The unique cyclic thermal input in laser additive manufacturing (LAM) induced by layerwise deposition manner has been one of the hot research topics. This technique has shed light on the potential of using intrinsic heat treatment (IHT) to tune microstructures and enhance the mechanical performance of materials. Therefore, this article elaborates on cyclic thermal input in LAM. Herein, the influence of process parameters, deposition direction, interlayer delay time, substrate preheating, and laser remelting on cyclic thermal input was reviewed in detail. One of our key findings was that the cyclic thermal input can significantly affect the microstructures such as grain orientation, phase composition, and second phase precipitation, which in turn affects the mechanical properties of materials. The IHT effect generated by cyclic thermal input provides an opportunity for material performance enhancement and new materials development. Hence, the understanding of internal relationships among composition-process-IHT effect-microstructures-mechanical properties is critical. This is not only essential for material performance enhancement through tailoring of IHT effect but also provides enlightenment for the research and development of LAM-specific new materials based on IHT effect.

The cleanliness, homogenization, and refinement of the high-quality steel are highly dependent on the high-temperature melt multiphase flow in the continuous casting mold. The high-temperature melt multiphase flow is unsteady-state turbulence that is coupled with heat transfer, mass transfer, phase change, chemical reaction, and electromagnetic effect, forming an extremely complex, unsteady, nonlinear, and nonequilibrium multiphysical fields, where various physical quantities are nearly impossible to on-line measure through on-site testing. With the similarity of flow and solidification processes ensured, both the physical experiment and the numerical simulation of multiscale transport phenomenon have emerged as the prime choices to study the formation mechanism of various defects in continuous casting slabs. However, in various forms, the conventional hydrodynamic problems, such as the high-temperature melt multiphase flow in various metallurgical reactors, is characterized by a considerable change in physical properties, complex constitutive equations, diverse influencing factors of phase interface, and large gradient of physical quantities near the boundary. In addition, in the multiphysical fields inside continuous casting mold, there exists complex and variable multiscale interface phenomena like large-scale interface deformation of the continuous phase, transport of discrete phase particle, and transition between continuous and discrete phase, as well as the multiscale turbulent vortex structure, which poses a great challenge to modeling of high-temperature melt multiphase flow. Compared with the single-phase flow, the multiphase flow is characterized by the topological variation of the phase interface. In this paper, the research progress on modeling the high-temperature melt multiphase flow in the continuous casting mold is discussed from the following four perspectives: the scale distribution of discrete flow interface, cross-scale phenomenon of mixed flow interface, multiscale phenomenon of solidification interface, and role of turbulence in revealing the multiscale phase interface structure. Finally, the potential study direction in the future is considered.

Advanced structural alloys that can withstand exceedingly high operating temperatures are in high demand. The high-temperature strength of these alloys needs to be above a certain level, above and beyond what can be offered by currently available alloys, while still having adequate room-temperature ductility to allow sufficient forming ability. In this study, Ta-W refractory alloys with W content ranging from 10% to 50% (atomic fraction) are prepared using arc-melting. All the Ta-W alloys are single-phase solid solutions with a bcc structure, and their average grain size decreases with increasing W content. Uniaxial compression tests are performed at both 25°C and 2000°C for the Ta-W alloys. The results suggest that the compressive yield strength of the Ta-W alloys increases with the W concentration at both temperatures, and they exhibit excellent compressive strength at high temperatures. In particular, the strength of the Ta-20%W alloy could reach as high as 236 MPa at 2000°C, a benchmark never reported for known alloys, while offering room-temperature shaping capability with a compressive strain over 40% at 25°C. A recent model based on screw dislocation activities in bcc concentrated solutions yields a reasonable prediction for the yield strength measured at both temperatures. Such Ta-W refractory alloys have the potential for load-bearing applications at extremely high temperatures.

Laboratory experiments demonstrate that the magnetic-beneficial {100} texture can be strongly produced using the so-called surface effect transformation treatment either in low-grade electrical steels or in high-grade 3%Si steels. In the latter case, the solid-phase transformation is introduced into Si steels by adding carbon and manganese elements. In addition, vacuum annealing and subsequent wet hydrogen decarburization are needed. Although such treatment differs remarkably from conventional industry production facilities, its superiority of producing extremely sharp {100} texture, immensely high magnetic induction, and low core loss keeps the method attractive for environmental friendly and high-efficiency rotating machines. Our previous results indicated that the heavy rolling reduction favors the rotated cube texture {100}<011> formation; however, the cube texture {100}<001> is expected due to the easiness of sheet cutting for iron core production in the industry. In this study, the influences of compositions on the formation of the cube texture, 25°-rotated cube texture, and rotated cube texture were investigated. The phase diagram features of the alloy consisting of strong cube texture were also examined. The aim is to establish the theoretical bases for quantitative control of the alloy composition suitable for cube texture in 3%Si electrical steels. Four steel compositions are designed using different combinations of carbon and manganese contents. Thus, the transformation temperatures, ferrite grain sizes, and pearlite volume fractions will be different, leading to distinct growth rates of {100} oriented grains during vacuum annealing at a constant temperature. They were cold-rolled by 50% reduction, which is beneficial for the cube texture formation. The results of experimental determination and calculated phase diagrams indicate that the alloy with lower carbon and Mn contents in the investigated four steel compositions shows a faster and stronger cube texture in the Mn-removal surface layer. The area fraction of the {100} texture in the Mn-removal layer of the alloy after vacuum annealing at 1100^oC for 30 min reaches 77.3%. In addition, the suitable decarburization temperature after the formation of the Mn-removal surface layer is discussed and suggested based on the calculated phase diagrams.

Under dynamic load, shear bands constitute the main deformation mode comparaed with quasistatic deformation. This study systematically investigates the influence of microstructures and strain rates of Ti-6Al-4V (TC4) alloys on their adiabatic shear behavior. TC4 alloys with three types of microstructures (lamellar, bimodal, and equiaxial) were successfully obtained via different thermal treatments. The dynamic mechanical properties, such as the critical shear strain rates of the hardening, softening transformation, maximum shear strength, critical shear strain rates of adiabatic shear-band nucleation and bearing time of the three types of microstructures were compared. Results indicate that compared with the lamellar bimodal and equiaxial TC4 alloys, the lamellar TC4 alloy shows the best dynamic mechanical properties, achieving higher shear strength and critical shear strain rates as well as the lowest adiabatic shear sensitivity. Microstructural analysis reveals that the adiabatic shear bands that formed in the three types of alloys are brittle. The width of the shear band decreases with increasing shear strain rate. Furthermore, at the same shear strain rate, the order of the widths of the shear bands is as follows: lamellar TC4 alloy > bimodal TC4 alloy > equiaxial TC4 alloy.

Selective laser melting (SLM) technology is gaining increasing attention in the field of additive manufacturing. Al-Cu-Mg alloy parts manufactured using SLM technology exhibit significant advantages in lightweight design and the integrated formation of complex structural parts in the aerospace field. However, because of their wide freezing ranges, Al-Cu-Mg alloys have a high cracking tendency at a high cooling rate. SLM technology was used to prepare Zr-modified Al-Cu-Mg alloys in this study. Al₃Zr particles were synthesized to directly add to Al-Cu-Mg alloy powders, and ZrH₂ particles were chosen to form Al₃Zr in-situ during SLM processes. The differences between the effects of adding Al₃Zr particles directly and forming Al₃Zr in-situ on the microstructures and the mechanical properties of SLMed Al-Cu-Mg alloys were analyzed. The results show that the common hot tearing in as-built Al-Cu-Mg alloys all disappear due to the addition of Al₃Zr nucleating agent and the in-situ formed Al₃Zr is more conducive to refining grains and improving the plasticity and the processing efficiency of SLMed Al-Cu-Mg alloys. When the laser energy density is 370 J/mm³, the grain size of the samples containing Al₃Zr and in-situ formed Al₃Zr particles are 1.88 and 1.28 μm, respectively. L1₂-Al₃Zr and undissolved or unmelted Al₃Zr particles are the nucleation particles generated by initial Al₃Zr particles; whereas, they are all metastable Al₃Zr (L1₂-Al₃Zr) synthesized in-situ. L1₂-Al₃Zr has a better nucleation ability than initial Al₃Zr particles. The ultimate strength of the heat-treated samples with initial Al₃Zr particles or in-situ formed Al₃Zr can reach (493 ± 2) or (485 ± 10) MPa, respectively. The elongation of the samples with the in-situ formed Al₃Zr is more than 30% higher than that of the samples containing Al₃Zr particles. SLMed Al-Cu-Mg alloys with in-situ formed Al₃Zr are more suitable for medium-high-speed processes because strong Marangoni flow aroused by high laser energy density is unnecessary for in-situ formed Al₃Zr to realize the dispersion of the grain refiner.

Electrodeposition of silicon from a cryolite-based melt is a possible solution for the mass production of silicon with high purity. Currently, deposition of Si from dissolved SiO₂ in cryolite-based melts occurs primarily in a graphite crucible using graphite and quasi-reference electrodes, resulting in series of problems, such as CO _x emissions due to carbon participation, non-significant peak positions on cyclic voltammetry (CV) curves due to melt electronic conduction, various reference standards of metal deposition potential, and insufficient investigations on electrode reaction mechanism due to melt composition complexity. In this work, a novel three-electrode electrochemical cell with Pt, O₂(air)|YSZ reference (RE), and counter electrodes (CE) was constructed using a Y₂O₃ stabilized ZrO₂ solid electrolyte (YSZ) tube, CV and potentiostat electrolysis tests were performed on Ir wire working electrode in Na₃AlF₆-5%SiO₂ (mass fraction) melt under the conditions of a complete carbon-free and 1323 K. The precipitation potentials of related metals on the cathode in the melt were investigated, and the electrodeposition law in the melt at different potentials was analyzed, using a combination of thermodynamic theoretical calculations, SEM observation, and EDS analysis. The results show that Si can be deposited on the Ir wire in a single step, and its peak potential is about -1.65 V on the CV curve, while the deposition potentials of Al, Na (Zr) are all negative than -1.8 V and increase negatively in turn. During potentiostatic electrolysis, intermetallic compound particles of Zr₅Si₄ are observed to generate at -1.8 V or -2.0 V, with a generation potential of -1.7 V to -1.8 V. The deposited Si, Al, and Na metals are mainly derived from oxygen-containing compounds produced by the Na₃AlF₆-SiO₂ melt itself but Zr metal from the ZrO₂ of the corrosion of YSZ tubes by the melt. The precipitation potentials of related metals (or intermetallic compounds) relative to Pt, O₂(air)∣YSZ RE agree well with thermodynamic calculations.

Silver-copper oxide (Ag-CuO) materials are gaining more and more interest in the low voltage switches' field owing to their lower material transfer characteristics. However, with increasing arc erosion during the make-and-break operations, the CuO microstructure's dynamic evolution is complicated by the interaction of the convection-diffusion with the flow path. Therefore, tuning the microstructure to maximize the arc erosion properties of Ag-CuO contact materials using the dynamic model is crucial for their application in switches. In this study, three-dimensional models of Ag-CuO contacts were reconstructed by phase identification and microstructure analysis, using the microstructure characteristics of the Ag-45CuO (skeleton-restricted Ag-CuO) and Ag-20CuO (island-restricted Ag-CuO) contact materials. In parallel, the arc erosion dynamics of the microstructure evolution and skeleton reconstruction process were tracked and explored by employing computational fluid dynamics simulations. Experiment and simulation findings both indicate that the repetitive thermal effect can cause the formation of a cratered and smooth molten pool surface in island-restricted Ag-CuO and skeleton-restricted Ag-CuO, respectively. The local gap of skeleton-restricted Ag-CuO contact can function as the driving force to reconstruct the CuO skeleton, the newly formed CuO with an anisotropic microstructure, which can impede Ag's segregation and evaporation in the molten pool. The restructures of CuO are unimportant for the island-restricted Ag-CuO contact, and the continuous erosion impact of island CuO can render the contact invalid. Additionally, the CuO microstructure's effect on the mechanical properties of Ag-CuO contacts was examined by employing the local three-dimensional models, which were reconstructed using the visual recognition technology combined with the finite element approach. The findings exhibit that the skeleton CuO structure was less susceptible to stress and strain concentration at the molten pool surface compared with the island CuO structure, which can efficiently disperse the local effect force on the molten pool and can substantially enhance the Ag-CuO contact's erosion resistance.

Due to their high strength and excellent anticorrosive properties, U-based amorphous alloys are quite promising for applications in nuclear-related fields. However, they face the challenge of crystallization due to high temperatures during some applications. Currently, focus on the crystallization mechanism of such materials is limited; thus, further investigation is required. Herein, using differential scanning calorimetry, both nonisothermal and isothermal crystallization kinetics of typical amorphous U₆₀Fe_27.5Al_12.5 alloy were investigated. This alloy was further analyzed using different theoretical methods. The alloy exhibited the glass transition activation energy of slightly more than 270 kJ/mol and the melt fragility value of about 22, indicating that it is a strong metallic glass material. Based on the first exothermal crystallization peak, this glassy alloy is believed to possess the crystallization activation energy of 205-275 kJ/mol within nonisothermal method and 280-390 kJ/mol within the other method. The former value is much lower than the latter, which is consistent with the results of the conventional amorphous alloys. This general trend is mainly because crystallization can be activated more easily by a continuous increase in temperature. The kinetic factor of the alloy was in the ranges of 3-4 and 2.5-3 under the nonisothermal and isothermal conditions, respectively, demonstrating that the devitrification of the noncrystalline U-Fe-Al alloy greatly depends on the nucleation process, which is prone to occur during a rise in temperature.

To obtain the stable interfacial structures of a δ'/θ'/δ' nanocomposite precipitate in Al-Li alloys, the formation enthalpy, interfacial energy, cleavage work, and ideal cleavage strength are calculated for all constructed interface structures at different growth stages. Thus, the results indicate that the δ'/θ'/δ' adopts an anti-phase a /2[110] interfacial structure when the θ' phase contains an odd number of Cu layers; conversely, it adopts an in-phase #2 interfacial structure. As θ' increases, these two structures transform by slipping a /2 along the [110] direction. Simultaneously, the heterogeneous nucleation of δ' achieves the stable δ'/θ' interfacial structure spontaneously. Under Rose's fracture model, this stable interfacial structure also possesses the highest bonding strength and the largest ideal cleavage strength. Finally, the crystal orbital Hamilton population and bond length analyses reveal the relation between the electronic bonding and structural stability. It is shown that the inter Al—Al interactions significantly influence the structural stability, which mainly originated from the 3p—3p orbital-pair contributions.

A thick-walled SUS316 saddle tube-pipe welded joint is used in nuclear power equipment. A very long computing time and huge memory space are needed to simulate welding residual stress when the thermo-elastic-plastic finite element method is used because of the complex shapes, large sizes, and many weld passes of this joint. To solve the computational problem, two efficient and accurate computational approaches were proposed based on MSC. Marc finite element software platform. In the first computational approach, the finite element model of the SUS316 saddle tube-pipe welded joint was established with the same dimensions as the actual joint. Two heat sources were used to balance the computing time and calculation precision. The moving heat-source model was used to simulate the heat input for the backing and cover passes. In contrast, the instantaneous heat-source model was employed to consider the heat input for the other passes. Considering the geometric symmetry, a quarter model was developed in the second computational approach, and the instantaneous heat-source model was used to model the heat input for all passes. In the material model, both work hardening isotropic rule and annealing effect were considered because SUS316 is sensitive to work hardening. The simulation results of the thermal cycle during the welding process and residual stress distribution in and near the fusion zone were compared using the measured data. The results of thermal cycles and the residual stress distributions obtained using two computational approaches matched the experimental measurements. When the first computational approach was used, not only the residual stress distribution in the whole welded joints could be obtained, but also the features of residual stress distribution near the weld start-end location were able to capture. The second computational approach could predict the magnitude and distribution of residual stress in the stable range of the joint and could save computing time and huge memory space. Thus, the second computational approach is useful for practical engineering applications.