Interface microstructure and bond strength of 1420/7B04 composite sheets prepared by diffusion bonding

The effect of temperature on interface microstructure and shear strength of 1420 A1-Li alloy and 7B04 A1 alloy composite plates prepared by diffusion bonding were investigated. The results indicate the optimum temperature for bonding the composite plates is 520℃, a sound bonding interface without continuous intermetallic compound layers and interfacial voids is obtained, and the shear strength value of bond joints can be as high as 190 MPa. An interfacial transition zone is formed due to the alloying elements mutual diffusion during the bonding process. Meanwhile, the effect of temperature on diffusion of alloying elements and interface reaction were discussed in detail, the results show that the higher temperature can increase the diffusion of alloying elements fluxes across the bonding interface, which can accelerate the closure of interfacial voids; meanwhile, when Mg atoms diffuse across the bonding interface, it can react with and break up the surface oxide films into discrete particles, and the removal of interface oxides increases the metal to metal bond areas and improves the bond quality.

Effect of Porous Copper Pore Density on Joint Interface:Microstructure and Mechanical Analysis

The effect of the pore density of porous copper(Cu)on brazed Cu/porous Cu was investigated.A filler with a composition of Cu⁃9.0Sn⁃7.0Ni⁃6.0P(Sn:Tin;Ni:Nickel;P:Phosphorus)and porous Cu with pore densities of 15 pores per inch(PPI),25 PPI,and 50 PPI were employed.The joint strength of Cu/porous Cu was evaluated with shear tests at different brazing temperatures.Characterizations of the joint interface and fractured surface were achieved with scanning electron microscope(SEM),energy dispersive X⁃ray spectroscopy(EDX),and X⁃ray diffraction(XRD).The micro⁃hardness test of Cu/porous Cu joint interface showed a high hardness value(HV)for 50 PPI porous Cu.This result was in line with its low shear strength.It was proved that the joint strength of Cu/porous Cu is dependent on the pore density of the porous Cu structure and brittle phases of Cu_(3)P and Ni_(3)P in the brazed interface.

Compressive Strength and Interface Microstructure of PCBN Grains Brazed with High-Frequency Induction Heating Method

In order to prepare monolayer brazed superabrasive wheels, the polycrystalline cubic boron nitride（PCBN）grains were brazed to AISI 1045 steel matrix with Ag–Cu–Ti filler alloy using the high-frequency induction heating technique. The compressive strengths of brazed grains were measured. Morphology, chemical composition and phase component of the brazing resultant around PCBN grain were also characterized. The results show that the maximum compressive strength of brazed grains is obtained in the case of brazing temperature of 965 °C, which does not decrease the original grain strength. Strong joining between Ag–Cu–Ti alloy and PCBN grains is dependent on the brazing resultants,such as TiB_2, TiN and AlTi_3, the formation mechanism of which is also discussed. Under the given experimental conditions, the optimum heating parameters were determined to be current magnitude of 24 A and scanning speed of0.5 mm/s. Finally, the brazing-induced residual tensile stress, which has a great influence on the grain fracture behavior in grinding, was determined through finite element analysis.

MICROSTRUCTURE CHARACTERISTICS AT THE BOND INTERFACE

Lift-off and section characteristics at the interface of thermosonic bond are observed by using scanning electron microscope （KYKY2800） with EDS-test. Results show that the peeling underdeveloped bonds simulate atorns （or doughnut） with an unbonded central region and ridged peripheral region is bonded hardly, Inside roundness at flip chip bonding center are discovered. Bond strength is located between the severely ridged periphery and the non-adhering central area of the bond. For constant force and time, the ridged area of the bond pattern increases when more power is applied. For constant force and power, the ridged location of the bonded region moves closer to the bond center with time. Results of EDS-tests at Au-Al and Au-Ag interfaces show that Kirkendall diffusibility at Au-Ag interface occur and the diffusing speed of Au-atomic is faster than that of Ag, and that intermetallic compounds at Au-Al interface is generated possibly. And these would be helpful for further research about thermosonic bonding.

Microstructure Characteristics of Interaction Layer of Zn-Al Eutectic Alloy with Al_2O_3p/6061Al Composites

The interaction between Zn-AI eutectic alloy and Al203p/6061AI composites in the vacuum furnace was investigated. Great attention has been paid to the elements diffusion, the microstructure and formation of the interface between Zn-AI eutectic alloy and Al2O3p/6061AI composites. Experimental results show that Zn-AI eutectic alloy has a good wetting ability to Al2O3p/6061 Al composites and the wetting angle decreases with increasing the temperature in vacuum. After the interaction, an interaction layer forms between Zn-AI alloy and Al2O3p/6061 Al composites. The phases in the interaction layer mainly consist of α-AI(Zn), Al2O3 and CuZn5 resulted from the diffusion of elements from the Zn-AI alloy. Several porosities distribute in the region near the interface of the Zn-AI alloy/interaction layer. The amount of shrinkage voids in the interacting layer is relevant to the penetration of Zn element into Al2O3p/6061Al composites which is a function of temperature. So it is necessary to lower heating temperature in order to limit the Zn penetration.

Interfacial Microstructure and Mechanical Properties of Al Alloy/Mg Alloy Laminated Composite Plates Fabricated by Equal Channel Angular Processing

KAl（7075）alloy/Mg（AZ31）alloy laminated composite plates were successfully fabricated by the equalchannelangular processing（ECAP）by using route A for 1,2,and 3 passes at 573 K,respectively.After fabrication,the 1-pass ECAPed laminated composite plates were annealed at different temperatures.The microstructure evolution,phase constituent,and bonding strength near the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates were evaluated with scanning electron microscopy,X-ray diffraction,and shear tests.The experimentalresults indicated that a 20 μm diffusion layer was observed at the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates fabricated by the 1-pass ECAP,which mainly included Al_3Mg_2 and Mg_（17）Al_（12） phases.With the increase of passes,the increase of diffusion layer thickness was not obvious and the form of crack in these processes led to the decrease of bonding strength.For 1-pass ECAPed composites,the thickness of diffusion layer remained unchanged after annealed at 473 K,while the bonding strength reached its maximum value 29.12 MPa.However,after elevating heat treatment temperature to 573 K,the thickness of diffusion layer increased rapidly,and thus the bonding strength decreased.

Microstructure Model of the Interfacial Zone Between Fresh and Old Concrete

A new model of repaired concrete which divides the bonding interface into a penetrating layer,a strongly-affected layer and a weakly-affected layer was put forward.The model is mainly based on the observation of the microstructure of interface between fresh and old (3 months to 60 years) concretes by using scanning electron microscopy.Then,the mechanism of the microstructure formed was analyzed.Finally,the relationship between the micro-structure and macro-mechanical performance of the interface was discussed.

The study of the adductor muscle-shell interface structure in three Mollusc species

The adductor muscle scar（AMS） is the fixation point of adductor muscle to the shell. It is an important organicinorganic interface and stress distribution area. Despite recent advances, our understanding of the structure and composition of the AMS remain limited. Here, we report study on the AMS of three bivalves： Mytilus coruscus,Chlamys farreri and Ruditapes philippinarum. Results showed that there were significant differences among their AMS structures. Both M. coruscus and C. farreri were found to have a columnar layer above the nacreous platelet shell structure at the AMS and this layer was more organized in M. coruscus. There was no distinguishable twolayer structure in R. philippinarum. Atomic force microscopy（AFM） and Fourier transform infrared spectroscopy（FT-IR） results showed that the AMS was much smoother than the nacreous inner shell in all the three species and the AMS had minor different compositions from the nacreous shell layer. SDS-PAGE（sodium dodecyl-sulfate polyacrylamide gel electophoresis） study of the proteins isolated from the interface indicated that there was a 70 k Da protein which seemed to be specifically located to the highly organized columnar AMS structure in Mytilus coruscus. Further analysis of this protein showed it contained high level of Asx（Asp＋Asn）, Glx（Glu＋Gln） and Gly.The special structure and composition of the AMS might play important roles in the stability, adhesion and function at this stress distribution site.

Microstructure evolution and diffusion mechanism of Nb/TiAl alloy diffusion-bonded joints

The interdiffusion behavior in Nb/TiAl alloy diffusion couples was studied.The process was carried out in the temperature range of 950-1400℃for 8 h in the vacuum hot-pressure sintering furnace.The microstructural evolution was observed by optical microscopy(OM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD)technique and transmission electron microscopy(TEM).The element concentration distribution at the bonded interface was obtained by scanning electron microscopy with an energy-dispersive X-ray spectroscopy(EDS)apparatus.The thickness of reaction interface increases with bonding temperature increasing.The formed phases in diffusion interface are found to be O-Ti_(2)AlNb,σ-Nb_(2)Al,δ-Nb_(3)Al and Nb solid solution(Nbss)at 1350℃.The average interdiffusion coefficient of the interface elements was calculated by the theory of Dayananda.The results indicate that Al diffuses faster than Nb and Nb diffuses faster than Ti in the Ti-Al-Nb system.Meanwhile,it is found that Ti promotes the diffusion of Al and Nb and Nb inhibits the diffusion of Ti and Al in the process of diffusion.

Microstructural evolution and mechanical properties of a low-carbon quenching and partitioning steel after partial and full austenitization

In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.

Analysis of interaction between dislocation and interface of aluminum matrix/second phase from electronic behavior

The inhibitory effect of the second phase on dislocation movement has long been deemed as a great con-tribution to the strengthening of alloys.We investigate the electronic behavior at theα-Al matrix/second phase interface to explore its inhibitory effect on dislocation movement.This work focuses on the dif-ficulty in dislocation movement on the interface ofα-Al/Al_(3)Sc,α-Al/θ’(Al_(2)Cu),andα-Al/T_(1)(Al_(2)CuLi)of aluminum-lithium-scandium alloy based on detailed transmission electron microscopy investigation and electron transport calculation.The more drastic the electron transport between two atoms at the inter-face,the more intense the interaction between them,corresponding to the larger difficulty in breaking and forming bonds between them during the movement process of the extra half plane of dislocation on the interface.The calculated difference in density of valence electrons and differential charge density atα-Al/second phase interface reveals that Al_(3)Sc is characterized by the largest resistance to dislocation movement compared toθ’(Al_(2)Cu)and T_(1)(Al_(2)CuLi).The large differential charge density between the in-terface of(100)Al_(3)Sc/(100)Al demonstrates the strong bonds betweenα-Al and Al_(3)Sc and the large difficulty for the extra half plane of dislocation to form or break bonds during the movement process atα-Al/Al_(3)Sc interface.The dislocation pile-up indicates a discernible hindering effect of theα-Al/Al_(3)Sc interface on dislocation movement.The hindering effect presented byα-Al/Al_(3)Sc interface is favorable for the tensile strength.

Interfacial microstructure and mechanical properties of stainless steel clad plate prepared by vacuum hot rolling

A stainless steel clad plate composed of stainless steel and carbon steel was prepared by vacuum hot rolling process, and its microstructure, especially the bonding interface, was evaluated using an optical microscope, a scanning electron micro- scope and a transmission electron microscope （TEM）. The corresponding mechanical properties were also assessed by means of hardness and shear tests. The results showed a bonding interface formed between stainless steel and carbon steel, which was relatively straight in macroscope but serrated in microscope. Decarburization layer and carbon-enriched layer were distinguished at the side of carbon steel and stainless steel near the interface, respectively, which should be related to diffusion of carbon and alloying elements. The carbon-enriched layer could also be identified as a recombination region, whose microstructure was mainly recognized as martensite by TEM. Consequently, the hardness was the highest at this region. Furthermore, the result of shear test at the bonding interface showed that the shear strength was 395 MPa and the fracture mode was dominated as ductile fracture, indicating the bonding interface with good quality.

Effects of Joining Conditions on Microstructure and Mechanical Properties of C_f/Al Composites and TiAl Alloy Combustion Synthesis Joints

Cf/Al composites and TiAl alloy were joined by combustion synthesis in different joining conditions. Effects of additive Cu, joining temperature and holding time on joint microstructure and shear strength were characterized by employing DTA, SEM, EDS, XRD and shear test. Results show that the additive Cu in the Ti-Al-C interlayer could significantly decrease the reaction temperature owing to the emergence of Al--Cu eutectic liquid. Reaction degree of the interlayer was influenced by joining temperature and holding time. Due to the barrier action of formed TiAl3 layer, reaction rate of Ti and Al was determined by the atoms diffusion. The reaction between Ti and AI was more sensitive to the joining temperature rather the holding time. The joints shear strength was influenced by joining condition directly. The maximum shear strength of CS joints was 25.89 MPa at 600 ℃ for 30 rain under 5 MPa. Interface evolution mechanism of the CS joint was analyzed based on the experimental results and phase diagram.

Temperature gradient driving interdiffusion interface and composition evolution in Ni-AI-Cr alloys

The interdiffusion interface microstructures and composition evolution of Ni-Al-Cr/Ni-Al-Cr layered alloys under different temperature gradients were studied using phase-field simulation.A precipitate-free zone forms near the interface of the layered alloys,and the interface does not move with time under temperature gradients.When Cr concentrations in the alloy layers are different,Al diffuses from a low-to high-temperature region,whereas Cr from a high-to low-temperature region.The width of the precipitate-free zone changes from 0.5 to 2.5μm as the temperature gradient changes fromΔT=0.625 K·μm^(−1) to 1.250 K·μm^(−1);the width of the interdiffusion zone is also enlarged.Additionally,the temperature gradient promotes the interdiffusion of elements through the interface.In contrast,when the initial Al concentration is different in the alloy layers,an uphill diffusion of Al occurs,which is driven by the chemical potential of Al.

Microstructure and Mechanical Properties of Galvanized Steel/AA6061 Joints by Laser Fusion Brazing Welding

Laser fusion brazing welding was proposed.Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface.Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding.The result showed that the tiny structure with the composition of a-Al and Al–Si eutectic was formed in the weld close to the Al side.And close to the steel side,a layer of compact Fe–Al–Si intermetallics,including the Al-rich FeAl3,Fe2Al5 phases and Al–Fe–Si s1 phase,was generated with the thickness of about 10–20 lm.Transverse tensile shows the brittlefractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases s1 and Al–Fe intermetallics.

Improving tensile-shear properties of friction stir lap welded dissimilar Al/Mg joints by eliminating hook defect and controlling interfacial reaction

To improve tensile-shear properties of fiction stir lap welded(FSLW) dissimilar Al/Mg joints, pin-tip profiles were innovatively designed and welding speed was optimized, and effects of them on formation, interface microstructure and mechanical properties of different FSLW joints were investigated. With increasing the welding speed, the tensile-shear load of FSLW joints produced by three pins presents an increasing firstly and then decreasing trend. Compared with Rpin, the hook and hole defect in the joints made by S-pin and T-pin are eliminated owing to additional eccentric force. Moreover, the joints obtained by T-pin at 75 mm/min have the highest tensile-shear load, and a maximum value of 3.425 kN is produced, which increases by 96.8%.Meanwhile, the pin-tip profile improves significantly the interface reaction depending on the welding temperature. For R-pin, thick brittle intermetallic compounds of about 6.9 μm Al3Mg2and 13.3 μm Al12Mg17layers at the welding interface derived from diffusion reaction are formed, resulting in continuous cracks. However, using T-pin can raise the interface temperature, and which makes the interface liquefy locally to generate only 2.2 μm Al3Mg2layer and dispersive(Al12-Mg17+Mg) eutectic structure. This can release high residual stress and remove welding crack, consequently enhancing the interface properties of T-pin joints.

Microstructure and secondary phases in epitaxial LaBaCo_2O_(5.5 + δ) thin films

Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5＋δ（LBCO） thin films grown on SrTiO3 （STO） substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]LBCO//[100]STO and （001）LBCO//（001）STO. Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 900 ℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001] direction of the film. In the film grown at a temperature of 1000 ℃, isolated nano-scale C0304 particles appeared, which promoted the growth of {111 } twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.

Flat friction spot joining of aluminum alloy to carbon fiber reinforced polymer sheets:Experiment and simulation

The Al alloy and carbon fiber reinforced polymer(CFRP)hybrid structures,incorporating the performance advantages of the two materials,have been attracting more attention in high-end manufacturing fields.In the current investigation,the flat friction spot joining(FSJ)was employed in joining the AA6061-T6 alloy and CFRP sheets.The significance of temperature distribution in influencing joint quality was highlighted through analyzing interface microstructural features,weld defect formation as well as fractography.To understand the role of thermal energy generation and conduction in the process comprehensively,a 3D thermal-mechanical coupling finite element model was established.The interfacial temperature was characterized by an uneven distribution behavior due to the inhomogeneous heat distribution.The peak temperatures on the top surface and Al alloy to CFRP interface at 1500 rpm rotational speed with 0.1 mm/s plunging speed were 498℃and 489°C,respectively.The peak interface temperature was reduced to286℃at 250 rpm,which produced an extremely small melted area.Compared with the plunging speed,rotational speed was found to be the predominant parameter for determining the joint property,which could be optimized to simultaneously realize the avoidance of thermal decomposition of CFRP,the sufficient melting duration time,and the wide enough melted area.Simulated thermal histories and melted area profiles were in agreement with experimental ones.The findings could be utilized to provide some feasible guidance for process optimization of dissimilar FSJ of metals and composites.

Multi-scale characterization and simulation of impact welding between immiscible Mg/steel alloys

Vaporizing foil actuator spot welding method is used in this paper to join magnesium alloy AZ31 and uncoated high-strength steel DP590,which are typically considered as un-weldable due to their high physical property disparities,low mutual solubility,and the lack of any intermetallic phases.Characterization results from scanning electron microscopy(SEM)and high-resolution transmission electron microscopy(HRTEM)of the weld interface indicate that the impact creates an Mg nanocrystalline interlayer with abundant Fe particles.The interlayer exhibits intact bonding with both DP590 and AZ31 substrates.To investigate the fundamental bond formation mechanisms at the interface,a finite element(FE)-based process simulation is first performed to calculate the local temperature and deformation at the interface under the given macroscopic experimental condition.Taking the FE results at the interface as inputs,molecular dynamics(MD)simulations are conducted to study the interlayer formation at the Mg/Fe interface during the impact and cooling.The results found a high velocity shearing-induced mechanical mixing mechanism that mixes Mg/Fe atoms at the interface and creates the interlayer,leading to the metallurgical bond between Mg/steel alloys.