The rapid advancement of big data and artificial intelligence has resulted in new data-driven materials research and development (R&D), which has achieved substantial progress. This fourth paradigm is believed to improve materials design efficiency and industrialized application and stimulate the discovery of new materials. The focus of this work is on the emerging field of machine learning-assisted material R&D, with an emphasis on machine learning predictions and optimization design. Following a brief description of feature construction and selection, recent developments in material predictions on phases/structures, processing-structure-property relationships, microstructure, and material performance are reviewed. This paper also summarizes the research progress on optimization algorithms with machine learning models, which is expected to overcome the bottlenecks such as the small size and high noise level of material data samples and huge space for exploration. The challenges and future opportunities for machine learning applications in materials R&D are discussed and prospected.

China has the most abundant magnesium resources in the world. Magnesium and its alloys have the advantages of low density, high specific strength, good damping property, and exceptional electromagnetic-shielding and energy-storage characteristics. They are one of the most promising lightweight materials. The enhanced applications of magnesium alloys can save energy and reduce emissions and are significant to the new Chinese energy strategy. However, magnesium alloys have a hexagonal close-packed structure and exhibit relatively low ductility. A bottleneck in expanding the application of magnesium alloys is improving the ductility of magnesium alloys. For more than ten years, efforts have been made to improve the ductility and plastic deformation ability. Progress has been made in plastic-processing technologies of magnesium alloys. The novel alloy design theory “solid solution strengthening and ductilizing” and advanced preparation technologies such as “melt self-purification through varying temperature” have been established. Series of new magnesium alloys with good ductility and corresponding alloy grades have been developed, where the impurity content of iron can be reduced to below 10 × 10^-6; the elongation was more than 60% for ultrahigh plasticity magnesium alloys and is above 10% for the ultrahigh-strength magnesium alloys (UTS > 550 MPa). New plastic-processing technologies, such as asymmetric extrusion, asymmetric rolling, asymmetric modification, cyclical multipass upsetting and squeezing, expansion control large ratio forging, and extrusion and forging composite forming, have been developed. These newly developed magnesium alloys and processing technologies weaken the basal texture in wrought magnesium alloys, improving the formability of sheets, tubes, profiles, and forgings and their product quality and reducing their product cost. These technologies have been successfully applied in the processing of magnesium sheets, pipe profiles, and forgings.

Metallic and covalent materials are important structural materials. Traditional strategies for strengthening materials compromise their ductility and toughness. Recent experimental results show that twinning can simultaneously improve the strength (hardness) and toughness of copper and diamond; as the inverse relationship between the strength and toughness of materials is broken, this has become a hot research topic. By studying the strengthening mechanism of nanotwinned copper and diamond, methods to simultaneously improve strength and toughness may be found. Herein, this paper presents a comprehensive overview of the recent developments in the experimental and theoretical studies of nanotwinned metals and covalent materials. The microstructures, fabrication methods, and mechanical properties of nanotwinned metals and covalent materials are summarized. Further, the strengthening mechanism of nanotwinned metals and the hardening mechanism of covalent materials are introduced. Finally, the research trend on the mechanical behavior of nanotwinned materials is discussed in detail.

Ni-Mn-X (X = Ga, In, Sn, and Sb) alloys undergoing the first-order martensitic transformation have received attention owing to their various functional behaviors (e.g., magnetic shape-memory, magnetocaloric, and elastocaloric effects), which can be developed as materials for application in novel-intelligent sensing and solid-state refrigeration. Recently, along the line of texturation and microstructure control for the polycrystalline alloys, our group has conducted a series of explorations on the crystal structure and microstructural features, martensitic transformation crystallography, and related functional behavior of polycrystalline Ni-Mn-X alloys. In this paper, the recent progress of our group's study has been summarized.

Mg-based alloys are good candidates for solid-state hydrogen storage because of their high hydrogen storage density and abundant resource. Meanwhile, Mg-RE-TM alloys have important applications in electrochemical energy storage as negative electrodes for Ni-MH batteries. However, Mg-based hydrogen storage alloys have some disadvantages, such as high temperature and slow kinetics for hydrogen absorption/desorption, poor cycle stability, and a narrow working temperature as an electrode in a Ni-MH battery. The research progress on Mg-based alloys for hydrogen storage and negative electrode of Ni-MH battery with wide working temperature is summarized in this review, combined with our recent year's research works. First, the main methods and mechanism for tuning the reaction of hydrogen absorption/desorption of Mg-based hydrogen storage alloys are described, followed by an introduction to the progress on tuning kinetics via in-situ formation of a multiscale and multiphase composite structure through hydrogenation. Second, a series of A₂B₇ types of RE-Mg-Ni alloys with excellent electrochemical performance and a wide working temperature has been developed using multiscale and multiphase synergy for application as a negative electrode of Ni-MH battery. Finally, the newly discovered mechanism of electrochemical performance degradation is described for Mg-Ni based amorphous alloy negative electrode for Ni-MH battery, and methods for selecting new electrolyte and surface protection are proposed for promoting the cyclic stability of Mg-Ni.

Wrought magnesium alloys have a wide range of applications by controlling the microstructure and optimizing the deformation process to improve the mechanical properties. Low-alloyed magnesium alloys have great advantages in formability, corrosion resistance, and light weight. Moreover, low alloying and high performance have become important trends in the development of wrought magnesium alloys. This study reviews the research progress of low-alloyed, high-strength, high-plasticity, and superplastic wrought magnesium alloys regarding alloy composition design, strengthening and toughening mechanisms, and processing technology. From the perspective of improving production efficiency and expanding application scope, the development trend of low-alloyed wrought magnesium alloys is proposed.

Metastable β titanium alloy has excellent overall properties, including low density, high specific strength, and good forming ability. Therefore, it has been successfully used to replace traditional high-strength steels in aerospace structural components with extremely-high strength requirements, resulting in significant structural weight reduction effects and greatly improved aircraft performance. The main method for preparing high-strength metastable β titanium alloy structural components is the combination of hot forming technology and heat treatment. The prerequisite for formulating and optimizing the processes is a thorough understanding of the alloy's deformation mechanism, followed by integrated control of the microstructure and properties of the components. Meanwhile, elucidating the relationship between the high-strength metastable β titanium alloy's deformation mechanism and its micromechanical properties will aid in the development of new alloys to meet the needs of aircraft for higher performance materials. Therefore, in this article, the deformation mechanism of the high-strength metastable β titanium alloy and its microstructure control methods was focused on and discussed, and first summarizes the research progress of the plastic deformation mechanism at room temperature, expounds the factors affecting the stability of the β matrix and the corresponding deformation mechanism evolution, analogizes the comprehensive influence of α phase characteristics on dislocation movement and the resulting mechanical performance. Furthermore, this article summarizes the hot deformation behavior and mechanism of a high-strength metastable β titanium alloy, analyzes the alloy's microstructure evolution and deformation mechanism in different phase regions and deformation stages, and discusses the alloy's work hardening and softening behaviors during hot deformation. Finally, the complex interaction of dynamic recovery or dynamic recrystallization and dynamic phase transformation in the microstructure control process of high-strength metastable β titanium alloy is briefly described, and the research status and development trend of multi-scale calculation models in alloy microstructure and performance prediction are discussed.

Titanium alloys are key materials for applications in major engineering areas, such as aerospace and marine equipment. Studies on structural titanium alloys focus on strengthening and toughening the alloys, especially the latter. The mainstream structural titanium alloys comprise both α and β phases. The optimization of the strength and toughness balance relies on the control of the compositions, volume fractions, and morphologies of both phases. In this study, some recent advances along the above line are reviewed, focusing on studies on the composition design, plastic-deformation mechanism, and microstructure tuning. Rational design of the compositions of both phases improved the deformation coordination within the α phase and across the α/β interface, suppressed the precipitation of brittle ω and α₂ phases, and resulted in improved plasticity and toughness through the α-deformation twin and β-deformation-triggered phase transformation. The multiscale microstructure enhanced the strength and toughness of the titanium alloy. Using the abovementioned approaches, a series of titanium alloys with an improved strength-toughness combination were developed and fabricated. Finally, an attempt was made to predict the prospect of technology development in the field of high-strength and high-toughness titanium alloys for various applications.

The research and development progress of laser additive manufacturing technology in superalloys are summarized in this paper. The technical characteristics and application of additive manufacturing in superalloys, formation mechanism, and the types of microstructure and metallurgical defects are introduced in detail. Moreover, the defect control methods of additive manufacturing of superalloys are summarized from the aspects of laser parameters and composition design, and the direction of laser process parameter optimization and composition optimization is clarified. Finally, the future development trend and research direction of laser additive manufacturing in superalloys are summarized and prospected from the aspects of process optimization and material design.

Benefiting from the rapid development in advanced characterization technologies, solute atom clusters in metal materials can now be quantitatively characterized in a high temporal and spatial resolution. This greatly promotes in-depth investigations on solute atom clustering. As for the widely-used Al alloys, solute atom clusters are attracting increasing attention not only as precursors for the precipitates during the aging process but also as a novel approach to strengthen and toughen the Al alloys. Experimental evidence has proved that solute atom clusters can simultaneously afford high strength and great ductility, indicating potential tailoring freedom to achieve an excellent strength-ductility combination. In this paper, the recent progress in solute atom clustering associated with Al alloys are summarized, including comprehensive characterization, thermodynamics and kinetics of formation, influencing factors, strengthening and toughening, and an application example. Ultimately, from the author's point of view, possible key directions for further studies of solute atom clusters are also proposed.

Additive manufacturing (AM) can produce complicated structures accurately and freely, giving the implant a macro and micro geometry, which makes the implant match the patient's defect site and realize the needs for personalized clinical treatment. Thus, AM provides a new manufacturing method for biodegradable metals. Presently, biodegradable metals are the hotspot issues of metallic biomaterials research. Additively-manufactured biodegradable metals are new research field. In this paper, a comprehensive review on the AM of Mg-, Zn-, and Fe-based biodegradable metals, which focuses on their processes and influencing factors, mechanical properties, biodegradation behavior, and biocompatibility, is given. Finally, the future development trend of the AM biomedical metallic materials is explored.

The International Thermonuclear Experimental Reactor (ITER) project is one of the world's largest and most ambitious international scientific research collaboration projects to date. Reduced activation ferritic/martensitic steel (RAFM steel) has been selected as the candidate material for test blanket module in ITER due to its excellent mechanical properties at high temperature, high thermal conductivity, low thermal expansion coefficient, and intense neutron irradiation swelling resistance. According to the reduced activation element selection approach, RAFM steels were created using Cr-Mo ferritic heat-resistance steels. However, RAFM steels have some disadvantages, including poor high-temperature endurance and type IV cracking in fusion-welded joints. The history of development, alloying principles, microstructural design principles, microstructure evolution and control, and solid-state joining technologies (diffusion bonding and friction stir welding) were discussed in this study. The pinning effect of nanoscale MX with excellent thermal stability on dislocations has been identified as a key factor in strengthening RAFM steel. In RAFM steel, the mechanism for a discontinuous martensitic transition during isochronal cooling has been elucidated. The microstructural formation, evolution, and failure of solid-state RAFM steel joints were shown, and its mechanical properties optimization due to thermo-mechanical treatment was realized.