Joint Seam Research Articles

Increasing joint strength by achieving carbon fibers’ continuity with ultrasonic assistance during soldering Cf/Al using ZnAl

Ultrasonic assistance was utilized during the soldering of carbon fiber-reinforced aluminum composites (Cf/Al) using ZnAl solder to enhance joint strength. The results indicated that carbon fibers migrated into the joint seam after Al substrate was eroded and the solder was expelled, effectively maintaining the continuity of the carbon fibers. A joint fully reinforced by carbon fibers was achieved with an ultrasonic application time of 60 s. Transmission electron microscopy revealed rapid wetting of the carbon fibers facilitated by ultrasound, characterized by an amorphous/nanocrystalline interface. The maximum joint strength reached 23.5 MPa, which is equivalent to 77.5 % of the Cf/Al.

Microstructure and properties of C/C and C/SiC composites brazed by reactive infiltration of Si[sbnd]Zr filler alloy

The joint between C/C composites and liquid silicon infiltrated-C/SiC composites was achieved using a Si10Zr (at. %) eutectic filler. The microstructure and mechanical properties of joints at different brazing temperature and holding time were characterized. The results showed that the melting filler infiltrated along the carbon fiber bundle gaps and formed SiC reaction layers at both interfaces. On the side of C/SiC composites, the residual silicon in the original base material dissolved into the molten Si10Zr alloy during the brazing procedure. The phenomenon resulted in intense infiltration of the liquid filler into C/SiC composites, which formed a unique C/SiC-Si-ZrSi2 multiphase-ceramic gradient structure. Excessive filler was squeezed out around the joint seam to form a fillet. The shear strength of the joint reached up to 37 MPa, with fracture occurrence in both substrates and the joint seam. Reliable bonding between C/C and C/SiC dissimilar composites was finally achieved.

Composition design for modified nickel nanopastes containing a low-melting element as additive for pressureless nanojoining

The use of Ni nanopastes for joining applications offers advantages over other methods. However, since it is based on solid-state processes, a pressure must be applied during the joining process, which represents a challenge. To overcome this, a novel concept is presented in this work, which introduces a low-melting additive to the Ni nanopaste. A liquid phase provides the potential to achieve a joint seam formation with both a reduced porosity and better adhesion to the base material without technical pressure during the process. In a comprehensive selection, elements such as Mg, Al, Ge, In, Sn, and Pr are identified as suitable additives. Their properties in binary phase systems with nickel are discussed. A modified Ni nanopaste with Ge as additive was used in promising initial experiments, which is a good starting point for further investigations.

Mechanically enhancing a brazed joint of WC-Co/3Cr13 by utilizing a nanoporous Cu lamina interlayer prepared by chemical dealloying

Ag-Cu-Ti brazing alloys may allow sound joining between WC-Co cemented carbide (YG20) and 3Cr13 stainless steel. However, the issue of excessive formation of agglomerated brittle Cu-Ti compounds in the joint seam, which deteriorates mechanical performance, is still a major processing drawback. Here, a nanoporous copper (NP-Cu) lamina, prepared by chemically dealloying an Mg67Cu33 (at. %) alloy precursor, was used as an interlayer for assisting the brazing process between YG20 alloy and 3Cr13 stainless steel. The effect of introducing the NP-Cu interlayer on the microstructure and mechanical properties of the joints was investigated. Results revealed that the Cu-Ti compounds in the brazing seam acquired reduced size and dispersed distribution by applying the NP-Cu interlayer. The technique outperforms the directly brazed alternative, with a shear strength increase of 70%. The interlayer contributed by its high specific surface and excellent surface metallurgical activity, overcoming the drawback of agglomerated Cu-Ti compound development. The new technique allows a process based microstructural and chemical control, with vast potential applications in the joining of WC-Co cemented carbide and stainless-steel materials.

Behavior of fire-retardant treated bolted timber–steel composites (TSCs) and effective charring depth based on experiment

ABSTRACT The bolted joints make timber–steel composites (TSCs) easily to be assembled; however, seams exist between the timber components for bolted TSC components resulting in the risk of fire spreading into the joint seam when the component is under fire. The efficient charring depth provided by timber needs to be clarified; furthermore, the raising temperature potentially affects the strength of steel component. In this study, TSCs were tested in fire for 1 hour, and the following issues were examined, including the experimental charring depth of timber components, the influence of fire-retardant finish in order to provide the efficient charring depth, and additionally the suggested charring depth are proposed for the design of TSCs. In conclusion, the charring depth in the seams was greater than the regulation values, and evaluation methods for the charring depth at seams should be reconsidered. Although the fire-retardant finish reduced the formation rate of the char layer, the flames still breached the seams. The results reveal that Douglas fir TSCs with fire retardant are the most efficient specimen, with effective charring depth 52 mm. While the effective charring depth of Douglas fir TSCs without fire retardant and Japanese Cedar TSCs with fire retardant are increased, at least 64 mm and 65 mm needed, respectively.

Chemically dealloyed Mg–Cu alloy lamina as an interlayer for reinforcing a C/C composite – TC4 alloy vacuum brazed joint

Here, a novel brazing interlayer of bicontinuous nanoporous copper (NP–Cu) lamina was produced by chemically dealloying a magnesium-copper (Mg–Cu) binary alloy and applied for brazing a C/C composite and TC4 alloy along with AgCuTi alloy brazing filler. SEM, EDS, XRD, XPS, TEM and SAED were used to characterize the differences in microstructure and phase distribution of the samples and compare with samples without an interlayer. Mechanical testing in the form of shear tests were conducted to evaluate the change in shear strength caused by the interlayer. The large specific area, uniform nano scale porosity and ligaments of the NP-Cu lamina interlayer induced the transformation of Ti–Cu compounds from their bulk agglomerates to dispersed fine particles and formed eutectic phases, which contributed to relieving the residual stress and enhancing the plasticity of the joint seam. This led to a shear strength increase of 185% as compared to samples without an interlayer.

Polysilazane-based high-temperature adhesives for the joints of amorphous SiBON ceramic composites

Amorphous SiBON ceramic integrated the advantages of SiO2 and BN can be used as heat-resistant wave transparent composites in radome, and corrosive-resistant high strength materials in aeronautics and astronautics, while it is a great challenge to bind the amorphous SiBON ceramic to solve the problem on difficulty of fabrication of large-sized. In this work, we prepared four kinds of polysilazane-based high-temperature adhesives to join amorphous SiBON ceramic. The joining strength was tested and compared after heat treatment at temperatures ranging from 200 °C to 1100 °C at different atmospheres. Satisfactory shearing strength and toughness (the strength of joints could reach above 25 MPa in air until breakage of ceramic substrate and maximum strength of joints was above 7.5 MPa in Ar) were achieved at the binding interface without pressure applied during joining. The mechanism for the interfacial binding was proposed by analyzing microstructure and chemical compositions. A normal B2O3-SiO2-ZrO2 glass-ceramic interlayer was formed in the joint seam in air, and amorphous SiCN and C3N4 ceramics were generated in the sample in Ar, which reinforced the binding strength of the lap amorphous SiBON ceramic. It is significant to find modified heat-resistant organic adhesives for binding amorphous ceramics to produce high strength ceramic joints in both air and inert atmospheres to resolve the problems on poor processing performance difficulty of fabrication of large-sized of ceramics.

The Instability Characteristics and Displacement Law of Coal Wall Containing Joint Fissures in the Fully Mechanized Working Face with Great Mining Height

Coal wall rib-spalling is regarded as a key technical problem influencing safe and efficient mining of fully mechanized working face with great mining height (FGH) while the coal wall stability is influenced by the strength of the coal body, of which the internal joint fissures have a crucial impact on the strength of the coal body. This research attempted to explore how the coal wall stability of FGH is influenced by the occurrence of joint fissures. This paper uses physical and numerical simulations to systematically analyze the instability characteristics and displacement law of FGH. Research results show that the form and scope of the instability of coal wall rib-spalling depend on the state of the coal seam joint fissures development area, and the development state of coal seam joint fissures is related to the combination of the coal seam joints; under the condition of hard coal, the coal wall stability is better at the inclination angle of 90°, and less stable at 45° and 135°; under the condition of medium-hard coal and joint surface inclination angle of 45° and 135°, the smaller the spacing of joint surface, the larger the area of the working face rib-spalling, and the less stable the coal wall.

Study on the Influence of Selected Fabrics and Stitching on the Strength of Upholstery Covers.

So far, no coherent and comprehensive method has been elaborated allowing investigation of tensile strength of upholstery seams dedicated to upholstered furniture. Producers of this type of furniture are interested in the assessment of the quality of upholstery material joints, which seems to be particularly important for ensuring the appropriate quality of products. Therefore, the objective of this research was to investigate the influence of the type of material used and the direction of the fabric cut on the strength of upholstery covers. Static tensile testing of selected upholstery fabric samples was performed, and an attempt was made to identify the most optimal fabric–seam joints. It was stated as a conclusion that the fabric tensile strength was the highest for Secret 10 fabric. In addition, the strength of upholstery covers is not influenced by the direction of the fabric die cut. For each fabric, a different configuration is preferable, as shown by results (Power 13: A-B, Secret 10: B-B, Soft 10: A-A). The method, implemented for upholstered furniture, allows for an objective assessment of the strength of upholstery covers and the selection of the most advantageous fabric–seam combination for future furniture designs.

Spark plasma joining of HfB2-ZrB2 based Ultra High Temperature Ceramics using Ni interlayer

Real-life applications of ultra-high temperature ceramics (UHTCs) mandates the joining processes to realize the final complex shapes, often resulting in the compromised performance of metallic interlayer. In the present work, two pre-sintered HfB2-ZrB2 (HZ) and HfB2-ZrB2-SiC (HZS) composites were joined using interlayer of Ni powders via spark plasma sintering (1100 °C, 18 MPa). Solid-state diffusion of Ni into UHTCs has resulted in the formation of continuous and crack free interface in both HZ/Ni/HZ and HZS/Ni/HZS joints. Microstructure and phase analysis revealed the presence of nearly equal Ni-rich joint seam (∼100 μm) and diffusion zone width (∼150 μm) in HZ/Ni/HZ joint. However, prominent reaction of Ni with SiC in HZS composite has formed Ni2Si, while exhibiting wider diffusion zone (∼200 μm) and thinner Ni-rich joint seam (∼30 μm). Thus, microstructural inhomogeneity in HZ/Ni/HZ joint resulted in an overall reduction of ∼38% in hardness from parent HZ region (15.6 GPa) to Ni-rich joint (∼10 GPa), whereas for HZS, a uniform micro-hardness of ∼16 GPa was obtained in all the three regions owing to microstructural homogeneity across the interface. Damage tolerance of the joints has also been investigated by micro-scratch testing, revealing dominant abrasive wear in the parent UHTC region, whereas plastic deformation along with the tensile cracks is observed in the Ni-rich joint seam of HZ/Ni/HZ joint. In contrast, microstructural homogeneity in HZS/Ni/HZS joint has resulted in similar abrasive wear along with limited tensile cracks in all the regions, including that of Ni-joint seam, making it suitable for attaining superior structural integrity in joining complex shapes.

Avoiding degradation and increasing joint strength of Al alloys by rapid ultrasonic soldering at low temperature

To avoid substrate softness, AA7075 were rapidly soldered using a Sn-9Zn solder at 200 °C under ultrasonication. The effect of acoustic intensity on the microstructure and mechanical properties of the soldered joint was studied. The acoustic intensity inside the solder was improved by decreasing the lap width without increasing the input ultrasonic power. Results showed that the softness of the substrate was almost avoided with minimal hardness decrease. The acoustic intensity increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. Pronounced erosion of the substrate occurred under high acoustic intensity. Thus, the content of Al in the joint seam increased from 3.35% to 10.84% after reducing the lap width from 0.8 mm to 0.2 mm. The joint seam was characterized by interlaced fine/coarse Sn-Zn eutectic. The Sn and Zn grains had average sizes of 2.31 and 0.31 μm in the fine eutectic and 3.03 and 0.41 μm in the coarse eutectic. Increasing the acoustic intensity during soldering can effectively increase joint strength. The maximum shear strength of 65.4 MPa and hardness of 29.5 HV were obtained in the joint soldered at 0.2 mm. The cavitation bubble with a nucleation diameter of 10 μm had a large liquid velocity of 7653 m/s, a temperature over 1800 K, and a pressure of 4 × 1012 Pa during its collapse.

Joining dense Si3N4 to porous Si3N4 using a novel glass-ceramic interlayer with precipitated β-LiAlSi2O6/Mg2SiO4

In this work, we developed a new β-LiAlSi2O6/Mg2SiO4 glass-ceramic interlayer to join dense Si3N4 and porous Si3N4 ceramics for high-temperature applications. The microstructure and phases of the joint were investigated using systematic analysis methods and the mechanism for the interfacial bonding was proposed. The double crystalline phases of β-LiAlSi2O6 and Mg2SiO4 precipitated in the joint seam during the joining process, forming a novel glass-ceramic interlayer with high crystallinity. Due to the good wettability of liquid glass on porous Si3N4, a gradient and dense infiltration layer was formed in porous Si3N4 and reinforced it, which improved the mechanical strength of the whole joint. In this case, the shear strength of the joint reached 78 MPa, and it could still maintain 74 MPa up to 850 °C, which fully demonstrated the high-temperature resistance of the joint.

Wetting and joining of surface-oxidized SiC ceramic with calcium lithium aluminosilicate glass filler

A novel strategy was developed to join SiC ceramics via a two-step method (i.e., SiC surface was modified by pre-oxidation treatment before bonding) using CaO-Li2O-Al2O3-SiO2 (CLAS) glass as the joining material. The wetting behavior, joint microstructure, bonding strength, fracture characteristics, and joining mechanism were investigated. Due to the formation of the SiO2 layer on the SiC surface by the pre-oxidation, the wettability of CLAS glass solder on the SiC matrix was significantly improved and the interfacial bonding was also enhanced. The microstructure of the joint revealed that the nanoscale eutectic structure composed of wollastonite and spodumene and the rod-shaped anorthite with micron-size were the main products in the joint seam. Besides, the content and size of anorthite in the joints increased with the increase of the joining temperature. Compared with one-step joining, the two-step method can obtain more reliable SiC/SiC joints due to the strong interfacial bonding. As a result, the optimal shear strength of 127 MPa was achieved at a joining temperature of 1240 °C, which was 119% higher than that obtained by the one-step joining method.

Mechanical Properties and Energy Conservation Analysis for The New Connection of The Fabricated Shear Wall

In order to investigate a reliable reinforcement connection form for the assembly nodes of the fabricated reinforced concrete shear walls with joint seams, and explore a reinforced bars lap splice method with easy control of construction quality, a new type of reinforced bars lap splice method with the additional X-shaped reinforcement at the assembly nodes is proposed. By changing the width of the assembly nodes, three fabricated shear wall models were designed. By using Abaqus finite element analysis software, the full-range numerical simulations of its mechanical properties under static load were carried out to study the behaviors of the new reinforced bars lap splice method, which were compared with the behaviors of the cast-in-place monolithic shear wall with the same design parameters and analyzed. The results show that the additional X-shaped reinforcement changed the force transmission path of the reinforced bars lap splice at the assembly nodes and reduced the cross-sectional stress of lap splice area, and improved the reliability of the weak part of the fabricated shear walls. The method also reduced the difficulty of assembling fabricated shear wall structure. Comparing the fabricated shear walls in the same assembly position, the analyses show that the reinforced bars lap splice with the additional X-shaped reinforcement is not sensitive to joint seam width, which can realize the shear walls can assemble with small seam width, and effectively improves prefabrication rate.

Dependence of the microstructure and properties of joints on acoustic intensity during the ultrasonic soldering of 7075 Al alloys

• Acoustic intensity of solder remarkably affects the microstructure and mechanical properties of joints. • High acoustic intensity was produced by applying a small lap width without increasing input ultrasonic power. • The melting point of Zn increased by 73.8 °C under the high pressure caused by bubble collapse. • Zn grains were significantly refined due to undercooling–induced direct solidification caused by cavitation. • Shear strength and hardness respectively increased by 24% and 17% when lap clearance decreased by 50%. In this work, 7075 Al alloys were ultrasonically soldered by pure Zn solder in air under different acoustic intensities. The dependence of the microstructure and mechanical properties of joints on acoustic intensity was revealed. Acoustic intensity is innovatively controlled by applying different lap widths without increasing the input ultrasonic power. The acoustic pressure inside the solder was simulated by finite element simulation, and results showed that the acoustic intensity increased by more than six times when the lap width decreased by 50 %. High acoustic intensity led to intense cavitation, thereby causing a pronounced erosion of substrate. The Al content inside the joint increased from 17.3%–24.5% when the clearance width decreased from 0.8 mm to 0.4 mm. The Clausius–Clapeyron equation helped explain that the melting point of Zn increased by approximately 73.8 °C under the high acoustic pressure caused by cavitation bubble collapse, which could cause the direct solidification of Zn and served as the main reason of grain refinement. Zn grains were refined from 6.9 μm to 4.2 μm when soldered at 0.8 mm and further to 3.5 μm when soldered at 0.4 mm because of the strong cavitation caused by high acoustic intensity. Acoustic intensity had a remarkable effect on the mechanical properties of joints. Joint shear strength and hardness increased from 117.3 MPa and 93.3 HV to 145.1 MPa and 109.4 HV, respectively, when the lap clearance width decreased from 0.8 to 0.4 mm. Particularly, the joint soldered at 0.4 mm failed through the substrate because of the high strength of the joint seam and the weakness of the substrate, which were explained through the Hall–Patch relationship, the Schmid factor, the dissolution of secondary phases, and the increase in high angle boundaries. This work provides a novel method by producing strong joints with fine grains without increasing input power.

Joining of Aluminum and Steel using AlSi12 Brazing Filler in a Protective Atmosphere Furnace: Microstructure and Mechanical Properties

Brazing of pure aluminum (Al) to steel using an Al-12 wt. %Si (AlSi12) filler metal and an Al brazing flux was performed in furnace filled with protective atmosphere. Microstructure characterizations of the full/fractured joints, tensile shear strength and micro-hardness tests were performed on the samples with holding time from 5-30 min at brazing temperature of 600 °C and additional thermal exposure of 30 min at temperature of 480 °C. It is found that the joint seam for all samples features roughly into four layers, among them, the layer adjacent to steel is an IMC layer and dominantly distributed with h phase. The tensile shear strength of joints is inversely proportional to the thickness of h phase layer and particularly governed by a specific zone which is located in the h phase layer, directly adjacent to the interface between h phase layer and steel and scattered with a lot of visible pores and cracks. Micro-hardness tests show the hardness of the h phase layer remains the highest for each holding time and increases with the increase of holding time. The higher hardness leads to the limited plasticity of the η phase and more fragile of this layer. Furthermore, great differences of hardness exist between the η phase layer and steel may also generate great stresses that induce the crack initiation in the specific zone and finally result in the failure of brazed joints.

Application of the eutectic high entropy alloy Nb0.73CoCrFeNi2.1 for high temperature joints

The eutectic high entropy alloy Nb0.73CoCrFeNi2.1 was manufactured by means of arc smelting and the obtained ingots were cut into 300-μm-thick foils, which were used as filler alloys to braze Crofer 22 APU to Hf-metallized yttria-stabilized zirconia (3YSZ). The brazing process was conducted in a vacuum furnace at 1200 °C for 5 min at a vacuum of 4.3·10–4 mbar. In order to minimize the intense diffusion and erosion of the steel substrate, a heating and cooling rate of 50 K/min was applied. Sound joints without any pores or flaws were obtained. The microstructure of the joints consisted of an HfO2 reaction layer at the ceramic interface and the same eutectic structure consisting of a Laves phase and a solid solution that was already detected in the smelted foil. The average hardness of the microstructure in the joint seam amounted to 352 ± 17 HV0.01 and the joints reached strength values up to 97 ± 7 MPa while the fracture area was always located at the ceramic interface in the HfO2 layer. Comparable joints, with AgCuTi3 as filler metal, brazed at 920 °C, only reached a shear strength of ~ 52 ± 2 MPa.

Fracture initiation pressure and failure modes of tree-type hydraulic fracturing in gas-bearing coal seams

Tree-type hydraulic fracturing is a new technology that can uniformly increase the permeability of coal seams. The existing initiation pressure prediction models do not fully consider the characteristics of coal seams and are not suitable for tree-type hydraulic fracturing. In this paper, an initiation pressure prediction model considering coal seam joints and gas pressure is established. In this model, the fracture failure modes of coal seam fracturing are calculated separately to accurately predict the failure mode and initiation pressure. Statistics and reasons are obtained for the fracture initiation position and the failure mode of tree-type hydraulic fracturing under different conditions. The fracture failure modes of a gas-bearing coal seam are mainly tensile failure and coal matrix failure, and tensile failure along bedding planes is the most common. The effects of 7 factors, including coal seam geological parameters, fracturing hole arrangement parameters and tree-type branch borehole arrangement parameters, on the fracture initiation pressure of tree-type hydraulic fracturing are analyzed. Among them, the angle between the tree-type branch borehole and the maximum principal ground stress direction is the only major influential factor that can be artificially controlled. The fracture initiation pressure is lowest when the tree-type branch borehole lies along the direction of the minimum principal ground stress. The results of a field experiment show that the theoretical initiation pressure and the actual initiation pressure are within 6.3%. In addition, compared with traditional fracturing technology, tree-type hydraulic fracturing technology can reduce the initiation pressure. The proposed model can provide a reference for field applications of tree-type hydraulic fracturing technology.

Study on the cutting performance in machining assembled hardened steel workpiece with torus cutter

Torus cutters are increasingly used in machining high-hardness materials because of high processing efficiency. However, due to the large hardness variation in assembled hardened steel workpiece, the tool wear occurs easily in machining process. This severely affects the machined surface quality. Here, we conduct a research on the tool wear and the machined surface quality in milling assembled hardened steel mold with a torus cutter. The experimental results show the abrasive wear mechanism dominates the initial tool wear stage of the torus cutter. As the tool wear intensifies, the adhesive wear gradually occurs due to the effect of alternating stress and impact load. Thus, the mixing effect of the abrasive and adhesive wears further accelerates tool wear, resulting in occurrence of obvious crater wear band on the rake face and coating tearing area on the flank face. Finally, the cutter is damaged by the fatigue wear mechanism, reducing seriously the cutting performance. With increase of flank wear, moreover, there are increasingly obvious differences in both the surface morphology and the cutting force at the two sides of the joint seam of the assembled hardened steel parts, including larger height difference at the two sides of the joint seam and sudden change of cutting force, as a result, leading to decreasing cutting stability and deteriorating seriously machined surface quality.

Soldering porous ceramics through ultrasonic-induced capillary action and cavitation

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.