Nickel and its alloys have good corrosion and high-temperature oxidation resistance. Cold-spraying (CS) can be applied to Ni and Ni-based composite coatings with good corrosion resistance, due to its advantages of low heat input, dense microstructure, high deposition efficiency, and fast deposition rate, etc. In terms of the open publications, this study summarized the prediction of the critical and particle velocities of Ni-powder particles during CS and then analyzed its deposition characteristics and bonding mechanisms; the property improvement of cold-sprayed Ni and Ni-based composite coatings can be achieved by adjusting the nozzle, powder, and gas parameters; CS combined with laser processing, shot peening, hot rolling, and other technologies can further improve the coating quality; the addition of ceramic particles can increase the strength and corrosion resistance of Ni and Ni-based composite coatings. Finally, several expectations for the widespread application of cold-sprayed Ni and Ni-based composite coatings were presented.
Preparing various types of coatings to strengthen the surface of materials is an effective technique to increase the materials' service performance. The qualities of the coatings can be considerably improved based on the service environment by altering their composition and microstructure without impacting the substrate's performance, thereby extending the equipment's service life. Recently, high- entropy alloys (HEAs) and their coatings have been the focus in materials science. The applications in surface engineering have developed rapidly owing to their outstanding strength, toughness, corrosion resistance, and wear resistance. By designing different HEA coatings and developing efficient preparation methods for surface engineering, HEA coatings are expected to be an ideal candidate for surface strengthening of key components suffering from wear, corrosion, and elevated temperature in an extreme environment. In this paper, the latest research results are detailed and the compositions, structures, properties, and wear and corrosion mechanisms of HEA coating from the characters viewpoint, classification, and preparation methods of HEA coatings are summarized. In addition, the issues that must be solved in the surface engineering field and the developing direction in the future were proposed.
The problem of inclusions is one of the key concerns in the production process of high-quality special steel grades. This study summarized the main inclusion types, and their formation, evolution, and removal mechanisms during the secondary refining process. Meanwhile, combined with studies and practices of the authors, some control measures of inclusions were also discussed. According to this study, the inclusion types after refining are generally different from that of initial deoxidation products, and the formation and evolution of these inclusions are closely related to the dissolved elements in liquid steel, e.g., Ca, Mg, and Ti. Although sometimes the compositions of the inclusions are the same, their different shapes and distributions can also lead to different grades of inclusions depending on the micrographic method. Overall, solid inclusions can be easily removed compared with liquid inclusions, and Al2O3 and MgO·Al2O3 inclusions have a higher removal efficiency in contrast to liquid CaO-Al2O3 system inclusions. Refining slag, refractory, and ladle glaze may have a great impact on the control of trace elements and evolution of inclusions in liquid steel; therefore, suitable slag basicity and slagging operations are important during the refining process. In the case of Al-killed steel grades, slag with a basicity of 4-7 leads to a good deoxidation result, while the slag basicity adjustment during the refining process is generally negative for the control of inclusions in Si-Mn-killed steel grades. Moreover, special attention should be given to the use of CaO-containing refractory. High-quality clean alloys and a suitable alloying stage can also be beneficial for the control of trace elements and the removal of inclusions in the alloys. Furthermore, during the refining process, excessive stirring should be avoided to reduce the flush-off of ladle glaze, and inclusion modification technologies should be considered with precautions. Some methods, e.g., the control of Ca content, the prevention of slag entrainment, and the removal of ladle filler sands, are helpful for the control of micro-inclusions. Recent studies on the inclusions appropriately explained many phenomena in metallurgical processes, indicating some new directions for inclusion control. In the near future, certain mechanisms (e.g., the growth of CaO-Al2O3 inclusions) still need further investigation, and some new technologies are also required to solve the known problems, e.g., complete removal of ladle filler sands.
Engineering nano-scale twin boundaries has been recognized as a novel strategy to achieve a superior combination of tensile strength, ductility, and fatigue limit in metallic materials. However, to date, the strain-controlled fatigue behavior of nanotwin (NT)-strengthened metals is still rarely explored, most possibly owing to the difficulty in preparing bulk fatigue samples. In this work, a bulk heterogeneously structured 304 stainless steel (304 SS) containing 30% volume fraction of NT bundles embedded in the micrometer-sized grain matrix was prepared and studied under constant plastic strain amplitude-controlled fatigue tests. A considerable fatigue life and much higher cyclic flow stress level, while maintaining a weaker degree of cyclic softening at larger strain amplitude, was achieved in NT-strengthened 304 SS, compared with its coarse-grained counterpart in the same strain-controlled fatigue tests. This is fundamentally distinct from the more obvious softening behavior of conventional nanostructured metals induced by strain localization at larger strain amplitude. Such exceptional low-cycle fatigue properties were attributed to the presence of a high-strength NT structure associated with novel mechanical stability and its co-deformation with surrounding grains, effectively suppressing strain localization and fatigue crack initiation.
There has been significant progress in the development of high-entropy alloys (HEAs) with unconventional compositions in the past decade to meet the demand from a wide variety of industries, such as automotive, shipbuilding, and aerospace. The fcc HEAs have attracted growing attention due to their superior mechanical and functional properties. However, these HEAs exhibit low or modest yield strength, limiting their potential industrial application. To enhance the strength of the fcc HEAs, materials researchers are exploring additional strengthening methods, such as grain refinement, solid solution strengthening, and precipitation strengthening. However, the strengthening approaches mentioned above suffer from the trade-off dilemma between strength and ductility. In this study, a new precipitation-hardened Fe53Mn15Ni15Cr10Al4Ti2C1 HEA was designed by adding Al, Ti, and C elements based on the fcc HEA. Then the HEA was treated utilizing heavy-deformation and various heat-treatment processes, tuning the microstructure and precipitate. The cold-rolled alloy microstructure presented rolling bands (including deformation twins) and a significant dislocation density. Furthermore, the HEA microstructure consists of rolling bands, high-density dislocations, and nanoscale precipitates following heat treatment at medium temperatures for an extended period. In particular, the HEA possessed a superior balance between strength and ductility, resulting from the significant precipitation strengthening effect of L12 precipitates that were coherent with the matrix in the microstructure as well as the improved strain-hardening ability due to the recovery of dislocations. The precipitation-hardened HEA with an inhomogeneous microstructure could be obtained through heat treatment at medium temperatures over long periods, which exhibited an excellent strength-ductility relationship.
With the rapid increase in thermal power generation units in China, the thermal power generation industry is facing pressures such as reducing costs, improving power generation efficiency and mitigating environmental problems. Thermal power generation units with a large capacity and high parameters result in high system efficiency, but they also amplify the corrosion failure problem of high-temperature components, especially the atmosphere/ash corrosion of outer tubes. Many studies regarding flue gas corrosion have shown that molten alkali metal sulfate can form on the surface of pipelines, causing severe corrosion damage, and the extent of corrosion is closely related to the sulfur content in raw coal. However, much attention has been paid to low-sulfur (standard coal combustion) environments in previous studies, with very few studies on high-sulfur environments. Austenitic stainless steels possessing a combination of excellent high temperature corrosion and fatigue resistances, are considered as promising construction materials for high temperature components in supercritical and ultra-supercritical fossil fuel power plants. Elements such as Cr and Nb have been shown to greatly affect the high temperature corrosion resistance of austenitic stainless steels; however few reports are available regarding the effect of Cr on corrosion resistance in high-sulfur flue gas environments and the effect of Nb on the corrosion resistance of Cr2O3-forming alloys. Therefore, in this study, the corrosion behavior of three types of austenitic stainless steels with different Cr contents was studied in a coal ash/high-sulfur flue gas environment at 700oC. Results showed that low Cr alloys formed a two-layered structure: an external Fe2O3 layer and an internal layer with Cr2O3 and CrS. Medium Cr alloys developed a similar structure oxide scale to low Cr concentration alloys, but the corrosion extent was modest. Conversely, a stable and dense Cr2O3 layer was formed on the surface of the high Cr alloys, showing higher corrosion resistance than the other two alloys. The Nb in the alloys had some influence on the corrosion resistance of the alloys. The NbC in the alloys oxidized to Nb2O5 and distributed in the oxide scale. The formation of Nb2O5 destroyed the integrity of the oxide scale and led to the easy cracking of the oxide scale.
The development of novel materials has experienced three paradigms: purely empirical, theoretical models, and computational materials science. Currently, the huge amount of data generated by experiments and simulations has facilitated a shift in materials science to a data-driven fourth paradigm. Therefore, the development of high-throughput automatic integrated computations and data mining algorithms based on material databases and artificial intelligence algorithms is critical for accelerating the design of novel materials. This paper presents an open-source distributed computational platform called Artificial Learning and Knowledge Enhanced Materials Informatics Engineering 2.0 (ALKEMIE2.0) based on the AMDIV (automation-modular-database-intelligence-visualization) design concepts. The ALKEMIE2.0 platform includes five core components of automation, modular, materials database, artificial intelligence, and visualization, which are suitable for the computational design of novel materials. The overall characteristics of ALKEMIE2.0 are divided into five pillars. ALKEMIE-Core integrates multiscale calculations and simulation software using the ALKEMIE-Plugin application programming interface. Its high-throughput calculation workflows that support 104 magnitude concurrencies are implemented by integrating the automatic frameworks of model constructions, calculation workflows, and data analyses. Furthermore, the platform is based on the ALKEMIE-Server, which can easily and automatically open daemon services and realize information interactions in distributed supercomputers. With its strong portability and scalability, ALKEMIE has been deployed in the National Supercomputing Tianjin Center. In addition, the multitype materials database called the ALKEMIE-Data Vault contains structure, task, workflow, and material property databases, which combined with the power of supercomputing, enables the rapid application of artificial intelligence algorithms in the design of new materials. In particular, the many user-friendly interfaces, which were elaborately designed using the ALKEMIE-GUI and are suitable for scientists with broad backgrounds, make structural building, work flowcharts, data analysis, and machine learning models more transparent and maneuverable. Finally, the main features of ALKEMIE2.0 are demonstrated using two examples of multiplatform deployment and high-throughput screening of binary aluminum alloys.
The development of material genomics engineering and intelligent material-processing technology provides new ideas for researching, developing, and manufacturing key thermal superalloy components of aeroengines. Based on the demand for superalloy materials and casting processing, a high-throughput dynamic simulation software system was developed. Combined with the screening criteria of nickel-based casting superalloy, a new nickel-based casting superalloy was selected and developed from more than 5.2 million-component combinations. High-temperature durability at 815oC and 400 MPa is better than foreign Inconel 939 superalloy. For the precision molding of complex superalloy casting, the data-driven process of the casting deformation is integrated, which reveals the correlation between the process parameters and size precision during solidification deformation. Thus, a data-driven process parameter optimization method is proposed herein. A data-driven casting outlet design method based on the model and algorithm, combined with the test design and multi-target genetic algorithm, which optimized the casting process parameters, was established, and the production rate of the casting process increased by 13.39% after the test verification. The combination of data-driven component design and data model-based process design will accelerate the development and application of aviation materials and components.
FeCrCo permanent magnet alloys draw wide attention because of their excellent machinability. These alloys can be deformed and extruded into thin wires or sheets for various applications, such as electric motors, telephone receivers, printers, and stereo cartridges. In these alloys, the content and distribution of Cr play an important role in improving their magnetic and hardness properties. To optimize both properties of these alloys, the effect of Cr must be studied. This study describes the effect of Cr content on microstructure, i.e., volume fraction, size, and composition of α 1 and α 2 phases in (84 - X)FeXCr15Co1Si (X = 20, 25, 30, 35, mass fraction, %) samples using atomic-resolution STEM. The effect of microstructure parameters on both Vickers hardness and magnetic properties was evaluated. STEM images showed that the average size of the α 1 phase increased from 26 nm to 55 nm with an increase in Cr content from 20% to 35%. When the content of Cr increased from 20% to 25%, the volume fraction of the α 1 phase increased by 12%, and when the content of Cr increased beyond 25%, the volume fraction remained the same. EDS results showed that with the increase of Cr content, in the (Fe-Co)-rich α 1 phase, the content of Fe decreased, whereas the contents of Cr and Co increased. By contrast, in the Cr-rich α 2 phase, the contents of Fe and Co decreased but the content of Cr increased. After step aging, hardness increased because of spinodal decomposition and continued to increase with an increase in Cr content. Remanence, coercivity, and magnetic energy product reached their maximum values when the content of Cr was at 25% and decreased as the content of Cr increased. The dependence of magnetic properties on the size, volume fraction, composition of α 1 phase, and difference in composition between α 1 and α 2 phases was discussed. The mechanism for hardening was also discussed, which increased with the Cr content.
Rare earth Mg alloys containing Gd elements can be used in aerospace, automotive, and other industrial fields owing to their high strength and creep resistance at room and high temperatures. However, the poor ductility of Mg alloys limits their application. Recently, it was discovered that the ductility of Mg alloy can be improved without compromising on its strength if sufficient amount of coarse grains is distributed in fine grains. In this study, taking the Mg-8Gd-3Y-0.5Zr (GW83K) alloy as an example, an approach for optimizing multimodal microstructures was investigated, which aimed to improve the mechanical properties of alloys. An alloy with a multimodal grain structure can be used as a particulate compound model, in which the grain boundary is considered the matrix, and different-sized grains are treated as different-types of particles embedded into the grain boundary matrix. A 2D finite element micromechanics model combined with Taylor-based nonlocal plasticity theory, which considers the size effect of the particles, was established to simulate the mechanical response of the multimodal structure Mg alloy in a tensile test. The model was verified through the experimental data of the stress-strain curve. Moreover, the effects of process parameters on the mechanical properties of the GW83K alloy were further evaluated by combining the grain structure under different annealing processes, simulated from a real space-time phase-field model as the geometric input of the finite element model. Finally, the relationships between the annealing parameters, multimodal structure, and mechanical properties of the GW83K alloy were described. The results show that the yield and tensile strengthes of the multimodal GW83K alloy presented a Hall-Petch relationship with the average grain size. The content and distribution of coarse grains greatly affected the plasticity of the GW83K alloy. By annealing the GW83K alloy at 623 K for 90 min, better plasticity could be achieved without sacrificing strength, which is helpful in promoting multimodal microstructural design.
