Abstract:To address the issues of rapid cooling rate during the solidification in underwater welding and the deterioration of the microstructure and properties, this work conducted local dry underwater welding experiments on 2205 duplex stainless steel using adjustable ring-mode laser. Meanwhile, compared with in-air welds, the effects of the power ratio between center and ring lasers on weld formation, microstructure and mechanical properties were investigated. The results show that the center laser mainly affects the penetration depth. With the increase in proportion of central power, the oxidation degree and surface roughness of the weld become more severe. In terms of microstructure, the underwater weld exhibits an increase in Widmanst?tten austenite content, but a decrease in or even disappearance of intragranular austenite, compared to welds produced with the same parameters in air. With the increase in proportion of ring laser, the austenite content in the weld shows no significant change, the grain size and aspect ratio of the weld decrease, the directionality of columnar crystal growth on both sides of the weld weakens, and the number of low-angle grain boundary increases. In terms of performance, the underwater joints exhibit slightly higher tensile strength but lower elongation than those welds in air. As the proportion of ring laser power increases from 1/3 to 2/3, the elongation of underwater joints increases by about 50%.

Abstract:The formation mechanism of repulsive transition in underwater wet welding was firstly analyzed. Affected by the aqueous environment, molten droplets during underwater welding are subjected to combined effect of multiple forces. The gas pressure, gas drag force, and plasma flow force acting on the droplet fluctuate dynamically with the generation location of arc bubbles and the position of cathode spots. These forces together serve as the main driving forces for the repulsive transition of the droplet. The surface tension impedes lateral detachment of the droplet from the wire tip, while gravity facilitates droplet separation from the wire tip to complete the transition. The influence of pulse frequency, duty cycle, and peak current on weld formation, droplet transfer, and welding stability in underwater wet welding was investigated using the orthogonal experimental method. The weld reinforcement variation coefficient was adopted to evaluate formation quality. The results indicate that optimal welding performance is obtained at a duty cycle from 15% to 20%, a peak current of 350 A, and a pulse frequency of approximately 20 Hz. By applying pulsed current during the peak current phase, the electromagnetic contraction force acting on the droplet is significantly enhanced, promoting droplet transfer and increasing the transition frequency.

Abstract:Thermal cycling has a significant impact on the microstructure and properties of narrow-gap welded joints in titanium alloy thick plates. In this study, a 60 mm-thick TC4 titanium alloy welded joint was fabricated using oscillating-wire magnetic-controlled arc narrow-gap welding technique. The evolution of the microstructure (α phase, β phase, and grain boundary α_GB), as well as changes in microhardness and its tensile properties under typical thermal cycling conditions were investigated through numerical simulation. The results show that high-temperature thermal cycling induces a complete α→β transformation, promoting the preferential growth of the α phase and forming coarse and uniformly-oriented α colonies. In contrast, subsequent low-temperature thermal cycling causes an incomplete α→β transformation, where lower cooling rate and temperature gradient weaken the preferential orientation, leading to the refinement of lamellar α phase. After the entire thermal cycling process, the thickness of lamellar α phase increases from 0.910.09 μm to 1.020.18 μm, and the proportion of residual β phase increases from 0.02% to 1.89%. The weld root layer exhibits the highest microhardness, attributed to grain refinement strengthening. The root layer also demonstrates the highest tensile strength, while the cap layer shows the highest elongation. The joints exhibit ductile fracture behavior overall.

Abstract:China has independently developed 10CrNi3MoV high-strength steel, which has become a crucial structural material for manufacturing submarine pressure hulls due to its high strength, excellent toughness, superior explosion resistance, and outstanding corrosion resistance. In this study, the response surface method was used to investigate the effects of laser power, scanning speed, and wire feeding speed on the dilution rate and deposition angle of the underwater single-pass deposition layer. Then the optimized underwater single-pass deposition process parameters were obtained. Based on this, the influence of the water environment on the formation, microstructure, and microhardness of the single-pass deposition layer was investigated. Compared with that in air, the faster cooling rate in the underwater laser melting deposition process leads to a larger deposition angle and a slower dilution rate in the underwater deposition layer. Additionally, the microstructure of the underwater deposition layer is finer, which results in a higher microhardness.

Abstract:Magnetically controlled plasma-flux cored arc welding (Plasma-FCAW), as an efficient hybrid arc welding method, is characterized by excellent deep penetration and low spatter. However, the welding process is susceptible to disturbances due to the complex underwater environment. To address this issue, a self-developed electromagnetic excitation device was used in this study to apply a transverse magnetic field to the underwater hybrid Plasma-FCAW process. This magnetic control facilitated flexible coupling between the two arcs, thereby effectively improving the stability of the hybrid welding process and the weld bead formation. On this basis, welding process experiments were carried out in water environment with different salinities and temperatures. The influence of the water condition on droplet transfer behavior, weld formation, as well as microstructure and properties was studied. The results show that increased salinity shortens the droplet transfer cycle, raises the cooling rate, and reduces the weld width. Water temperature significantly affects arc stability and droplet transfer behavior: the droplet transfer cycle shortens at low temperature, while it becomes irregular at high temperature. Both increased salinity and decreased water temperature increase the content of side-plate ferrite and acicular ferrite in the weld zone. In contrast, higher water temperature increases the pearlite content in the heat-affected zone, thereby affecting the hardness of weld.

Abstract:With the rapid development of marine engineering, the research and application of underwater welding technology has become the key to marine engineering construction. In this review, the classification and characteristics of underwater welding were briefly described. The influence of underwater environment, welding materials, and welding process on the quality of underwater wet welding was analyzed. The application of in-situ observation method and external auxiliary means in the field of underwater wet welding was introduced. The research results of underwater local dry-laser welding with powder feeding/wire feeding were summarized. The research progress of underwater dry method under different water depths was introduced. The research results in the field of underwater friction-stir welding were analyzed.

Abstract:The strength and damping properties of Co-Ni-Cr-Mo-based alloys with 0.5wt% Nb addition after various plastic deformation and heat treatment processes were investigated. Through Vickers hardness tests, free resonance Young's modulus measurements, and microstructure analysis, the effects of dislocation density, vacancy formation, and recrystallization on the alloy performance were clarified. Results indicate that increasing the rolling reduction enhances damping property due to higher dislocation density, whereas aging below the recrystallization temperature reduces damping property via dislocation pinning by the Suzuki effect. Recrystallization heat treatment restores the original structure and damping level. This alloy possesses tensile strength of approximately 1500 MPa and logarithmic decrement value δ^-1 in the range of 2×10^-4–3×10^-4, demonstrating superior mechanical properties compared with the Ti-based alloys, which makes it an excellent candidate material for ultrasonic tools and medical applications.

Abstract:In-situ tensile tests were conducted on a chemically corroded third-generation single-crystal superalloy DD9 at 980 and 1100 ℃. The phase transformation in the surface areas during the tensile process was analyzed using field emission scanning electron microscope, energy dispersive X-ray spectroscope, electron probe X-ray microanalysis, and transmission electron microscope. The phase transformation mechanism on the surface and the influence mechanism were studied through observation and dynamic calculation. During tensile tests at elevated temperatures, chemical corrosion promotes the precipitation of topologically close-packed (tcp) μ phase and σ phase on the alloy surface. Both the precipitation amount and size of these two phases on the surface at 1100 ℃ are greater than those at 980 ℃. The precipitation of tcp phase on the alloy surface results in the formation of an influence layer on the surface area, and the distribution characteristics of alloying elements are significantly different from those of the substrate. The depth of the influence layer at 1100 ℃ is greater than that at 980 ℃. The precipitation of tcp phase prompts the phase transition from γ phase to γ′ phase around the tcp phase.

Abstract:The solidification microstructure and room-temperature mechanical properties of K4750 superalloys prepared by gravity casting and centrifugal casting were investigated. Their second phase distribution, grain size, element segregation, distribution of shrinkage defects, room-temperature mechanical properties and fracture morphology were analyzed comparatively. Results show that the as-cast K4750 superalloys prepared by both casting processes consist of γ matrix phase, intragranular MC-type carbide, fine and dispersed intragranular γ' phase, as well as MC-type and M₂₃C₆-type carbides at grain boundary. However, the precipitate size is found to be more refined in the centrifugal casting process. The average grain size of as-cast K4750 superalloy decreases from 4.52 mm (gravity casting) to 2.22 mm (centrifugal casting). Furthermore, the area fraction of shrinkage defects is reduced from 1.75% (gravity casting) to 0.27% (centrifugal casting). The K4750 superalloy prepared by gravity casting exhibits well-aligned dendritic structures, whereas centrifugal-cast superalloy shows fragmented dendrites and a reduced degree of elemental segregation. The K4750 superalloy samples prepared by centrifugal casting exhibit excellent room-temperature mechanical properties, with yield strength, ultimate tensile strength and elongation of 632 MPa, 938 MPa and 11.2%, respectively. Compared to the gravity-casting counterpart, its ultimate tensile strength is increased by 20.6%, which can be attributed to the combined effects of grain refinement, γ' phase refinement and a reduction in casting defects.

Abstract:Low cycle fatigue failure is the main failure mode of tenon part of single crystal turbine blades. Due to the difference between the actual working load and the design load, the stress leading to fatigue failure often needs to be given after fatigue failure, and the fracture is a comprehensive reflection of load and temperature. Quantitative analysis of the fracture and inverse fatigue stress have important engineering application value in blade failure analysis. The unique microstructure and crystal structure of single superalloy make its fatigue fracture characteristics different from those of polycrystalline materials. The main fatigue fracture characteristics of single crystal superalloy are slip plane rather than fatigue band. A model and method for quantitative analysis of crack tip plastic zone were presented in this paper. There is a certain angle between fatigue fracture and load of single superalloy, which is a composite cracking mode rather than a type Ⅰ cracking mode. According to the cracking characteristics of single superalloy, using the test data of DD6 single-crystal high-temperature alloy under the condition of 530 ℃ and strain ratio r=0.05, the hysteresis loop of its different life intervals was analyzed. The results show that the life span is between one thousand and ten thousand times, and its hysteresis loop is very narrow; the life span is greater than ten thousand times, and its hysteresis loop is basically a straight line. in addition, DD6 single-crystal high-temperature alloy under the conditions of 530 ℃ and strain ratio r=0.05 has the small yielding characteristics. Based on this, for the low-cycle fatigue fracture, the characteristics of crack initiation and extension stage and its fracture characteristics were studied, and a quantitative analysis model of fatigue stress fracture was established by considering the composite cracking and based on r_p in the plastic zone at the crack tip. The quantitative analysis of fatigue stress fractures at different locations was carried out using a total of 12 crack locations for 3 specimens. The analysis results show that the error of fatigue initiation stress is within 1.3 times, and that of inverse extrapolation result of the first stage of extension is within 1.5 times of the dispersion band. The results provide models and methods for quantitative fracture analysis of stresses in single-crystal superalloys mainly by slip-surface cracking (non-fatigue strips).

Abstract:During the vacuum induction melting (VIM) casting process of Monel K-500 alloy, a large number of shrinkage defects are likely to occur in the upper part of the ingot, resulting in low yield and poor quality. To address this issue, this study investigates the thermal and physical properties and solidification process of Monel K-500 alloy through thermodynamic calculations using Jmat-Pro. The experimental results show that the solidification range of Monel K-500 alloy is between 1250 and 1350 °C. The solidification path is: L→L+γ→L+γ+MC→γ+MC+M₇C₃→γ′+γ+MC+M₇C₃. During the solidification process, as the mass fraction of the residual liquid phase decreases, Ni exhibits negative segregation, while Cu exhibits positive segregation. Combining the thermodynamic calculation results with a finite element model (FEM), a simulation of the industrial VIM casting process for Monel K-500 alloy of 6 t was conducted. The simulated results were compared with the actual shape and size of the shrinkage defects in the upper part of the induction ingot to verify the reliability of the casting model. In addition, this study explores the effects of different pouring parameters on shrinkage defects in VIM ingot based on the model. The results show that the addition of a riser has the most significant improvement on the shrinkage defects in VIM ingot. As the riser volume ratio increases, the volume of shrinkage defects in the ingot decreases significantly, with no shrinkage defects present in the ingot at a riser volume ratio of 20%. When the pouring speed is in the range of 2.5–17.5 kg/s, the volume of shrinkage defects in the VIM ingot decreases as the pouring speed decreases. However, when the poring speed is below 7.5 kg/s, the shrinkage defects move inward within the ingot.

Abstract:The effects of different sand blasting processes on recrystallization defects and the occurrence of recrystallization in 4777DS alloy were studied using optical microscope and scanning electron microscope. The analysis of the recrystallization structure on the alloy surface after sandblasting shows that the depth of recrystallization on the alloy surface increases with the increase in sandblasting intensity, time, and gravel diameter, and the decrease in sandblasting distance. After sandblasting, the deformed sample shows that the γ′ phase near the sandblasted surface changes from a butterfly shape to a long strip shape, and some of the deformed γ′ phase surrounds the areas with greater deformation. At the same time, a large number of dislocations distributed in the γ matrix channels and γ′ phase are observed by TEM. The different γ′ phases between dendrites affect the growth of recrystallization, resulting in the formation of wavy grain boundaries. No inhibitory effect of eutectic or carbide on recrystallization has been found. Due to the small size of surface recrystallized grains and the presence of residual stress, a new layer of recrystallized grains will form in the subsurface.

Abstract:The in-flight heating process of cerium dioxide (CeO₂) powders was investigated through experiments and numerical simulations. In the experiment, CeO₂ powder (average size of 30 μm) was injected into radio-frequency (RF) argon plasma, and the temperatures were measured using a DPV-2000 monitor. A model combining the electromagnetism, thermal flow, and heat transfer characteristics of powder during in-flight heating in argon plasma was proposed. The melting processes of CeO₂ powders of different diameters, with and without thermal resistance effect, were investigated. Results show that the heating process of CeO₂ powder particles consists of three main stages, one of which is relevant to a dimensionless parameter known as the Biot number. When the Biot value≥0.1, thermal resistance increases significantly, especially for the larger powders. The predicted temperature of the particles at the outlet (1800–2880 K) is in good agreement with the experimental result.

Abstract:The effect of trace addition of 0.1wt% Y on the grain refinement and mechanical properties of Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys at as-cast and heat-treated states was investigated. Results show that the addition of 0.1wt% Y into the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys can elevate the nucleation temperature of the Al₃(Sc, Zr) phase, leading to the preferential precipitation of the Al₃(Sc, Zr) phase and increasing the amount of Al₃(Sc, Zr) phase in the matrix. Al₃(Sc, Zr) phase can also act as a heterogeneous nucleation site in the α-Al matrix to promote nucleation and refine grains. The addition of element Y changes the precipitation phase characteristics at the grain boundaries in the as-cast alloy, which changes the distribution characteristics of secondary phases from initially continuous and coarse strip-like distribution at grain boundaries into the discontinuous dot-like and rod-like distribution. Besides, the size of secondary phases becomes smaller and their amount increases. Under the combined effects of grain refinement strengthening and precipitation strengthening, the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc-0.1Y alloy after 175 °C/10 h aging treatment achieves an ultimate tensile strength of 412 MPa and an elongation of 6.3%. Compared with those of the alloy without Y addition, the ultimate tensile strength and elongation of the added alloy increase by 16.1% and 53.7%, respectively.

Abstract:Given the considerable global interest in the preparation of Ti and TiC, a novel reduction method for TiO₂ in a CH₄-H₂ atmosphere was proposed, and the reduction thermodynamic behavior, phase equilibrium, and energy consumption of TiO₂ during its reaction with a CH₄-H₂ gas mixture were investigated. The results indicate that the reaction proceeds via a stepwise reduction pathway from TiO₂ to Ti(C, O), with the Magnéli phase (Ti_nO_2n-1) and Ti₃O₅ serving as intermediate phases. Notably, the reduction of TiO₂ by H₂ is more challenging than that by CH₄, which may be attributed to the inhibitory effect of H₂ on the surface carbon precipitation. For the complete carbonization of 1 mol TiO₂, the total energy required at 1000, 1100, and 1200 ℃ is 1159, 925, and 977 kJ/mol, respectively, which may be related to the shift of gas-phase equilibrium and the increase in side reactions at high temperatures.

Abstract:The hot compression deformation behavior of Mg-6Zn-1Mn-0.5Ca (ZM61-0.5Ca) and Mg-6Zn-1Mn-2Sn-0.5Ca (ZMT612-0.5Ca) alloys was investigated at deformation temperatures ranging from 250 ℃ to 400 ℃ and strain rates varying from 0.001 s^–1 to 1 s^–1. The results show that the addition of Sn promotes dynamic recrystallization (DRX), and CaMgSn phases can act as nucleation sites during the compression deformation. Flow stress increases with increasing the strain rate and decreasing the temperature. Both the ZM61-0.5Ca and ZMT612-0.5Ca alloys exhibit obvious DRX characteristics. CaMgSn phases can effectively inhibit dislocation motion with the addition of Sn, thus increasing the peak ?ow stress of the alloy. The addition of Sn increases the hot deformation activation energy of the ZM61-0.5Ca alloy from 199.654 kJ/mol to 276.649 kJ/mol, thus improving the thermal stability of the alloy. For the ZMT612-0.5Ca alloy, the optimal hot deformation parameters are determined to be a deformation temperature range of 350–400 ℃ and a strain rate range of 0.001–0.01 s^–1.

Abstract:With the advancement of laser powder bed fusion (LPBF) additive manufacturing, efficient utilization of powders outside the conventional particle size range (15–53 μm) has become critical to improving powder efficiency. This study investigated process optimization, microstructure, and mechanical properties of coarse AlMgScZr alloy powders (53–150 μm) in LPBF. The controlled variable method was employed to analyze parameter effects on density, defects, microstructure, and mechanical properties. Results show that the coarse powder exhibits a narrow process window with high sensitivity of forming stability to parameter fluctuations. The optimized parameters are a layer thickness of 100 μm, a laser power of 450 W, and a scanning speed of 900 mm/s. This parameter set achieves a relative density of 99.3%±0.2%. Microstructural analysis reveals fine equiaxed grains near fusion boundaries transitioning to columnar grains within molten pools, without observable secondary precipitates. The as-printed samples show a microhardness of 99.7±8.9 HV_0.1, tensile strength of 336.5±8.0 MPa, and elongation of 12.7%±0.4%.

Abstract:A combination of single factor and Box-Behnken response surface method was employed to optimize the impurity removal process during the evaporation crystallization of ammonium tungstate solution to prepare ammonium paratungstate (APT) with higher purity. Firstly, to reduce the total content of four impurities (Na, K, S and Mo) in APT, the preferred range of crystallization temperature, stirring speed and initial concentration of ammonium tungstate solution was preliminarily determined by single factor method. Secondly, the impurity removal process during the evaporation crystallization of APT was further optimized by Box-Behnken response surface method, and the interactive effects of three factors on the total amount of four impurities in APT was studied. The results show that the order of influence of three factors on the total content of four impurities is as follows: initial concentration of ammonium tungstate solution>evaporation temperature>stirring speed. The optimum process conditions are an evaporation temperature of 94 ℃, a stirring speed of 1.25 m/s, and an initial ammonium tungstate concentration of 73 g/L. Under the experimental conditions, the total content of four impurities in the prepared APT is reduced to 39.351 mg/L, which corresponds to a relative error of merely 4.110% compared to the optimal prediction value of the response surface method model. Consequently, the purity of APT reaches 4N level. The generated APT crystal is a columnar cuboid morphology with a small amount of broken crystals. The layered structure is obvious, the particle size distribution is uniform, and the grain refinement is obvious.

Abstract:Two groups of WC-Co and WC-Ni-Fe cemented carbides with varying binder phase contents were prepared using the same process. The research explored the trends in the microstructure changes and the differences in properties between WC-Co and WC-Ni-Fe cemented carbides. The results show that the binder phase of both WC-Co and WC-Ni-Fe cemented carbides exhibits a single-phase structure. As the binder phase content in the alloy increases, there is an increase in average grain size and a decrease in hardness and coercive magnetic force. Additionally, cobalt magnetism, bending strength, and impact toughness all exhibit upward trends. In comparison, the WC-Co cemented carbide exhibits higher coercive cobalt magnetism, magnetic force, and bending strength than WC-Ni-Fe cemented carbide. However, WC-Ni-Fe cemented carbide exhibits better impact toughness with a higher binder phase content, reaching up to 5.9 J/cm². The frictional behavior of WC-Co and WC-Ni-Fe cemented carbides is similar, but the wear degree of the alloys gradually increases as the binder phase content increases. When the contents of binder phase content are the same, the wear resistance of WC-Co cemented carbide is superior to that of WC-Ni-Fe cemented carbide.

Abstract:By modifying the existing plasma rotating electrode atomization (PREP) powder production equipment, the core-shell structure powders with low nitrogen content in the core and high nitrogen content on the surface were successfully prepared by adjusting the nitrogen flow rate during the powder-making process with pure titanium rods. The particle size distribution, microscopic morphology, and microstructure of the powders were systematically characterized using a standard vibrating sieve, laser particle size analyzer, X-ray diffractometer (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscope (XPS). The results show that the particle size of the powders with nitrogen gas were smaller than that without nitrogen gas. As the nitrogen flow rate increases from 3 L/min to 8 L/min, the particle size exhibits a trend of first decreasing and then increasing. Introducing nitrogen gas can significantly suppress the formation of satellite powders in pure titanium metal powders and make the surface of the powders smooth, but it can also result in elongated and insufficiently spheroidized shaped powder particles in the powder. Under different nitrogen gas flow rates, nitrogen is uniformly distributed on the powder surface, forming a Ti-N_x microstructures shell layer, and the nitrogen content on the powder surface layer is significantly higher than that in the core.

Abstract:In this research, the effect of charging temperature on the hydrogen damage behavior of TA15 alloy was studied. The results show that the strength of the alloy increases first and then decreases with the increase in charging temperature under the condition of 800–900 K, 10 MPa, and hydrogen charging for 1 h, but the elongation decreases continuously. When the charging temperature is 800 K, the tensile strength of the alloy increases by 9% compared with the as-received samples, while the elongation decreases by 12%. When the charging temperature is 900 K, the tensile strength of the alloy decreases by 85%, and the alloy is completely brittle fracture (the embrittlement index reaches 100%). The microanalysis demonstrates that as the hydrogen charging temperature increases from 800 K to 900 K, the hydrides in the alloy undergo a transformation, shifting from precipitating predominantly along the α/β phase boundary to precipitating within the α and β phases. The sizes and quantities of these hydrides increase significantly, resulting in a change in the way of the hydrogen cracking of the alloy. Rather than occurring along the α/β phase boundary, as previously observed, the cracking now propagates along the hydrides within the α and β phases or along the hydride/matrix interfaces.

Abstract:Graphene/copper-based composite heat sinks demonstrate extensive application potential in military equipment thermal management, high-power electronic packaging, new energy vehicles, and 5G communication systems, due to their outstanding properties, including high thermal conductivity, tunable thermal expansion coefficients, excellent mechanical strength, and low density. However, the industrial-scale application of these composites faces critical challenges during the fabrication of components with complex structures, such as inhomogeneous dispersion of graphene within the copper matrix and poor interfacial bonding between the two phases, which substantially undermine the overall performance of graphene/copper-based composites. To address these issues, the preparation methods for graphene/copper-based composite heat sinks were reviewed. For each method, a rigorous analysis was presented to clarify its inherent advantages and unavoidable restrictions. Furthermore, the latest research progress in addressing three core scientific challenges was synthesized, including uniform dispersion of graphene, interfacial optimization mechanisms, and molecular dynamics simulations for elucidating the structure-property relationships. Finally, the future development directions of graphene/copper-based composite heat sinks in engineering applications were prospected.

Abstract:The multi-principal element characteristic of high-entropy alloys has revolutionized the conventional alloy design concept of single-principal element, endowing them with excellent mechanical properties. However, owing to this multi-principal element nature, high-entropy alloys exhibit complex deformation behavior dominated by alternating and coupled deformation mechanisms. Therefore, elucidating these intricate deformation mechanisms remains a key challenge in current research. Neutron diffraction (ND) techniques offer distinct advantages over traditional microscopic methods for characterizing such complex deformation behavior. The strong penetration capability of neutrons enables in-situ, real-time, and non-destructive detection of structural evolution in most centimeter-level bulk samples under complex environments, and ND allows precise characterization of lattice site occupations for light elements, such as C and O, and neighboring elements. This review discussed the principles of ND, experiment procedures, and data analysis. Combining with recent advances in the research about face-centered cubic high-entropy alloy, typical examples of using ND to investigate the deformation behavior were summarized, ultimately revealing deformation mechanisms dominated by dislocations, stacking faults, twinning, and phase transformations.

Abstract:To meet the growing demand for enhanced material properties of aero-engines, the alloying element content of wrought superalloys is increasing, which leads to the difficulty of ingot casting. Excessive addition of alloying elements in superalloys tend to induce cracking under the combined action of thermal stress and phase transformation stress. Once cracks occur, it will not only interfere with the stability of process parameters such as current and voltage in the subsequent remelting process, but also raise scrap rate of the ingot, and exert an irreversible impact on the performance and reliability of the final product. Cracks in ingot, as a complex metallurgical defect during superalloy casting, has become a critical technological bottleneck, restricting the size scaling of high-alloyed superalloy ingots. Then, this paper reviews the recent research progress on the causes of cracking in wrought superalloy ingots during triple-melting processes, as well as various influencing factors in crack formation. Corresponding inhibition measures are also proposed for different cracking causes. The research direction of ingot cracking is prospected, aiming to provide a theoretical basis and technical reference for producing defect-free superalloy materials.

Abstract:Tantalum, as a high-performance biometallic material with bioaffinity, is widely used in bone structure reconstruction and bone function repair. Porous tantalum exhibits excellent mechanical properties, biological properties, as well as in vivo osseointegration and bone ingrowth performance, showing outstanding clinical treatment effectiveness. This review based on recent research of our team and combined with literature analysis, reviewed the latest research progress in additive manufactured porous tantalum materials, including fabrication processes, structural design and optimization, mechanical properties, biological properties (cell-material interactions), in vivo osseointegration and bone ingrowth capabilities, and clinical applications. In particular, additive manufactured porous tantalum materials and orthopedic implants allow for the precise design and regulation of three-dimensional interconnected biomimetic porous structures, excellent static and dynamic mechanical properties, and bone conduction and bonding abilities. These materials are easy to manufacture anatomically matched personalized products, with promising applications in the repair of bone defects and the treatment of bone diseases.

Abstract:The structures of NbTi, Nb₃Sn, MgB₂, and Bi-based superconducting materials are complex. The uniformity of coordinated deformation among metals, between metals and powders, and within core wires determines the processing quality and mechanical properties of wires. The structures of wires and dies, processing parameters, and deformation conditions are important factors affecting their coordinated deformation behavior. The finite element numerical simulation method is an important engineering tool for analyzing and evaluating the coordinated deformation behavior of superconducting wires under multiple factors. This approach can accurately and intuitively simulate the coordinated rheological behavior during the forming process of multi-layer and multifilament composite superconducting wires, as well as the stress/strain distribution among composite phases and their interfaces. This review summarizes recent progress in finite element simulation of superconducting wire forming. It covers the establishment of finite element models, selection of constitutive models, and setting of boundary conditions for superconducting wire forming. At the same time, the review discusses the affecting mechanism of deformation parameters, die structure, and processing technique on coordinated deformation behavior, as well as recent advances in multi-scale analysis.