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As main components of magnesia-based refractories, magnesia exhibits excellent properties such as high refractoriness and good basic slag corrosion resistance. However, magnesia produced from CaO containing cryptocrystalline magnesite has limited application owing to the low hydration resistance and poor thermal shock resistance (TSR). This work aimed to investigate the reinforcing effects of microscale monoclinic ZrO2 on free CaO containing magnesia for optimizing mechanical properties, TSR and hydration resistance. The results showed that adding ZrO2 could promote the removal of the open pores, strengthen the interface bonding between various grains and produce crack deflection, which improved flexural strength and fracture toughness. As a result, the TSR of the specimens was enhanced effectively due to increased strength and toughness and reduction in the thermal expansion coefficient. Besides, as the ZrO2 was introduced, hydration resistance of the specimens improved significantly, mainly attributing to the decrease in apparent porosity and elimination of the free CaO by forming CaZrO3 and cubic ZrO2 phases.

SiC porous ceramics (SPCs) are key functional medium materials, which are widely applied as porous burners. However, SPCs produced via the polyurethane sponge replica technique usually exhibit a randomly distributed cellular structure, leading to vulnerability and a low combustion efficiency for the porous burners. In this study, SPCs were structurally designed via novel 3D printed resin template technique; this endowed the SPCs with synergistically optimized strength and combustion characteristics. SPCs containing tetrakaidecahedron, octahedron and cubic cells were successfully prepared via SiC slurry coating and sintering in air. The cell parameters determined the strength and combustion properties of the SPCs. The SPCs containing cubic cells exhibited the largest strength and strain, because more struts were present parallel to the loading direction; this is more advantageous for stress bearing compared to those vertical to the loading direction. The tetrakaidecahedron cell facilitated the formation of a disturbance effect within the SPCs to a higher extent than the cubic and octahedron cells, thereby enhancing the heat exchange performance between the fluid and porous framework. Hence, the SPC with tetrakaidecahedron cells exhibited the best combustion properties, which resulted in the highest surface temperature and lowest pollution emission.

We demonstrate flat-top, sharp-edge, silicon add-drop filters using apodized grating-assisted contradirectional couplers (contra-DCs). Periodic sidewall corrugations are imposed on both sides of two asymmetric strip waveguides for contradirectional coupling between the first two TE supermodes of a two-waveguide system. Gaussian apodization is applied to suppress the sidelobes. By laterally shifting the positions of both waveguide Bragg gratings in a complementary manner, which is called complementary lateral-misalignment modulation, our devices avoid phase errors which impair the spectral responses for conventional lateral-misalignment modulated contra-DCs. We demonstrate a complementary lateral-misalignment modulated (CLMM) contra-DC that has a flat-top, rapid roll-off, drop-port spectral response with a sidelobe suppression ratio (SLSR) of 20 dB. We also demonstrate a series-cascaded CLMM contra-DCs that has a higher SLSR of 39 dB and a sharper filtering edge. ©

Glass-forming ability is a long-standing concern in the field of metallic glasses (MGs), which greatly limits their maximum casting size and extensive applications. In this work, we report an ultrasonic-assisted rapid cold welding of bulk MGs without using any additives. MGs with various compositions are welded together under a 20,000-Hz high-frequency ultrasonic vibration without losing their amorphous nature. The ultrasonic technology offers the advantages of rapid bonding (< 1 s) at low temperature (near room temperature) and low stress (< 1 MPa). According to the phenomenon observed in the experiment, the activated fresh atoms diffuse through the broken channel port under continuous rupture of the oxide layer, and the ultrasonic vibration accelerates the atomic-diffusion process. Finally, stable bonding of the MG interface is realized. This universal ultrasonic-assisted welding process can realize the composition design of dissimilar MGs as well as tuning of new materials with new performance.

So far, many investigations have reported that Zr-based bulk metallic glasses (BMGs) could be precisely and flexibly shaped by electrical discharge machining (EDM). However, EDM induced crystallization and roughness is still a bottleneck. In this research, bench-mode electrochemical surface smoothing (ESS) in the NaCl-ethylene glycol (EG) electrolyte has been proposed to post-process the spark erosion treated Zr-based BMGs in order to solve the abovementioned problems. The utilization of the NaCl-EG electrolyte overcomes the difference in electrochemical dissolution mechanisms of multiple components contained in Zr-based BMGs. Taking a sort of Zr-based BMGs, Vit1 (Zr41.2Ti13.8Cu12.5Ni10.0Be22.5), as an example, voltammetry and chronoamperometry methods have been performed on the BMG surface before and after wire-EDM, respectively, in the NaCl-EG electrolyte to reveal the steady and transient electrochemical behaviors. In order to achieve high-efficiency and high-quality ESS of Zr-based BMGs, a 3D printed setup with lateral flushing has been developed, combined with the micron sized inter-electrode gap (IEG) and the pulse current. The surface morphologies after ESS have been compared to evaluate the effects of the initial surface morphologies, dwell time, and pulse parameters. The surface material properties and mechanical performance before and after ESS have also been investigated by EDS, XRD, XPS, and nanoindentation. The results suggests that the proposed ESS method is capable of quickly eliminating the crystalline layer induced by the thermal shock and reducing roughness caused by the discharge craters, which has been finally validated by fast ESS of two Zr-based BMG molds with ruled surfaces in the NaCl-EG solution.

Low-carbon MgO–C refractories are facing great challenges with severe thermal shock and slag corrosion in service. Here, a new approach, based on the incorporation of nano-sized ZrO2–Al2O3 composite powder, is proposed to enhance the thermal shock resistance and slag resistance of such refractories in this work. The results showed that addition of ZrO2–Al2O3 composite powder was helpful for improving their comprehensive performances. Particularly, the thermal shock resistance of the specimen containing 0.5 wt% composite powder was enhanced significantly which was related to the transformation toughening of zirconia and in-situ formation of more spinel phases in the matrix; also, the slag resistance of the corresponding specimen was significantly improved, which was attributed to the optimization of pore structure and formation of much thicker MgO dense layer.

Fused silica (SiO2) ceramic crucibles with α-Si3N4 coating are commonly used for smelting photovoltaic silicon (Si). However, SiO2 ceramics will inevitably undergo crystallization and large volume change during the high-temperature service, which will lead to crucible cracking and deteriorate the quality and yield of the Si ingot. In this work, α-Si3N4/SiO2 ceramics are fabricated by introducing α-Si3N4 into SiO2 ceramics to inhibit crystallization. The results show that the introduction of α-Si3N4 can effectively inhibit crystallization of SiO2 ceramics at temperature higher than 1450 °C. Only 5 wt% cristobalite form in SiO2 ceramic with 20 wt% α-Si3N4 (heated at 1550 °C for 30min). The crystallization activation energy of SiO2 ceramic containing 20 wt% α-Si3N4 increases by 2.27 times to 931.2kJ/mol compared with that of pure SiO2 ceramic (409.6kJ/mol). The inhibition crystallization effect and increased activation energy derive from the in-situ formation of O–Si–N chemical bond and physical isolation of SiO2 particles by α-Si3N4 powders.

The new route for recycling fly ash was proposed to prepare SiC reticulated porous ceramics (SRPCs) with high strength and increased efficient filtration for molten metal filtration. The effects of fly ash on the rheological characteristics, microstructure evaluation and wetting behavior between SRPCs and molten metal were investigated. It was found that the fly ash was beneficial to thixotropic property of SiC slurry when its content was less than 30 wt%. Furthermore, fly ash in SRPCs was completely transformed into mullite with needle-shape at 1300 °C, forming a porous structure containing micro pores and windows. SRPCs containing 20 wt% fly ash exhibited a higher strength because of the improved rheological properties of SiC slurry and the optimized microstructure in skeleton. In addition, the added fly ash in SRPCs could increase the contact angle between skeleton substrate and molten metal via microporosization of skeleton, thus exhibiting the potential ability to improve the filtration efficiency.

The microstructure evolution and the pitting corrosion resistance of a supermartensitic stainless steel after deep cryogenic treatment process were clarified through X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM) and electrochemical methods. The results showed that the microstructure of supermartensitic stainless steel mainly consisted of reversed austenite, tempered martensite, and M23C6 carbides after tempering. The deep cryogenic treatment promoted the refinement of the martensite laths and the precipitation of the carbides in comparison with the traditional process. TEM analysis indicated that the segregation of Si atoms at the boundary was found at the interface between carbide and martensite. The pitting corrosion potential of the specimens subjected to deep cryogenic treatment decreased with the elevated tempering temperature, and the lowest pitting corrosion potential was found at the tempering temperature of 650 °C. The sensitivity of the pitting corrosion potential was attributed to the precipitation of M23C6 carbides and Si atoms segregation. Si atoms segregation engendered the formation of Cr-depleted zone near M23C6 and impeded the recovery of Cr-depleted zone.

Developing materials with tailorable properties has been the long-sought goal of humankind. Forming composite materials with superior properties by combining two or more materials has emerged as a competitive means in the search and design of new materials. However, it is still a grand challenge to use metallic materials as a binder for composites because of their lack of adhesion. In the present work, we proposed a facile and flexible route to synthesize composites using metallic glass as a glue to bond various materials, ranging from conductors to insulators, and metals to nonmetals, together. The mechanical, magnetic and electrical performances of the composites can be manually regulated by changing the addition ratios of the metallic glass glue and the corresponding admixture. In addition, porous structures were also obtained and tuned by dissolving the soluble admixture in water. In principle, our approach provides a new idea for the fabrication and optimization of composites using metallic materials as binders. The outcome of our current research opens up a window not only to synthesize composite materials with tailorable properties universally and flexibly, but also towards the discovery of potential multi-functional metal containing composites.

Breakthrough of glass forming ability limitation has been a longstanding pursuit in metallic glasses. In present work, an ultrasonic welding technology was used to achieve this goal. The La55Al25Ni5Cu10Co5 rods were bonded together. Results of computed tomography and scanning electron microscope show that the weld seam tends to narrow gradually and disappear with the increase of welding energy. X-ray diffraction indicated that it preserves completely amorphous structure. In addition, the hardness of the weld position increased with the increase of energy, showing the interfaces bonded together.

Microstructures with hydrophobic surfaces have been widely used in industrial fields such as self-cleaning and drag reduction. With the aim of fabricating microplastic parts with a hydrophobic surface, the paper processed the mould insert with micro-groove arrays from 304 stainless-steel plate through low-speed wire electrical discharge machining (LS-WEDM). And the micro-groove arrays were designed to U shape with bottom radius of 70 μm and depth of 110 μm. Ultra-high molecular weight polyethylene (UHMWPE) powders were used as raw material to fabricate microplastic parts with hydrophobic surface structures by micro ultrasonic powder moulding (micro-UPM). The parameters of the micro-UPM process were obtained by the single-factor test method. Under the ultrasonic energy of 1200 J, welding pressure of 100 kPa and pressure holding time of 8 s, microplastic parts with well surface morphology (Ra =1.36 μm) and replication rate (97.76 %) were successfully fabricated. The surface contact angle of the microplastic part was 135.4°, which indicated well surface hydrophobicity.

SiC reticulated porous ceramics (RPCs), as the key functional components, are widely applied in field of molten-metal filtration. However, the hollow struts with triangular tips caused by burnt out of polymer foam reduced the strength of SiC RPCs, which limited their engineering application. Aiming to reveal the effects of template strut morphology on the mechanical performance of SiC RPCs, templates with triangular, square and circular cross sections were designed by additive manufacturing. Subsequently, SiC RPCs with varied strut structures were prepared by slurry immersion, followed by sintering at elevated temperature. The blunt of template strut improved the mechanical property of SiC RPCs, samples with circular hollow struts showed the highest crushing strength and strain than that of triangular and square hollow struts. From the results of simulation calculation, triangular hollow struts led to the significant stress concentration in the connection of struts and their middle parts, while the smaller stress uniformly distributed in the whole SiC skeleton as hollow struts became circle, thereby the improved mechanical properties were obtained in SiC RPCs.

As the key component for porous media burner, the sufficient strength of SiC reticulated porous ceramics (RPCs) is necessary due to the scour of hot flue gas. However, SiC RPCs prepared with template replica method often exhibited serious oxidation and low strength when the foam was burnt out. In the present work, a sol-coated Al powder with high hydration resistance was introduced into the silicon carbide slurry to promote mullite formation in SiC skeleton, meanwhile reduce the SiC oxidation ratio of sample during the heat treatment. Firstly, the silica-sol coated Al with uniform silica-sol was successfully prepared via dip coating to improve the ability of hydration resistance of Al powder. Furthermore, sol-coated Al with spherical morphology improved rheological properties of silicon carbide slurry, including viscosity and rheological behavior. In addition, the evolution mechanism of sol-coated Al in SiC RPCs was revealed. The AlO2(g) and AlO(g) was first formed in the system, thus significantly reducing the SiC oxidation ratio in SiC RPC. The partial pressure of AlO(g) increased with the sintering temperature, the needle-shaped mullite formed at 1300 ○C when it dissolved in the microsilica, while lumpy mullite formed as SiC was the silica source in SiC RPCs. The addition of sol-coated Al was beneficial to optimize the microstructure of SiC skeleton, resulting in higher compressive strength of SiC RPCs.

The dry–wet cycle and high temperature exposure are important factors affecting the normal use and durability of concrete structures. The objective of this work is to investigate the mechanical properties of cement mortar specimens after combinations of dry–wet cycles and high temperature exposures, uniaxial compressive tests on cement mortar specimens were carried out under the following two sets of conditions: (1) high temperature treatment followed by a dry–wet cycle and (2) a dry–wet cycle followed by high temperature treatment. The results show that the compressive strength of specimens increases with the number of dry–wet cycles. After a dry–wet cycle and then a high temperature treatment procedure, the compressive strength of a specimen will first decrease and then increase with the number of dry–wet cycles. The strain at the peak stress of cement mortar decreases as the number of dry–wet cycles increases. At present, there are few research results about the mechanical properties of concrete first after combinations of dry–wet cycles and high temperature exposures. The work in this paper can enrich the results in this area.

Electrical discharge machining (EDM) has been widely used in the machining of mechanical parts. However, the parts obtained by EDM have recast layers and micro-cracks on their surface, which seriously affect their mechanical properties. In order to remove the recast layers and micro-cracks resulted from EDM, this paper proposed to combine micro-EDM with negative polarity micro-EDM. First, the mechanical part was machined using conventional EDM, after which the surface of the part had a distinct recast layer and micro-cracks. As the conventional EDM was nearing completion, the power supply was replaced by a micro-EDM power supply and then the part was processed by micro-EDM to reduce the thickness of the recast layer. After micro-EDM, the part was processed by negative polarity micro-EDM, which can remove the recast layer and the micro-cracks on the surface of the part. Conventional EDM was performed on 304 stainless steel using a copper electrode with voltage of 250 V, pulse width of 7 ms, and pulse interval of 5 ms. The experimental results showed that the recast layer and micro-cracks on the surface of the part were obvious and the surface quality of the part was poor. After that, the same part was sequentially subjected to micro-EDM and negative polarity micro-EDM with voltage of 110 V, pulse width of 0.5 μs, and pulse interval of 15 μs. The experimental results showed that the recast layer and micro-cracks on the surface of the part were almost invisible and the surface quality of the part was greatly improved.

Durability of cement mortar and concrete materials under sea water condition is always an important research topic. The objective of this work is to understand the mechanical properties of corroded cement mortar after high temperature, the cement mortar specimens after high temperature were placed in water and sodium sulfate solution, and then the uniaxial compression tests were carried out on the cement mortar specimens after corroded. Test results show that both the differences of compressive strength and strain at the peak stress after high temperature caused by high temperature, are relatively small when the specimens are eroded in water, and the differences are relatively high when the specimens are eroded in sodium sulfate solution. The compressive strength of the cement mortar specimens under normal temperature eroded in sodium sulfate solution is highest, and that eroded in water is lowest. The compressive strength of specimen after high temperature eroded in water is highest and that eroded in sodium sulfate solution is lowest. The strain at the peak stress of specimen, whether after high temperature or not, is highest when eroded in sodium sulfate solution, and that eroded in water is lowest. At present, there are few research results about the mechanical properties of concrete first after high temperature and then after sea water corrosion. The work in this paper can enrich the results in this area.

Three-dimensional (3D) microelectrodes can be fabricated by laminating multilayer copper microelectrodes. When the 3D microelectrode is used for micro electrical discharge machining (micro-EDM), the 3D microstructure can be obtained with an up-and-down reciprocating motion. The process is simple and the machining efficiency is high. In micro-EDM process, the 3D microelectrode has wear, which affects the shape accuracy and dimensional accuracy of the microstructure. To obtain the wear characteristics and predict the wear of the 3D microelectrode, the paper discretized 3D microelectrode into several microelectrodes with square cross-sections. The discretized 3D microelectrodes comprised a number of α-type electrodes, β-type electrodes, and γ-type electrodes. The wear of these microelectrodes was studied by numerous experiments, and the wear characteristics of individual microelectrodes were integrated to obtain the wear characteristics of the 3D microelectrode. The study found that the wear of these three types of electrodes was linearly related to the machining depth. The fit slope of the α-type electrode was equal to − 0.24071, and it had the most wear. The fit slope of the β-type electrode was equal to − 0.21524, and it had the second-highest wear. The fit slope of the γ-type electrode was equal to − 0.19767, and its wear was the lowest. Finally, a 3D microelectrode with semi-cylindrical features was used for micro-EDM to verify the correctness of the wear characteristics. The experimental results were compared with the theoretical calculation, and the theoretical calculation of the 3D microelectrode wear was basically consistent with the experimental results. The maximum error between the theoretical calculation and the experimental results was 21.85 μm, and the minimum error was 3.16 μm.

The insufficient strength and thermal shock resistance of mullite reticulated porous ceramics (RPC) limited their application in porous media combustion. To strengthen mullite RPC, the struts with three layers were prepared using the combined approaches of polymeric replica and vacuum infiltration. The effects of residual stress within the struts on thermal shock resistance of mullite RPC were investigated by finite element analysis (FEA). The results showed that the strut was composed of the coating of reaction-bonded mullite, middle layer of mullite skeleton and the triangular filling layer. The triangular voids and surface cracks were eliminated in the formed struts, resulting in a higher strength of mullite RPC than that of hollow strut. In addition, FEA results indicated that the residual compressive stress formed in the coating of strut after mullite RPC was sintered at 1450 °C and 1500 °C, while the residual tensile stress formed at 1550 °C. The larger residual compressive stress within the strut coating was beneficial to enhance the thermal shock resistance of mullite RPC.

In this work, a rapid and controllable ultrasonic vibration method for forming Al-based metallic glass at room temperature is proposed. This method can dramatically improve the forming ability of Al-based metallic glasses, which are virtually brittle at room temperature and have almost no supercooled liquid region at high temperatures. Under ultrasonic vibration, Al-based metallic glasses exhibited obvious plastic flow, with a maximum deformation degree up to 58% and an average deformation degree up to 43%. It is worth mentioning that no crystalline peaks were found on the X-ray diffraction patterns after deformation under ultrasonic vibration, and the mechanical properties remained the same as the primary sample. The present results provide a new approach for the deformation and forming of Al-based metallic glasses, which can significantly broaden their applications.

Double skin steel-concrete composite walls offer structural merits over conventional reinforced concrete walls in terms of high strength, good ductility and convenience for construction. The stability of the external steel faceplates is significantly influenced by the types of internal mechanical connectors and the ratio of connector spacing to plate thickness. In this paper, a new type of steel truss was proposed as the fastener to connect the two faceplates. Compressive tests were conducted on three full-scaled composite walls with different truss spacing. The structural response of the walls was comprehensively discussed in terms of failure modes, load-axial displacement response, buckling stress, stiffness, ductility, strength index, load versus out-of-plane displacement response, and load-strain curves. The influences of truss spacing on key parameters were explored in details. The test results showed that the truss spacing could considerably affect the buckling shapes, load-carrying capacity, stiffness and ductility of the specimens.

Based on a planned process design path, a foil queue microelectrode (FQ-microelectrode) is applied sequentially in micro-electrical discharge machining (micro-EDM) in which the micro-EDM results can superimpose to produce the 3D micro-structure. However, in this process, each foil microelectrode (F-microelectrode) inevitably experiences wear, and the wear has an unfavorable effect on the machining accuracy of 3D micro-structure. In this study, the wear of F-microelectrodes for different technological parameters is studied in detail. The experimental results show that the first three pieces of the F-microelectrodes exhibit serious wear, and the wear values are all over 7 μm. As the processing proceeds, the wear of the microelectrode gradually decreases to 2 μm, as a result of an improvement in the processing environment. To ensure the machining accuracy of 3D micro-structure, this paper compensates the wear of the first three pieces of the F-microelectrode through rough and finish machining. Finally, based on the experimental results, a 3D micro-structure with good form accuracy can be fabricated in cemented carbide with pulse width Ton = 80 ns, pulse interval Toff = 160 ns, and machining voltage V = 100 V.

Tool wear is a prominent problem during drilling of carbon-fibre-reinforced polymer (CFRP). This paper investigated the tribological behaviors and wear mechanism of CFRP against tungsten carbide under dry friction condition. The influence of load, temperature and sliding velocity on friction coefficient were studied. The wear morphology was detected and showed the inhomogeneity and anisotropy of CFRP have important influence on wear characteristics. Moreover, running-in process will have a positive influence on the subsequent friction process under certain conditions. A novel method which adopted pre running-in was thus proposed to improve tool life, and the effectiveness was verified by drilling tests. Present work reveals the wear mechanism of CFRP against tungsten carbide, and provides a new idea for reducing tool wear.

The three-layered struts within SiC reticulated porous ceramics (RPC) were designed to improve the thermal characteristics and thermal shock resistance of porous burner. The effects of strut structure and its composition on the flame stability limits, flame temperature and thermal damage resistance of porous burner were investigated. The results showed that three-layered struts consisted of continuous mullite coating, middle layer of SiC skeleton and inner layer of reaction-bonded mullite after sintering at 1450 °C. Compared to porous media with single layer, RPC with three-layered struts possessed the combined effects of high thermal conductivity and heat radiation because of its middle layer of SiC skeleton and in-situ formed mullite coating. The three-layered struts in porous media extended the flame stability limits and increased the flame temperature of porous burner. Furthermore, the formation of three-layered struts eliminated strut defects and formed continuous mullite coating, thereby significantly improving the oxidation resistance and thermal shock resistance of RPC, which increased the service life of porous burner.

Flexible forming process-polymer powder medium based flexible forming (PPFF) is presented in this research. The metallic bipolar plate (BPP) for a proton exchange membrane (PEM) fuel cell, with a micro-scale flow channel on its surface, is formed using rigid die forming and PPFF process, respectively. Pure copper C1100 (with a thickness of 0.1 mm), annealed at 450 °C for 1 h in vacuum condition, is selected as blank material. The forming experiments are carried out at room temperature in dry friction condition. By comparing the limit forming depth, fracture topography, section wall thickness distribution and surface forming quality of micro-scale flow channels between rigid die forming and PPFF process, it reveals that PPFF process could be developed as a feasible technique to fabricate the bipolar plates of PEM fuel cells. The PPFF process has the following advantages: greater forming depth, more uniform wall thickness distribution, and low cost of the die.

In this paper, we proposed the terahertz technique to measure the liquid level of Chinese liquor in sealed pots. We analyzed the transmission process of terahertz pulse in the sealed pots and established a model of the relationship between terahertz pulse interval and liquor level. The measurement results are in good agreement with the theoretical model. The results show that the terahertz technique can realize the high precision measurement of liquor level. The absolute and relative errors are less than ±40 μm and 0.014%, respectively. In addition, we also evaluated the influence of dewdrop on the measurement accuracy. The results show that dewdrop only leads to a deviation of 18 μm. The results prove the value of terahertz technology in the field of liquid level monitoring.

The sandwich composite wall with truss connectors is a new type of double-steel-plate composite wall, which consists of two external steel plates, square steel tubes at both ends, and in-fill concrete. The external steel plates are constrained by the steel trusses, thereby possessing superior mechanical performance. In order to study the fire resistance of the sandwich composite wall, 4 full-scaled walls were tested under one-side ISO-834 standard fire, aiming to investigate the effects of axial compression ratio, truss spacing to thickness ratio, and steel plate thickness on the fire resistance of the walls. The temperature, axial displacement and transverse displacement of key parts of the walls were measured. Experimental results indicate that, the walls could maintain sufficient load-bearing capacity as specified by the Class I fire resistance rating of Chinese Code. The fire endurance of the wall was controlled by its thermal insulation. The deformation pattern of the walls under the fire was overall deflection toward the unexposed surface, and the steel plate exposed to the fire experienced obvious local buckling. The axial compression ratio and the truss spacing to thickness ratio had great effects on the deformation behavior of the walls. When the axial compression ratio was reduced from 0.5 to 0.3, the axial deformation of the wall was changed from compression-predominant to expansion-predominant deformation. A larger truss spacing to thickness ratio led to more obvious buckling of the steel plate exposed to the fire. It is recommended to restrict the truss spacing to thickness ratio of the wall in engineering design.

Constructing regular micro-structures with certain geometric characteristics on the surface of the polymer part can obtain some specific functions. Micro ultrasonic powder molding (micro-UPM) is an efficient processing technique for the fabrication of well-filled micro-structured Polypropylene (PP) parts. The micro-structure array on the surface of the core insert was obtained by low speed wire electrical discharge machining (WEDM-LS). PP polymer surfaces with micro-structured patterns were successfully replicated from the core insert surface after micro-UPM. By studying the detailed topography characterizations of micro-structured PP parts, the effects of processing parameters (ultrasonic energy, welding pressure and holding time) on the micro-structured filling show that when PP polymer was formed under the conditions of 1000 J, 115 kPa and 8 s during micro-UPM, well-filled micro-structured parts can be obtained. Besides, without low surface energy coating modification, the water contact angles (WCAs) of micro-structured PP parts increased from 85.3&deg, to 146.8&deg, indicating that the wettability of the surface can be changed by replicating the micro-structure on PP parts after micro-UPM.

We successfully fabricate high-entropy alloys and amorphous alloy composites by adopting the proposed ultrasonic vibration method. The low-stress, low-temperature method enables us to create composites that combine both amorphous and crystalline properties. Microscopic observations and computed tomography measurements indicate good bonding quality without pores or cracks in the composites. Due to the unique structure which mixes soft and rigid phases, the composite exhibits improved mechanical performance compared to that obtained from a pure single phase. Our results are promising for the manual design and fabrication of smart materials containing multiple phases and compositions.

The applicability of micro-electrical discharge machining (micro-EDM) using laminated 3D microelectrodes to eliminate defects such as numerous micro-stripes that are prone to appear on the sidewalls of microstructures manufactured via micro-electrochemical machining (micro-ECM) was examined. The study proposes the fabrication of 3D microstructures with laminated 3D microelectrodes through micro-EDM with deionized water containing B4C powder having a particle size of 1 μm. First, the effect of different machining voltages, B4C concentrations, and microelectrode back-off distances on the unilateral gap was investigated. The results indicated that a machining voltage of 100 V, a B4C concentration of 3 g/L, and a microelectrode back-off distance of 200 μm resulted in a 69 μm unilateral gap of the 3D microstructures. Given the effect of micro-EDM and that B4C is a semiconductor, the plasma discharge channels were enlarged, and the material removal was uniform. This significantly improved the machining efficiency. Furthermore, the polishing of B4C on electrode surfaces and workpiece surfaces smoothly removed the processing attachments with dielectric and ensured efficient and stable machining. Based on the optimized process parameters and after 1.5 h, 3D microstructures with a depth of 800 μm with a square-shaped blind hole and with semicircular and rectangular islands were obtained, and the corresponding roughness (Ra) of the bottom surface was 0.389, 0.388, and 0.392 μm. However, the corresponding microelectrodes wear was low and approximately corresponded to 20, 15, and 15 μm.

Purpose The purpose of this paper was to study the influence of properties of printed circuit boards (PCBs) on the temperature during micro drilling and obtain the influential mechanism of PCBs based on temperature measurement. Design/methodology/approach Experiments were carried out to study the influence mechanism of PCB properties on micro hole drilling temperature under high spindle speed. The temperature measurement platform was applied, then the influence of components ratio of PCBs on the temperature of micro-drilling was analyzed by using comparative analysis method. The mass ratio of each kind of material in the PCB was defined as four levels and the influence mechanism of properties of PCBs based on temperature measurement was summarized. Findings Average filler and lower resin would have a positive impact on micro hole drilling temperature, and the smaller filler size and the even distribution would make it better. Originality/value An infrared temperature measurement platform was applied and influential mechanism of PCB properties on temperature was analyzed, which could provide the reference value on the optimization of temperature during micro drilling.

3D-reticulated porous (3D-RP) SiC ceramic was fabricated by polymer sponge replica technique with SiC ceramic slurry (77 wt% solid content). Furthermore, pure alumina slurry and alumina slu...

Workpiece deformation in stack drilling can lead to interlayer gaps and non-coaxiality, which bring adverse effects to the hole quality and assembly quality. Nowadays, large numbers of fasteners are required to assemble the stacks for satisfactory hole qualities, which will also lead to extreme low efficiency and high cost. This study aims to reveal the formation and quantitative evaluation of the non-coaxiality, and to explore how the pre-installed fasteners reduce the interlayer gaps and non-coaxiality, thus to contribute in designing more efficient layout of the fasteners. First, a simplified 2-D model that involves effects of the pre-installed fasteners in stack drilling is built and the deformation of the stacks is theoretically analysed. Based on the calculation results, three types of patterns of non-coaxiality are revealed and explained, i.e., Type I caused by pure bending, Type II caused by horizontal displacements and Type III caused by local deformations at the holes. With consideration of these characteristics, a combined evaluation criterion for non-coaxiality in stack drilling is proposed and a method of measuring the non-coaxiality is developed. Then, the outcomes of the pre-installed fasteners brought to the deformations of the stacks are explained using theoretical analysis for the simplified 2-D model. As the accurate deformations of the 3-D stacked structures cannot be obtained in 2-D model, finite element simulations are also adopted to study the non-coaxiality and the interlayer gaps quantitatively. Finally, the demonstration experiments of stack drilling are conducted and the results agree with the simulation results that the non-coaxiality of neighbouring holes of the fasteners can be reduced.

We developed a facile ultrasonic vibration route is developed to synthesize BMGs and metallic glass-glass composites., Design of bulk metallic glasses (BMGs) with excellent properties has been a long-sought goal in materials science and engineering. The grand challenge has been scaling up the size and improving the properties of metallic glasses of technological importance. In this work, we demonstrate a facile, flexible route to synthesize BMGs and metallic glass-glass composites out of metallic-glass ribbons. By fully activating atomic-scale stress relaxation within an ultrathin surface layer under ultrasonic vibrations, we accelerate the formation of atomic bonding between ribbons at a temperature far below the glass transition point. In principle, our approach overcomes the size and compositional limitations facing traditional methods, leading to the rapid bonding of metallic glasses of distinct physical properties without causing crystallization. The outcome of our current research opens up a window not only to synthesize BMGs of extended compositions, but also toward the discovery of multifunctional glass-glass composites, which have never been reported before.

Mullite reticulated porous ceramics (RPC) are one of the key components for porous media burner, the mechanical properties of mullite RPC decided the service life of the burner. However, the irregularities of cellular structure made it difficult to reveal the fracture behavior of mullite RPCs. In this study, the three-dimensional (3-D) structures of mullite RPCs were analyzed by X-ray computed tomography. The strength and damage behavior of mullite RPCs were respectively investigated via the compression tests and finite element modeling based on the actual 3-D model, also the corresponding strengthening mechanism was proposed. The results indicated that the reconstructed 3-D model exhibited the real microstructure of mullite RPCs, containing the hollow struts and strut defects. The Young's modulus calculated from actual 3-D structures was lower than that from Gibson-Ashby theory. In addition, the surface defects preceded triangular tips to generate the area of stress concentration, leading to the fracture behavior first occurred at the strut defects. With the formation of dense strut in mullite RPCs, the stress uniformly distributed in the whole solid skeleton, thus significantly improving the damage resistance of mullite RPCs.

Despite the excellent properties, amorphous alloys find limited applications and to find plastic forming ability has been a longstanding problem. In this work, an effective ultrasonic assisted micro-shear punching (UMSP) method is proposed for amorphous alloys. By applying ultrasonic vibration and molten plastics viscous medium, a series of shapes and products with micro-length scale to macro-length scale can be successfully fabricated in 50 ms. Different from traditional crystalline alloys, the amorphous alloys become soft at certain regions during the ultrasonic hammering owing to the unique disordered structures, thereby resulting in the low-stress forming approach.

To investigate the effects of femtosecond laser ablation on the surface morphology and microstructure of ultrafine-grained copper, point, single-line scanning, and area scanning ablation of ultrafine-grained and coarse-grained copper were performed at room temperature. The ablation threshold gradually increased and materials processing became more difficult with decreasing grain size. In addition, the ablation depth and width of the channels formed by single-line scanning ablation gradually increased with increasing grain size for the same laser pulse energy. The microhardness of the ablated specimens was also evaluated as a function of laser pulse energy using area scanning ablation. The microhardness difference before and after ablation increased with decreasing grain size for the same laser pulse energy. In addition, the microhardness after ablation gradually decreased with increasing laser pulse energy for the ultrafine-grained specimens. However, for the coarse-grained copper specimens, no clear changes of the microhardness were observed after ablation with varying laser pulse energies. The grain sizes of the ultrafine-grained specimens were also surveyed as a function of laser pulse energy using electron backscattered diffraction (EBSD). The heat generated by laser ablation caused recrystallization and grain growth of the ultrafine-grained copper; moreover, the grain size gradually increased with increasing pulse energy. In contrast, no obvious changes in grain size were observed for the coarse-grained copper specimens with increasing pulse energy.

The non-coaxial stacked holes caused by cutting deformation is a common problem in stack drilling, particularly for low-rigidity structure, and the non-coaxiality in carbon-fibre-reinforced plastic and aluminium (CFRP/Al) stack drilling has not been studied. Because of the non-homogeneous behaviour and poor machinability of CFRP, the non-coaxiality in CFRP/Al stack drilling is significantly different from previous studies on Al/Al stack drilling. Focusing on the non-coaxiality in CFRP/Al stack drilling, this paper proposed the mechanism of the non-coaxiality through both experiments and numerical study. Severe non-coaxiality occurrences were observed in the CFRP/Al stack drilling experiments. To explain the observation, the macroscopic mechanics theory of composite was applied to obtain the engineering constants of composite laminates, which are necessary for the numerical model. This application leads to the development of an optimized simulation model to predict the interlayer gaps and non-coaxiality. The numerical results that predict the non-coaxiality are consistent with the experiments, which verified the rationality of simulation model. Furthermore, the effect of the thrust force and clamping force on both interlayer gaps and non-coaxiality were studied. The interlayer gaps gradually increase with the increase in thrust force but decrease with the clamping force. Moreover, the thrust force has a complicated effect on the non-coaxiality. The non-coaxiality first decreases and subsequently increases with the increase in thrust force, which can be attributed to the “tilt effect” in the lower layer. In addition, the non-coaxiality increases with the clamping force in the simulation experiment range. The work in this paper enables us to understand the particularity of the non-coaxiality in CFRP/Al stack drilling and select the appropriate cutting parameters for CFRP/Al stack drilling.

Ultra-precision machining and forming of metallic materials is of great significance in the fields of catalysts, sensors, and biomedical devices. In present work, the multi-scale cold embossing of CoCrFeNiMn high entropy alloy (HEA) with structures ranging from macro-scale to nano-scale was investigated at room temperature. In less 7 s, the macro patterns, the shapes of Arabic numerals, 5 μm wide gratings, 30 μm diameter hemispherical arrays, and ∼270 nm nanowires were formed rapidly. The highest replication of the HEA cold embossing was up to 98%. A series of slip bands were detected in the cold embossed HEA structures, which can accommodate more dislocations and facilitate the plastic deformation process. Moreover, dislocation pile-up and large angular rotation within grains are observed in the deformation areas, which is favorable to contain dislocation cells, leading to grain refinement and an increase in hardness. In addition, the multi-scale HEA can be used as a high-temperature resistant mold for forming thermoplastic materials such as plastics and metallic glasses at temperatures up to 900 °C. Our researches provide candidate materials and novel methods for the facile preparation and various applications of hyperfine structures.

The metadynamic recrystallization behavior of Cr-Co-Ni-Mo ultrahigh-strength martensitic stainless steel was studied in a double-pass isothermal compression test, and a metadynamic recrystallization kinetics model for softening was established. The results showed that the metadynamic recrystallization softening rate of the steel not only depended on the deformation temperature and strain rate but was also related to the dynamic precipitation and the local shear bands in the steel. When the deformation temperature was below 1050 °C, the dynamically precipitated M6C carbides pinned the grain boundaries and hindered metadynamic recrystallization. When the steel was deformed at a deformation temperature of 1000∼1050 °C and a strain rate of 1.0∼5.0 s−1, a large number of local shear bands were generated. The local shear bands increased the number of nucleation sites for dynamic recrystallization and enhanced the softening rate of metadynamic recrystallization.

The effect of solution pH, Cl− concentration and temperature on the electrochemical corrosion behavior of PH13-8Mo steel in acidic solution was investigated by using the electrochemical tests, scanning electron microscopy and X-ray photoelectron spectroscopy. The PH13-8Mo martensitic precipitation hardened stainless steel is in the passivity state when the pH value is above 3.0, below which the anodic polarization curves of the steel are actively dissolved. The corrosion current density gradually decreases with increasing the solution pH and decreasing Cl− concentration and solution temperature. Pits are initiated on the sample surface in the presence of the Cl− and gradually developed into uniform corrosion with increasing the Cl− concentrations. Moreover, the corrosion is more serious with an increase in solution temperature.

Silicon carbide reticulated porous ceramics (SiC RPCs) were fabricated by polymer replica technique. The effects of nitride whisker template on the growth of mullite, the strut structure and mechanical properties of SiC RPCs were investigated. Prepolyurethane (PU) open-cell sponge was first coated by SiC slurry consisting of SiC, reactive Al 2 O 3 , microsilica and Si powder, then it was nitridized at 1400 °C in a flowing N 2 atmosphere to prepare SiC preforms. Subsequently, these preforms were treated by vacuum infiltration of alumina slurry and fired at 1450 °C in air. The results showed that Si 2 N 2 O whiskers grew on the surface and in the matrix of SiC preforms after nitridation. The diameter of struts in SiC RPCs increased after vacuum infiltration process because alumina slurry was easily adhered by the surface nitride whiskers. In addition, such whiskers inside the strut of SiC preforms acted as the template to promote the growth of column-liked mullite in SiC RPCs. The mechanical properties and thermal shock resistance of SiC RPCs were greatly improved due to the special interfacial characteristics of multi-layered struts as well as better interlocked column-liked mullite in SiC skeleton.

The double skin composite wall (DSCW) with steel truss is an innovative lateral load resisting member which composed of two steel plates, core concrete, concrete-filled steel tubes (CFSTs) as boundary members, and steel truss connectors. The effects of the aspect ratio and the flange wall width on the seismic performance are investigated based on the quasi-static test of full-scale T-shaped DSCWs with steel truss. The failure mode, load-displacement response, shear strength, ductility, energy dissipation, shear deformation, and stress distribution of the specimens were analyzed. The test results showed that the failure mode of the T-shaped DSCW with steel truss specimens with aspect ratios of 2.0 and 2.5 was flexure-shear failure, which was characterized by shear buckling of the steel plate, local buckling, and fracture of the boundary members, and of crushing of core concrete. The T-shaped specimens with a small aspect ratio have a higher shear strength, ductility, energy dissipation capacity, and shear deformation proportion. The T-shaped specimen with a long flange wall also has a higher shear strength, but the ductility, energy dissipation capacity, and shear deformation proportion are small. The stress distribution indicates that the T-shaped specimen is more likely to failure due to the insufficient flexural strength of the boundary member. The theoretical formula for the flexural strength of T-shaped DSCW with steel truss is established, and the validation results show that the formula is accurate and safe.

ZrO2 (3Y)–Al2O3–SiC(w) ceramics with excellent mechanical properties were fabricated by oscillatory pressure sintering. The influence of sintering temperature on density, microstructural evolution and mechanical properties of such ceramics was studied in this work. The results showed that the selection of proper sintering temperature was favorable for controlling the transformation of t-ZrO2 into m-ZrO2, growth of ZrO2 grains and densification of specimens. The optimal relative density, bending strength, Vickers hardness and fracture toughness of specimens were up to 98.54%, 528 MPa, 13.19 GPa and 7.79 MPa·m1/2, respectively. Moreover, the interfacial characteristics at the phase boundary of ZrO2/SiC(w), Al2O3/SiC(w) and ZrO2/Al2O3 were semi-coherent relationship, which was beneficial for increasing the resistance of crack propagation, consequently improving the bending strength and fracture toughness of such ceramics.

A hybrid process combining ultrasonic injection molding and electrical discharge machining was proposed to realize the economic, high-precision, and environmental-friendliness production of glass fiber reinforced polypropylene microstructured parts. First, the prism array microstructures were processed on tungsten carbide-cobalt (WC-8 wt% Co) substrate by low-speed wire electrical discharge machining and used as the mold core. Then, the glass fiber reinforced polypropylene composite (GF/PP) was melted under ultrasonic vibration, and the surface microstructure of the mold core was replicated. The experimental results show that this method can efficiently and accurately manufacture microstructured parts, and the microstructure has a high replication rate up to 95.5%. By replicating the microstructure, the surface contact angle of GF/PP parts increased from 57.1° to 134.9°, and the wettability changed from hydrophilicity to hydrophobicity. The mechanical properties test results show that the GF/PP parts fabricated by ultrasonic injection molding had excellent mechanical properties, and the 30% GF/PP parts show the highest tensile strength of 56.9 MPa. This work provides a new option for fabricating fiber reinforced composite parts.

The static recrystallization (SRX) behavior of an ultrahigh-strength stainless steel (UHSSS) was investigated via double-hit isothermal compression tests. The results revealed that the kinetics of static recrystallization and the corresponding microstructural evolution were not only prominently influenced by the deformation parameters and initial microstructures but also suppressed due to the precipitation of M6C carbides below 1050 °C, which sufficiently pinned the boundaries. Numerical models for predicting the recrystallized fraction and grain sizes were proposed based on the experimental results. The kinetics model could predict the process of SRX in the deformation temperature range from 1050 °C to 1150 °C well, whereas there were some deviations between the predictions and experimental results due to the interaction of the M6C carbides and SRX when the deformation temperature was below 1050 °C.

This paper describes an experimental study to investigate the seismic behavior of double skin composite walls (DSCWs) with steel truss. Based on the results of seven specimens tested at full-scale, the influence of aspect ratio, axial compression ratio, and truss spacing to thickness ratio on the seismic behavior of DSCW with steel truss are considered. The failure mode, load-displacement relationship, strength, ductility, stiffness, energy dissipation capacity, and shear deformation were analyzed. The results showed that the aspect ratio had the most significant influence on the failure mode and seismic behavior of the specimen. For specimens with an aspect ratio of 2.0, shear compression failure dominates, while for specimens with an aspect ratio over 2.0, flexure shear failure dominates. The strength and initial stiffness decreased with the increase of aspect ratio, but the ductility and energy dissipation became better with the increase of aspect ratio. The axial compression had a little positive effect on the strength, but the specimen with a smaller axial compression ratio had better ductility and energy dissipation. The large truss spacing to thickness ratio weakened the external restraint effect of the steel truss on the steel plates, leading to premature buckling and failure of the specimen.

High frequency printed circuit board (PCB), as the significant support for 5G technology, has been receiving intense attention from the increasing number of scholars. Concerning precision fabrication of high frequency PCBs, micro hole drilling is deemed as one of the extremely crucial challenges. In this study, the coated drill bits’ wear and micro hole quality were investigated through the drilling experiments of high frequency PCBs. Results showed that two kinds of coated drill bits exhibited well in terms of hole registration accuracy. Using diamond like carbon coated drill bits could obtain fewer burrs than drilled with diamond coated drill bits before drilling 200 holes, but the burr height increased very slowly with the increment of hole number when using diamond coated drill bits. Taking the combination of aluminum sheet and phenolic aldehyde board as the entry board was conducive to obtaining less burr, and the micro drill bits with helix angles of 40° and 42° were contributed to achieving less burr too. Additionally, decreasing the feed rate could lessen the hole blocking.

Silicon carbide reticulated porous ceramics (SiC RPCs) with multi-layered struts were fabricated by polymer replica technique with SiC slurry, followed by infiltrating alumina slurries containing andalusite under vacuum condition. The effects of andalusite addition on the microstructure and mechanical properties of SiC RPCs were investigated, also the residual stress within the multi-layered strut was predicted. Theoretical calculations showed that the residual tensile stress generated in the outer layer of SiC RPCs because of its larger thermal expansion coefficient of infiltration slurry than that of SiC slurry at elevated temperature. Furthermore, the addition of andalusite reduced the thermal expansion coefficient and Young's modulus of infiltration slurries, thereby significantly reducing the residual stress of the outer layer in multi-layered struts. The reduced residual tensile stress within the outer layer was beneficial to eliminate surface cracks on the struts, thus improving the mechanical properties and thermal shock resistance of SiC RPCs.