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This study focuses on the transient liquid phase (TLP) bonding of DD5 single-crystal superalloy to CrCoNi-based medium-entropy alloy (MEA) using a BNi-2 filler alloy. The microstructure and mechanical properties of the TLP-bonded DD5/MEA joint were evaluated, and the microstructural evolution mechanism was investigated. The formation of the isothermal solidification zone (ISZ) depended on the diffusion of the melting-point depressants (Si and B elements) from the liquid filler into the DD5 and MEA substrates, as well as the dissolution of the substrates. Boron diffused along the γ channel of DD5 and reacted to form M5B3 boride, herein referred to as the diffusion-affected zone (DAZ I). Similarly, the Cr5B3 boride precipitated in the Ni-rich MEA matrix adjacent to the MEA substrate (i.e., DAZ II). Additionally, a coherent orientation of [0]BCT // [0 1 1]FCC and (0 0 2)BCT // (2 0 0)FCC was detected between M5B3 boride with a body-centered tetragonal (BCT) structure and the face-centered cubic (FCC) matrix. The performance of the joint was dominated by the properties of the bonding seam. As the bonding time increased from 20 to 80 min, the athermal solidification zone (including eutectic microstructure) was gradually replaced by the ISZ exhibiting excellent plastic deformation capability, and the shear strength of the joint was improved. The maximum shear strength (752 MPa) was achieved when the eutectic-free joint was bonded at 1050 °C for 80 min. The fracture morphology revealed a mixture mode, indicating the initiation of cracks in the DAZ II, mainly propagating in the ISZ, and passing through the DAZ I.

In this study, the isotherm wetting and spreading behaviors of molten Ag-Zr filler on ZrC-SiC ceramic surface was investigated using a sessile drop method in vacuum. The effect of Zr content in Ag-Zr filler on the wetting behavior was studied, and the wetting mechanism was revealed in details. The results showed that the contact angle of Ag-Zr filler on the ZrC-SiC surface decreased from 140 ° to 20 ° with the Zr content varied from 0 to 8 wt.%, and the Zr was the key factor to the wetting process. The wetting dynamic analysis illustrated that the interfacial reaction controlled the wetting of Ag-Zr filler on the ZrC-SiC surface. Due to the Zr activity difference at Ag-Zr/ZrC interface, the ZrC released C into Ag-Zr filler, and reacted with Zr to form new-born ZrC with higher Zr content. The formation of the new-born ZrC promoted wetting and spreading of Ag-Zr filler on ZrC-SiC surface.

A ZrC-SiC and TC4 gradient structure (ZTGS) was additively manufactured through the laser deposition technique and brazing process. The research results indicated that SiC-reinforced TC4-based gradient layers could be obtained on the TC4 surface by laser deposition. ZrC-SiC and TC4 coated with gradient layers were brazed using an AgCuTi filler to fabricate the ZTGS. The effects of the gradient structure and brazing parameters on the ZTGS strength were investigated. With an increase in Layer II and Layer III thickness, the ZTGS shear strength increased. The brazing temperature and holding time affected the ZTGS shear strength by controlling the formation and distribution of the Cu4Ti phase in the brazing zone. The strengthening mechanism of the ZTGS was revealed by analyzing the residual stress distribution in the ZTGS. Compressive residual stress was formed in ZrC-SiC adjacent to the TC4 substrate or the deposited gradient layer, which was found to negatively affect the properties of the ZTGS. The increase in gradient layer thickness reduced the maximum residual stress in ZrC-SiC, and the effect of Layer III on the residual stress was more significant than that of Layer II. The calculated residual stress evolution matched the ZTGS property values well, revealing the strengthening mechanism.

Alclad layer is a challenge to ensure the mechanical properties of refill friction stir spot welding (RFSSW) alclad 7050/2524 joint. In this study, RFSSW with suspension rotating process (SRP) was designed to improve the mechanical properties by strengthening the alclad layer. The thermal cycles, microstructures and mechanical properties of the joints welded without and with SRP were compared. The results indicated that SRP increased the high temperature dwell time of the stir zone bottom, which promoted more alloy being stirred into and mixing with the alclad, beneficial for strengthening the alclad. When with SRP, the tensile shear strength of joint reached 11 kN, improved by about 30% compared with joint without SRP.

Ultrasonic C-scan was conducted to detect the defect size of TC4 diffusion-bonded joints quantitatively. Additionally, C-scan images were obtained using the amplitudes of time-domain signal, main frequency of frequency-domain signal, and amplitudes of main frequency in power spectrum as the characteristic parameters. The results demonstrated that the C-scan detection based on the time-domain amplitude was feasible to characterize the defects with sizes larger than double the focal spot diameter of the probe accurately and quantitatively. When the defect size was larger than the focal spot diameter, the detection error of using the main frequency of frequency-domain signal was below 5%. For defects smaller than the diameter of the focal spot, the highest detection accuracy was obtained by ultrasonic C-scan based on the power spectrum.

TC4 (Ti–6Al–4V) titanium alloy and Al5(HfNbTiZr)95 refractory high-entropy alloy were successfully diffusion bonded at a temperature range of 800–1000 °C for 60 min under 5 MPa. The microstructure and mechanical properties of the diffusion bonded joints were investigated. The diffusion bonding seam of the joint contained two different zones, namely: a reaction zone with acicular titanium structures (Zone I); and a continuous solid solution reaction zone (Zone II) which inherited the orientation of the matrix Al5(HfNbTiZr)95. The highest microhardness of reaction zone reached 6.82 GPa, located in the boundary of TC4 and the acicular titanium structure zone. The effects of bonding temperature on the microstructure and mechanical properties of the joints were revealed. As bonding temperature increased, all the reaction zones grew in a parabolic manner with an increase in the bonding temperature. The shear strength of the joints ranged from 55.56 MPa to 777.06 MPa as the bonding temperature increased. The maximum shear strength of 770.06 MPa was obtained at a bonding temperature of 950 °C for 60 min under 5 MPa, and the fracture located in the TC4 substrate illustrated a typical ductile fracture mode.

A new 70Mn–25Ni–5Cr (wt. %) filler with no traditional melting-point depressants (MPDs) of Si/B was used for transient liquid phase (TLP) bonding a directionally solidified (DS) superalloy based on Ni3Al intermetallic compound (IMC) at 1150 °C, a pressure of 2 MPa for 10–120 min. Experimental results show that the joint can be divided into 3 zones, isothermally solidified zone (ISZ), athermally solidified zone (ASZ) and diffusion-affected zone (DAZ), which was similar to microstructure of typical TLP joint bonded by Ni based filler. The joint microstructures were mainly composed of γ-Ni, γ′-Ni3(Al, Ta), MC and M23C6 carbides. Besides, in the ISZ, due to the enrichment of Al, which diffused from the base metal (BM), strip-shaped Ni(Mn, Al) phases formed in such region. The ASZ included γ-Ni and compounds of “equiaxed Ni(Mn, Al) + acicular Ni3Ta” owing to the composition segregation during the later stage of solidification. Moreover, as the bonding time increased, the volume fraction of Ni(Mn, Al) and MC carbides decreased owing to homogenization of alloying elements. After bonding for 120 min, sufficient isothermal solidification (IS) of filler can also decrease segregation of Mn/Al in front of the S/L interface and the Ni(Mn, Al)+Ni3Ta compounds were eliminated almost. Thus, the highest tensile strength was 816.9 MPa of the TLP joint of 120 min, which has been equivalent to that of BM (812 MPa). However, due to the existence of a few residual large MC carbides in the joint, which can induce the stress concentration and decreased the ductility of the joints, the highest joint elongation of 4.4% was only about 40% of the BM.

A self-consistent analytical model for predicting qualities of a joint welded by continuous drive friction welding (CDFW) was developed based on the Onsager-Ziegler maximum entropy production principle (OZ-MEPP), dislocation kinetics, and the CDFW analytical model developed in our previous work. The microstructure and mechanical properties of the friction-welded joint can be predicted by the model requiring only the geometric, thermal, and physical parameters of the specimens without any assumed or premeasured response parameters. The accuracy of the model was verified by the microstructure and properties of the joints fabricated by CDFW of 304 stainless steel. The results indicated that the model is feasible and effective for forecasting the grain size and yield strength of the joints, which means it is possible to use a single thermodynamic state function, i.e., entropy production, for predicting the qualities of a CDFW joint, especially when the joined alloy has a simple phase composition.

The AgCuSnTi filler was designed to braze Gr/2024Al composite and Ti6Al4V titanium alloy through investigating the effect of Sn and Ti addition in AgCuSnTi filler on the microstructure and mechanical property of the joint. The results showed that Sn and Ti addition decided the distribution of compounds (Al2Cu and Al5CuTi2 phases) in the brazing seam. The increasing of Sn content could enhance the flowability of brazing alloy, and promote the compounds to be dispersive in the brazing seam. Ti in the filler induced the formation of Al5CuTi2 phase instead of Al2Cu phase. When the Gr/2024Al and Ti6Al4V were brazed using the AgCuSnTi filler with 3 wt.% Ti and 27 wt.%Sn at 680℃ for 10 min, the Al2Cu and Al5CuTi2 phases were dispersed in the brazing seam. The maximum shear strength of the brazed joint was 17 MPa and cracks propagated in the Gr/2024Al substrate. In addition, Ni/Nb/Ni composite interlayers were designed to strengthen the Gr/2024Al composite and Ti6Al4V titanium alloy joint, and the joint strength increased to 24 MPa owing to the adoption of the interlayers.

In order to braze Gr/2024Al composite at low temperature to keep its heat insulation property, a novel thermal explosion assisting brazing method was designed. Through this method, the thermal explosion reaction of Ti-Al-C-Cu interlayer offered additional heat, and AgCuTi filler reacted with Gr/2024Al composite under the melting point of AgCuTi. Based on the theoretical calculation and DSC analysis, the composition of Ti-Al-C-Cu interlayer was designed. The microstructure and mechanical properties of brazed joint was investigated, and the brazing parameters were optimized. The results showed that AgCuTi reacted with the Gr/2024Al composite to form Ti3AlC2 layer, and a continuous TiAl3 layer acted as the reaction layer near the TC4 alloy. The high preheating temperature and long holding time would promote the reaction of AgCuTi filler, Gr/2024Al and Ti-Al-C-Cu interlayer, and Al5CuTi2 phase volume in the brazing zone increased. The Al5CuTi2 distribution affected the joint strength significantly. The optimized joint strength reached 11 MPa when the joint was brazed at 650 °C for 15 min.

The immersion ultrasonic C-scan ((IUCT) test was conducted for evaluating the bonded ratio of the TC4 diffusion bonded joints. The signal characteristics reflected by the typical bonding states of the joint, gap, kissing bond, microvoids and sound bond were investigated in the time and frequency domain. Moreover, as for the bonding state of microvoids, its local bonded ratio exhibited a linear relationship with the relative amplitude of its echo signal in the time domain. Based on the echo signal characteristics and the linear relationship about microvoids, a MATLAB algorithm program was developed to calculate the global bonded ratio of bonding interface directly from echo signal of IUCT. The results demonstrated that joint bonded ratio and mechanical properties, especially the tensile strength, could be quantitively evaluated by the combination of IUCT test and the developed MATLAB program.

Numerical simulation method was employed to reveal the mechanism of manufacturing a rotary friction welding joint, in which a two-dimensional finite element model was constructed based on a comprehensive friction coefficient model to simulate the thermo-mechanical coupling during rotary friction welding. Experiments were focused on rotary friction welding of SUS304 in diameter of φ25 mm at 900 rpm under 80 MPa, of which the joint were studied on evolutions of temperature field, stress fields (i.e., both stress-Z and effective stress) and tensile strength corresponding with the corona-bond evolution. Thereafter, the simulation focused on the effect of rotation speed that varied as 500–2500 rpm, in which the minimum welding time necessary to cover a welding cycle was issued. The finite element model was shown valid by the consistency of comparison between simulation and experiment. Transition temperature fields (in contours) were verified in good agreement with transition morphologies of the joints as experimentally characterized by the corona-bonds. The results show that, rotary friction welding process can be classified into two stages: the corona-bond evolution and the plastic flow. The former stage is characterized by the corona-bond that develops and fills out the interface, in which the temperature is kept raising and the stress field kept varying; whereas the latter stage is denoted by the extrusion of flash that keeps forming at constant temperature and stress fields (i.e., both stress-Z and effective stress). The tensile test reveals that the latter stage makes negligible contribution to the joint strength, which falls in the range as 660–688 MPa as the welding time is regulated from 1.8 to 15 s. Thus, time consumed on former stage was ascertained to be the minimum welding time, which ranges in 1.5–2.9 s for SUS304 in φ25 mm of diameter welded under 80 MPa at the rotation speed of 500–2500 rpm.

This study focuses on the brazing of Al2O3 ceramic to Ti2AlNb alloy using composite filler metal (AgCu28 modified with micron-scale Al2O3 particles). The effect of Al2O3 particles concentration on the microstructure and mechanical properties of Al2O3/Ti2AlNb joint were investigated. Ti3(Cu, Al)3O has been identified as the main product of the reactions at the alumina–brazing alloy interface. The addition of Al2O3 particles significantly reduced the mismatch of coefficients of thermal expansion between Al2O3 ceramic and Ti2AlNb alloy substrates, relieving the residual stresses of the joint. Nevertheless, a high concentration of Al2O3 particles led to excessive Ti3Cu3O phase exhibiting high elasticity modulus surrounded Al2O3 particles which impaired the plastic deformation ability of the brazing beam, thus, decreased the joint strength. The maximum shear strength of 110.49 MPa was achieved when the joint was brazed at 880 °C for 10 min using AgCu28 + 2 wt % Al2O3 particles filler metal. The fracture morphology revealed that the cracks initiated in the brazing seam, and mainly indicating the propagation of cracks occurred in the Al2O3 ceramic substrate.

As a generalization of sober spaces, we introduce the concept of countably sober spaces and prove that some topological constructions preserve countable sobriety. In particularly, we prove that the category with countably sober spaces and continuous mappings is a complete category. We give some characterizations of countably sober spaces via countable filters and obtain the Hofmann-Mislove Theorem for countably sober spaces.

Vacuum brazing on TC4 (Ti–6Al–4V) titanium alloy was performed by using Ag foil as the filler metal. Two steps were designed, in which the TC4/Ag/TC4 samples were brazed at 1000 °C for 10 min and followed by a diffusion process at 800 °C for 60–360 min. The microstructural characteristics and the mechanical properties of joints were analyzed. The results indicated that the reaction zones of the joints mainly consisted of α+β lamellar structures with the distributions of acicular and micron-sized particle phases of TiAg attached to Ti2Ag. As the diffusion time increased, the characteristics of the intermetallic compounds (IMCs) at the joints changed accordingly, as the morphology of IMCs became spherical from acicular, and the amount of IMCs was decreased. Furthermore, the microhardness test results indicated that the lowest hardness values were observed at the centers of the joints. A maximum tensile strength of 864.5 MPa was obtained for the joint diffused at 800 °C for 120 min, and its fracture path was more curved than those of the other joints. Based on the shear test results and fracture analysis, regardless of diffusion time, the joints were fractured at the region of the reaction zone along the IMCs.

A three dimensional and Coupled Eulerian–Lagrangian (CEL) model for the refill friction stir spot welding (RFSSW) of 2524-T3 aluminum alloy was developed based on the ABAQUS/Explicit. The distribution of stress and temperature field at the joint area, at five different rotational speeds, were simulated and verified using experimental studies. The simulation results showed that with increasing rotational speed, heat production by friction and plastic deformation was enhanced, while the stress was reduced. Moreover, internal voids, the typical defect, were found on the bottom edge of the stir zone, and the propensity for the voids were the lowest at the rotational speed of 2800 rpm (rpm); this was verified using the immersion ultrasonic C-scan test (IUCT) test results. Based on the simulation results, isothermal compression test results and electron backscatter diffraction (EBSD) analysis results of the joint, the relationship between grain size and the Zener–Hollman parameter at the stir zone (SZ) was also established, thereby providing an in-depth understanding and detailed rationalization of the RFSSW processes.

In this study, brazing of Al0.3CoCrFeNi high-entropy alloy to FGH98 superalloy was achieved using a BNi-2 filler metal. The microstructure of the Al0.3CoCrFeNi/FGH98 joint was examined, and mechanical properties of the joints brazed at different brazing temperatures were evaluated. During the brazing process, boron diffused from the filler alloy into the Al0.3CoCrFeNi substrate, and mainly reacted with Cr to form the Cr-rich boride exhibiting Cr5B3 structure. Eventually, the reaction zone was composed of a Cr-rich boride and Ni-rich HEA matrix with a coherent relationship of [0 1 1]Ni-rich HEA//[2 4 0]Cr-rich boride and (2 0 0)Ni-rich HEA//(0 0 2)Cr-rich boride. The dissolution of the FGH98 substrate induced the island-like (γ + γʹ) phase in the brazing seam. With the brazing temperature increasing, the voids and borides disappeared, and finally the brazing seam transformed into homogeneous Ni(s.s). Moreover, when the brazing temperature reached 1090 and 1110 °C, the volume of intergranular Cr-rich borides increased significantly, and the precipitation of carbides (or borides) in the FGH98 substrate adjacent to the brazing seam was dispersive. The optimum shear strength of 454 MPa was obtained when the brazing was carried out at 1070 °C for 10 min, and ductile fractures occurred in the joint during the shear test.

In this study, the refractory high entropy alloy Al5(TiZrHfNb)95 was diffusion bonded (DB) with the intermetallic compound (IMC) Ti2AlNb under 5 MPa at 970–1100 °C in vacuum. The microstructure and element distribution were analyzed using a scanning electron microscope (SEM) and mechanical properties were evaluated by nanoindentation and shear tests. The typical microstructure of DB joint was Ti2AlNb substrate/solid solution/scattered Al3Zr5/solid solution/Al5(TiZrHfNb)95 substrate, which the discrete brittle Al3Zr5 phase was arranged along a straight line in the bonding surface, and gradually elongated and dissolved as the bonding temperature increased from 970 °C to 1100 °C. The formation of Al3Zr5 was attributed to the lowest Gibbs energy of all the possible IMCs in the range of the welding temperature. In the joining region, the IMC Al3Zr5 had the highest hardness (9.01 GPa) and modulus (143.37 GPa) but the lowest elastic recovery (20.37%), thus, it tended to cause stress concentration at the phase interface and induced crack initiation, which had a detrimental effect on the shear strength of joints. The shear strength of DB joints improved with the increase of bonding temperature and reached the highest (427 MPa) at 1100 °C owing to is lowest Al3Zr5 content. As the bonding temperature increased, the fracture of the joint transformed from intergranular brittle to ductile.

Laser cladding induces high tensile residual stress (RS), which can compromise the quality of a specimen. Therefore, it is critical to accurately predict the RS distribution in cladding and understand its formation mechanism. In this study, functionally graded material (FGM) layers were successfully deposited on the surface of a titanium alloy Ti6Al4V sheet by laser cladding technology. A corresponding thermo-mechanical coupling simulation model of the laser cladding process was developed to investigate the formation mechanism of RS in the laser cladding FGM layers. The results show that high tensile RS forms in cladding components. Subsequent cladding can effectively alleviate the RS in cladding components although the position of maximum RS remains unchanged. The measurement results of the longitudinal RS on the top and bottom surfaces of cladding components by the X-ray diffraction (XRD) method agreed with the simulation results, thereby proving the accuracy of the simulation. In addition, the formation mechanism of RS in the laser cladding FGM layers was revealed by discussing the individual impact of each material property on RS. It was indicated that the RS distribution in the laser cladding FGM layers was significantly affected by material properties (in particular, coefficient of thermal expansion and Young’s modulus), except for the temperature gradient induced by the laser cladding process.

The arrival of the media era has also brought about the diversity and novelty of news interview methods, and the controversial hidden interview is one of the important interview methods. In recent years, more and more journalists use implicit interviews to get the audience's attention, followed by a series of legal issues such as news infringement. Hidden interview as a double-edged sword, if not grasp the "degree" of interview, not only difficult to reveal the truth, often counterproductive, resulting in violations of privacy rights, therefore, how to avoid the hidden interview in the news practice of news infringement has become a problem that every journalist should ponder.

Rotary friction welding was conducted on A286 with a diameter of ϕ25 mm under 300, 900 and 2100 rpm to understand the structural response of the joint welded at different rotation speeds. Joint morphologies, grain structures inside the morphologies and the corresponding mechanism that governs its formation were characterized and investigated using electron backscattered diffraction (EBSD), which focused on three featured zones located at the center, 1/2R and periphery of the joint. The influence of structural response on joint properties was also investigated. Results show that the morphology of the joint evolves from ‘disk shape’ to ‘near-line shape’ and ‘scissors shape’ as the rotation speed increases from 300 rpm to 2100 rpm. At low rotation speed, refined and recrystallized grains were formed inside disk shape morphologies. Whereas, sub-grains and deformed grains were evolved at the middle (900 rpm) and high (2100 rpm) rotation speed. The recrystallized grains surrounded by the ‘disk shape’ morphology have a positive effect on the joint strength compared with the sub-grains and deformed grains confined by the ‘near-line shape’ and ‘scissors shape’ morphologies.

Directional solidification (DS) of intermetallic compounds Ni3Al based superalloys were joined by solid-state diffusion bonding (SSDB) with the joining interface perpendicular to the solidified direction. The joining process was conducted with a 4 μm pure Ni interlayer at 1100 °C under 15 MPa for 2–7 h. The results showed that the microstructure characteristics of the SSDB joints, microvoids, tiny carbides, a higher volume fraction of γ′ phase and high angle grain boundaries (HAGB) formed in the interlayer region, were significantly different from that of the base metal (BM). The joint of the best mechanical property, strength of 926 MPa and elongation of 7.2%, was produced by the bonding time of 7 h owing to the decrease of the microvoids and the large carbides with the bonding time increasing. However, the relative (ratio between the joint and the BM) tensile strength of the joint was merely 90% due to the existence of high angle grain boundaries (HAGB) generated after the recrystallization of the interlayer. Moreover, because microvoids were not vanished completely and the strain mismatch caused by the structure of the interlayer region, the hard center region (higher volume fraction of γ′ phase) and soft interface region (lower volume fraction of γ′ phase), so the stress concentration were produced between the joint and the BM under the tensile load. Therefore, the relative elongation of the SSDB joint was only 57%.

Reliable brazing of ZrC-SiC ceramic and TiAl alloy was achieved using active Ag Zr filler metal. During the brazing process, Ti and Al were dissolved into the filler metal, and TiC+(Ti,Zr)3SiC2 layer formed due to the reaction between the ZrC-SiC and Ti. Meanwhile, strong affinity of Ti, Al and Zr produced dispersive (Ti,Zr)(Al,Ag) in the brazing seam. The effect of Zr content and holding time on the microstructure and mechanical property of the joints was investigated. With the increase of Zr content, the formation of (Ti,Zr)(Al,Ag) phase was promoted and its volume became large. The consumption of Ti in (Ti,Zr)(Al,Ag) phase restrained the formation of TiC, decreasing the thickness of TiC layer. Excess Zr addition could induce large bulks of (Ti,Zr)(Al,Ag) and cracks in the brazing seam. The holding time mainly affected the distribution of Ti-Zr-Al-Ag phases in the brazing seam. The joint strength reached a maximum value of 65 MPa when the Zr content of the filler was 5 wt% and holding time was 5 min. The crack propagated in the ZrC-SiC ceramic substrate.

An analytical model was developed based on the thermodynamic theory of Onsager-Ziegler maximum entropy production principle (OZ-MEPP) and the relevant dynamic laws, and used for characterizing the steady-state system of the severe plastic deformation (SPD) produced by continuous drive friction welding (CDFW) without any pre-assumed or measured response parameters. The accuracy and universality of the model were verified by the CDFW experiments of eight kinds of alloys, the results of which indicated that the model could precisely predict the temperature, axial shortening rate, welding power. Moreover, the coefficient of friction, traditionally regarded as an empirical parameter, could be forecasted too.