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The metallization of the SiC ceramic was realized with Sn0.5Zn at a relatively low temperature of 250 °C with the assistance of ultrasonication. This process avoided the use of high temperature, vacuum, or long holding time in traditional metallization methods. Results indicate that fine metallization without defects can be completed under ultrasonication excitation for 20 s. The bonding mechanism was forming a nano-scale layer of non-uniform but continuous amorphous zinc suboxide (ZnO 1-x) (even when the Zn was only 0.5 (wt%)), which acted as a transition region from the SiC ceramic substrate to the Sn0.5Zn metal layer. The tensile strength between the Sn0.5Zn layer and the SiC was 12.3 MPa. The acoustic pressure in the liquid Sn0.5Zn pool was calculated via COMSOL Multiphysics software. The simulation results show that alternating positive and negative acoustic pressure existed in the liquid Sn0.5Zn metal, with the highest amplitude of more than 107 Pa, thereby generating the cavitation effect. The collapse of cavitation bubbles resulted in micro-jets, hot spots, and a high cooling rate, promoting the movement of Zn atoms toward the SiC surface and the formation of ZnO 1-x. [ABSTRACT FROM AUTHOR]

Investigations on ultrasonic welding of thermoplastic composites always focus on carbon fibre-reinforced thermoplastics so far. This study marks the first attempt at joining glass fibre-reinforced polyphenylene sulphide (GF/PPS) using ultrasonic welding. Attributed to the high observability of the glass fibre-reinforced thermoplastic, new discoveries on bonding formation and mechanism of void defect evolution were acquired. A special pattern of alternating high and low heat input regions was revealed, which was independent of welding energy variations and presented an inherent characteristic of ultrasonic welded GF/PPS joints. Squeeze-out and thermal degradation of matrix induced two primary defect types: larger voids with a size of approximately 100 μm were formed in the matrix between fibre bundles at the joint edge at lower welding energies and were diminished at excessive welding energy; smaller microvoids within 10 μm were formed within the fibre bundles at moderate welding energies and were increased in prevalence with higher energy levels. The research identified four distinct fracture modes that are strongly influenced by the welding energy and closely linked to the lap shear strength (LSS) of the joint. The GF/PPS joint achieved a maximum LSS of 22.6 MPa, which is the state-of-the-art welding joints, typically resulting from fracturing in the welded adherend. These findings provide valuable insights for refining the ultrasonic welding process of thermoplastic composites. [Display omitted] [ABSTRACT FROM AUTHOR]

Resistance welding, a favored method for joining thermoplastic composites, often faces the challenge of nonuniform bonding which leads to weak bonding at the overlap edge and compromises joint integrity. This study proposes a novel modification to traditional resistance welding by incorporating ultrasonic during the final stage of the process. We employed various durations of resistance welding and ultrasonic to join the GF/PPS composites, which yielded significant improvements in bonding strength and welding efficiency. Applying ultrasonic introduced a self-adaptive temperature compensation mechanism, enhancing the temperature at the overlap edge while diminishing the temperature difference between the center and edge of the overlap. This method also improved fusion bonding by encouraging resin flow along the unfused interface at the overlap edge, thereby expanding the bonding area. Notably, the introduction of ultrasonic revealed a new bonding mechanism involving the interaction between molten PPS and unmelted PPS, which was thoroughly examined. The results revealed a 19% increase in lap shear strength and a 40% reduction in welding time for joints with ultrasonic compared to those without ultrasonic. [ABSTRACT FROM AUTHOR]

In this work, porous Si 3 N 4 ceramics were successfully and ultrasonically soldered using Sn9Zn2Al solder through sonocapillary and cavitation. Si 3 N 4 ceramics were first ultrasonically wetted and then soldered. The results show that porous Si 3 N 4 ceramics can be wetted in the air within extreme short time of 10 s under ultrasonic. The capillary filling distance of the solder into the ceramic micro-channels achieves a value of 60 μm within 10 s and increases with prolonged ultrasonic time and high ultrasonic power. The infiltrated solder tightly bonded with the ceramic rod. The shear strength of the joint increases at prolonged ultrasonic time and becomes stable after 60 s. A geometric model is built to analyze the infiltration mechanism of the solder, and the result shows that the acoustic pressure inside the solder can reach 4 MPa, which is much higher than the pressure (0.32–1.4 MPa) needed for the sonocapillary action. The wetting mechanism of the solder to the ceramic is analyzed based on the cavitation bubble dynamics calculation. The high liquid velocity, pressure and temperature caused by the collapse of the cavitation bubble serve as the main factors that wet the ceramic. • Porous Si 3 N 4 ceramics are successfully and ultrasonically wetted and soldered by Sn9Zn2Al solder. • The joint can be obtained at a low temperature of 240 °C and short time of 10 seconds. • The solder infiltrates the ceramic through sonocapillary, and the mechanism is analyzed. • The wetting mechanism of solder to ceramic is studied based on the cavitation bubble dynamics calculation. [ABSTRACT FROM AUTHOR]

AlN ceramic was successfully wetted and then joined with nonactive Sn9Zn eutectic solder assisted by ultrasonication in air. The effect of ultrasonic time on the formation of joint was studied. Results indicated that the defect-free joint can be obtained at an ultrasonic time of 5 s. Two regions, namely, AlN/Sn (s,_s) and AlN/Zn (s,_s), were found in the bonding interface. Zn and O accumulated in the AlN/Sn (s,_s) interface. An amorphous and nanocrystalline layer of ZnO formed in the hard-wet AlN surface. And Zn (s,_s) directly bonded with AlN. The low temperature and fast bonding of the AlN was attributed to the high pressure and temperature caused by cavitation effect. The shear strength of the joint increased from 10.6 MPa to 30.7 MPa when the ultrasonic treatment time increased from 5 s to 150 s. With the prolongation of ultrasonic time, more AlN ceramic particles entered the solder and acted as the reinforcing phase. • AlN ceramic was rapidly wetted with a nonactive solder (Sn9Zn) in 5 s assisted by ultrasonication at 230 °C. • Wetting was realized by an amorphous and nanocrystalline ZnO at AlN/Sn interface, and Zn directly bonded with AlN. • The shear strength of the joint was 30.7 MPa with a short wetting time of 150 s. • The triggering mechanism of acoustic cavitation on wetting was analyzed through finite element simulation and calculation. [ABSTRACT FROM AUTHOR]

Abstract An ultrasonic-induced capillary action method was used to join porous ceramics for the first time. Results indicated that under ultrasonication, the solder infiltrated the porous ceramics and formed a soldered joint. The solder infiltration distance increased with prolonged ultrasonication time and reached 42 μm at an ultrasonication time of 120 s. Ceramic particles were eroded off and flowed into the joint seam because of the intense cavitation within narrow clearances. A fully penetrated layer formed near the joint seam at 120 s. This joint seam had high strength, so cracks propagated throughout the ceramic substrate during shear tests. Overall, our method was suitable for joining porous and microporous materials. Highlights • Porous ceramics were successfully joined by ultrasonic soldering. • Under ultrasonication, solder infiltrated the porous substrate to form a composite region. • Joint shear strength reached 33 MPa at 120 s, and crack propagated throughout the substrate. [ABSTRACT FROM AUTHOR]

Abstract An ultra-rapid transient liquid phase bonding method was successfully used to join AZ31B Mg alloys by using pure Zn interlayers in air. The bonding time was shortened to 1 s with ultrasonic assistance. Eutectic structures, MgZn, and MgZn 2 formed at relatively low temperatures of 360 °C and 370 °C. Only eutectic structures were observed at a high temperature of 380 °C because the entire joint was filled with eutectic liquid phase at this moment. MgZn 2 had higher hardness and modulus than those of MgZn. The shear strength of joint was inversely proportional to its width. The joint fractured through MgZn 2 at 360 °C and 370 °C, and through eutectoid structures at 380 °C. Graphical abstract Unlabelled Image Highlights • AZ31B Mg alloys were successfully bonded within 1 s with the assistance of ultrasonic. • Joint was formed through liquid phase bonding and diffusion at temperatures lower than 370 °C. • Shear strengths were 31 and 42 MPa when crack propagated through MgZn 2 and Mg Zn eutectic, respectively. [ABSTRACT FROM AUTHOR]

Joint seam is always the weak region of the welded joint. The soldered/brazed ceramic joint always fails through the joint seam due to lower strength of the solder/braze. In this work, to fabricate ceramic joint stronger than its substrate, ultrasonic vibration was used when brazing porous Si 3 N 4 ceramics. Results show that the brazing can be directly realized at 450 °C in air because ultrasonic cavitation can break the oxide layers of braze. Under ultrasonication, high acoustic pressure is obtained in braze, thus it rapidly infiltrates into the porous ceramics. Then, tight bond is realized between the ceramic and braze within several seconds because of the cavitation phenomenon. The transmission electron microscope results show that the main bonding medium at the ceramic/braze interface is an amorphous Al 2 O 3 layer. Shear test reveals that long ultrasonic time is beneficial to the shear strength of the joint. Wetting times longer than 10 s produce joint stronger than the ceramic substrate. This work provides a new insight when joining other porous materials. • Porous Si 3 N 4 ceramics joints stronger than the substrate was fabricated by ultrasonic brazing. • Short ultrasonic time of 10 s and low temperature of 450 °C produce joint stronger than the ceramic substrate. • The wetting interface is characterized by amorphous Al 2 O 3. [ABSTRACT FROM AUTHOR]

We used ultrasonic-assisted transient liquid bonding (UATLP) to join dissimilar Al/Mg alloys with pure Zn interlayer in the air to prevent the formation of Al Mg intermetallic compounds (IMCs). The effects of bonding temperature, ultrasonic power, sonotrode pressure, and interlayer thickness on the microstructure and mechanical properties of the bonded joints were studied. Results showed that the addition of Zn interlayer could effectively depress the Al Mg IMCs. The oxide layer on the Al substrate is incompletely removed at bonding temperature below 380 °C, the Mg side is bonded by eutectic phase, and the Al side is bonded by diffusion. The joint is characterized by Mg Zn eutectic (containing ternary IMCs) and IMCs of MgZn and MgZn 2 layer. MgZn 2 is the weak point of the joint under such a condition, and the joint has shear strength of approximately 20 MPa. The oxide layer on the Al substrate is completely removed when the temperature exceeds 380 °C, the large amount of Al that flows into the joint results in a Mg 32 (Al,Zn) 49 layer adjacent to the Al substrate. The joint gains its maximum strength of 28.4 MPa when thin MgZn 2 and discontinuous Mg 32 (Al,Zn) 49 exist adjacent to the Al substrate. High ultrasonic power, large sonotrode pressure, and thin Zn interlayer could reduce the thickness of MgZn 2. • Al/Mg alloys are bonded through ultrafast ultrasonic-assisted TLP in the air with Zn interlayer to avoid Al Mg IMCs. • IMCs of Al 3 Mg 2 and Al 12 Mg 17 are depressed, and MgZn and MgZn 2 formed when temperature is below 380 °C. • Mg 32 (Al,Zn) 49 , strengthened by nanosize Al particles, formed in joint when temperature is above 380 °C. • The joint gains its maximum strength when thin MgZn 2 and discontinuous Mg 32 (Al,Zn) 49 form adjacent to the Al substrate. • High ultrasonic power, large sonotrode pressure and thin Zn interlayer could reduce the MgZn 2 thickness. [ABSTRACT FROM AUTHOR]

• Cavitation characteristics of GaIn melt during the ultrasonic-induced spreading process are studied in situ by high-speed photography. • The cavitation cloud, single cavitation bubble, stable cavitation bubble, their sizes and life periods are identified. • The bubble density decreases with the spreading of the droplet, which is explained by acoustic pressure. • A non-cavitation region showing increasing width as the droplet spreads consistently appears at the spreading front due to the acoustic pressure loss. • A cavitation threshold measuring method is proposed, and the cavitation threshold of eutectic GaIn alloy is identified to be approximately 0.65 MPa. Cavitation is widely used in many fields, but the nature of cavitation, especially in metallic liquids, remains unclear. In this work, the cavitation bubble characteristics during the spreading of eutectic GaIn liquid droplet subjected to ultrasonication were studied in-situ by high-speed photography. The types, diameters, variations, and life cycles of cavitation bubbles were identified. Results show that the bubble density gradually decreases during the droplet spreading process because of the decreased acoustic pressure inside the thinned liquid. The cavitation presents strong/weak change characteristics with a period of dozens of acoustic periods (T, 50 µs). Cavitation clouds with large sizes and long lifetimes are observed at the early-spreading stage. Tiny cavitation bubbles emerging and collapsing within 1 T dominate the cavitation field in the late-spreading stage. Stable cavitation bubble showing continuous nucleation and collapse but minimal changes in its position is also observed. A non-cavitation region consistently appears at the spreading front because the acoustic pressure is below the cavitation threshold. The width of the non-cavitation region gradually increased as the size of the spreading area increased. A cavitation threshold measuring method is proposed based on the cavitation observation and simulation and the cavitation threshold of eutectic GaIn alloy is identified to be approximately 0.65 MPa. The cavitation bubble dynamics result shows that the cavitation bubbles with different nucleation diameters have different life periods the same growth velocity. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a method of producing uniform particle strengthened bonds between pieces of aluminum metal matrix composite (Al-MMCs), of strength equal to that of the substrate material. SiC particle reinforced Zn-based filler metals were fabricated by mechanical stir casting and ultrasonic treatment, and then used to join pieces of SiCp/A356 composite with the aid of ultrasonic vibration. The filler metals made by mechanical stirring were porous and contained many particle clusters. Ultrasonic vibration was used to disperse the agglomerates and prevent further coagulation of SiC particles during joining, but the method failed to eliminate the porosity, resulting in a highly porous bond. The filler metal treated by ultrasonic vibration was free of defects and produced a non-porous bond strengthened with uniform particles between pieces of SiCp/A356 composite. The presence of surface oxide films at the bonding interface significantly degraded the performance of SiC particle reinforced bond. Removal of this oxide film by at least 4s of ultrasonic vibration significantly increased the bond strength, reaching a value equal to that of the substrate metal. [Copyright &y& Elsevier]

Abstract: Ultrasonic aided interactions between Zn–Al alloy and Al2O3p/6061Al composites were investigated. Ultrasonic vibration imposed on the composite plate can cause high cavitation intensity in the liquid Zn–Al alloy which disrupts and flakes off surface oxides, thereby allowing the Zn–Al alloy to wet the bare composite surfaces and form a metallurgical bond. Whether the undermining phenomena occurred or not, the spreading of Zn–Al liquid over the composite did not occur until the ultrasonic vibration amplitude reached 10μm. The Zn–Al liquid spread quickly over the composite despite that the surface oxide had not been fully disrupted when the ultrasonic vibration higher than 10μm was applied. When undermining phenomena occurred during interaction, the oxide layer at the interaction interface was firstly lifted up by the undermining alloy, suspending in the Zn–Al liquid, and subsequently broke up by the ultrasonic excitation. Gas escaping from the base metal was observed to be helpful in decohesion of the oxide layer from the composite. When undermining phenomena did not occur during interaction, the removal of the oxide layer was based upon the melting of the nether base metal. The disruption of oxide initiated from the composite surface where the drop center located and the surface oxide layer near the drop edge was lastly removed. [Copyright &y& Elsevier]

Abstract: The ultrasonic vibration liquid phase bonding of Al2O3p/6061Al in air has been investigated. The surface oxide film can be sufficiently removed, resulting in the bond metal turning into a composite material in which reinforcements are distributed uniformly and have metallurgical bonds with the matrix. The strength of bonded joints increases with the ultrasonic vibration amplitude. [Copyright &y& Elsevier]

Abstract: The friction stir welding of AZ31Mg/1060Al has been investigated. The welds were formed when the stirring pin was off the centerline to AZ31 or to 1060, and are characterized by intercalation lamellae. Al3Mg2 and Al12Mg17 cause the weld to crack during friction stir welding on the centerline of the weld. [Copyright &y& Elsevier]

Abstract: Effects of the bonding thermal cycle and heat treatment on thermal expansion behaviors and mechanical performance of SiCp/A356 composites and their joints were investigated. Joints were made by using the vibration liquid phase (VLP) diffusion bonding process, and treated by the solution and aging. It has been found that the CTE of the base metal is not significantly influenced by the bonding thermal cycle and decreases slightly after the solution and aging treatment. The constituent phases of the base metal are composed of α-Al (Si), SiC and a compound of Al3.21Si0.47. The presence of the bond region shows no deleterious effect on the CTE of the bonded joint. After heat treatment, the CTEs of VLP bonded joints decreased with the bonding temperature and were lower than those of the as-bonded joints or the SiCp/A356 composites. The tensile strength of VLP bonded joints increases with the bonding temperature due to an increase of the volume fraction of SiC particles and the Al content and a decrease of the Zn and CuZn5 content in the bond. The disappearance of CuZn5 and occurrence of Al0.71Zn0.29 in the bond region may account for the increased strength of the joint after heat treatment. The constituent phases of VLP bonded joints are composed of α-Al (Si), SiC and two compounds of Al3.21Si0.47 and Al0.71Zn0.29. [Copyright &y& Elsevier]

The TLP bonding of Al2O3p/6061Al using Cu/Ni/Cu interlayers at 580 °C has been investigated. A pure Ni, Al0.9Ni1.1 and Al-based solid solution zone exists in the bond region. The shear strength of joints increases with holding time. The Al0.9Ni1.1 zone is the preferential failure source for the bonded joints. [Copyright &y& Elsevier]

Rapidly homogenized joining has been a longstanding pursuit in the forming manufacturing of lightweight alloys structures. In this study, ultrasound energy was introduced into the joining process to accelerate cross-scale diffusion (direct grain migration rather than atomic-scale diffusion), and a homogeneous 6063Al joint was fabricated using a Zn-40Sn alloy at 360 °C in air. The network architecture joint composed entirely of α-Al grains was formed with a sandwich structure consisting of Sn@Al 2 O 3 /MgO as the grain boundary. The tensile strength of the joints was higher than that of the base metal in only a very short diffusion time (180 s). Physical effects of ultrasound in the Sn-Zn molten metal induced violent intergranular penetration, resulting in the decohesion and migration of the α-Al grains from the base metals and realizing a rapidly homogenized joining. This provides a foundation for full-strength joining of high-strength aluminum alloys with low thermal damage. [Display omitted] [ABSTRACT FROM AUTHOR]

• Two inclusion algorithms are proposed for one-unambiguous regular expressions. • The inclusion algorithms are used in the subtyping algorithms for DTDs and for RRTGs. • Several experiments are conducted to evaluate the above algorithms. One-unambiguous regular expressions are used in DTD and XML Schema. It is known that inclusion for one-unambiguous regular expressions is in PTIME. However, there has been few studies on algorithms for the inclusion. In this paper we present algorithms for checking inclusion of one-unambiguous regular expressions. A classical way is based on automata, following which one algorithm is provided and improvements are given. The other algorithm is based on derivatives, utilizing a property presented here that the number of derivatives of a one-unambiguous regular expression is finite. We have applied the algorithms to XML typechecking. The results of experiments with the algorithms are also included. First we give comparisons of the efficiency of our algorithms by experiments. Since after our work Hovland has given another algorithm, we also included his algorithm in the experiments. The results show that both of our algorithms are more efficient than Hovland's algorithm for one-unambiguous regular expressions, and under the inclusion mode (see Section 6) the derivative-based algorithm is more efficient than the automata-based one for small expressions, while for large expressions the latter is more efficient. Then we have conducted preliminary experiments by implementing typechecking of XML using the algorithms. The results show that typechecking using our algorithms is more efficient than typechecking using XDuce. Comparisons of the algorithms with CDuce are also given. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced aluminum matrix composites (C f /Al) are widely used in various industries. But they are difficult to join because it is hard to realize the wetting and continuity of the carbon fiber in joint. To solve this problem, C f /Al are joined by ultrasonic soldering in this work. Results show that the C f /Al can be wetted within 5 s under ultrasonic. Transmission electron microscope result shows that the surface of the wetted carbon fiber is covered by an amorphous-nanocrystalline layer, which is formed due to the high solder velocity, temperature and pressure caused by cavitation. Carbon fibers flow into the solder after the Al matrix is eroded, guaranteeing its continuity in the joint. Limited carbon fibers flow into the joint at low ultrasonic power of 333.3 W, while a fully carbon fiber reinforced composite joint is obtained at 1000 W. The soldered joints have higher strength than the C f /Al substrate, and its formation mechanism is discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Study effect of Co-doping on improving the gas-sensing property of anatase TiO 2 to NH 3. • Co-doped TiO 2 achieves room temperature (RT) gas-sensing and response improvement. • Response of Co-doped TiO 2 at RT is 7 times higher than TiO 2 operated at 180 °C. • DFT simulation study shows that co-doping changed the band structure of TiO 2. • The mechanism is analyzed from energy band, charge distribution, and adsorption. Improved gas sensors based on pure anatase TiO 2 and Co-doped TiO 2 nanoparticles were evaluated. A cobalt-doped TiO 2 nanoparticle with a diameter of 40 nm was first synthesized. The morphology of the nanoparticles was analyzed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The doped Co ion was confirmed to have entered the TiO 2 lattice. Subsequently, gas sensors with different Co-doping concentrations were developed to investigate gas sensitivity to NH 3. Compared with pure anatase TiO 2 operating at 180 °C, Co-doped TiO 2 samples were developed as NH 3 gas sensors operating at room temperature. The 20% Co-doped sample exhibited the best performance, with a response value of 14 for 50 ppm NH 3 , which was 7 times higher than that of pure TiO 2. The response and recovery times of the sensor were only 25 and 48 s, respectively, and exhibited both good stability and selectivity. Based on density functional theory (DFT), the calculated bandgap of Co-doped TiO 2 decreased by 72% compared to pure TiO 2. Structural simulation and mechanism analysis elucidated the good gas-sensing performance at room temperature and the property enhancement of the Co-doped TiO 2 gas sensor. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics are widely used materials but very difficult to join. In this work, we successfully ultrasonically soldered porous Si 3 N 4 ceramic rapidly at a low temperature of 230 °C. The wetting and bonding mechanism at the ceramic/solder interface was studied. Results showed that the solder rapidly infiltrated the micro-channels of the ceramic during soldering, and high ultrasonic power contributed the sonocapillary distance. Zn and O acted as the main bonding elements. Bonding was realized by the formation of nanocrystalline and amorphous ZnO x region at the wetting interface. Rapid bonding was achieved due to the high liquid velocity, high temperature, and high pressure caused by the collapse of the cavitation bubbles. [Display omitted] • Porous Si 3 N 4 ceramics are successfully soldered within 10 s at 230 °C with the assistance of ultrasonic. • The solder rapidly infiltrates the ceramics through sonocapillary, the infiltration layer widens at high ultrasonic power. • Nanocrystalline and amorphous ZnO x formed at the wetting interface, and the wetting of solder to Si 3 N 4 is achieved. • The wetting mechanism is explained from the viewpoint of bubble dynamics. [ABSTRACT FROM AUTHOR]