Isothermal solidification process of pure metal Al was studied by molecular dynamics (MD) simulation using EAM potential. The effects of different cooling rates on the isothermal solidification process of metallic Al were studied. Al was first subjected to a rapid cooling process, and then it was annealing under isothermal conditions. The mean first-passage times (MFPT) method and Johnson-Mehl-Avrami (JMA) law were used to qualify the solidification kinetic processing, and the nucleation rate, critical nucleus size, Avrami exponent and growth exponent of grains were calculated. Results show that the nucleation rate and critical size decrease as the cooling rate increases. Also, an increase in the cooling rate leads to the increase of grain growth rate. At all investigated cooling rates, nucleation and growth processes are in the typical three-dimensional growth mode.

To investigate the microstructural evolution of wrought-nickel-based superalloy GH4169 from the original ingot to the finished product of manufacturing processes, different kinds of etchants and etching methods were used to show the fine precipitates and their morphologies. The obtained microstructures can vary in size, type, distribution, location, formation, and interactions of multiple phases, which were observed and analyzed by optical microscopy (OM), scanning electron microscopy (SEM), and an energy dispersive spectrometer (EDS). The dendrite segregation behavior of as-cast superalloy GH4169 was investigated. In addition, the microstructural evolution mechanism of second-phase particles during dynamic recrystallization was analyzed. This work sheds light on the evolution of the second-phase structure of nickel-based superalloys during the preparation process, providing guidance for process development and visual interpretation of the relationships between microstructure and properties.

Metal nanostructured materials, with many excellent and unique physical and mechanical properties compared to macroscopic bulk materials, have been widely used in the fields of electronics, bioimaging, sensing, photonics, biomimetic biology, information, and energy storage. It is worthy of noting that most of these applications require the use of nanostructured metals with specific controlled properties, which are significantly dependent on a series of physical parameters of its characteristic size, geometry, composition, and structure. Therefore, research on low-cost preparation of metal nanostructures and controlling of their characteristic sizes and geometric shapes are the keys to their development in different application fields. The preparation methods, physical and chemical properties, and application progress of metallic nanostructures are reviewed, and the methods for characterizing metal nanostructures are summarized. Finally, the future development of metallic nanostructure materials is explored.

In this paper, the research progress on the strengthening of copper and copper alloy is reviewed. The research shows that traditional strengthening methods are often accompanied by the decrease of plasticity, and there are limitations in size, cost, and other aspects in the process. The in-situ nanoparticle strengthening and plasticizing technology proposed in recent years can avoid the above problems. In this paper, the idea of in-situ nanoparticle strengthening is introduced to realize the simultaneous enhancement of strength and ductility of as-cast pure copper and tin bronze alloys. The effects of in-situ precipitation of iron-rich nanoparticles on the microstructure, and mechanical properties of different copper alloy systems, are systematically elucidated based on the former characterization and mechanical testing results. The results show that the in-situ introduction of iron-rich nanoparticles in the copper systems induces the formation of a nano precipitate-fine grain (NPFG) structure, which greatly improves the strength and ductility of copper alloys. The evolution of size, distribution, number density, morphology evolution in iron-rich nanoparticles, and the formation mechanism of NPFG structure, as well as the mechanism of NPFG strengthening and toughening, are summarized. An industrial-applicable casting process is proposed to prepare bulk NPFG structured copper alloys with complex shape, high strength, and high ductility.

A high-strength low-alloy steel with balanced strength and ductility was reported. A product of the strength and elongation (PSE) at a break of ~19 GPa% was obtained. The microstructure of the material was investigated by scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy methods. Phase transformation follows the K–S orientation relationships. Interconnecting structures generate due to the variant interactions within one prior austenite grain. The multi-phase microstructure containing both soft and hard phases contributes to good plasticity. The homogeneously distributed NbC nanoparticles make up the loss of strength ascribed to the soft retained austenite and keep the strength at an extremely high level.

The Nb-V-Ti-N-C system microelements coupling precipitation behavior in high strength naval steel was thermodynamically analyzed. The effects of micron/nano particles on the microstructure, mechanical properties, and corrosion resistance were also studied by an in situ scanning electron microscopy (SEM) tensile test, transmission electron microscopy (TEM) analysis, and electrochemical polarization measurements. The results show that the solid solution amount of Nb, V, Ti, N, or C decreases in the steels as the temperature decreases. Carbonitrides begin to precipitate at 1506.39 °C in N1 steel, and the carbonitrides are nano-scale. Meanwhile, carbonitrides begin to precipitate at 1628.74 °C in N2 steel, which is 116.69 °C higher than the corresponding liquidus temperature of 1512.05 °C; carbonitrides with micron scale are formed in the metal melt. The tensile test revealed that with the increase in titanium content from 0.05% to 0.1%, the strength increases while the elongation decreases. The in situ SEM test results indicated that lower plasticity are associated with the carbonitrides of micron-scale, which are the micro crack sources under stress. Polarization test results indicated that pitting corrosion may easily occur at the abnormally large-sized (Nb, V, Ti)(C, N) carbonitrides.