Data on diffusion kinetics of superalloys is crucial for gaining a thorough understanding of the mechanisms underlying the phase transition and microstructural evolution of superalloys. Further, it is the basis for the design and development of novel Co and Nb-Si-based superalloys. Herein, the common elements used in preparing superalloys and their corresponding functions are systematically summarized. In addition, the contribution of our research group in the establishment and improvement of databases on multicomponent diffusion kinetics of novel Co and Nb-Si-based superalloys is presented in detail. Furthermore, the machine learning method for self-diffusion coefficient and impurity diffusion coefficient, the experimental method for mutual diffusion coefficients, and the molecular dynamics method for tracer diffusion coefficients in the alloy systems are briefly discussed. In addition to providing a brief introduction of the applications of the databases in the simulation of microstructural evolution and alloy design, an outlook on the development of the databases on diffusion kinetics and related applications is presented.
Tungsten is the most promising candidate as plasma facing material in nuclear fusion reactors because of its high melting point, high thermal conductivity, low sputtering rate, and low tritium retention. However, when exposed to low-energy high flux plasma, tungsten undergoes micro/nanoscale damage, such as surface blistering and surface nanostructure, on its surface. These damage structures can degrade thermal and mechanical properties, thereby adversely affecting the reservice performance of tungsten. In this paper, the current research status of the damage behavior of tungsten when exposed to H/D plasma was focused. The research progress of the mechanisms of surface blistering nucleation and growth, as well as the effects of irradiation defects on thermal conductivity, mechanics, and service performance was summarized. These data can provide a theoretical basis for optimizing the microstructure of tungsten materials, thus improving its service performance and extending its service life.
Multiscale residual stress exists throughout the manufacturing process of engineering components, from design and production to processing and servicing. This stress can impact the machining accuracy, structural load capacity, and fatigue lifespan of these components. Therefore, accurate measurement and regulation of residual stress are critical for ensuring the longevity and reliability of engineering components. However, precise characterization of residual stress is challenging owing to its multilevel and cross-scale distribution traits and dynamic evolution under various conditions, such as temperature and load. Compared with laboratory X-ray measurement methods, neutron diffraction (ND), synchrotron-based high-energy X-ray diffraction (HE-XRD), and synchrotron-based X-ray microbeam diffraction (μ-XRD) techniques offer increased penetration depth and better time and spatial resolutions. In addition, the ability to attach environmental devices enables nondestructive and accurate in situ characterization of three types of residual stresses: macroscopic residual stress, intergranular or interphase microscopic stress, and intragranular ultramicroscopic stress. ND is currently the only nondestructive method capable of accurately measuring three-dimensional (3D) stress at centimeter-level depths within engineering components. HE-XRD, due to its high flux, excellent collimation, and millimeter-level penetration depth for metals, can be utilized for in situ studies of intergranular and interphase stress evolution and partitioning during deformation. The μ-XRD employs a submicron focused beam and differential aperture technology to analyze depth information of a sample. By conducting point-by-point scanning, it can capture 3D distribution of microscopic stress inside a single grain. Furthermore, our group has developed a novel method and device for depth stress characterization based on differential aperture technology under synchrotron-based high-energy monochromatic X-ray transmission geometry, and can measure stress gradients with high precision from the surface to the interior of engineering materials at millimeter-level depths. This study presents the measurement principles, application ranges, and applications of the above-mentioned multiscale stress characterization technologies based on the neutron/synchrotron facilities as well as envisaging the future development of related technologies.
Vibration and noise are considered as public hazards that can affect the daily life of people. The use of additional sound insulation devices or curing of components by design can reduce certain vibration and noise; however, these methods are greatly limited by weight, cost, and vibration-damping effect. Damping materials primarily convert vibration energy into other forms of energy through internal friction to reduce vibration and noise, which is the most direct and effective way to reduce vibration and noise from the material itself. As a new structurally and functionally integrated ferrous material, low-stacking-fault-energy and high-manganese transformation-induced plasticity steel has outstanding damping characteristics based on a large number of ε-martensite and stacking faults as damping sources. It also has unique comprehensive advantages in mechanical properties, cost, and scope of application, indicating its broad application potential. Based on previous research results, this paper primarily summarizes the research and development of high-manganese damping steel at home and abroad. First, the microstructural features of high-manganese damping steel are introduced, and the complex thermal/deformation-induced transformation behavior among austenite, ε-martensite, and α'-martensite is investigated. Second, the mechanical behavior, work-hardening mechanism, damping performance, and the mechanism of high-manganese damping steel are summarized and analyzed. The influence of several strengthening effects on mechanical properties is compared, and the key factors affecting the damping properties of high-manganese damping steel are clarified. Finally, the problems in the research and development of high-manganese damping steel are highlighted, and future research is prospected.
Weight reduction of materials is an eternal topic. Recently, Fe-Mn-Al-C steels with low density and good comprehensive properties have attracted considerable interests in the fields of material research and industries. In Fe-Mn-Al-C steels, various microstructures can be produced and various mechanical properties can be achieved by rationally designing alloying compositions and process parameters. In the new-generation lightweight, high-strength Fe-Mn-Al-C steels, microstructural evolution and deformation mechanisms possess many characteristics that differ from those in other steels, and several novel aspects in physical metallurgy are involved and require to be thoroughly researched. In this paper, recent progress on the role of alloying elements, the relationship between microstructures and mechanical properties, and deformation mechanisms was reviewed and the future directions of research are proposed. To provide a solid foundation for the development and applications of the new type of Fe-Mn-Al-C lightweight steels, alloy design, microstructural design and control, quantitative analysis of deformation mechanisms, and forming and service properties should be focused.
The deformation coordination of grain boundaries determines the nucleation and evolution of microvoids and affects the damage and fracture behavior of materials. However, grain boundary deformation is extremely complex and difficult to predict owing to the difference in intergranular orientation and grain stress state. Among them, two important ways of coordinating deformations are the accumulation of dislocations at grain boundaries and intergranular transfer. The geometric relationship of the activated intergranular slip systems determines the difficulty of slip transfer and the uniformity of deformation at grain boundaries. Moreover, owing to the complex grain boundary conditions of polycrystalline materials, it is difficult to accurately measure the actual stress state and deformation of grain boundaries, so there is a substantial discreteness between the experimentally observed slip transfer behavior and theoretical prediction results. Herein, based on the advantages of the crystal plasticity finite element method (CPFEM) in polycrystalline model construction, grain orientation, and mechanical boundary condition setting, the ferrite-ferrite symmetrical tilt and twist bicrystal models under different stress states was used to analyze the impact of stress state and relative grain orientation on grain boundary strain coordination and hardening behavior. The results show that the intergranular slip transfer factor and the resolve shear stress factor determine the strain uniformity at the grain boundary. The deformation uniformity at the grain boundary is positively correlated with the slip transfer factor, which mainly controls the intergranular deformation coordination behavior. However, the deformation at the grain boundaries of soft-oriented grains (determined by stress state and orientation) is uniform, and the slip transfer factor has little effect on strain coordination. When the slip transfer factor and the resolve shear stress factor are very small, strain concentration at the grain boundary easily occurs, making intergranular deformation coordination difficult. Therefore, the prediction results of intergranular deformation coordination combined with the slip transfer factor and resolving the shear stress factor are reasonable. In addition, the flow stress of the bicrystal model is negatively correlated with the slip shear stress factor, and the uneven deformation at the grain boundary easily causes geometrically necessary dislocations to proliferate and promote grain boundary hardening.
High-entropy alloys (HEAs) have attracted considerable research attention in the material field because of their outstanding mechanical properties. For metallic materials, grain boundary plays a crucial role in the mechanical behavior and plastic deformation mechanisms. To show the effect of grain boundary on deformation mechanisms in HEAs, the mechanical behavior and evolution of deformation systems in the equiatomic FeMnCoCrNi HEA bicrystals with various orientation combinations during uniaxial tension are investigated using molecular dynamic simulations, and the effect of the orientation relationship between the grain boundary and tensile direction on mechanical behavior is demonstrated. The findings reveal that for all models studied, dislocations nucleate preferentially at the grain boundary and slip into the grains on both sides. Grain boundaries are widened and curved during deformation. Necking tends to occur at the grain boundary when the grain boundary is perpendicular to the tensile direction, which decreases flow stress with increasing loading. For the model with a grain boundary parallel to the deformation direction, the model's flow stress remains at a level above 1 GPa during the whole plastic deformation. The bicrystal with a combination of [111] and [110] orientations shows the most significant fluctuation of flow stress and the highest work hardening ability compared with other models. The decrease in stress with deformation is due to the slip of numerous dislocations, while the high strain hardening ability is caused by the formation of ε-martensite, stacking faults, and twins. Furthermore, the deformation behavior of FeMnCoCrNi, FeCuCoCrNi HEAs, and pure Cu are compared. Compared with Cu, the larger lattice distortion in FeMnCoCrNi and FeCuCoCrNi HEAs makes the grain boundaries coarser, which makes dislocations easy to nucleate under loading, and the formation of ε-martensite is the most outstanding in FeMnCoCrNi HEA with a lower stacking fault energy. The results of this study can guide the design of microstructures and orientations in high-performance HEAs with micron- and nanoscaled grains.
Recrystallization texture is determined by the competition among various texture components during nucleation and grain growth. The stored energy and orientation gradient depend on the grain orientation in the deformed microstructure. Texture components, nucleating at positions with high stored energy and a sharp orientation gradient have kinetic advantages, can consume the nucleation sites and potential growth space of recrystallized grains in adjacent deformed grains. Segregation elements can hinder nucleation and growth of recrystallization grains by reducing grain boundary mobility, and thus prevent texture components with kinetic advantages from invading adjacent deformed grains. It is valuable to provide a basis for precise recrystallization texture design and control by investigating the competitive relations among recrystallization texture components under the intervention of segregation elements. The recrystallization texture competition in a body-centered cubic Fe-3%Si alloy containing Sb was studied through experiment and simulation. It was found that the segregation element can weaken the γ (<111>//ND, ND—normal direction) and strengthen the α (<110>//RD, RD—rolling direction), as well as other recrystallization texture components with low stored energy, by inhibiting the invasion of γ-recrystallized grains into adjacent deformed grains. The two dominant factors for segregation effects are deformation texture and critical invasion radius. A quantitative model, based on nucleation and growth kinetics, was proposed to explore the effect of critical invasion radius and deformation texture on recrystallization texture competition mediated by segregation elements. It was found that segregation elements can prolong the invasion incubation period and reduce the invasion rate to inhibit the consumption of α-deformed grains by γ-recrystallized grains. The inhibition effect initially strengthened and then weakened with the increasing γ deformation texture.
The rapid development of aeroengines has led to high demand heat resistant blades. As a result, fabricating techniques and designing materials have taken center stage in producing aeroengines. Additive manufacturing (AM), which integrates design and manufacturing, has advantages in preparing blades with complex cavity structures. However, commercial Ni-based superalloys have poor additive manufacturability and are prone to defects such as cracks, severely hindering the development of the AM of superalloy blades. Therefore, finding a high-performance superalloy with excellent additive manufacturability is necessary. To alleviate this problem, many crack susceptibility criteria and test methods have recently been proposed to evaluate the crack susceptibility of alloys from a compositional and/or process point of view. However, the rapid prediction of the crack susceptibility of superalloys remains a challenge, hindering the widespread screening and designing of superalloys for AM. Nevertheless, using machine learning (ML) in conjunction with thermodynamic calculation may effectively predict the properties of alloys, and this combination is anticipated to grow as an important tool for designing alloys with low crack susceptibility for AM. Based on the aforementioned context, this study reports the development of an ML prediction model after combining experimental data and thermodynamic calculations to establish a Ni-based alloy crack susceptibility database. This ML model has an excellent prediction effect (R2 = 0.96 on the training set and R2 = 0.81 on the validation set) and enables accurate prediction of the crack susceptibility of the experimental alloys and published alloys. It is verified that a hot crack is the most typical type of crack in Ni-based superalloys during AM. The influence of elements on crack susceptibility is also analyzed using the SHapley Additive exPlanation method. Precipitation-strengthening (Al and Ti) and trace (C and B) elements greatly influence crack susceptibility. A small amount of Re can inhibit cracks, but excessive amounts produce a topologically close-packed phase, deteriorating the crack susceptibility and mechanical properties. The influence of other alloying elements on crack susceptibility is roughly ranked as follows: Re, W, Cr, Mo, Ta, and Co, which can provide a screening method for the composition design of subsequent AMed superalloys.
This study utilizes the Pandat software to design a novel ternary alloy, Mg-0.2Ce-0.2Ca (mass fraction, %). The Mg alloy samples are extruded conventionally and provide high strength and low alloying with yield strength of approximately 364 MPa and total content of only approximately 0.4%. The microstructures at different stages of extrusion are characterized, revealing the existence of twin in the Mg-0.2Ce-0.2Ca alloy throughout the extrusion process, indicating high twin migration resistance. In the middle and later stages of extrusion, dynamically recrystallized grains nucleate at regions of intersected twinning variants, leading to a significant reduction in the proportion of twinning interfaces. Moreover, during the early stage of extrusion, a large number of <c + a> dislocations are stored in the Mg-0.2Ce-0.2Ca alloy, and the dislocation-dominated recovery/recrystallization mechanism is functional until the late stage of extrusion due to the high slipping resistance of dislocations. This mechanism directly contributes to the formation of ultrafine grains in present Mg alloy. The results show that the addition of Ca increases the resistance of twinning motion in the Mg matrix, while the addition of Ce and Ca induces multisystem slip, which are the main mechanisms for regulating the microstructure evolution of Mg-Ce-Ca alloy during extrusion. These findings have significant implications for the development of new high-strength, low-alloyed Mg alloys.
