With the advancement of technology, the exploration of space, oceans, and underground resources continues to deepen. An ever-increasing demand for devices that operate under extreme conditions propels the need for the precise control of the thermal expansion properties of the materials used. Zero thermal expansion metals exhibit constant dimensions despite temperature variations, a unique feature that imparts these metals a significant application value in high-precision and high-stability devices. This article summarizes the research progress on zero thermal expansion metals since the discovery of Invar alloy over a century ago. It provides an overview of the definition, classification, and historical development of zero thermal expansion metals. Furthermore, this article introduces several main mechanisms inducing zero thermal expansion in metals and highlights several categories of metals with excellent zero thermal expansion properties and high application value. Moreover, it discusses the crystal structures, zero thermal expansion properties, and methods for controlling the thermal expansion properties of different types of metals. The coupling relationship between the magnetism, phase transitions, and thermal expansion properties is explored. Finally, the article provides a perspective on future trends in the development of zero thermal expansion metals.

The FGH4720Li superalloy is produced by GH4720Li through the powder metallurgy (P/M) process, a method that effectively addresses the shortcomings of the original alloy production process, such as significant segregation, low alloying levels, and manufacturing difficulties. The P/M method also results in a finer and more uniform microstructure. However, during the service life of superalloys, the thermodynamic conditions can degrade the microstructure, potentially affecting their mechanical properties. There is currently limited research on how the microstructure and properties of FGH4720Li P/M superalloy evolve under near-service conditions. Therefore, it is essential to investigate this evolution to provide valuable insights for the manufacture of turbine disks. In this study, the microstructure evolution of FGH4720Li P/M superalloy and the variations in its yield strength have been examined after subjecting it to stress rupture for 500, 1000, and 2000 h at 600 and 650 ^oC under a stress level of 500 MPa. The results show that the yield strength of FGH4720Li P/M superalloy remains relatively high, at 1120 MPa, after stress rupture at 650 ^oC. Furthermore, the microstructure of FGH4720Li P/M superalloy undergoes a complex transformation during stress rupture. The secondary γ' phase's morphology gradually changes from an ellipsoidal shape to a flowerlike shape and ultimately to a cubic shape with rounded corners. The coarsening in the polymerization growth of tertiary γ' phases is also observed. To understand the changes in yield strength after stress rupture, a precipitation strengthening prediction model specifically designed for high γ' phase content and a multi-mode distribution of γ' phases was utilized. This calculation confirmed that the alteration in the content and size of the tertiary γ' phase is the primary factor responsible for the yield strength changes in the alloy.

Primary Mg-air batteries have attracted considerable attention in the field of standby emergency energy storage in the wilderness because of their high theoretical voltage (3.1 V) and appreciable specific energy (6.8 kWh/kg). However, because of the severe self-corrosion and sluggish anodic kinetics of Mg anodes, the actual performance of Mg-air batteries is far from the theoretical limits. To synergistically enhance the discharge voltage and specific energy of Mg-air batteries, a low-alloyed Mg-1Ag (mass fraction, %) anode was developed, and its microstructure, electrochemical behavior, and discharge properties were evaluated. The results showed that the extruded alloy mainly consisted of equiaxed grains with an average grain size of (14.19 ± 2.27) μm. The anode studied exhibited a typical extrusion texture with a basal pole perpendicular to the transverse direction, and the texture intensity was 11.05. Additionally, the extruded alloy was shown to exhibit localized segregation of Ag. The Mg-air battery based on the Mg-1Ag alloy as the anode exhibited a stable discharge process. In addition, the cell voltage and specific energy reached 1.344 V and 1374.34 mWh/g at 10 mA/cm², respectively. The acceptable discharge performance of the anode was mainly due to the redeposition of metal Ag on the electrode surface, the multi-cracked discharge product film, and the non-basal-oriented grains with a high-volume fraction.

Ti₂AlNb-based alloys, as emerging lightweight high-temperature structural materials, have shown great potential for aerospace applications owing to their outstanding creep resistance, strong plasticity, and impressive high-temperature oxidation resistance. However, the material has yet to see widespread use owing to its poor formability and processability. Compared to traditional melting and forging methods, powder metallurgy has proven to be an effective method for preparing this alloy with a required shape, thereby circumventing phase transformation during hot working. The properties of Ti₂AlNb-based alloy can be enhanced by adding stabilized elements to the B2 or α₂ phase. Among these metallic elements, V has been demonstrated to effectively increase the ductility and high-temperature strength of Ti₂AlNb-based alloys. However, the mechanism of the V addition's effect on the microstructure and properties of Ti₂AlNb-based alloys during aging treatment has not been systematically clarified. Therefore, investigating the influence of powder sintering and post-heat treatment on the microstructure and properties of Ti-22Al-25Nb-1V alloys is crucial for accelerating their industrialization process. This investigation forms the basis of this work. A detailed study on the role of V in the microstructure and deformation responses of the Ti₂AlNb alloy was performed. This involved preparing V-added and V-free Ti-22Al-25Nb alloys via spark plasma sintering. Then, the sintered alloys were solution treated at 1300 ^oC for 4 h and subsequently aged at temperatures from 800 ^oC to 1050 ^oC for 2 h for microstructure modification. The detailed microstructure of the alloys was analyzed using X-ray diffraction and electron microscopy. The results revealed that by adding V, the volume fraction of the residual α₂ phase improves. The microhardness of the V-doped alloys is significantly enhanced compared to the undoped alloys and reached a maximum value of 503 HV at an aging temperature of 850 ^oC. This α₂ phase pins the grain boundary during heat treatment, resulting in an alloy with a refined grain size. Additionally, V additions can inhibit the B2 + α₂ → O transition, promoting a finer O/α₂ phase precipitate and higher hardness. Furthermore, microstructural analysis proved that the segregation of V and Nb in the B2 phase will cause the “curved” structure, including Nb- and V-rich B2 and Nb- and V-lean α₂ phases. The partial replacement of Nb by V reduced the lattice parameter in the B2 phase, which further improves the hardness of this alloy.

The application of Ti-Ni binary alloy at high temperatures is hindered by its low phase transition temperature. To enhance this transition temperature, researchers have explored the addition of metal Hf to Ti-Ni alloy. However, Ti-Ni-Hf high-temperature shape memory alloy exhibits brittleness and lacks favorable thermal deformation characteristics. Thus, a comprehensive investigation of its thermal deformation behavior is essential. During the hot working process, the material undergoes shape and microstructural changes, which are influenced by various processing factors. Consequently, optimizing processing parameters, including temperature, strain, and strain rate, is crucial for producing defect-free components with the desired microstructure. To optimize the hot working technology, single-pass compression tests on a Gleeble-3800 thermo-simulation machine were conducted and the hot deformation behavior and workability of the high-temperature shape memory alloy Ti₃₀Ni₅₀Hf₂₀ were explored. These tests covered a temperature range of 700-900 ^oC and a strain rate range of 0.01-10 s^-1. Flow stress-strain curves for Ti₃₀Ni₅₀Hf₂₀ under different deformation conditions were generated and the evolution of the alloy's microstructure at varying deformation temperatures under a strain rate of 0.01 s^-1, as well as at a deformation temperature of 900 ^oC with different deformation rates were examined. Utilizing a dynamic material model, a processing diagram was constructed and the impact of process parameters on the alloy's processing performance was analyzed. The results indicate that the recrystallization of Ti₃₀Ni₅₀Hf₂₀ high-temperature shape memory alloy increases with the deformation temperature. This alloy exhibits negative temperature sensitivity and positive strain sensitivity, with flow stress increasing as the strain rate rises and decreasing with higher deformation temperatures. A constitutive equation for Ti₃₀Ni₅₀Hf₂₀ high-temperature shape memory alloy during hot working is established, employing the Arrhenius hot deformation equation. The calculated strain activation energy was determined to be 527.447 kJ/mol. It revealed a consistent match between the theoretical and actual peak stress values. Through the assessment of the hot working diagram, the optimal processing parameters are identified as a deformation temperature in the range of 880-900 ^oC and a strain rate of 0.01-0.04 s^-1.

The Mg-Al-Zn-Mn-Ca magnesium alloy, after hot rolling, forms an elliptical texture, providing good application prospects. However, challenges such as poor symmetry, similar to basal textures, persist in elliptical texture formation. This study explores optimizing the texture of Mg-2Al-02Zn-0.4Mn-0.5Ca Mg alloy sheets using a hot rolling-shearing-bending (HRSB) treatment to improve their room temperature mechanical properties. The research systematically investigates structural evolution during the annealing process and the mechanism behind nonbasal texture formation, using EBSD, XRD, and other characterization techniques. The results show that after annealing at temperatures above 350 ^oC following hot rolling, the sheets develop an elliptical texture extending toward the transverse direction (TD). Following HRSB treatment and annealing at 400 ^oC annealing, the {\mathrm{10}\overline{\mathrm{1}}\mathrm{2}} extension twins generated during deformation remain uncrystallized, leading to an increase in the relatively symmetrical texture components between 20° and 70°. This also results in the formation of a ring texture. However, as the annealing temperature increases to 450 ^oC, the {\mathrm{10}\overline{\mathrm{1}}\mathrm{2}} extension twins nearly disappear, precipitation phases increase, and the nucleation of randomly oriented grains during recrystallization causes the circular texture characteristics to disappear. During the HRSB deformation process, the pyramidal <c + a> slip becomes significantly activated, dominating the primary dislocation density. The low-energy grain boundaries caused by the co-segregation of Al and Ca atoms at the grain boundaries, as well as the orientation gradient induced by the non-basal slip, jointly contribute to the formation of the non-basal texture.

ZM6 (Mg-Nd-Zn-Zr) alloy is a typical casting magnesium alloy with low density, high specific strength and stiffness, good vibration damping performance, good machinability, and good heat resistance. It is widely used in aerospace and aviation fields. However, metallurgical or machining defects are inevitable while processing due to the complicated shapes and large scales of aviation components. Failure to repair them may lead to significant economic loss. Laser deposition repair can be applied to aerospace components because of the advantages of small heat input and high molding accuracy. This work focuses on repairing the aerospace ZM6 magnesium alloy components using laser deposition, addressing the metallurgical defects and service damage to the components. The changes in the microstructure and mechanical properties of the repaired ZM6 samples before and after solution aging (T6: 520 ^oC, 8 h + 220 ^oC, 14 h) treatment were compared. The results show that the microstructure of the repaired zone of the as-deposited sample consists of fine α-Mg grains. The secondary phases distributed mainly at grain boundaries showed a continuous network, and a small number of the dot- and rod-shaped secondary phases were distributed inside Mg grains. The average hardness of the repaired zone is (60 ± 2) HV_0.1, and the tensile strength, yield strength, and elongation were 137.47 MPa, 111.61 MPa, and 5.57%, respectively. The fracture occurred in the base metal, and the tensile fracture mode comprised transgranular and intergranular brittle fractures. After T6 treatment, the microstructure of the repaired zone comprised fine α-Mg grains and abnormally coarse grains, and β′ phase was precipitated inside the grains. The average hardness of the repaired zone increased by 17.5% compared to that of the as-deposited samples, and the abnormally coarse and fine grains led to various hardness fluctuations. The tensile strength and yield strength of the T6-treated samples increased by 49.8% and 75.6%, respectively, but the elongation decreased. The fracture location of the tensile sample was in the repaired zone because of the formation of abnormally coarse grains.

V_{100 - x} Cr _x (x = 8 or 10, atomic fraction, %) hydrogen-separation alloys undergo cracks during cold rolling and are difficult to be shaped via room temperature processing. However, the addition of rare-earth element Y can greatly improve their cold-rolling plastic deformation ability, facilitating the low-cost fabrication of V-based alloy membranes for hydrogen separation with high flux on a large scale. In order to achieve both high hydrogen-permeation efficiency and service life, insight into the hydrogen permeability and hydrogen-embrittlement resistance is required on the basis of excellent cold-rolling formability. In this work, the effects of Y addition on the microstructure, cold-rolling formability, hydrogen permeability, and hydrogen-embrittlement resistance of as-cast V_{100 - x - y} Cr _x Y _y (x = 8, y = 1; x = 10, y = 0, 1, 3) hydrogen-separation alloys were studied using an oxygen-nitrogen-hydrogen analyzer, a cold-rolling machine, a hardness tester, a tension machine, and a hydrogen-permeation device as well as via XRD, SEM, TEM, and EPMA. In addition, the causes of the embrittlement of the V_{100 - x} Cr _x alloys and plasticization mechanism of V-Cr-Y alloys were explained. The microstructure formation and hydrogen-embrittlement resistance of V-Cr and V-Cr-Y alloys were also analyzed. Results showed that V-Cr alloys show a single-phase equiaxed grain microstructure, while V-Cr-Y alloys show a composite microstructure comprising a dendritic solid solution and secondary-phase particles located in the inter-dendritic region. The addition of Y in binary V-Cr alloys remarkably reduces the hardness, thereby greatly improving cold-rolling formability. Among the V₉₁Cr₈Y₁, V₈₉Cr₁₀Y₁, and V₈₇Cr₁₀Y₃ alloys, V₉₁Cr₈Y₁ showed the lowest hardness (108.88 HV) and highest maximum cold-rolling reduction rate (94.5%). Although the hydrogen permeability of the V-Cr-Y alloys was lower than those of Y-free alloys, it was still 2.5-3.0 times higher than those of commercial Pd₇₇Ag₂₃ alloys. Moreover, the V-Cr-Y alloys showed much better hydrogen-embrittlement resistance than those of V-Cr alloys and could be slowly cooled to room temperature without rupture. Rare-earth metal Y as a scavenger could react with O and S to form secondary-phase particles, exerting a purification effect, which softened the matrix and reduced the resistance of alloys to plastic deformation. Thus, high-performance V-Cr-Y alloy membranes with an excellent combination of formability and hydrogen-embrittlement resistance were prepared.

Plastic deformation of amorphous alloys below the glass transition temperature is inhomogeneous and highly localized within narrow shear bands. However, the processing and manufacturing of amorphous alloys in their supercooled liquid state exhibit unique advantages for engineering application. Although the discovery of bulk metallic glasses has substantially expanded the processing time and temperature window, experimental research on the supercooled liquid states of amorphous alloys remains widely limited to narrow regions near either their glass transition temperature or melting point. The crystallization of supercooled liquids severely limits the characterization of their kinetic behavior in the high-temperature region. Therefore, an enhanced comprehensive understanding of supercooled liquid characteristics and crystallization kinetic behavior of metallic glasses is necessary. Zr₆₁Ti₂Cu₂₅Al₁₂ amorphous alloy shows broad application prospects in the fabrication of flexible mechanism components and biological implants because of its high fracture toughness, high elastic strain limit, and good biocompatibility properties. Six orders of magnitude (10^-2-10⁴ K/s) of heating rate changes were achieved for Zr₆₁Ti₂Cu₂₅Al₁₂ metallic glass by combining flash differential scanning calorimetry (FDSC) with conventional DSC. This implies that the kinetic characteristics of the alloy supercooled liquid is dependent on the heating rate of the alloy over an ultra-extensive temperature range. The kinetic behavior of the alloy supercooled liquid lags behind the rapid changes in temperature, and both follow the Vogel-Fulcher-Tammann equation. The small variation in the fragility index (m = 35-47) indicates that the supercooled liquid structure changes gently with temperature, thereby showing a “strong” liquid behavior. An average m ≈ 45 is obtained over the entire temperature range from the glass transition temperature to the melting point via time dimension coordinate translation. The dependence of crystal growth on temperature during the crystallization process of the Zr₆₁Ti₂Cu₂₅Al₁₂ amorphous alloy indicates that the activation energy of crystal growth gradually decreases with increasing temperature, and the reduction in activation energy per unit temperature obtained here is approximately 0.5 kJ/(mol·K). Near the glass transition temperature, decoupling occurs between crystal growth kinetics and viscous flow. The kinetics coefficient for crystal growth (U_kin) follows a power law relationship with viscosity (η) over a wide temperature range when an exponent ξ = 0.84 is introduced: U_kin ∝ η^-ξ.

High-strength low-density steels are strongly recommended in the automotive industry because they can reduce weight and CO₂ emissions without affecting structural safety. In this study, a novel Cr-alloyed austenitic steel with a low density of 6.50 g/cm³ was designed. It was subjected to two types of processing routes. One includes cold rolling with a thickness reduction of 35% followed by aging at 450 ^oC for 1.5 h (known as 35CR-T). The other route includes cold rolling by 75%, short annealing at 925 ^oC for 10 s, and final aging at 450 ^oC for 1.5 h (known as 75CR-AT). Both resultant specimens exhibited excellent tensile properties; the specific yield strength and total elongation of the 35CR-T and 75CR-AT specimens reached 211.5 MPa·cm³/g, 15.6% and 210.0 MPa·cm³/g³, 21.5%, respectively. The microstructure of the former comprises relatively coarse austenite grains with high-density dislocations as the matrix and coarse κ-carbides, whereas that of the latter comprises fine recrystallized austenite grains and more extensive intragranular κ-carbides with a finer size. Consequently, greater dislocation strengthening contributes to the yield strength (YS) of the former, whereas more significant grain refinement and precipitation strengthening contribute to the YS of the latter. Therefore, both specimens have the same YS after considering all strengthening contributors. Moreover, the recrystallized austenite grains in 75CR-AT allow the sequential evolution of the dislocation substructure from planar-slip dislocations, Taylor lattice, and high-density dislocation wall to the microband during tensile deformation. By contrast, the dislocation microbands formed in the austenite grains of 35CR-T specimen suppress the dislocation multiplication and sequential evolution of dislocation substructures, resulting in poorer ductility compared with that of 75CR-AT specimen.

Recently, the problem of high-voltage direct current (HVDC) interference suffered by buried oil and gas pipelines has attracted widespread attention among research communities. Hence, accurately assessing the corrosive impact of HVDC interference on buried metal pipelines and performing effective protection procedures for the prevention of such corrosion have become priority issues that need to be resolved for producing reinforced pipelines. To date, the effect of the cathodic protection of the pipeline on the corrosion behavior of X80 steel under HVDC interference has rarely been reported. Hence, in this study, the corrosion behavior of X80 steel without cathodic protection conditions before HVDC interference and the effect of these protection conditions on the corrosion behavior of X80 steel under HVDC interference were studied through laboratory simulation experiments. Results showed that the corrosion rate of X80 steel was 170.81 μm/h without cathodic protection under 20 V DC interference for 1 h. When the cathodic protection pretreatment potentials were -0.85, -0.95, -1.05, and -1.20 V, the corrosion rates were 124.39, 87.13, 54.56, and 1.45 μm/h, respectively. The effect of various cathodic protection pretreatment potentials on the corrosion behavior of X80 steel under HVDC interference was clarified based on the product surface membrane layer, polarization, and EIS results. For the cathodic protection pretreatment potential of -0.85 to -1.05 V, the sample products after HVDC interference mainly showed a mixture of green rust GR1, calcium, and magnesium deposits; the corrosion rate of the sample products decreased with the increasing negative cathodic protection pretreatment potential under DC interference due to the gradual increase in the quality of the calcium and magnesium deposited layer on the surface of the sample products. At -1.20 V cathodic protection polarization potential, the corrosion rate of the sample products was substantially lower than that at other potentials because passivation of the products occurred under the combined action of high cathodic protection potential and HVDC interference.

Reinforced concrete has become the preferred choice for modern building structures owing to its long durability, strong structure, flexible, and diverse designs, wide availability, and low cost. Traditional carbon steel bars are prone to corrosion in marine environments, resulting in problems such as steel bar breakage and concrete cracks, thereby affecting the safety and reliability of marine engineering structures. Therefore, using high-performance corrosion-resistant alloy steel bars can effectively solve the problem of steel corrosion in marine engineering and improve the durability and maintainability of engineering structures. Concrete is a highly alkaline environment when it is free from erosion, and the pH value of its pore solution is 12.5-13.6. When steel bars are exposed to this environment, a stable passive film forms on their surface. This spontaneously formed passive film can keep the steel bars in a passive state, preventing corrosion and considerably extending the service life of reinforced concrete structures. The differences in the composition and structure of the passive film on steel bars represent important reasons for the different corrosion resistance performances of steel bars in concrete. To study the passive behavior of corrosion-resistant rebars (20MnSi steel, 3Cr steel, and 9Cr steel) with different Cr contents (0, 3%, and 9%, mass fraction) in simulated high-alkaline concrete pore solution, electrochemical measurements (including open circuit potential, electrochemical impedance spectroscopy, polarization curve, and Mott-Schottky curve) were used to study the changes in the properties of the passive film on the surface of the rebars over time. XPS was used to analyze the composition and structure of the passive film. The results show that a passive layered film was formed on the surface of the rebars in the simulated high-alkaline concrete pore solution, and the structure, composition, and protective properties of the passive film were closely related to the Cr content and passivation time of the rebars. The passive film of 20MnSi steel was mainly composed of Fe(III) compounds in the outer layer and Fe(II) oxides in the inner layer. The outer layer of the passive film of 3Cr steel and 9Cr steel comprised Fe(III) and Cr(III) oxides and hydroxides, and the inner layer comprised Fe(II) oxides and Cr(III) compounds. The passive films formed by the three types of rebars exhibited n-type semiconductor properties within the potential range of -0.8 to 0.2 V (vs SCE). As the immersion time increased, the defect density in the passive film decreased, leading to decreased corrosion current density of the rebars and improved corrosion resistance. When the Cr content is increased, the point defect density of the passive film decreases. At the same time, the passive film becomes dense, resulting in improved corrosion resistance of the rebars.

The cellular automaton (CA) model exhibits a notable disadvantage of substantial anisotropy, triggered by the square cells, adjacent cell structures, and intrinsic features of the sharp interface model. This disadvantage leads to limitations in simulating dendritic growth with random preferred orientations during the solidification of alloys, particularly in the context of sixfold symmetric alloys. In the present study, drawing inspiration from the processing concept of diffuse interfaces and the gradient energy term in the phase field model, a function concerning the gradient of the field variable associated with the cell state is constructed and the diffusion equation for the field variable is derived. Consequently, a novel field-variable diffusion CA (FCA) model is proposed, which addresses the growth kinetics of the solid-liquid interface in accordance with the lever rule. The proposed model considers constitutional supercooling and the Gibbs-Thomson effect, employing the concentration potential method to manage solute diffusion and redistribution. The growth rate of interface cells is modulated by introducing a field-variable diffusion term. The analysis reveals that within the square-grid discretization mode, the model demonstrates validation under various conditions, focusing on the steady-state characteristics of the dendritic tip and growth kinetics of the sixfold symmetric Mg-6%Al (mass fraction) alloy. The findings are consistent with the predictions of the LGK model, suggesting that the FCA model can effectively emulate dendritic morphology with multifold symmetry and random preferred orientations, and elucidate critical dendritic arm behaviors, such as competitive dendritic growth and coarsening.