons with thickness around 20 μm have been fabricated through melt-spinning. Different heat treatments were performed on the FeHfB ribbons, and the relations among heat treatments, microstructure, and magnetic properties have been explored. Properties such as coercivity (Hc) of 2.0 Oe and saturation magnetic flux density (BS) of 1.2 T have been achieved in samples with exchange coupling. The losses can be minimized by balancing the hysteretic and eddy current losses and can be further reduced with additional magnetic field annealing. At 5 MHz with peak magnetic flux density of 20 mT, the materials show core losses comparable to the best ferrites, but with higher permeability value of about 200 and superior saturation induction of more than 1 T. [ABSTRACT FROM AUTHOR]