Abstract:A series of Al-xSi-yGe filler metals (x=4–12 and y=10–40, wt%) were prepared, and the effect of Si and Ge on microstructure and melting characteristics of filler metals was studied. The thermodynamic model of Al-Si-Ge ternary alloy was established to analyze the phase formation mechanism of filler metals based on Miedema model, Tanaka model, and Toop equation. This research provided a basis for the composition optimization of filler metals and the analysis of metallurgical reaction process between filler metals and base materials. Results show that Al-Si-Ge alloy is composed of Al-Ge eutectic phase, Al-Si eutectic phase, and primary Si. Ge addition promotes the precipitation of primary Si. Ge is the main melting point depressant element of filler metals. With the increase in Ge content from 10wt% to 40wt%, the solid phase line of filler metals remains unchanged, whereas the liquidus temperature decreases from 567.65 °C to 499.96 °C. With the increase in Ge content of filler metal, Ge content in eutectic Si phase is increased, the endothermic peak of Al-Si eutectic reaction according to thermogravimetry curve becomes smoother, and Al-Si eutectic temperature is decreased. Ge addition can reduce the free energy of Al-Si alloy system. The lowest point of free energy is located on Al-Ge side. The eutectic Ge phase with the composition similar to pure Ge composition is the most likely to appear in the microstructure of filler metals, whereas the eutectic Si phase with the composition similar to pure Si composition is the least likely to appear. The thermodynamic calculation results are consistent with the experiment results.

Abstract:Ag-Cu-In-Ti low-temperature filler was used to braze the diamond and copper, and the effects of brazing temperature and soaking time on the microstructure and mechanical properties of the joints were investigated. In addition, the joint formation mechanism was discussed, and the correlation between joint microstructure and mechanical performance was established. Results show that adding appropriate amount of In into the filler can significantly reduce the filler melting point and enhance the wettability of filler on diamond. When the brazing temperature is 750 °C and the soaking time is 10 min, a uniformly dense braze seam with excellent metallurgical bonding can be obtained, and its average joint shear strength reaches 322 MPa. The lower brazing temperature can mitigate the risk of diamond graphitization and also reduce the residual stresses during joining.

Abstract:Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation, microstructure, and mechanical properties of the joints. Results show that under different welding parameters, with the decrease in welding heat input, the weld surface is smoother. The Ti/Al joint interface is flat without obvious Ti and Al mixed structure, and the hook structure is not formed under optimal parameters. Due to the enhanced breaking effect of the stirring head, the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min, thereby deteriorating the mechanical properties of joints. Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone. Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min, the maximum tensile shear strength of joint is 289 N/mm.

Abstract:Zirconium-titanium-steel composite plate with the size of 2500 mm×7800 mm×(3+0.7+22) mm was prepared by explosive welding+rolling method, and its properties were analyzed by ultrasonic nondestructive testing, phased array waveform shape, interface structure shape, electronic scanning, and mechanical property testing. Results show that the rolling temperature of zirconium-titanium complex should be controlled at 760 °C, and the rolling reduction of each pass should be controlled at 10%–25%. The explosive velocity to prepare zirconium-titanium-steel composite plates should be controlled at 2450–2500 m/s, the density should be 0.78 g/cm³, the stand-off height should be 12 mm, and the explosive height of Zone A and Zone B should be 45–50 mm. Explosive welding combined with rolling method reduces the impact of explosive welding and multiple heat treatment on material properties. Meanwhile, the problems of surface wrinkling and cracking, which occur during the preparation process of large-sized zirconium-titanium-steel composite plate, can be solved.

Abstract:Short process forming techniques for brazing and soldering materials can shorten the process, improve product quality, and increase production efficiency, which has received much attention from welding researchers. This review mainly summarized the research reports on short process forming techniques for brazing and soldering materials. Firstly, the traditional process and its shortcomings were presented. Secondly, the latest research of short process forming technologies, such as continuous casting technique, atomization powder technique, solder ball forming technique, and rapid solidification technique, was summarized, and the traditional forming performance of several brazing and soldering materials was introduced. Finally, the current restrictions and research trends of short process forming technique for brazing and solder materials were put forward, providing theoretical guidance and reference for related research and technique development in brazing and soldering field.

Abstract:AgCu filler was used to braze Zr and CoCrFeMnNi high-entropy alloy (HEA). The effects of brazing temperature and holding time on the microstructure and mechanical properties of the joints were analyzed. The results show that the typical microstructure of the joints brazed at 850 ℃ for 10 min is HEA/Cr_ss/Zr(Cr,Mn)₂/Zr₂(Co,Cu,Ni,Fe)+Zr₂(Ag,Cu)+Zr(Cr,Mn)₂/Zr. The joints have the maximum shear strength of 103.1 MPa. As the brazing temperature or holding time rises, the thickness of Cr-rich solid solution and Zr(Cr,Mn)₂ layer are increased, the content of Zr₂(Co,Cu,Ni,Fe) and Zr(Cr,Mn)₂ phase is increased whereas the content of Zr₂(Ag,Cu) phase is decreased. Finally, the failure mechanism of the joint was analyzed. Under the action of shear force, as the brazing temperature or holding time rises, the fracture position of the joint shifts from the Zr(Cr, Mn)₂ layer to the Zr₂(Co, Cu, Ni, Fe) phase fracture in the center of the brazing seam.

Abstract:Ti-10Zr-10Cu-10Ni powder was used as a brazing filler for vacuum brazing of commercial pure titanium TA1 at 880 ℃ for 30 min and 910 ℃ for 30 min. Following this, interface microstructure and performance analyses were carried out on two sets of distinct brazed joints. The results show that the microstructure of the two sets of joints is made up of TA1+acicular α-Ti+eutectoid (α-Ti+(Ti, Zr)₂(Cu, Ni)+ residual filler/TAl. The Zr elements are scattered in the eutectoid structure, residual filler and acicular α-Ti, while the Cu and Ni elements are mostly distributed in the eutectoid structure and residual filler. The mechanical properties of the two types of brazed joints differ significantly. When exposed to of brazed joint, the tensile strength of brazed joint at room temperature is around 174 MPa. The room temperature tensile strength rises to around 491 MPa when it is subjected to 910 ℃. The hardness of the material exhibits a progressive rise from the base material to the welding center. At 910 ℃, the greatest recorded hardness (HV) is around 2842 MPa, while at 880 °C, the maximum hardness (HV) reaches 3724 MPa. The mechanical difference between the two joints is mostly caused by the separation of Zr element, which create a brittle, layered intermetallic compound. Fracture analysis of the specimens reveals that the cracks in both sets of interfaces propagate along the weld seams. The fracture surface at 880 ℃ exhibits cleavage fracture characteristics, while at 910 ℃ it demonstrates a ductile fracture mode.

Abstract:To realize high quality and high efficiency welding of large thickness titanium alloy, a flux-cored welding wire was developed by optimizing the synergistic mechanism of metal powder cores. The microstructure evolution of the interlayer region of the welded joint was studied, the stress distribution in the process of laser welding was analyzed by numerical simulation, and the ultra-narrow gap laser welding of TC4 titanium alloy plate with 96 mm in thickness was realized. The results show that the average tensile strength of the upper, middle and lower parts of the welded joint is 935 MPa, the average yield strength is 794 MPa, and the elongation is 20%. The average value of the impact toughness of the upper, middle and lower welded joints at room temperature is 31 J, and the microstructure and properties of the welded joints are well distributed along the wall thickness direction. With the pass of welding increasing, the change from compressive stress to tensile stress occurs in the welded seam center; the high stress zone of transversal and longitudinal residual stress is not in the surface of the sample, but in the welded seam with 6 mm to the surface, and the maximum tensile stress is 1030 MPa.

Abstract:The transient liquid phase bonding (TLP) welding test of DD5 Ni-based single crystal superalloy was carried out under welding conditions of 1280 ℃, 12 h, 0.01 MPa using the self-developed TLP interlayer material. The microstructure and precipitates of the welded joint were analyzed using SEM and the thermodynamic software JMatPro. The results show that the thickness of the interlayer has a significant impact on the microstructure of the welded joint. When the thickness of the interlayer is 120 μm, the microstructure and composition of the weld and the base metal tend to be consistent, and no obvious brittle precipitates are formed; the γ′ phase in the weld zone and matrix are basically combined. When the thickness of the interlayer is 160 and 200 μm, the athermally solidified zone (ASZ) is composed of brittle phases such as sunflower-like eutectic structure, fishbone-like borides, and block carbides rich in Ta and Hf. After post weld heat treatment (PWHT), the γ′ square degree of weld zone is significantly improved, and the size is basically consistent with that in the substrate. The stress rupture test was conducted under the condition of 980 ℃, 248 MPa. When the thickness of the intermediate layer is 120 μm, the stress rupture life can reach 145.54 h. And the results show that as the thickness of the intermediate layer increases, the stress rupture life of the joint continues to decrease, and the fracture mode changes from ductile fracture to brittle fracture.

Abstract:To address the unclear matching issue between the vacuum brazing process of sandwich panel with metal rubber core and its material properties, simulation and orthogonal experimental methods were employed to investigate the influence of heating rate, maximum heating temperature, and holding time on the shear performance and connection strength. In addition, the shear damage behavior of the sandwich panel was analyzed by macro and micro method. The results indicate that sandwich panel prepared by vacuum brazing process exhibits excellent shear and connection strength. During the vacuum brazing process, the temperature deviation at all selected sample points is less than 10 K. Additionally, the residual stress is primarily concentrated at the junction of the wire and the solder, and the nearer the distance to central region, the smaller the residual stress. The maximum residual stress is negatively correlated with the shear performance and joining strength of the sandwich panel. Moreover, the optimum technological parameter (1090 ℃,4 ℃/min and 20 min) of the brazing process for fabricating the sandwich panel is obtained by range analysis.

Abstract:Nb_0.74CoCrFeNi₂ high-entropy powder brazing was used to braze C/C composites and GH4169. The effects of brazing temperature and holding time on the microstructure and shear strength of the joints were investigated to reveal the formation mechanism of the joints. Results show that the typical structure of joint is Cr₂₃C₆+(Cr,Ni)₂₃C₆/(Cr,Ni)₃C₂+NbC/fcc+Ni(s,s)+NbNi₃. With the reaction progressing on the side interface of the composite, the Cr element is gradually consumed, forming a unique gradient interfacial structure, which is conducive to relieve the residual stresses of the joint. With the increase in brazing temperature or the prolongation of holding time, the internal defects of the joints gradually disappear, but the thickness of the brittle interfacial reaction layer increases sharply, and thus the joint shear strength shows a tendency of first increasing and then decreasing. When the brazing temperature is 1260 ℃ and the holding time is 25 min, the shear strength of the brazed joint is up to 139.6 MPa, and the shear strength at high temperature of 1000 ℃ is still as high as 89.7 MPa. The high shear strength originates from the diffusion and infiltration of filler into the composite material side, which forms a strong interfacial reaction bond.

Abstract:To investigate the effect of laser remelting on the microstructure and properties of diamond/Ni-based composite coatings, diamond/Ni-based composite coatings were prepared on the surface of Q235 by induction heating. The macroscopic morphology, microstructure, elemental distribution and mechanical properties of the coatings before and after laser remelting were analyzed by ultra-deep field microscope, laser confocal microscope, scanning electron microscope, energy spectrometer, X-ray diffractometer, hardness tester and abrasive wear tester. The results show that after laser remelting, the number of exposed diamonds on the surface decreases and the average roughness of the surface of the composite coating decreases from 5.58 μm to 4.88 μm. The number of hole defects in the microstructure is significantly reduced, and the carbide in the microstructure aggregates and grows up, while the enrichment degree of Cr element increases around the diamond; there is no significant change in the microhardness of the brazing alloy and the abrasion-resistant properties of the coating.

Abstract:The composite structure of carbon-fiber-reinforced-thermoplastic (CFRTP) and aluminum alloy can combine the excellent properties of these materials, and has great application potential in rail transit, aerospace and other fields where lightweight needs to be considered. Welding technology has the advantages of strong stability and high sealing, which is a new technology to explore the preparation of CFRTP and aluminum alloy composite structures. However, due to the large differences in physical and chemical properties of dissimilar materials, the welding joint has low compatibility and poor weldability, and the current welding process conditions are not clear about the bonding mechanism of the welded joint. Therefore, the molecular dynamics (MD) simulation method was adopted in this study, and polyamide 66 (PA66) was used as the matrix material of carbon fiber-reinforced PA66 (CFRPA66). The motion and interaction mechanism of PA66 and Al atoms under different temperatures and pressures during welding were studied. The results show that the changes of temperature and pressure during the welding process exert significant effects on the atomic diffusion and bonding behavior at the interface between PA66 and Al. When the reaction time is 10 ps, the absolute value of the interaction energy reaches the maximum value at 550 K or 1.5 MPa. The simulation results provide a theoretical basis for the optimization of welding process parameters between CFRPA66 and Al alloy, and lay a solid foundation for the industrial application of CFRTP/Al alloy composite joints.

Abstract:This study addresses the lack of brazing materials suitable for low-temperature brazing of AlN ceramics and Al. By adding elements In and Sn to AgCuTi brazing materials to lower their melting points, new low-temperature brazing materials Ag-28Cu-35In-2Ti and Sn-19Ag-14.35Cu-17.5In-1Ti were prepared to achieve good bonding of AlN/Al joints. The low-temperature brazing process, joint microstructure and properties of AlN ceramics and Al using two types of brazing materials were explored. Results show that for Sn-19Ag-14.35Cu-17.5In-1Ti brazing materials relatively stable compounds such as InSn₃ and Al₃Ti form at the solder joints. Ag-28Cu-35In-2Ti brazing material generates relatively stable compounds such as Al₂Cu, AgIn₂, and TiAl₃ at the solder joint, and the joint strength increases with the increase in welding temperature. To prevent the diffusion and precipitation of In, Ni plating is chosen on the surface of Al, but it reduces the thermal conductivity of the joint. It is found that using Ag-28Cu-35In-2Ti brazing material for welding contributes to the highest joint strength of 20.28 MPa at 640 ℃ for 30 min; under the condition of 620 ℃ for 15 min, the thermal diffusion coefficient can reach 65.941 m²/s. This brazing material provides a new method for highly reliable connection of AlN ceramics/Al.

Abstract:Diamond/AlSi composite coatings were prepared on Ti-6Al-4V alloy matrix by ultrasound-assisted brazing coating technology. The effects of ultrasonic brazing process parameters on the microstructure of diamond/AlSi brazing coating were investigated. The interfacial reaction mechanism between AlSi filler metals and diamond on the matrix under ultrasonic action was discussed. The results show that TiAl₃ compounds and a large number of Ti(Al_1-xSi_x)₃ compounds are mainly formed in the contact interface between titanium alloy matrix and AlSi filler metals. The growth of Ti(Al_1-xSi_x)₃ is mainly affected by the interfacial reaction and the diffusion rate of atoms to the reaction site. Ultrasonic treatment can improve the wetting and spreading effect of AlSi filler metal on the matrix by cavitation effect to achieve the wetting of diamond particles by inactive AlSi brazing filler metal. The mechanism is that the intermetallic compound Ti(Al_1-xSi_x)₃ is formed at the interface between AlSi filler metals and the substrate. Ti(Al_1-xSi_x)₃ is broken and dispersed throughout the brazing coating by ultrasonic cavitation and acoustic streaming effect, ultimately leading to the reaction of Ti, an element in the titanium alloy matrix, with diamond to form TiC.

Abstract:Sapphire/metal welding connection faces the challenge of poor wetting of sapphire surface by brazing materials. The interface structure of the sapphire/Ag-Cu-3Ti/TC4 alloy brazed joint, the effects of temperature and holding time on the shear properties, and the mechanism of interface connection were studied. The results show that the sapphire side forms a dense metallurgical reaction layer. The microstructure of the reaction layer is composed of Ag base solid solutions, Cu base solid solids and the crystal. TC4 alloy side forms a crispy layer and a crystal infiltration area. With the increase in brazing temperature, the shear strength of the brazed joint reduces significantly. As the holding time is prolonged, the shear strength of the brazed joint increases firstly and then decreases. The fracture surface of the brazed joint exhibits a mixed fracture morphology of the sapphire brittle fracture and filler metal “adhesive type” fracture. The brazing connection relies solely on the metallurgical bonding strength between a small portion of Ag-Cu-3Ti brazing metal and the sapphire. During the brazing process, Ti and Cu diffuse towards the sapphire side and accumulate on the surface of Al₂O₃. Sufficient solid-liquid interaction occurs at the interface to form stable intermetallic compounds, and the TC4 alloy side grains continuously grow towards the matrix, resulting in a significant increase in the shear strength of the brazed joint.

Abstract:In order to improve the surface wear resistance of titanium alloys, TC4 (Ti-6Al-4V) was selected as the matrix material, and diamond particles (20%, mass fraction) and CuTi alloy powder (10%, mass fractions) were added to Al-12Si filler metal. The diamond composite wear-resistant brazing coating on TC4 surface was prepared by induction brazing under argon protection. The effects of particle size of CuTi alloy, brazing temperature, and isothermal reaction time on the microstructure and wear resistance of composite coatings were studied. The results indicate that the composite coating is mainly composed of α-Al, Ti(Al_1-xSi_x)₃, CuAl₂, and diamond particles. Reducing the particle size of CuTi alloy powder and increasing the brazing temperature can promote its full reaction with the brazing alloy. With the increase in temperature and insulation time, the CuAl₂ phase at the grain boundary between α-Al and Ti(Al_1-xSi_x)₃ gradually disperses, improving the hardness of the brazing alloy coating. However, excessive insulation can cause the CuAl₂ phase to start growing and to overlap with each other to form a coarse network structure, resulting in a significant increase in brittleness and a decrease in wear resistance of the brazed coating alloy.

Abstract:Aluminum/steel bimetallic structures show a good application prospect in lightweight vehicle manufacturing due to the low density of aluminum alloy and the high strength and low cost of steel. Nowadays, aluminum/steel components can be prepared easily and rapidly by welding and additive manufacturing techniques. However, there are some urgent problems such as the differences in physical properties between Al and steel, the formation of continuous Fe-Al intermetallic compounds, which decrease the mechanical properties of aluminum/steel interface of the components. The weldability of aluminum/steel dissimilar metals was discussed, as well as the development status of aluminum/steel dissimilar metal welding and the regulating and eliminating methods of Fe-Al intermetallic compounds. Moreover, the latest investigations on the arc additive manufacturing and laser additive manufacturing of aluminum/steel bimetallic components were also expounded. The similarities and differences between additive manufacturing and welding of aluminum/steel components were investigated. Finally, several suggestions for further research directions of aluminum/steel dissimilar metal welding and additive manufacturing were proposed.

Abstract:The microstructures and mechanical properties of Al-8.3Zn-3.3Cu-2.2Mg alloys prepared via hot extrusion and liquid forging methods were investigated. Results show that based on DEFORM simulation analysis, the optimal hot extrusion parameters are determined as ingot initial temperature of 380 °C and extrusion speed of 3 mm/s. The hot-extruded aluminum alloy after T6 heat treatment presents superior mechanical properties with yield strength of 519.6 MPa, ultimate tensile strength of 582.1 MPa, and elongation of 11.0%. Compared with the properties of gravity-cast and liquid-forged alloys, the yield strength of hot-extruded alloy increases by 30.8% and 4.9%, and the ultimate tensile strength improves by 43.5% and 10.2%, respectively. The significant improvement in tensile strength of the hot-extruded alloys is attributed to the elimination of casting defects and the refinement of matrix grain and eutectic phases. In addition, the hot-extruded alloy demonstrates superior plasticity compared with the liquid-forged alloy. This is because severe plastic deformation occurs during hot extrusion, which effectively breaks and disperses the eutectic phases, facilitating the dissolution and precipitation of the second phases and inhibiting the microcrack initiation.

Abstract:Impact of texture type on the magnetic properties of ultrahigh density perpendicular magnetic recording media L1₀-FePt thin film was investigated, so were the texture formation and evolution mechanism. Reuss, Voigt, and Hill models were used to determine the anisotropic elastic modulus of L1₀-FePt thin film with fiber texture. Then, the elastic strain energies of thin films under various stress conditions were calculated. Results reveal that the stress condition has a significant influence on the fiber texture evolution. When the L1₀-FePt thin film is subjected to compressive in-plane strain prior to ordering phase transformation, the formation of {100} fiber texture is promoted. On the contrary, the ordering phase transformation under tensile in-plane strain promotes the {001} fiber texture formation.

Abstract:Four machine learning algorithms were used to predict the solid solution phases of high-entropy alloys (HEAs). To improve the model accuracy, the K-fold cross validation was adopted. Results show that the K-nearest neighbor algorithm can effectively distinguish body-centered cubic (bcc) phase, face-centered cubic (fcc) phase, and mixed (fcc+bcc) phase, and the accuracy rate is approximately 93%. Thereafter, CoCrFeNi₂Al_x (x=0, 0.1, 0.3, 1.0) HEAs were prepared and characterized by X-ray diffractometer and energy disperse spectrometer. It is found that their phases are transformed from fcc phase to fcc+bcc phase, which is consistent with the prediction results of machine learning. Furthermore, the influence of Al content on the microstructure and tribological properties of CoCrFeNi₂Al_x (x=0, 0.1, 0.3, 1.0) HEAs was evaluated. Results reveal that with the increase in Al content, the nanohardness and microhardness increase by approximately 45% and 75%, respectively. The elastic limit parameter H/E_r increases from 0.0216 to 0.030, whereas the plastic deformation resistance parameter H³/E_r² increases from 0.0014 to 0.0045, which demonstrates an improvement in nanohardness with the increase in Al addition amount. In addition, the wear rate decreases by 35% with the increase in Al addition amount. This research provides a new idea with energy-saving and time-reduction characteristics to prepare HEAs.

Abstract:As-forged WSTi6421 titanium alloy billet after β annealing was investigated. Abnormally coarse grains larger than adjacent grains could be observed in the microstructures, forming abnormal grain structures with uneven size distribution. Through electron backscattered diffraction (EBSD), the forged microstructure at various locations of as-forged WSTi6421 titanium alloy billet was analyzed, revealing that the strength of the β phase cubic texture generated by forging significantly influences the grain size after β annealing. Heat treatment experiments were conducted within the temperature range from T_β-50 °C to T_β+10 °C to observe the macro- and micro-morphologies. Results show that the cubic texture of β phase caused by forging impacts the texture of the secondary α phase, which subsequently influences the β phase formed during the post-β annealing process. Moreover, the pinning effect of the residual primary α phase plays a crucial role in the growth of β grains during the β annealing process. EBSD analysis results suggest that the strength of β phase with cubic texture formed during forging process impacts the orientation distribution differences of β grains after β annealing. Additionally, the development of grains with large orientations within the cubic texture shows a certain degree of selectivity during β annealing, which is affected by various factors, including the pinning effect of the primary α phase, the strength of the matrix cubic texture, and the orientation relationship between β grain and matrix. Comprehensively, the stronger the texture in a certain region, the less likely the large misoriented grains suffering secondary growth, thereby aggregating the difference in microstructure and grain orientation distribution across different regions after β annealing.

Abstract:SS316L alloy coupled with Inconel625 alloy were combined with Ti6Al4V or Inconel718 alloy through wire arc additive manufacturing technique to manufacture functionally graded materials (FGMs). Two FGMs, namely 60% SS316L+20% Inconel625+20% Ti6Al4V composite and 60% SS316L+20% Inconel625+20% Inconel718 composite, were prepared. The tensile strength, elongation, yield strength, hardness, cross section area of the parent material, and composition were analysed. Results illustrate that the 60% SS316L+20% Inconel625+20% Inconel718 composite has better mechanical properties than 60% SS316L+20% Inconel625+20% Ti6Al4V composite, and the comprehensive properties of 60% SS316L+20% Inconel 625+20% Ti6Al4V composite are better than those of the parent material SS316L. Hence, the composite of 60% SS316L+20% Inconel625+20% Inconel718 is optimal. Due to its high strength, the 60% SS316L+20% Inconel625+20% Inconel718 composite has great application potential in the field of high pressure pneumatic tool and defence tool.

Abstract:This article took K439B alloy with a temperature bearing capacity of 800 ℃ as the research object to study the γ′ phase morphology in the standard heat-treated condition, and the γ′ phase evolution and coarsening behavior during aging at 800 ℃ for 6000, 7000, 8000, and 10 000 h. The results indicate that the γ′ phase at the dendrites in the alloy is fine and uniform, while the γ′ phase between the dendrites presents two types. After long-term aging, the bimodal γ′ phase is still retained in the interdendritic region, and the γ′ phase transforms from spherical to cubic shape without any rafting phenomenon. During the long-term aging process, the γ′ phase size of the K439B increases, but the change in volume fraction is not significant. The variation of γ′ phase size with aging time conforms to both Lifshitz-Slyozov-Wagner (LSW) and theory of interface diffusion control (TIDC) models. The internal reason is believed to be the equivalent diffusion rate of elements between the matrix and interface.

Abstract:WC-25Co cemented carbides were prepared by laser directed energy deposition technology using spherical WC-12Co composite powder and spherical Co powder as raw materials. The effects of laser power on the microstructure and friction and wear properties of WC-25Co cemented carbides were studied. The results show that the Co particles melt and form liquid phase, which significantly improves the deposition quality of WC-12Co. The increase in laser energy promotes the flow of Co liquid phase, and the densification degree and microstructure uniformity of the alloy are significantly increased. The alloy structure is composed of WC phase and Co phase, and no decarburization phases such as Co₃W₃C, Co₆W₆C and W₂C are found. With the increase in laser power, the alloy hardness increases gradually, and the wear rate decreases first and then increases. At the laser power of 1400 W, the wear rate in WC-25Co cemented carbide is the lowest, which is (0.81±0.11)×10^-5 mm³/(N·m). The wear mechanism is mainly abrasive wear, and there is also a small amount of oxidation wear.

Abstract:GH4141 nickel-based superalloy is a key material for turbine disks, fasteners and engine cases, which is generally fabricated through traditional casting-forging/rolling processes. In this study, the hot working behavior of hot-rolled GH4141 superalloy was studied. The hot deformation behavior of the hot-rolled GH4141 superalloy at deformation temperatures of 1050–1150 °C and strain rates of 0.01–1 s^-1 was studied through Gleeble hot-compression experiments, and the hot deformation constitutive equation of the alloy during the deformation process was constructed. In addition, based on the microstructure evolution analyses under different deformation conditions, the dynamic recrystallization rules during the hot deformation process were clarified. A dynamic recrystallization model of the alloy was constructed and the dynamic recrystallization fraction can be accurately predicted by this model. It is found that the dynamic recrystallization fractions are increased with the increase in the deformation temperature, the decrease in strain rate, or the increases in amount of deformation. From the viewpoints of degrees of dynamic recrystallization, the optimal deformation parameters are determined as deformation temperature at 1150 °C and the strain rate of 0.01–0.1 s^-1.

Abstract:Hot compression tests were conducted on extruded Mg-Mn-Ce alloys under deformation temperatures of 723–873 K and strain rates of 0.0001–0.1 s^-1. Based on the obtained true stress-strain curve, the influence of deformation temperature and strain rate on material flow stress was analyzed. A constitutive relationship was established based on Arrhenius and BP-ANN models, and its accuracy was evaluated. Using the constitutive data obtained from the BP-ANN model, a hot processing map was plotted and numerical simulations were conducted. The results indicate that as the deformation temperature increases and the strain rate decreases, the flow stress of the alloy decreases. The BP-ANN model established has higher prediction accuracy, with a correlation coefficient of 0.9990 and an average relative error of only 2.69%. The hot working range of the alloy should be selected within the range of 0.001–0.01 s^-1 and 773–823 K. The numerical simulation and experimental results are in good agreement and can be used to guide the thermoplastic forming of alloys.

Abstract:Lamellar metallic materials comprising lamella units with different mechanical properties can form a unique lamellar heterostructured material. The heterostructures could induce various strength-ductility synergetic mechanisms due to the action of multi-type and multi-scale heterogeneity. Multiple lamellar morphologies have emerged with the diversification of material preparation means and processing treatments, and thus new requirements and design criteria have been derived for optimizing the lamellar microstructure. Optimizing the microstructural lamellar design and exploring the relation between mechanical behavior and micro/nano-lamellar structures will not only contribute to establishing the design theory about laminated metallic materials, but also accelerate its practical application. In this paper, the research progress on laminated metallic materials in recent years was reviewed. Classification of metallic lamellar structures, their mechanical properties and strength-ductility mechanisms were introduced and discussed in detail. Finally, perspectives on the future research trends and challenges of lamellar structures were briefly stated.