Nanolayered metallic composites exhibit many extraordinary properties, such as high strength, high radiation damage resistance, and good thermal stability. Therefore, it has broad potential applications in many fields. However, similar to other nanocrystalline metallic materials, the strength-ductility trade-off in nanolayered metallic composites is significant. Therefore, how to effectively balance the strength and ductility of nanolayered metallic composites is still a huge challenge in interface engineering. When the layer thickness is reduced to the nanoscale, the proportion of the interface increases substantially, and the density of mobile dislocations in grains decreases sharply, at the same time interface becomes the main source of plastic deformation. Thus, research into the relationship between the interface structure and its plastic behaviors is the key to understanding the microdeformation mechanisms of nanolayered metallic composites and their influence on mechanical properties. Based on the latest research progress, taking typical nanolayered metallic composites as examples, the key points, such as strengthening mechanisms, interface structures, plastic behaviors, and interface design methods are disscussed, and the prospects for future research trends are proposed. This review provides theoretical guidance for developing high-strength and high-ductility nanolayered metallic composites via interface engineering.

Grain boundaries (GBs) are important planar defects in polycrystalline materials, and they are crucial in plastic deformation and recrystallization of materials. A fundamental understanding of GB deformation kinetics is critical for material design using GB engineering. Although GB dominated structural evolutions have been reported to proceed via different modes, the disconnection-based model has recently become a widely acknowledged approach to unify the GB dominated plasticity. In this paper, recent progresses of GB dominated plasticity in metallic materials based on disconnection-mediated GB migration have been reviewed. Disconnection dynamics, including nucleation, propagation and interactions between different disconnections, were found dominating the shear-coupled GB migration. Lateral motion of different GB disconnections contributes to the overall GB migration, during which dynamic interactions prevail. In the three-dimensional network of GBs, GB-defect interaction and triple junctions can further influence the shear-coupled GB migration by providing extra disconnection sources, which readily change the intrinsic disconnection dynamics. These disconnection-based GB kinetics are generally applicable in the migration of GBs with different structures, as well as other modes of GB dominated deformation. Based on the aforementioned, the effects of GB plasticity on mechanical properties and deformation of metallic materials are further discussed. This review provides a unified understanding of disconnection-based GB plasticity, which not only enriches mechanistic understanding of interface plasticity in metallic materials but also holds important implications for GB engineering toward advanced high-performance metallic materials.

The 7075 alloy is widely used in the manufacture of aerospace components, such as aircraft wings and fuselage plates, owing to its high strength and light weight. Moreover, it is well-suited for manufacturing these massive aviation components using creep aging forming (CAF) technology. In this present study, the effect of creep aging on the mechanical properties of under-aged 7075 alloy was systematically studied in detail by means of a uniaxial creep tensile test and a stress-free artificial aging test. EBSD, SEM, and TEM observations were used to characterize the evolution of dislocations and precipitates with creep aging time. A quantitative analysis was performed on the relationship between mechanical properties and microstructure evolution. The results show that creep aging greatly improves the plasticity of the under-aged 7075 aluminum alloy while maintaining its high strength. The mechanical properties of the alloy are sensitive to creep stress. The sample aged for 6 h under 260 MPa and 426 K has the maximum yield strength, reaching 537.9 MPa. In comparison to the artificial aging sample, the dimple distribution of the creep aging sample is denser and the grain is more inclined toward a high Schmid factor orientation, which is 15% higher than the artificial aging sample. TEM results show that the primary phase in the crystal is η′ phase. The size of the precipitated phase in the crystal grows with increasing creep aging time from 3.04 nm for 2 h to 4.27 nm for 6 h and the volume fraction increases from 0.22% to 0.46%. The size of the grain boundary precipitates increases and the transition from continuous to discontinuous occurs. The EBSD results show that no significant change in the recrystallization and subgrain ratio occurred in any of the samples, and the average grain size remains approximately 80 μm. The distribution of geometrically necessary dislocations (GND) decreases first and subsequently increases with the extension of creep aging time. The contribution of grain boundary strengthening to the yield strength contribution model is shown to be essentially constant at about 17 MPa, and the coupling effect of dislocation and precipitation strengthening is the primary reason for the increase in strength.

7N01 aluminum alloy is the main load-bearing structure material for bullet train bodies due to its high specific strength, high specific stiffness, good magnetic-shielding ability, strong corrosion resistance, and good formability and weldability. The fatigue performance of materials and components used in bullet trains determines their security. It is unavoidable that there is pre-deformation during the assembly process of aluminum alloy components, which will influence the active service and fatigue performance of the aluminum alloy. It is important not only to clarify the relationship between pre-deformation and fatigue performance but also to reveal the mechanism of pre-deformation on the fatigue fracture of 7N01 aluminum alloy, to ensure the security of the bullet train. In this study, the effect of pre-tensile deformation on the fatigue property, fatigue fracture initiation, and fatigue crack propagation characteristics of a commercial 7N01 aluminum alloy plate at under-aged conditions was studied using tensile and fatigue tests combined with microstructure analysis. As the pre-tensile deformation increased to 20%, the results showed that the shape, size, number, distribution of second phase particles, as well as the size and morphology of thin strips grain of under-aged 7N01 aluminum alloy plate were almost the same. However, the under-aged 7N01 aluminum alloy plate has a significant strain-hardening effect after pre-tensile at room temperature, with the yield strength, tensile strength, and hardness increased from 181 MPa, 233 MPa, and 95 HV (without pre-tensile deformation) to 254 MPa, 271 MPa, and 117 HV (after 20% pre-tensile deformation), while the elongation decreased from 23.2% to 5.2%. Under the 175 MPa pulsating tensile load condition (stress ratio R = 0), the overall fatigue life of the under-aged 7N01 aluminum alloy plate first reduced, then prolonged, and then decreased as pre-tensile deformation increased. Without pre-tensile deformation, the fatigue life of under-aged 7N01 aluminum alloy plate is about 6.06 × 10⁵ cyc, and when prolonged by about 75%, it reaches about 1.06 × 10⁶ cyc after 5% pre-tensile deformation. However, the fatigue life of the under-aged 7N01 aluminum alloy plate is decreased to 4.21 × 10⁵ and 2.89 × 10⁵ cyc after 3% and 20% pre-tensile deformation, respectively. The evenly distributed high-density dislocations or dislocation cells resulted in 5%-16% pre-tensile deformation in the under-aged 7N01 aluminum alloy plate, which can prolong the fatigue life of the alloy plate by over 23%.

Lightweight Fe-Mn-Al-C steels are promising candidates for automobile structural materials and have gained increased scientific and commercial interest owing to their outstanding mechanical properties and low density. To date, several studies have been conducted to illustrate the mechanism of phase transformation, strengthening, and strain hardening under solution and aging state. Moreover, prestrain before aging as a low-cost and simple method to tailor precipitates and control properties has been widely reported; however, it has been barely investigated in the Fe-Mn-Al-C alloy system. Therefore, in this study, the effects of pre-cold rolling and two-step aging on the microstructure and mechanical properties of Fe-30Mn-11Al-1.2C (mass fraction, %) austenitic low-density steel are investigated using EBSD, TEM, and universal testing machine. Results showed that the yield strength (YS) significantly increased via the two-step aging from 580 MPa (at solution state) to 1120 MPa, but the uniform elongation (UE) sharply decreased to approximately 0. However, after the pre-cold rolling and two-step aging, the YS of the material further improved to 1220 MPa, and the UE significantly increased to 18.2%, which implies an improvement in the comprehensive mechanical properties of the material. According to the microstructure analysis, the increase in YS after the two-step aging was caused by the ordering strengthening effect of κ' carbide. Further, the pre-cold rolling could introduce heterogeneous nucleation sites, inducing intragranular precipitation. The combination of the precipitation strengthening of the precipitates and deformation strengthening induced via the pre-cold rolling further increased the YS of the material. Moreover, these intragranular precipitates could improve the work hardening capability, which is the root cause of the high plasticity of materials. This process provides a novel idea for improving the performance of austenitic low-density steels.

Zinc possesses a moderate degradation rate compared to magnesium and iron. Accordingly, it has been studied as a biodegradable metal in recent years. However, its mechanical properties barely meet the clinical requirements of implant applications. Moreover, the non-uniform corrosion mode of zinc can result in the premature mechanical failure of the implants. In the present study, a hot-extruded Zn-2Cu-0.5Zr (mass fraction, %) alloy was fabricated with improved mechanical properties and degradation behavior suitable for implant use. The microstructure of the Zn-2Cu-0.5Zr alloy was composed of a Zn matrix, CuZn₅ phase, and Zn₂₂Zr phase. Owing to the evenly distributed second phase particles and refined grain size, the yield strength, ultimate tensile strength, and elongation of the hot-extruded Zn-2Cu-0.5Zr alloy were improved to 192 MPa, 213 MPa, and 61%, respectively, which were significantly higher than those of Zn and Zn-2Cu alloy. Furthermore, the refined grains also rendered a more uniform degradation mode to the Zn matrix than Zn and Zn-2Cu alloy. In conclusion, the hot-extruded Zn-2Cu-0.5Zr alloy may find promising applications in implants.

Metallic rubidium (Rb) has great potential in various fields, such as energy, catalysis, and medical treatment. Fragmenting bulk Rb to the nanoscale is essential for its efficient application in these fields. However, as an alkali metal with a high chemical activity, Rb reacts violently with trace water, oxygen, and others; thus, preparing nanosized Rb is challenging. This study proposes a sample solid-liquid transformation and ultrasonic dispersion method to prepare Rb nanoparticles (NPs) utilizing Rb's low melting point. This method uses the ultrasonic emulsification of liquid Rb in a specific liquid (toluene) to form a colloidal Rb solution. Typically prepared Rb NPs are nearly spherical with an average size of approximately 45 nm. Further, the average size increases with a decrease in ultrasonic power. When the ultrasonic power falls to 320 and 240 W, the average NP size rises to 55 and 70 nm, respectively, demonstrating good controllability of the proposed method. Further experiments demonstrated that Rb NPs can ignite toluene at relatively low temperatures (say 120^oC) within 1 s. When the temperature is up to 250^oC, toluene can be ignited in 0.25 s. This study not only provides a new method for synthesizing Rb NPs but also offers new opportunities for novel energy-containing materials and ignition devices.

Fe-based amorphous and nanocrystalline alloys can be used for technological applications on iron core materials owing to their high permeability, low coercivity, and core loss. However, when compared to Si-steels, their application is limited owing to low saturation magnetization. Thus, the saturation magnetization of Fe-based amorphous and nanocrystalline alloys should be improved, which may reduce the content of metalloid elements, and thus, the amorphous forming ability. Consequently, as-spun Fe-based amorphous and nanocrystalline alloys with high saturation magnetization may be incompletely amorphous. In this case, annealing processes should be modified by investigating crystallization behavior because traditional annealing processes with low heating rates may degrade ferromagnetic exchange and soft magnetic properties owing to grain-size inhomogeneity. Fe₇₆Ga₅Ge₅B₆P₇Cu₁ ribbons were fabricated using the melt spinning technique, and their crystallization behavior and mechanism were studied. Results showed that two exothermic peaks are present in the DSC curve, which correspond to the precipitation of α-Fe(Ga, Ge) and Fe(B, P) phases. Under nonisothermal conditions, the initial activation energy is greater than the apparent activation energy. According to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, for an incomplete amorphous alloy, the crystallization process combines the growth of pre-existing nucleus and nucleation, whereas the nucleation rate decreases. Moreover, a rapid heating annealing process is conducive to the formation of a uniform and dispersed nanocrystalline structure. It was found that the magnetic properties of the annealed alloy with a heating rate of 100 K/min was better than those with 10 and 50 K/min. Further, the optimal initial permeability was 2.86 × 10^-2 H/m, and the coercivity was 1.77 A/m.

The plastic deformation of amorphous alloys at room temperature is limited to small shear band zones and minimal strain. However, amorphous alloys in the supercooled liquid region exhibit superplasticity and have high forming ability. Zr₆₁Cu₂₅Al₁₂Ti₂ (ZT1) and Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (Vit105) amorphous alloys have excellent forming ability and similar mechanical properties at room temperature or low temperature. They have broad application prospects as flexible components, but little work has been conducted on the superplasticity of ZT1. This work examined the rheological behavior of the supercooled liquid of two amorphous alloys to provide a theoretical basis for microplastic deformation. ZT1 and Vit105 amorphous alloys were prepared by copper mold suction casting. The high-temperature rheological behaviors of the two amorphous alloys were investigated using Gleeble3500. Variations in temperature and strain rate influence the steady-state stress obviously in the supercooled liquid region. Theological transformation behaviors of the different Zr-based amorphous alloys were analyzed based on the viscous flow model. The plastic deformation in the supercooled liquid region included brittle fracture caused by local shear in low-temperature range or at a high strain rate, non-Newtonian rheology at high strain rates in the middle-temperature range, and Newtonian rheology at low strain rates in the high-temperature range. In the plastic deformation process at a low strain rate, nanocrystals are formed inside the amorphous alloy due to the combined actions of thermal and stress driving forces. With a compressive rate less than 1 × 10^-3 s^-1, ZT1 and Vit105 exhibited Newtonian flow over the temperature ranges of 678-703 K and 703-738 K, respectively. According to the free volume model, the calculated activation volumes for ZT1 and Vit105 were 0.137-0.590 nm³ and 0.123-0.234 nm³, respectively. The much smaller activation volume in Newtonian flow was associated with the higher diffusibility and atomistic mobility of the free volume in the material. The Vit105 amorphous alloy showed higher stability and glass formability, which is more convenient for thermoplastic processing, due to the combination of a high glass transition temperature and fragility parameter.

Thirty-two groups of data of composition and performance of silver alloy electrical contact materials prepared via casting were collected from the literature to quickly find high-performance silver alloy electrical contact materials. The key alloy factors affecting the alloy properties were identified using the feature selection method. The prediction model of alloy electrical conductivity and hardness was established using a support vector machine (SVM) algorithm, which achieved the rapid design of alloy composition. Three composition designs of Ag-19.53Cu-1.36Ni, Ag-10.20Cu-0.20Ni-0.05Ce, and Ag-11.43Cu-0.66Ni-0.05Ce (mass fraction, %) with excellent predictive performance were selected for experimental validation under industrial production conditions. The error between the performance prediction and experimental results is less than 10%, the electrical conductivity of the three alloys designed is greater than 79%IACS, and the Vickers hardness is greater than 87 HV. Both the electrical conductivity and hardness are better than those of previous silver alloy electrical contact materials prepared via casting. The above results show that the machine learning composition design method established in this study has good reliability, helps improve the efficiency of alloy composition design, and quickly finds silver alloy electrical contact materials with excellent comprehensive properties.

High-end steel products play an essential role in economic development and infrastructure projects. Nowadays, continuous casting is an important production process of high-end steel products due to higher efficiency and lower energy consumption. However, the quality and properties of end products, such as steel billets, bloom, and bar, will be affected by internal segregation defects, which are closely related to solidification structure characteristics. In the research on the solidification structure characteristics of billets, the columnar to equiaxed transition (CET) determination is of great significance to determine equiaxed crystal zones and the quality control of continuous casting billets. In this work, the secondary dendrite arm spacing (SDAS) of typical dendrites was measured and analyzed using the actual solidification structure of continuous casting billets and the mutation of SDAS during the solidification process from the billet surface to the center was found. Combined with the two-dimensional temperature field numerical model of the billet cross section, it can be seen that the CET will affect the heat transfer process in the billet and this will be reflected as the mutation of SDAS in typical dendrites. This work proposed a new method for the quantitative determination of CET in the continuous casting billets based on this mutation, and the starting position of the maximum SDAS increase rate is determined as the starting position of the CET. The CET positions calculated using the new method correspond to changes in the thermal gradient and growth rate in the billet, and are consistent with the positions of the actual solidification structure morphology transformations, which prove the effectiveness of this method.