Digital manufacturing revolutionizes conventional manufacturing processes into digital models, enabling intelligent control over the entire production process to rapidly create products tailored to specific requirements. Metal three-dimensional (3D) printing, a complex physical process, is characterized by strong multiphysics interactions, highly time-varying disturbances, intrinsic nonlinear relationships, and multiple variables and objectives. Achieving full-process digital control in metal 3D printing has the potential to overcome current bottlenecks, such as inconsistent part quality and unstable performance, thereby advancing high-quality 3D printing technology. This work investigates metal 3D printing characteristics and fundamental digital manufacturing principles. It subsequently provides an overview of research progress in the digital manufacturing of metal 3D printing, encompassing three critical aspects: online monitoring of the 3D printing process, digital simulation, and the interaction between physical and information systems. Finally, the work discusses the future research focus of digital manufacturing in metal 3D printing, offering insights into its development prospects.

The surging demand for Nd-Fe-B-based rare earth (RE) permanent magnets has led to a sharp increase in the consumption of critical RE elements, such as Nd, Pr, Dy, and Tb. As a result, the high cost of these elements has become a major issue. Judging from the perspective of economy and resource availablity, the overstock of abundant and inexpensive RE resources, including La, Ce, and Y, offers a new opportunity to develop cost-effective permanent magnets containing no critical RE elements. RE-Fe-B magnets based on full high-abundance REs, i.e., (Ce, La, Y)-Fe-B type magnets, are expected to serve as an alternative to fill the performance gap between hard ferrites and bonded Nd-Fe-B magnets. This approach can not only meet the diversified demand for permanent magnet materials in the middle- and low-end markets, but also contribute to a balanced use of RE resources. At present, however, the recognition and understanding of Ce-, La-, and Y-based RE-Fe-B permanent magnets still require further research, and the performance of these magnets in the laboratory is quite low, which makes practical applications difficult. Based on the latest domestic and overseas developments and the research results obtaned by the authors' research group, this review summarizes the research progress on Ce-, La-, and Y-based RE-Fe-B permanent magnetic alloys and associated densified magnets. The analysis highlights the magnetic properties and metallurgical behavior of rapidly quenched RE-Fe-B alloys, alloying composition design, and element interactions in multicomponent, rapidly quenched (Ce, La, Y)-Fe-B alloys. Moreover, the relationship between the preparation process, microstructure, and magnetic properties of bulk RE-Fe-B densified magnets is discussed. Finally, the improvement and future development trends of full high-abundance RE permanent magnets are also explored.

Normalizing is an important process that is widely employed in the industrial production of highly permeable grain-oriented silicon steel (GOSS). This is because it yields a proper microstructure, which is subsequently subjected to cold rolling, primary recrystallization, and secondary recrystallization-annealing. As a result, the sharpness Goss texture can be developed and GOSS posseses excellent magnetic properties. In this study, the influence of normalizing process parameters, including the heating rate, solution temperature, second-stage isothermal holding temperature and period for transformation, and cooling rate, on the resultant microstructures and inhibitors in the normalized GOSS were systematically investigated. Two types of distinct regions exist in the hot-rolled GOSS before normalization: the lamellar carbon-riched region elongated along the rolling direction, which is mainly composed of pearlite, and large ferrite region between the former regions. These two regions are alternately distributed from the subsurface to the center of the steel sheet. During heating and the solution processes, austenitization occurs only in the lamellar carbon-riched regions accompanying carbide dissolution, while no transformation occurs in the ferrite regions. An increase in either the solution temperature to up to 1200^oC or its period to up to 3 min leads to the formation of more austenite. And the widely adopted solution condition of 1120^oC for 3 min cannot dissolve all the formed lamellar carbides in the hot-rolled GOSS, leading to the nonuniform carbon concentration of the formed austenite in different regions. Consequently, some austenite can be retained after most of them transformed into martensite during water quenching. Moreover, all the results on microstructural characterization, in situ dilation experiment, and thermodynamic calculation show that austenitization continues to occur at the second-stage phase transformation temperature (900~950^oC), instead of the commonly believed γ→α phase transformation. Therfore, inhibitor precipitation cannot be promoted by this phase transition. Furthermore, the fine nanosized inhibitors can precipitate in the ferrite region because the inhibitor's solubility is greatly reduced with decreasing temperature and in the pearlite regions accompany with the austenitic-to-pearlite transformation during air cooling below 900^oC. An increase in the heating rate and solution temperature cause additional inhibitors in the hot-rolled GOSS to dissolve during the solution stage and reprecipitate to a fine size during the subsequent cooling. After normalization, the main types of inhibitors are AlN, the composite precipitates of AlN and MnS, and TiN.

Compared to second- and third-generation nuclear power systems, the Generation IV fission and future fusion reactors have higher service temperatures and irradiation doses, as well as harsher corrosive conditions and complex alternating loads. The structural materials for advanced reactors need to be researched and developed further. The oxide dispersion strengthened (ODS) steel has excellent high-temperature performance and irradiation resistance and is considered a promising structural material for advanced nuclear power systems. To reveal the effect of aging on microstructure and mechanical properties of ODS steel at near-service temperatures, the evolution of carbide M₂₃C₆ and nano-oxide particles (NPs) as well as the changes in the mechanical properties of 9Cr ODS steel after aging at 700^oC for varying durations were studied using SEM, TEM, and tensile testing. M₂₃C₆ rapidly precipitated along grain boundaries, gradually aggregated, and grew during early aging (≤ 200 h). While the NPs showed no noticeable change. During the midstages of aging (200 and 1000 h), NPs and carbides grew stably. In the later stages of aging (2000 and 3000 h), carbide particles grew to the micron scale. The average size and number density of the NPs tended to be stable. Compared to the initial 9Cr ODS steel, the growth rate of the average size was 19.7%, and the reduction rate of the number density was 27.1%. Dislocation cells and recovered subgrains appeared within some grains because of the pinning effect of NPs on continuous proliferation dislocations. The tensile strength rapidly decreased at the initial stages of aging. In the intermediate and later stages of aging, although the average size of the NPs increased and the number density decreased, its pinning effect was still prominent. Continuous proliferation dislocations were observed in the matrix, so the tensile strength remained stable. Furthermore, the tensile elongation was low during aging time of 1000 and 2000 h.

Although 300M steel is one of the preferred materials for aircraft landing gears and other key load-bearing components in aviation because of its ultra-high strength and excellent ductility, its susceptibility to corrosion fatigue fracture during service in “high temperature, high humidity, and high salt” marine environments is a significant safety hazard. Surface strengthening can effectively improve the corrosion fatigue resistance of materials, thereby improving the reliability of components and extending their service life. Hence, the surface nanocrystallization of 300M ultra-high strength steel via supersonic fine particle bombardment (SFPB) and its effect on the corrosion fatigue behavior of the material in 3.5%NaCl solution was systematically investigated and the surface morphology, microstructure evolution, and residual stress relaxation of 300M steel after corrosion fatigue were characterized. After SFPB, the grain size near the surface was observed to have reduced to the nanoscale, forming gradient nanostructures and high amplitude residual compressive stress. The SFPB treatment effectively improved the corrosion fatigue life of 300M steel at the same loading-stress level. After corrosion fatigue, the grain size of the SFPB-treated 300M steel remained at the nanoscale near the surface, and the increase in the loading stress level caused a significant increase in the dislocation density in the subsurface layer and the number of deformation twins. During the corrosion fatigue loading, the residual compressive stress induced by SFPB in the surface layer of 300M steel relaxed to various degrees, with the degree of residual stress relaxation being significantly higher for higher loading stress levels.

Lead-cooled fast reactors using liquid lead or lead-bismuth eutectic (LBE) alloy coolants have attracted international attention due to their unique advantages in safety, economy, and sustainable development. The availability of suitable core materials is one of the key challenges restricting the development and application of the lead-cooled fast reactor technology. Ferritic/martensitic steel is one of the important candidates for nuclear reactor fuel cladding, but the dissolution of Cr and Ni occurs in it upon contact with high-temperature LBE, resulting in cladding failure. Adding Si can improve corrosion resistance, and based on this property, previous work developed a high-Si ferritic/martensitic steel for LBE alloy-cooled fast reactor. Recently, pre-oxidation treatment was proposed to further improve the corrosion performance of steel in contact with LBE. However, the structure of the oxide film formed after the pre-oxidation of 12Cr ferritic/martensitic steel, the effect on corrosion resistance, and the failure mechanism are not clear. In this study, a pre-oxidized film was formed on the steel surface and its structure was characterized. Steel corrosion experiments using oxygen-saturated LBE at 550^oC were also performed to analyze the influence of pre-oxidation treatment on the LBE alloy coolant corrosion resistance of steel. The results demonstrated that the oxide films formed when steel is pre-oxidized at 720^oC in 1%O₂ + 99%N₂ atmosphere for 1 h are mainly (Fe, Cr)₂O₃ and MnCr₂O₄ oxides. The oxide films can effectively prevent the outward diffusion of Fe in steel and the inward diffusion of O in LBE, thereby improving the corrosion resistance of steel to stagnant oxygen-saturated LBE alloy coolant at 550^oC. However, due to the high diffusion rate of Mn and its high solubility in LBE alloys, the Mn in the pre-oxidized film will gradually diffuse and dissolve into the LBE alloy, rendering subsequently a part of the oxide film ineffective and forming a localized corrosion zone. After 1000 h of Pb-Bi corrosion, the local corrosion area on the alloy surface can reach 60%. This study revealed the microstructure, protective effect, and failure mechanism of the pre-oxidized film on the surface of high-Si ferritic/martensitic steel, and suggested research directions for further improving the effectiveness and stability of the pre-oxidized film.

TiAl alloys are considered potential structural materials because of their low density, good high-temperature strength, and creep resistance. However, their low-temperature brittleness and poor high-temperature workability lead to narrow processing windows, which hinder their industrial applications, low pressure turbine blades of high-performance engines and thermal protection system for hypersonic space vehicles, for instance. Extensive studies on alloying and hot mechanical processes have been conducted to control the microstructure and then enhance the inherent ductility of TiAl alloys. Alloying is considered as an effective method to stabilize softening phases or refine grains to optimize microstructural homogeneity and hot workability. Thus, β-solidifying γ-TiAl alloys represented by Ti-(40-45)Al-(2-8)Nb-(1-8)(Cr, Mn, V, Mo)-(0-0.5)(B, C) (atomic fraction, %) alloys were designed. Nb and Mo are added as β-phase stabilizers. Meanwhile, B, C, and Y serve as grain refiners, and they are added to increase the hot workability. However, multiple phases, precipitation, and corresponding phase transformations are introduced, leading to complex flow localization and deformation incompatibility. Therefore, considerable effort has been exerted on thermo-mechanical processing to improve the microstructural homogeneity of these alloys. The interaction among work hardening, recovery, recrystallization, and multiphase transformation under different deformation conditions easily aggravates flow localization and deformation incompatibility, which are inadequately studied. Therefore, a comprehensive understanding of the deformation behavior among multiphase β-solidifying γ-TiAl alloys is necessary. In this work, the uniaxial hot compressions of the β-solidifying γ-TiAl alloys with the nominal compositions of Ti-44Al-5Nb-1Mo and Ti-44Al-5Nb-1Mo-2V-0.2B were conducted. The microstructure of the alloys under different temperatures and strain rates was contrastively studied using SEM-BSE and TEM. The effects of V and B on the microstructural evolutions and deformation mechanisms were analyzed. The results indicated that the addition of V and B contributed considerable differences in microstructure and thermal mechanical sensibility. The Ti-44Al-5Nb-1Mo-2V-0.2B alloy showed high-temperature deformation ability. The deflection of residual lamellae and the formation of shear bands were the main deformation mechanisms, and a nearly lamellar microstructure with a nonuniform grain size was easily generated at 1250^oC for the Ti-44Al-5Nb-1Mo alloy. On the contrary, for the Ti-44Al-5Nb-1Mo-2V-0.2B alloy, the deformation-induced lamellae decomposition of lamellar (α/γ) (L(α/γ) for short)→α + γ + β/B2 and γ→α and the spheroidization or dynamic recrystallization of α and B2 grains could be promoted with the increase of deformation temperatures and decrease of strain rates. Consequently, the microstructural homogeneity was greatly improved. Furthermore, specific deformation conditions of the microstructural control, including a nearly full lamellar and nearly duplex microstructure, were presented in this work.

Al-Li alloy has become an optional material for load-bearing components in aerospace because of its low density, high specific strength, and good fatigue performance. Currently, the widely used casting process to fabricate large Al-Li alloy structural parts has the issues of active and highly toxic Li elements, high equipment cost, long production cycle, limited forming size, and low material utilization. Wire and arc additive manufacturing technology uses an arc heat source to melt the raw materials, mostly prealloyed wires, and directly deposits the materials layer-by-layer by controlling the required components using a computer. It has the technical advantages of a short processing cycle, high material utilization, and a large frame formation, providing a new possibility for forming large Al-Li alloy components. Currently, the prealloyed welding wire is usually used as a raw material for arc additive manufacturing, but it is challenging to make high-performance Al-Li alloy wire and Li is strongly ablated under a high-temperature heat source. In situ metallurgy with an arc melt pool has prepared Al-Li alloys with good internal quality and superior performance potential while reducing manufacturing costs. Therefore, exploring the controllable addition of Li elements during the deposition process is necessary. Herein, the Al-Cu-Li alloy sample was successfully fabricated using a multimaterial arc melting deposition technology combining Al-Li alloy powder and 2219 Al-Cu alloy wire. The grain morphology, phase composition, and hardness of the as-built alloy sample were further analyzed. The as-built Al-Cu-Li alloy sample comprises fine equiaxed grains of 10-20 μm with semi-continuous reticular eutectic θ (Al₂Cu) phases at the grain boundaries. T_B (Al₇Cu₄Li) and T₁ (Al₂CuLi) phases can be observed near the grain boundaries under the influence of thermal cycling. T₁ phases with significant strengthening effects can be observed in the middle and bottom of the sample. The number density of the T₁ phase is higher in the bottom part compared to the middle, but the size of the T₁ phase is relatively larger because the bottom of the sample near the substrate experienced more thermal cycling. The maximum hardness of the as-built Al-Li sample is 126.7 HV_0.1, slightly higher than that of the other wire and arc additive manufactured using 2219 Al-Cu alloys, mainly owing to the fine equiaxed grains and the T₁ phases formed via thermal cycling.

Zirconium alloys are widely used as fuel cladding materials in water-cooled nuclear reactors due to their properties such as small thermal neutron absorption cross section, good corrosion resistance to high-temperature steam and high-pressure water, excellent mechanical properties and good compatibility with UO₂. However, under loss of coolant accident (LOCA) conditions, zirconium alloy undergoes high-temperature steam oxidation and loses its structural integrity, threatening nuclear reactor safety. With the development of the nuclear power industry, increasing demands are put forward for zirconium alloys to withstand higher burnup; hence, studying their behavior under high-temperature steam oxidation during simulated LOCA is crucial. Fe is a significant alloying element in zirconium alloys, and its addition can improve their properties. Zr-1Nb alloy is a commercial alloy with excellent corrosion resistance, and adding an appropriate amount of Fe (0.1%-0.4%; mass fraction) can further enhance the corrosion resistance of the Zr-1Nb alloy under normal operating conditions. However, the effect of adding Fe on the high-temperature steam oxidation behavior of the Zr-1Nb alloy is unclear. Therefore, the oxidation behavior of Zr-1Nb-xFe (x = 0, 0.05, 0.2, and 0.4; mass fraction, %) alloys were investigated in steam at 800, 900, 1000, 1100, and 1200^oC for 3600 s using a simultaneous thermal analyzer with a steam generator. The microstructure and microhardness of the samples before and after oxidation were analyzed using a metallographic microscope and Vickers hardness tester. The results revealed that adding Fe generally reduced the high-temperature steam oxidation resistance of Zr-1Nb-xFe alloys from 800^oC to 1100^oC for 3600 s. The effect of Fe contents on the oxidation behavior of the Zr-1Nb alloy was complex and did not show a consistent change with increasing Fe content. When oxidized at 1200^oC for 3600 s, the difference in Fe content had hardly any effect on the high-temperature steam oxidation resistance of Zr-1Nb-xFe alloys. As the oxidation temperature increased, the oxidation kinetics of the four alloys generally changed from a parabolic to a linear pattern, even occurring to multiple transitions, which was closely related to the change process of the α↔β phase for the zirconium matrix and the monoclinic (m) ↔ tetragonal (t) phase for ZrO₂.

GH4169D is an age-strengthened nickel-based superalloy designed according to the improved GH4169 superalloy, which has become a remarkable candidate material for aero engines' hot-end components. However, large columnar grains and obvious anisotropy of mechanical properties often occur in this superalloy, which is fabricated by conventional wire and arc additive manufacturing (WAAM). To solve these problems, hybrid arc and micro-rolling additive manufacturing (HARAM) has been proposed. HARAM operates by combining WAAM with the rolling process. Herein, GH4169D superalloy samples were fabricated by WAAM and HARAM. Further, microstructures and mechanical properties of the samples under different heat treatments were investigated. Results show that with micro-rolling applied, large columnar grains became finer. In addition, the tensile strength of HARAM-ed GH4169D was significantly improved compared with WAAM-ed GH4169D (48 MPa in the X direction and 90 MPa in the Z direction), and the anisotropy of mechanical properties of HARAM-ed GH4169D was effectively eliminated. Homogenization plus solution plus double aging heat treatment effectively eliminated Laves segregation phase and induced the recrystallization of HARAM-ed GH4169D, leading to more finer and uniform grains than those without heat treatment, thereby, making the comprehensive properties optimal (the tensile strength and elongation were 1366 MPa and 25.0% in the X direction and 1354 MPa and 24.6% in the Z direction, respectively).

Since the 2011 Fukushima nuclear accident, much attention has been given to accident-tolerant fuel cladding coating. In this study, micro-arc oxidation (MAO) and high-power pulsed magnetron sputtering were employed to deposit MAO/Cr composite coatings on the surface of Zirlo alloy. The effects of micro-arc oxidation time on the microstructure, mechanical properties, and high-temperature steam oxidation resistance of MAO/Cr composite coatings were investigated. Results showed that when the micro-arc oxidation time was enhanced from 3 min to 9 min, the (200)-plan texture coefficient increased from 83% to 100%. Moreover, with the increase in micro-arc oxidation time, the composite coating fracture toughness first increased, and then decreased after reaching a peak of 4.64 MPa⋅m^1/2 in 6 min. After steam oxidation at 900°C for 1 h, the composite coating systems showed delamination. Among them, MAO3min/Cr and MAO6min/Cr coatings gained less weight, whereas MAO9min/Cr coating gained more weight and formed a large number of microcracks on its surface cross-section. It can be observed that the obtained composite coating with a 6-min micro-arc oxidation has both excellent mechanical properties and outstanding resistance to high-temperature steam oxidation.

Zirconium alloys have been widely used because of their good mechanical properties, corrosion resistance, and suitable neutron absorption cross section. However, with the development of engineering technology, the requirements on the service performance, safety, and microstructure stability of zirconium structural materials are increasingly high. Creep refers to the phenomenon where the strain of the material increases with time under the action of stress lower than the yield strength, which will lead to the deformation of the structural material and eventually its failure. It is also an important problem faced by zirconium cladding materials in nuclear reactors. Nanocrystalline zirconium is a strengthening and toughening method, which may also improve other properties of nuclear materials. However, there are very few investigations on the microscopic creep mechanism in the atomic scale of nanocrystalline zirconium. Improving the creep resistance of zirconium materials plays an important role in the safety of components. Therefore, studying the creep behavior of nanocrystalline zirconium and its atomic mechanism is conducive to its better application in industries. In this study, the tensile creep behavior of nanocrystalline α-Zr under different conditions was investigated via molecular dynamics simulation. The main influencing factors of the creep process were analyzed and the influence of polycrystalline structure evolution and deformation mechanism during the steady-state creep process was studied. The effect of irradiation on the creep process was preliminarily explored. Results showed that temperature, stress, irradiation, and grain size affect the creep behavior of nanocrystalline α-Zr. Increasing the temperature and stress level and refining the grains can promote the creep process. The microstructure of the system changed significantly after the creep. Some grains grew up with the creep deformation process, while others gradually shrank, or even disappeared. During deformation, the lattice distortion gradually propagated from the grain boundary to the grains, partly reducing the degree of the hcp order. Simulation results showed that grain boundary migration is the main deformation mechanism of nanocrystalline α-Zr during steady-state creep. Increasing the temperature and stress level will thicken the grain boundary and promote the microstructure evolution. After the cascade collision due to neutrons of different energy levels, a large number of point defects were produced in the system and their diffusion contributed to the creep; these defects were finally collected at the grain boundary, improving the grain boundary mobility. Increasing the irradiation energy can increase the number and size of irradiation defects, promoting the creep process of the nanocrystalline system.