In the past decade, a unique composite system consisting of Nb nanowire and NiTi shape memory alloy matrix has attracted considerable attention. One of the works published in Science proposed that the NiTi-Nb composite has superior properties, including high strength (1.65 GPa), low Young's modulus (25.8 GPa), and quasi-linear superelasticity (6.4%). In particular, given the quasi-linear superelasticity of this composite, (1) continuous stress-induced martensitic transformation occurred even at the beginning of tensile loading, which indicated that the external stress required to start the transformation was reduced to almost zero; (2) the transformation (stress-strain) curve is a “hardening type” rather than a “plateau type,” with apparent Young's modulus of 25.8 GPa, and (3) the amount of quasi-linear superelasticity deformation is 6.4%, which is higher than that of conventional binary NiTi alloy. This work focused on the quasi-linear superelasticity property. Thus, an in situ NiTi-Nb composite was prepared by vacuum induction melting, hot forging, and wire drawing. Microscopic analysis showed that Nb nanowires were distributed in parallel inside the nanocrystalline NiTi matrix along the wire axial direction. Quasi-linear superelasticity was obtained after 9% pre-deformation, with a yield stress of 1.7 GPa, apparent Young's modulus of 34 GPa, and quasi-linear superelasticity deformation of ~5.5%, which is similar to the result proposed in Science. In situ synchrotron XRD measurements were conducted to analyze the effect of pre-deformation on the coupling effect between NiTi and Nb nanowire. The origin and deformation mechanism of the quasi-linear superelasticity were systematically studied.Results revealed that coupling tensile stress in NiTi, which was generated by pre-deformation, increased gradually with the increase of the pre-deformation strain, thereby providing a driving force for stress-induced martensitic transformation. The external stress required to start the transformation could be reduced to almost zero in some local areas as a result of the coupling tensile stress. The initial velocity of transformation increased with the increase of the coupling tensile stress in NiTi. Therefore, a continuous transformation with relatively high velocity was obtained even at the beginning of tensile loading after a proper pre-deformation. Furthermore, the gradient distribution of coupling tensile stress inside B2-NiTi led to the “hardening-type” transformation (stress-strain) curve.

Due to their excellent combination of low density, high strength, and stiffness, third-generation Al-Cu-Li-Mg alloys are important lightweight materials in the aerospace industry. Precipitation strengthening or hardening, which is controlled by precipitates, including the structure, size, morphology, distribution, and volume fraction of precipitates, is mainly responsible for the alloy's excellent mechanical properties. The precipitates in Al-Cu-Li-Mg alloys mainly include T₁, S, δ', δ'/θ'/δ', θ', GPB, and various metastable phases. In practice, the Al alloys are inevitably stored for a period at ambient temperature before subsequent processing during which natural aging occurs. Natural aging has an important effect on the precipitation behavior of subsequent artificial aging in Al-Cu-Li-Mg alloys, but the related mechanism is still highly controversial. To solve this problem, the effects of natural aging treatment on the microstructure and mechanical properties of an Al-2.95Cu-1.55Li-0.57Mg-0.18Zr alloy treated by artificial aging at 160^oC were investigated using TEM, three-dimensional atom probe (3DAP), three-dimensional electron tomography (3DET), and mechanical property testing. It was discovered that natural aging significantly changed the artificial aging hardening behavior and caused two strengthening peaks in the alloy's hardness curve. The Mg-rich and Cu-Mg clusters and δ' precipitates formed during natural aging were first dissolved at the initial stage of artificial aging, which resulted in a decrease in hardness. Then, large numbers of GPB zones formed uniformly and dispersedly, followed by the formation of T₁ precipitates with the increase of aging time, which caused the increase in hardness. The hardness reached its first peak value at 96 h. Following that, GPB zones dissolved and the hardness decreased again. When the aging time was continuously exceeded, the volume fraction of T₁ precipitates and the number of lath-like S precipitates increased, so the hardness increased again and reached the second peak value at 192 h. In other words, the atomic clusters that form during natural aging can significantly modify precipitation behaviors and the evolution of mechanical properties during artificial aging.

As lightweight requirements rise in transportation, aerospace, and other industries, magnesium alloys have a great application prospect. However, the low formability capabilities of magnesium alloys lead to a severe limit in applications. At present, there are many reports on the influences of texture and second phases on the formability of magnesium alloys at room temperature. Nevertheless, the dominant factors affecting the formability performance of magnesium alloys at room temperature are not clear. In this study, the development of the microstructures and texture of Mg-xZn-0.5Er (x = 0.5, 2.0, 3.0, 4.0, mass fraction, %) alloy sheets were studied, and the impact of the texture and second phases on the formability of these sheets were also investigated. The findings showed that the increase in Zn addition led to an early and complete dynamic recrystallization (DRX) in Mg-Zn-Er alloys sheets, and these recrystallized grains would expand significantly during subsequent hot rolling processes. These recrystallized grains with a large size were typically elongated and then helped to create a strong basal texture. Thus, it was discovered that the microstructures of these sheets were typically made up of equiaxed and elongated grains. The formability performance of these sheets was strongly related to the size of the second phases and the texture. The formability of the sheets containing microscopic second phases mainly depended on the basal texture, while the formability of the sheets which contained coarse second phases was mostly influenced by the second phases and basal texture. Particularly, when the component of the coarse second was larger, the formability would get more inferior due to the predominant role of the second phase at room temperature.

Recently, medium-Mn steel, used in the automotive industry, has attracted increasing attention as the one of the most promising candidates for the third generation of advanced high strength steels owing to its reasonable cost and excellent mechanical properties. In this study, the effect of intercritical annealing temperature on the microstructure and mechanical properties of a new composition steel was investigated, and its strengthening mechanism and related reasons were analyzed. In addition, a ultra-high product of strength and plasticity (> 70 GPa·%) of hot rolled medium manganese steel with a segregation band was eventually obtained. The results show that the grain size and orientation in the packet (defined by the original austenite grain boundary) significantly affect the mechanical properties and deformation microstructure of the material obtained under different temperatures. The obvious precipitation and dissolution processes of carbides occur at higher temperatures, and thus influence the mechanical stability of reversed austenite. During the tensile process, because it is easier to deform, the favorable packets in the non-segregation zone form an elongated-strip fine-grain zone along the loading direction, while the unfavorable packets form fragmentary grain regions. Moreover, martensite transformation preferentially occurs at the obvious orientation inside the austenite grain and the boundaries where large strain is accumulated. Through coordinated deformation, the adjacent packets eventually tend to form alternate distribution of the two kinds of micro-zone substructures, which is accompanied by the significant evolution of low-angle grain boundaries related to the dislocation activity. Due to the wide distribution of grain size in one packet, the reversed austenite in the non-segregation zone can withstand large deformation, which makes the austenite in the segregation zone undergo sufficient strain-induced martensitic transformation (SIMT), to obtain excellent combination of strength and toughness.

The grain boundary diffusion (GBD) process is a remarkable achievement in sintered Nd-Fe-B permanent magnet manufacturing. Furthermore, the coercivity can be considerably improved by diffusing heavy rare earth (HRE) elements into the magnet along the grain boundary, and the reduced HRE consumption can also be realized. However, compared with parameters of GBD, previous research has focused less on improving the magnet. In this study, the magnet was prepared using low melting point alloy Nd₉₀Al₁₀ before GBD modification, after which the corresponding Tb-GBD was completed. The magnetic property results indicated that the coercivity increased to 1439 kA/m, which was 530 kA/m higher than the unmodified magnet. Thus, the effects of the grain boundary structure and composition on the coercivity were analyzed. The addition of Nd₉₀Al₁₀ did not affect the Curie temperature of the magnet, but it reduced the low-temperature phase transition temperature. The Tb replaced Nd at the margin of main phase, which moved the diffraction peak to the right in the XRD spectrum. Moreover, a clear Tb-rich shell surrounding the main phase formed in the diffused magnet modified by Nd₉₀Al₁₀ at the depth of 20 μm, and the shell could still be clearly observed at 100 μm. However, the main phase was surrounded by the continuous grain boundary when the depth increased to 500 μm in Nd₉₀Al₁₀ modified magnet by GBD. The Tb-rich shell was observed by TEM and a noncrystalline Nd-rich phase was observed. The content peak of the Nd element appeared in the central region of the Nd-rich phase. This, the diffused depth and usage efficiency remarkably improved, because the Nd-rich phase acted as a channel for Tb diffusion, with the concentration of Tb being as high as 35%.

Titanium (Ti) and its alloys have been widely used in the medical field for dental and orthopedic surgeries owing to their excellent mechanical and biological properties. However, much effort has been devoted to the surface modification on Ti-based implants for better biological response in medical applications. Bioactive layers with micro- and nano-scale structures and morphologies can increase the specific surface area of the implants and facilitate rapid osseointegration, which has shown good biological behaviors both in the laboratory and clinical setting. Sandblasting and acid-etching (SLA) technology has become one of the most commonly used surface modification processes for currently marketed dental implants, since it can be easily operated and is efficient. However, studies on etching behavior are still limited. In this study, concentrated hydrochloric acid ((36%-38%)HCl, mass fraction) and mixed diluted acid (20%HCl : 30%H₂SO₄ = 1 : 1, volume fraction) were used to etch Ti6Al4V, and an ultrasonic field was applied to the acid etching treatment. The influence of different etching parameters on the surface structure and morphology of Ti6Al4V was discussed, including the acid etching reagent, acid etching time, and ultrasonic field. Moreover, through the combination of SLA and induction heating treatment (IHT) oxidation, the micro- and nano-scale hierarchical structure was prepared on the surface of Ti6Al4V. The evolution of surface topography, chemistry, roughness, wettability, and bioactivity of the hierarchical structure was discussed. The micro-scale composite pores combing dozens of micron pores and several micron pores were obtained by SLA. Within a certain etching time range, with the prolonging of the etching time, the step structure on the inner wall of the micro-pores becomes more obvious, and ultrasound can accelerate the acid etching. After the IHT at 800^oC, the micro- and nano-scale hierarchical surface with micro-scale composite pores and nanoscale oxide was obtained. Compared with the SLA surface, there was a decrease in surface roughness and an increase in wettability. Furthermore, after soaking in simulated body fluid (SBF) for 14 d, a homogeneous hydroxyapatite (HA) layer was formed on the micro- and nano-scale structured Ti6Al4V surface, suggesting high biological activity of the fabricated structure.

The corrosion behavior of engine materials of airplanes working in marine environments is accelerated by the synergistic effects of NaCl particles and water vapor at high temperatures. This work examined the corrosion behavior of GH4169 alloy with a NaCl solution spraying at 600^oC using an oxidation kinetics test and micro characterization technology in the aspects of corrosion kinetics, corrosion layer phase composition, and microstructure. The weight gain of the GH4169 alloy corroded in the NaCl solution spraying environment was much lower than that in solid NaCl + wet O₂ after 20 h corrosion at 600^oC. The corrosion products of the GH4169 alloy in the NaCl solution spray environment were less complex than those in the solid NaCl + wet O₂ environment, but they were denser. In addition, Cl was concentrated in the inner layer of the corrosion products and accelerated the corrosion of GH4169 alloy via an “active oxidation” mechanism at the initial stage. When NaCl deposition was increased, the corrosion mechanism of GH4169 alloy changed gradually to Cl-induced “active oxidation.” The sensitivity of GH4169 alloy in the NaCl solution spray environment at 600^oC was analyzed. Overall, the sensitivity of elements in GH4169 alloy to chlorine activated corrosion was Ti > Al > Nb, Cr > Fe > Mo, Ni, whereas the sensitivity of the oxides was TiO₂ > MoO₂ > Cr₂O₃(Nb₂O₅) > Fe₂O₃ > Al₂O₃ > NiO.

Atmospheric corrosion is ubiquitous in transportation, infrastructure, and other areas, and it always reduces the service life of materials. Bogie, an important component of the high-speed railway, performs bearing, guiding, damping, traction, and braking. The safe operation of the high-speed railway is inextricably linked to its service performance. However, for the high-speed railway bogie, its service environment constantly changes as per the operation of the train and being in various atmospheric environments, such as the ocean, pollution, damp-heat, and severe cold for a long time. Therefore, special attention must be paid to the effect of atmospheric corrosion on its service life. The use of weathering steel in bogie has effectively balanced the cost and service life. With the advancement of science and social growth, previous materials are no longer capable of meeting the current service life requirements. G390NH is provided for investigation as a newly designed weathering steel for the bogie. In this study, the corrosion behavior and the product layer evolution law of high-speed rail bogie steel G390NH in simulated marine and industrial atmospheric environments are investigated using periodic wetting tests combined with corrosion kinetics, conventional electrochemistry, microscopic morphology, and corrosion product composition analysis. It demonstrates that the two ions (Cl^- and $SO_{3}^{2-}$) have different corrosion mechanisms on the material. In simulated marine atmosphere environment, Cl^- has a higher penetrating capacity, and the rust layer consists of unsteady Fe₃O₄ and γ-FeOOH; furthermore, coupled with the effect of alternating dry and wet, corrosion always maintains a high rate and the rust layer does not give a very effective protection function. However, in the acidic $SO_{3}^{2-}$ environment, although the corrosion is accelerated, a layer of corrosion-resistant Cu is enriched in the inner rust layer and simultaneously, and a large amount of α-FeOOH is promoted, which greatly enhances the corrosion resistance of the rust layer.

The rapid development of rail transit has led to the proposition of higher requirements for the mechanical properties of springs and spring steels. Thus, bogies have been identified as the key components for trains to achieve high speed since they are connected with train bodies and wheel sets through springs. Alternatively, since the properties of spring steel materials have an important effect on the safety and comfort of high-speed trains, the development of spring steels with ultra-high strength and good plasticity has attracted the attention of researchers and industrial circles. However, simultaneously improving strength and plasticity has remained an important challenge for the research and development of high-end steels. Notwithstanding, machine learning has recently made substantial progress in designing and predicting various materials, and is expected to become a powerful tool for clarifying the relationship between the composition, process, and properties of complex alloys like steels. Based on the above background, this study reports the realization of rapid chemical composition and heat treatment process-design parameters for new spring steels, using a performance-oriented machine learning design system with high strength and good plasticity (tensile strength (2050 ± 50) MPa, elongation 10.5% ± 1.5%) after collecting literature data on spring steels and other typical quenched + tempered steels. Experimental studies were also carried out to obtain a further optimized heat treatment process (heating at 950^oC for 30 min and oil quenching + tempering at 380^oC for 90 min and water cooling). Investigations revealed that the tensile strengths of the two new spring steel materials developed were 2183.5 and 2193.0 MPa, their yield strengths were 1923.0 and 2024.5 MPa, their elongations after fracture were 10.5% and 9.7%, and the area reductions were 42.4% and 41.5%, respectively, with grain boundary strengthening and dislocation strengthening being the main strengthening mechanisms of the new spring steels. It was also observed that the fine grain size and appropriate amounts of austenite made the spring steels maintain good plasticity and have ultra-high strength. Moreover, compared with the existing ultra-high strength steels at the same strength grade, the new spring steels had significant technological and cost advantages. Hence, based on the above research, a new method and theory are provided to design chemical composition and heat treatment processes for quenched and tempered steels.

UN is a candidate fuel for light water reactors and fast reactors due to its high density, high thermal conductivity, and high melting point. The highly densified UN particles are desirable to strengthen the fuel structure and delay the release of fission gas. However, the mechanism of densification during sintering is still unclear from the view point of existing experimental results. Therefore, it is essential to simulate the densification process during sintering using the phase-field (PF) method. In the present work, the rigid body action of translation and rotation was introduced in the PF model. This work analyzed the effects of the advection flux of rigid body motion on the formation of the sintered neck, the equilibrium dihedral angle, and the densification during sintering. The simulation results showed that the introduction of advection flux of rigid body motion accelerated the formation of the sintering neck in the early stage of sintering, while such an effect was not obvious in the later stage. The equilibrium dihedral angle of the model with advection flux was consistent with that of the model, which only contained surface diffusion. The densification stomatal shrinkage was divided into three stages: surface diffusion dominated stage, advection flux dominated stage, and final densification progress. The increase in translational mobility accelerated the densification speed and increased the final density after densification, although this effect reached saturation after a certain threshold. Stable trigeminal grain boundaries (GBs) with 120° were formed when densification was completed. The characteristics of the sintered morphology of polycrystalline UN, such as trigeminal GBs, pore shrinkage, and densification, were consistent with the experimental results.

The flow and interaction between slag, metals, and bubbles are very complicated phenomena in metallurgical processes, such as desulfurization in hot metal pretreatment, steelmaking process in a converter, and second refining process. The molten steel or hot metal can be entrained into the slag when a bubble or bubbles flow through the slag-metal interface during the metallurgical process. The bubble entrainment behavior can increase the heat and mass transfer and, in turn, increase the chemical reaction efficiency of the slag-metal interface. Investigating the entrainment behavior helps in understanding the interaction between bubbles and liquid phases. The current study focuses on the effects of bubbles and slag properties on the bubble entrainment behaviors at the slag-metal interface. The results show that the bubble size is the most important factor influencing the entrainment, followed by the slag density. The slag viscosity and interfacial tension of the slag-metal interface show a weaker effect on the entrainment. In particular, the entrainment volume of steel and maximum area of the slag-metal interface increase by 7.41 and 3.67 times when the bubble diameter increased from 10 to 16 mm, respectively. When the slag density increases from 2000 to 5000 kg/m³, the entrainment volume of steel and maximum area of the slag-metal interface increase by 62.3% and 13.1%, respectively. The increasing in slag viscosity and interfacial tension is less affected by slag entrainment and interface area. The entrainment volume of steel and maximum area of the slag-metal interface are decreased by 30.6% and 6.4% when the interfacial tension of the slag-metal interface increases from 0.65 to 1.10 N/m, respectively. Similarly, when the slag viscosity increases from 0.05 to 2.0 Pa·s, the entrainment volume of steel and maximum area of the slag-metal decrease by 18.4% and 10.2%, respectively.

Activity interaction coefficients for solutes in alloy melts can be predicted by combining Miedema model with extrapolation models. However, the treatment of the binary interaction terms in traditional extrapolation models lacks a clear physical mechanism, which reduces the prediction reliability of models based on traditional extrapolation. The unified extrapolation model (UEM) can mathematically cover all traditional extrapolation models by introducing the contribution coefficient determined by property difference between two elements. In this study, a new model for activity interaction coefficients was built by using UEM to couple with the Miedema model and Tanaka excess entropy relation. The new model can explain the prediction characteristics and application scope of models based on traditional extrapolation in terms of the relation between the contribution coefficient and the property difference. The obtained results favorably agree with the experimental results.

The modification of eutectic Si to fiber morphology from coarse plate-like morphology is essential for producing an Al-Si hypoeutectic alloy. Furthermore, chemical modification through the addition of modifying elements, such as Na and Sr, to melt is the most widely used method in industrial production to improve microstructures. Recently, the effect of rare earth metals on the eutectic Si modification has also attracted considerable attention, especially for the economical element La. Key factors influencing eutectic Si modification in Al-Si hypoeutectic alloy by trace La are theoretically explored. The results demonstrate that the solubility of La in the primary α-Al phase and interaction parameter between La and Al (or Si) primarily contribute to the eutectic Si modification. When the addition level of trace La is within its solubility in the primary α-Al phase, La distributes in α-Al and eutectic Si, and the modification effect increases with the La addition level. When the addition level of trace La is greater than its solubility in α-Al, a ternary compound containing Al, Si, and La exists before the eutectic reaction due to the significant value of the interaction parameter between La and Al (or Si). Calculated results further prove that the composition of the ternary compound is AlSiLa due to the substantial value of heat for the formation of AlSiLa and the small value of interfacial energy between Al melt and AlSiLa. Under this condition, La distributes in α-Al, AlSiLa, and eutectic Si, and the La content in α-Al and eutectic Si almost remain constant. Thus, the modification effect almost stays unchanged with La addition. A suitable modification effect is achieved when the La addition level is around its solubility in the primary α-Al phase.