In recent years, the demand for high-performance aero-engines has become crucial in China, and the service environment of turbine disk alloy becomes increasingly severe. A series of high resistant cast & wrought superalloys for turbine disks, such as GH4065, GH4720Li, GH4068, and GH4151, with working temperatures > 700°C, have been studied, produced, and applied widely. The current studies on cast & wrought alloys for turbine disks in China were summarized under the categories of homogenization treatment, cogging, disk forging, and microstructure and property regulation to promote the development of these superalloys and improve their comprehensive properties. The difficulties encountered during the research and preparation of these hard-to-deform superalloys and explored the alloys' potential development trend were outlined. The review would improve the production stability of the disk superalloys and promote their development.

The continuous casting tundish is one of the key metallurgical reactors for the sequence casting process of liquid steel, which is a recent novel technology equipped with heating and temperature control units to produce improved quality casting strands and their hot rolling products. To maintain a stable casting temperature for sequence production under given superheating and casting speeds, a tundish technology equipped with heating and temperature control units is required. Aiming at addressing some issues in the application of two typical heating technologies, plasma and channel induction, in tundishes for special steel production, we investigated the heating principles and features of instrumentation. The challenges in the development and applications of plasma heating and discussed the details of the channel induction heating technique adopted in the industry were reviewed. The heating coil designs, arrangements, and the effects on the fluid flow, temperature, and magnetic fields in tundishes were also analyzed, paying special attention to inclusion removal. Finally, our recent study and applications regarding this issue are presented with special attention to the understanding, new findings, and suggestions for the novel tundish technology for its applications and further improved steel quality.

The forging-additive hybrid manufacturing technology combines the advantages of traditional manufacturing in terms of efficiency and cost with the refined, flexible, and rapid prototyping characteristics of additive manufacturing. It provides an effective solution for efficient forming of large components. The bonding zone between the wrought-substrate and laser-deposition zones is the fundamental key in the properties of the entire component. In this study, laser solid forming (a powder-feeding laser additive manufacturing technology) was used to deposit bulk samples on a wrought Ti-6Al-4V substrate that contained a bi-modal microstructure. The microstructure in the bonding zone between the substrate and laser-deposition zones under different inputs of linear energy density were studied. The results show that the microstructure in the bonding zone varied from the bottom to the top due to the different influence extents of the heat source. Because of the lower peak temperature, the bi-modal microstructure at the bottom of the bonding zone still retained the initial morphology but contained a certain degree of coarsening. A mixed structure that contained equiaxed α, lamellar α, and a large number of secondary α in the middle of the bonding zone occurred with the increase in temperature and prolonging of the holding time. Meanwhile, the peak temperature of the upper part exceeded the β-phase transition temperature, which exhibited a Widmanstätten structure consisting of lamellar α and the so-called ghost area that was formed due to insufficient element diffusion. In the tensile tests, the fracture position of all bonding samples fabricated with various linear energy densities were very far from the bonding zone, indicating a better strength of the bonding zone than that of the wrought substrate and laser-deposition part. In addition, when the linear energy density was 100 J/mm, the yield and tensile strengths of the composite fabricated sample were larger than that with linear energy densities of 133 and 200 J/mm because the feature size of the α phase in the bonding and additive zones was smaller. Both the yield and tensile strengths of the hybrid fabricated specimen decreased with the increase in the linear energy density, whereas the elongation increased.

Ca-P coating not only enhances the corrosion resistance of biodegradable magnesium alloys but also contributes to the formation of new bones and promotes bone integration around implants. However, the Ca-P coatings may have defects like porosity, low adhesion, and coarse grains, which lead to prefailure in the early stage and then the coatings cannot meet the requirements of long-term clinical service. Amino acids can induce the formation of calcium-bearing phosphates on biodegradable magnesium alloy. To clarify the influence of amino acid groups on film formation, Phenylalanine (Phe), Methionine (Met), and Asparagine (Asn) were used to regulate the degradation rate of magnesium alloy. Three amino acid-induced Ca-P (Ca-P_Phe, Ca-P_Met, and Ca-P_Asn) coatings were prepared on AZ31 magnesium alloy via a constant temperature water bath method at a temperature of 60^oC. Additionally, the morphology of the coatings, composition distributions, and phase structures were observed and analyzed via SEM, EDS, XRD, FTIR, and XPS. The corrosion resistance of the coating in simulated body fluid (Hank's solution) was investigated through electrochemical polarization, AC impedance, and hydrogen evolution tests. The formation mechanisms of amino acid additive-induced Ca-P (Ca-P_Phe, Ca-P_Met, and Ca-P_Asn) coatings on AZ31 magnesium alloy were probed. Results showed that the thicknesses of Ca-P, Ca-P_Phe, Ca-P_Met, and Ca-P_Asn coatings were about (3.47 ± 0.47), (6.06 ± 0.77), (7.63 ± 1.70), and (8.23 ± 1.37) μm, respectively. The main constituents of the amino acid-induced Ca-P coatings were CaHPO₄ and Ca₁₀(PO₄)₆(OH)₂ (HA). The results of electrochemical polarization curves, EIS, and hydrogen evolution tests demonstrated that the addition of amino acids enhanced the corrosion resistance of the Ca-P coatings, which was ascribed to the inhibition and adsorption of amino acid molecules on AZ31 magnesium alloy. The adsorption of the amino group was mainly achieved through the coupling of the lone pair electrons of nitrogen atoms with the surface, whereas the carboxyl group combined with Mg²⁺ via their oxygen atoms. Additionally, heteroatoms in amino acids could share their lone pair electrons with the vacant molecular orbitals of the magnesium alloy. A formation mechanism of amino acid-induced Ca-P coating was proposed.

Understanding the mechanism of the effects of magnetization treatment on the mechanical properties of materials for applications in magnetic field-assisted machining and magnetic treatment strengthening is of great significance. Pearlite and tempered martensite 45CrNiMoVA steels were magnetized by a pulsed magnetic field. Nanoindentation experiments were conducted to examine the effects of a pulsed magnetic field on the residual stress, hardness, and elastic modulus. The effect of pulsed magnetic treatment on the microstructure of the magnetic domain was analyzed by measuring the hysteresis loop and via magnetic microscopy. A magnetic pulse treatment could increase the residual compressive stress on the sample surface. The hardness of pearlite and tempered martensite 45CrNiMoVA steel was increased by 1.85% and 1.84%, respectively, after the magnetic pulse treatment. The magnetic pulse treatment had an insignificant effect on the elastic modulus of pearlite 45CrNiMoVA steel but had a considerable effect on tempered martensite 45CrNiMoVA steel. After the magnetic pulse treatment, the elastic modulus of the tempered martensite 45CrNiMoVA steel increased by 4.48%. In the magnetization process, the stress and strain of the micro-region material caused by the movement of the magnetic domains was the main mechanism responsible for strengthening the mechanical properties of 45CrNiMoVA steel.

As a crucial transmission component and basic component in mechanical equipment, gears have extremely high requirements for homogeneity of elements. However, the banded segregation defects in a rolled bar will reduce the hardenability of the finished gear and cause uneven deformation in heat treatment. Generally, the formation of banded defects is believed to inseparable from semimacro segregation in the bloom castings. Spot segregation in gear steel bloom and banded segregation defects in a rolled bar were experimentally studied to explore its evolution. The correlation between the spot segregation and banded defects was clarified from the aspects of morphology characteristics, position distribution, element segregation, and spacing statistics using hot acid etching, dendritic etching, electron probe microanalysis (EPMA), and statistical calculations. The evolution law of spot segregation and the possibility of elimination of banded defects in the heat treatment stage were also discussed. Experimental results show that spot segregation mainly exists in the central equiaxed crystal area of the castings, and solute elements such as C, Mn, and Cr in the segregated spot show positive segregation. The wide banded defects are consistent with the spot segregation in their geometrical location and element distribution pattern. Morphologically, there are two types of banded defects in which the dendrite microsegregation and the independently existing spot segregation are changed into separate band structures during the hot rolling process, while the interconnected spot segregations convert into a type of converged band defect through the hot deformation. Thus, more fine and coarse banded defects have been observed in the final rolled bar products than the numbers of as-cast spot segregation. Heat treatment through heating and insulation at 1200^oC can reduce the degree of solute segregation in the banded defects with a width less than 40 μm, but it shows little beneficial effect on the more coarse-sized banded defects, which suggests that they should be controlled from the original as-cast dendrite morphology during the casting process.

To satisfy the requirement for martensite stainless steel layers with high efficiency, an optimized FeNiCrMo alloy layer was prepared using the laser cladding technique. The microstructure and frictional wear behavior of the cladding layer (a single layer with a thickness exceeding 2 mm) were investigated. The results confirmed a homogeneous thickness and crack-free character of the cladding layer. In the microstructure, equiaxed, dendritic and cellular grains were distributed along the thickness direction, and martensite and Cr/Mo-rich ferrite were observed in the dendritic and inter-dendritic regions, respectively. The frictional coefficient and wear volume of the cladding layer increased under increasing applied loads in a block-on-ring wear test, and the wear mechanism was dominated by abrasive and oxidative wear types. Under higher loads, adhesive wear prevailed. In a ball-on-disc wear test, increasing the temperature decreased the frictional coefficient and increased the wear volume. Oxidative and fatigue wear dominated the wear mechanism under this condition.

Al_19.3Co₁₅Cr₁₅Ni_50.7 is a eutectic high entropy alloy with a lamellar structure and good high-temperature properties. To study the thermal deformation behavior of the samples (diameter 8 mm, height 10 mm), the samples were hot compressed using the Gleeble-3500 thermal simulation-testing machine. The true stress-true strain curves were obtained for strain rates between 0.001 and 0.1 s^-1 and deformation temperatures from 973 K to 1273 K. According to the Arrhenius model, the constitutive equation of the alloy in the strain range of 0.1-0.7 is established, and the deformation activation energy and material parameters under different strain conditions were obtained. With the strain (ε) as the independent variable, the material constants are fitted using the sixth order polynomial, such that the material constant of a certain strain, and the constitutive equation of the strain is obtained. Finally, the constitutive equation is verified. Based on the power dissipation theory and instability criterion of the dynamic material model, the power dissipation and instability diagram are constructed, and the hot working diagram in the strain range of 0.3-0.7 for the Al_19.3Co₁₅Cr₁₅Ni_50.7 high entropy alloy is established by the superposition of the two diagrams. The results show that the flow stress curve at 1273 K presents dynamic recovery characteristics, while the flow stress curve at other temperatures presents dynamic recrystallization characteristics, and the flow stress increases with a decrease in the deformation temperature or an increase in the strain rate. The constitutive equation was established and verified, and the decision coefficient R² = 0.956, which was relatively high, indicates that the established flow stress constitutive model could predict the flow stress of the alloy. After high-temperature compression, compared with the as-cast microstructure, the strip-shaped B2 phase has some bending after hot deformation, and even fracture may occur under the condition of a high-strain rate. The original fine lamellar B2 phase grows into coarse lamellar, and based on the dynamic material model (DMM) theory, the stable zone and unstable zone are determined, and the optimal process parameters are determined.

For nickel-based GH4720Li superalloys, fine-grained structures can be obtained via hot deformation in a two-phase area. However, obvious recrystallized grains' coarsening occurs because of the lack of prime γ' pinning grain boundary when hot deformation occurs in a single-phase area. Much attention is directed to the hot deformation of GH4720Li alloys with fine grains. Moreover, several studies have reported the hot deformation behavior of coarse-grained GH4720Li alloys, with maximum grain sizes of several hundred microns. However, only a few studies report about the hot deformation of GH4720Li alloy with millimeter-level coarse grains. Coarse grains recrystallize incompletely and can reduce the hot deformation plasticity of GH4720Li alloy. Thus, to clarify the coordination feasibility between recrystallization and the hot deformation plasticity of GH4720Li alloy with millimeter-level coarse grains, the hot deformation behavior of GH4720Li alloy with millimeter-level coarse grains was investigated under different deformation parameters (deformation temperature of 1130, 1160, and 1190°C; strain rates of 0.001, 0.01, 0.1, and 1 s^-1; and engineering strain of 50%) and compared with the hot deformation behavior of fine-grained GH4720Li alloy. The results show that the GH4720Li sample with millimeter-level coarse grains is more sensitive to the deformation temperature, but the fine-grained GH4720Li alloy is more sensitive to strain rate. The completely recrystallized structure of the GH4720Li sample with millimeter-level coarse grains can be obtained in the range of 1160-1190°C and 0.001-0.01 s^-1. However, a meager strain rate can cause an undesirable and obvious grain growth. After comprehensively combining the recrystallization control range and the hot deformation plasticity of millimeter-level coarse-grained GH4720Li alloy, it was found that the millimeter-level coarse-grained GH4720Li alloy should be thermally deformed at a moderate deformation temperature and a reduced strain rate of 1160^oC and 0.01 s^-1, respectively, to obtain the uniform equiaxed grains structure without cracking, and better deformation.

The classical eutectic growth theory, first developed by Jackson and Hunt in 1966, is simple and easy to use. However, the derivation of the classical model does not consider the model changes when one of the eutectic phases in transformation is an intermetallic compound. Moreover, the derivation of the model does not demonstrate the mathematical method to solve the diffusion equation and determine the Fourier coefficient, and without this, it is difficult to deeply understand and master the theoretical application. Based on the classical Jackson-Hunt theory, this study derives the eutectic growth model considering the compound phases and demonstrates the process involved in the solution of the diffusion equation to determine the solute distribution coefficient. The steps for using the model are supplemented and then the application methods of other similar models in eutectic transformations involving the compound phase are provided. The calculation of the model shows that under the same undercooling, the eutectic growth rate increases with the decrease of the compound phase concentration (CB). This parameter change compensates for the insufficient growth resistance of the compound phase owing to the small solute distribution coefficient. Therefore, the span of the eutectic phase diagram with the compound phase involved in the transition is narrowed; the smaller the solute partition coefficient of the eutectic phase, narrower is the phase diagram span.

Metallic materials are widely used in automotive, medical equipment, architecture, aerospace, and other fields. However, friction and wear are inevitable with the use of metallic materials. Therefore, it is important to study the friction and wear mechanisms of these materials for prolonging their service life. In the present work, microscratch test was carried out on sixteen metallic materials with a Rockwell C 120° diamond indenter to investigate the effects of the progressive normal force on the scratch responses of the materials. By increasing the normal force linearly from 5 mN to 30 N, both the penetration and residual depths increase linearly. The elastic recovery rate firstly increases rapidly, and then remains nearly stable. When the penetration depth is smaller than the transition depth of the indenter, only the sphere is in contact with the material, resulting in a nonlinear increase in the residual scratch width; when the conical part of the indenter is in contact with the material, the residual scratch width increases linearly. The asymptotic elastic recovery rate and scratch hardness increase linearly with the yield strength. The scratch friction coefficients of pure Mo, pure W, and 40Cr always increase nonlinearly with normal force, and the scratch friction coefficients of other metals firstly increase nonlinearly and then remain nearly stable. The variation of the scratch friction coefficient can be explained by a geometrical contact model. Adhesion friction and ploughing friction play almost the same role in the friction mechanism of QT500, and ploughing friction plays the major role in the friction mechanism of other materials under large normal forces. The asymptotic scratch friction coefficient decreases linearly with the increase of the asymptotic scratch hardness and the ratio of asymptotic scratch hardness over the elastic modulus.