Austenitic stainless steels (ASSs) are important materials which are used widely in the primary circuits of pressurized water reactors (PWRs). The performance of the ASSs in PWR primary water has been outstanding. However, stress corrosion cracking cases have been identified in ASS components in the primary loop of PWR nuclear power plants since the end of 20th century. Most stress corrosion cracking cases occurred in low flow or stagnant zones in the dead-leg regions, where the primary water chemistry was contaminated with anionic impurities. Cold work has been identified to be necessary for stress corrosion cracking for components operating in locations where the water is well circulated. Machining and other surface treatments can always introduce cold work to ASS components. Therefore, considerable research efforts have been invested to understand the nature of the surface deformation layer on ASS introduced during machining processes and by other surface treatments, as well as the corrosion and stress corrosion crack initiation behaviors of the machined surfaces in simulated PWR primary water. This paper reviews the research progress on the surface deformation layer on ASSs introduced by various processes, and the effects of surface deformation on the corrosion and stress corrosion crack initiation behavior of ASSs. The key issues that remain to be solved are summarized, and possible solutions are suggested.

Mg alloys are attractive in the fields of aerospace, automotive, and biomedical engineering, owing to the advantages of light weight, high specific strength, excellent damping property, good biocompatibility, and in vivo degradable property. However, conventional methods for manufacturing Mg alloys, such as casting and deformation processing, yield low-quality large-scale monolithic and complex structures, which hinder the applications of Mg parts. Additive manufacturing (AM) is a burgeoning alternative to manufacture monolithic parts through layer-by-layer deposition of metallic materials using 3D model data. In this paper, the latest research progress in AM of Mg alloys, which focuses on technological processes and influencing factors, macro and microstructures, mechanical properties, and corrosion properties of parts manufactured primarily by selective laser melting (SLM) and wire and arc AM (WAAM), are comprehensively reviewed. Currently, additively manufactured Mg parts with a relative density > 99% have been achievable through both SLM and WAAM after process optimization, and their mechanical properties and corrosion resistance have been comparable to those of casting and wrought parts, indicating a great potential for engineering applications. Finally, the future development trend and research direction of AM of Mg alloys are proposed from the perspectives of materials design, process improvement, and performance evaluation.

TiAl-based alloy coating produced by laser melting deposition exhibits excellent properties of high temperature and corrosion resistance and has a wide application potential across many fields. However, the wear resistance of the coating is poor, which limits its long-term usage in harsh and complex working environments. In this study, TiB₂ reinforced TiAl-based alloy composite coatings are prepared by laser melting deposition to improve their wear resistance, and a theoretical reference for further exploring the applications of TiAl-based alloy composites in surface engineering is presented. TiAl-based alloy coatings with different TiB₂ contents (0, 10%, 20%, 30%, mass fraction) were prepared on the surface of TC4 alloy using the laser melting deposition process. The effects of TiB₂ content on the microstructure and mechanical properties of the coatings were systematically studied using XRD, OM, SEM, microhardness tester, indentation method, wear tester, and laser confocal microscope. Planar, columnar, and equiaxed crystal distributions were observed along the thickness direction from the bottom. With an increase in TiB₂ content, the height of columnar crystal gradually decreased. TiB₂/TiAl composite coatings are composed of a TiAl alloy matrix phase (γ + α₂) and a TiB₂ enhanced phase. Most of the directly added TiB₂ particles do not melt, but the outer layer of the directly added TiB₂ particles dissolves within the molten TiAl alloy, following which primary and secondary TiB₂ are precipitated in situ. The primary TiB₂ has a particle form and the secondary TiB₂ has a needle or flake form. With the increase of TiB₂ content from 0 to 10%, the matrix of the coating is noticeably refined, but an increase in TiB₂ content (20% and 30%) do not produce further refinement. With the increase of TiB₂ content from 0 to 30%, the surface hardness of the coating increases from 530.5 HV to 738.4 HV, the fracture toughness decreases from 7.75 MPa·m^1/2 to 3.17 MPa·m^1/2, the wear rate decreases from 3.98 mg/mm² to 0.42 mg/mm², and the wear degree and roughness of the wear surface also decrease. Furthermore, the wear mechanism of the coating without TiB₂ is mainly microscopic cutting, supplemented by multiple plastic deformations. When the mass fraction of TiB₂ is 10%, the wear mechanism of the coating is mainly microscopic cutting, supplemented by microscopic fracture. As the TiB₂ content increases, the wear mechanism gradually turns to microscopic fracture. When the mass fraction of TiB₂ is 30%, the wear mechanism of the coating is mainly microscopic fracture, supplemented by microscopic cutting.

During the use of fossil fuels, about two-thirds of the energy that is discharged into the environment in the form of waste heat are barely utilized and cause considerable environmental pollution and intense CO₂ emission. Thermoelectric materials directly convert heat energy to electricity, thus, improving the utilization efficiency of fossil energy and reducing environmental pollution. Skutterudite CoSb₃ has been widely studied as one of the materials for thermoelectric applications in the middle-temperature region. CoSb₃-based skutterudites are narrow bandgap semiconductors with a high-electrical conductivity and Seebeck coefficient. Meanwhile, thermoelectric performance of bulk CoSb₃ has been considerably improved via doping and design of nano structures. Herein, P-type CoSb₃ was synthesized via melt-annealing-spark plasma sintering process. The effect of Ce-doping content on microstructure and thermoelectric properties of CoSb₃ and the effect of La doping on decoupled thermoelectric performance were studied. Compared with Ce_0.8Fe₃CoSb₁₂, the Seebeck coefficient of La_0.1Ce_0.8Fe₃CoSb₁₂ increased with temperature, electrical resistivity decreased from 25 μΩ·m to 15 μΩ·m at 300 K, and power factor simultaneously increased from 480 μW/(m·K²) to 642 μW/(m·K²) at 673 K. The La_0.1Ce_0.8Fe₃CoSb₁₂ thermal conductivity decreased with La or Ce doping to ~1 W/(m·K), and the corresponding thermoelectric figure of merit reached 0.45 at 723 K in the temperature range from 300 K to 723 K. Al-Ni coating was deposited on the sintered bulk skutterudite via magnetron sputtering method. It was demonstrated that the coating did not degrade the thermoelectric performance, while the coating elements were uniformly distributed across the sintered bulk La_0.1Ce_0.8Fe₃CoSb₁₂. The welding behavior of P-type La_0.1Ce_0.8Fe₃CoSb₁₂ was studied using a Ag₄₀Cu₆₀ solder and a Mo₅₀Cu₅₀ electrode sheet. The interface of this thermoelectric material was prone to cracking and pore formation, while the elements at the interface have not demonstrated remarkable diffusion. This indicates an efficiency of the interface bonding, which may be used in the fabrication technologies of thermoelectric devices.

GH3535 alloy has been used as the main structural material of molten salt reactor, which exhibits good high-temperature strength and excellent corrosion resistance to the molten salts. The intergranular cracking of GH3535 was detected after four years of operation of the molten salt reactor experiment, which was attributed to the inward diffusion of fission products Te. Grain boundary engineering (GBE) has been successfully applied to enhance the grain-boundary-related properties of the materials by increasing the frequency of low Σ coincidence site lattice grain boundaries and tailoring the grain boundary network. The in situ three-point bending test was used to assess the cracking properties of Non-GBE and GBE samples following Te infiltration at 700^oC for 500 h. Fractal analysis statistics of various types of grain boundaries and cracks following in situ three-point bending tests were used. The result shows that the fractal dimension of cracks is in accord with that of the random grain boundaries (RGBs). The stronger the fracture resistance of materials, the lower the value of the RGB fractal dimension. The GH3535 alloy GBE samples with a bigger average size and more uniformly distributed twin grain clusters will have greater cracking resistance.

The Mg-Al series alloys are well known for their low density, high specific strength, and superior damping capability. However, the application of Mg-Al series alloys is often limited by inadequate mechanical properties. To fulfill the growing demand for lightweight structural components, ultra-fine grained magnesium alloys with superior mechanical properties have gained attention. Mechanical milling and powder metallurgy were used to produce the AZ61 ultra-fine grained magnesium alloy with super-high tensile characteristics. The effects of mechanical milling on the grain size, precipitates, texture, and tensile properties of AZ61 ultra-fine grained magnesium alloy were investigated. The grain size of the AZ61 alloy produced by mechanical milling and powder metallurgy was reduced from 0.91 μm to 0.68 μm when compared to that produced by non-mechanical milling. Mechanical milling accelerated the dynamic precipitation and refining of Mg₁₇Al₁₂ while weakening the basal texture. The yield strength, tensile strength, and elongation of AZ61 ultra-fine grained magnesium alloy are 393.1 MPa, 431.9 MPa, and 8.5%, respectively, which are superior to the AZ61 alloy produced by other processes. The theoretical grain refinement and Orowan strengthening mechanisms of AZ61 alloy were calculated, and it shows that the grain refinement strengthening contributes more than 90% of the yield strength. The Orowan strengthening was overestimated when Mg₁₇Al₁₂ was distributed at grain boundaries. The weakening of basal texture resulted in a reduction in yield strength. The fracture mechanism of the AZ61 alloy without mechanical milling is dominated by oxidation on the surface of the AZ61 powder, which initiates interparticle debonding. The fracture mechanism of the AZ61 alloy with mechanical milling is dominated by deformation mismatch between the deboned powders and the stronger bonded powders, and the increase in the amount of Mg₁₇Al₁₂ along the grain boundary.

Eutectic high-entropy alloys (EHEAs) have been explored as possible options for high-temperature applications due to their controlled microstructure and excellent mechanical properties. In particular, EHEAs possess good liquidity and castability, allowing their possibility for real-size industrial manufacturing. However, despite their importance as a structural material index, the tribological properties were rarely investigated in the EHEAs field. In this study, a kilogram-scale AlCr_1.3TiNi₂ EHEA was produced using electromagnetic levitation melting and direct casting approach. The EHEA's microstructure and chemical composition were investigated using a TEM and APT techniques. The AlCr_1.3TiNi₂ EHEA's tribological properties were examined from room temperature to 800^oC using a rotational ball-on-disk tribometer (HT-1000). Meanwhile, for comparison, a GH4169 nickel-base superalloy was chosen. The corresponding wear mechanisms were also thoroughly discussed. The findings exhibit that the as-cast AlCr_1.3TiNi₂ EHEA, which had an ultrafine lamellar structure, consisted of a disordered bcc phase and an ordered L2₁ phase with lattice misfit of approximately 2%. The average interlamellar spacing was about 350 nm. Additionally, a large number of nanoprecipitates contains in the L2₁ lamellae central region. Below 600^oC, the AlCr_1.3TiNi₂ EHEA's primary wear mechanism was abrasive wear, and its wear rate was lower than that of the GH4169 alloy. At 800^oC, distinct plastic deformation features were observed on the worn surface of EHEA. The EHEA exhibited a much higher friction coefficient than that of the GH4169 alloy at 800^oC, but their wear rates were similar. The wear resistance improvement of GH4169 alloy at high temperature was ascribed to the formation of oxide film on its worn surface, and the AlCr_1.3TiNi₂ EHEA's excellent wear resistance mainly resulted from good structure stability and high hot hardness. Current findings offer new insights into the industrial application of EHEA in high-temperature fields.

Concentrated multicomponent alloys (CMCAs) or high/medium-entropy alloys (HEAs/MEAs) possess outstanding comprehensive properties, causing them to have the potential to be the next generation of structural materials. Phenomena occurring under dynamic tensile loading or high/low temperature of such alloys have been hardly investigated. However, its understanding is essentially needed in their application in automotive, aerospace, and military industries. Meanwhile, the suitable constitutive equations of CMCAs under such cases have been rarely investigated. In this work, the thermodynamic behavior of equiatomic CrFeNi MEA with single-phase fcc structure has been systematically investigated at strain rates from 10^-3 s^-1 to 1800 s^-1 and temperatures from 77 K to 1073 K. The results showed that as the deformation temperature decreased from 1073 K to 77 K, the yield stress was improved significantly from 125 MPa to 415 MPa. Meanwhile, the uniform elongation increased from 2% to 82%. The abnormal uniform elongation appearing at 673 K was closely related to dynamic strain aging. As the strain rate increased from 10^-3 s^-1 to 1800 s^-1 at a constant temperature of 77 K, the strength increased significantly (e.g., the yield stress increased from 415 MPa to 595 MPa), and the uniform elongation remained unchanged, still maintaining 68% at 1800 s^-1. After deformation, there were no second phases attributed to a large Ni amount in the alloys. Some deformation twins appeared at 77 K. Based on the experimental results, the relationship between yield stress and temperatures/strain rates could be successfully revealed using the ZA model. Moreover, regression analysis and constraint optimization established two phenomenological constitutive models (JC and KHL models) and three physically-based constitutive models (PB model, ZA model, and NNL model). JC and PB models had the highest and lowest description accuracy, respectively. Besides, the JC model was hard to describe the case that the work hardening decreased due to the change of temperature or strain rates, and the PB model was unsuitable in characterizing the complex work hardening behaviors.

Zirconium alloy is frequently used in the nuclear industry as a reactor fuel cladding material. Uniform corrosion of zirconium alloys has received much attention because it is one of the material's life-limited properties. To study their long-term uniform corrosion behavior, two types of Zr-Sn-Nb-Fe-V alloy claddings, one with a high niobium content and one with a low niobium content, were exposed to 400^oC and 10.3 MPa of superheated steam for 800 d. Both alloys clearly exhibit periodic oxide densification-transition. Different quantitative methods were used to study the evolution and mechanism of multiple oxide features. The periodic layers of oxide morphologies are still observed even after two times of transitions. Periodically, columnar grains and the defect layer appear. The undulation intensity (related to the “cauliflower” morphologies) and the equivalent thickness of tetragonal zirconia (t-ZrO₂) at the metal/oxide interface increase with corrosion time in pretransition oxides and decrease at transition time. The evolution of both features in the subsequent oxide densification-transition period is the same as initial densificationtransition cycle. The critical value of the interface undulation intensity is approximately 0.25 for both alloys. The critical thickness of t-ZrO₂ is approximately 450 nm for low-niobium alloy and approximately 200 nm for high-niobium alloy. Both features periodically reach critical conditions. The evolution of undulation intensity provides an excellent explanation for the production of isolated and interconnected lateral cracks. Additionally, the transformation of t-ZrO₂ to monoclinic zirconia (m-ZrO₂) results in cracking of the oxide and produces interconnected, tiny equiaxed defects at the interface. Both lateral cracks and equiaxed defects are both important components of the defect layer. It is hypothesized that the synergetic effects of interface undulation and t-ZrO₂ transformation affect the transition. The occurrence of periodic transitions is strongly correlated with the periodic behavior of oxide features reaching critical conditions. The volume of oxygen vacancy in t-ZrO₂ was presumably evaluated by studying the Raman shift of the characteristic t-ZrO₂ peak of 280 cm^-1. As a result, the amount does not change considerably during oxide densification but decreases during the transition period. The Raman shift of t-ZrO₂ in low-niobium alloys is approximately -1.2 cm^-1 less than that in high-niobium alloys, indicating that the low-niobium alloys have a greater volume of oxygen vacancies. It is proposed that the difference in the corrosion behavior of two alloys is derived from the difference in the volume of oxygen vacancies.

A seawater corrosion test platform to simulate the dynamic seawater/air interface is constructed, comprising an electric putter, a time relay, and four corrosion electrochemical sensors. The localized corrosion mechanism of 2024 aluminum alloy in a simulated dynamic seawater/air interface is investigated by corrosion potential monitoring, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) measurements, and the analysis of the surface and cross-section morphology. The differences in the corrosion behavior at the seawater/air interfacial region and that of full immersion region are discussed. The results showed that the corrosion products at the dynamic seawater/air interfacial region are continuously distributed, which is mainly due to the dissolved Al³⁺ flowing from the pits and reacting with the oxygen in the dynamic seawater/air interfacial region. The distribution of corrosion products in the entire leaching area is more dispersed. As aluminum alloy is immersed and removed from water periodically, the corrosion potential fluctuates periodically with an amplitude of 5-10 mV. Due to the high corrosion potential in the seawater/air interfacial region, the aluminum alloy above the waterline behaves as the cathode, and that below the waterline acts as the anode. However, because of the subtle difference in the corrosion potential, the galvanic corrosion effect is not obvious. The results of EIS revealed that the high-frequency capacitive arc radius of both seawater/air interfacial region and full immersion zone increased first and then decreased, and the corrosion product film in the interface zone had better corrosion resistance than that in the full immersion zone. The results of the EN test showed that the fluctuation amplitude of current noise decreased first and then increased, indicating that the local corrosion sensitivity decreased first and then increased. The slope of the high-frequency linear region of the power spectral density of current noise was less than -20 dB/dec, indicating that the corrosion type was local corrosion. The pit size at the seawater/air interface was much smaller than that in full immersion region, because the oxygen in the seawater/air interface region could be easily reduced within the pits by consuming H⁺, thereby increasing the pH value within the pits.

As advanced aero engines and heavy-duty gas turbines require high service temperatures, how to maintain better performance and damage tolerance of superalloys at high service temperatures has emerged as a critical issue in the application of superalloys. Previous research has shown that temperature rise has no effect on the crack growth rate of alloys placed in a vacuum. However, in air, fatigue crack growth rate is observed to significantly depend on temperature. According to the sample fracture, which is an oxide-covered intergranular fracture, oxygen atoms significantly affect the performance of superalloys. As first-principle calculation method has advanced rapidly in recent years, it can eliminate the effect of irrelevant impurity atoms on the weakening of grain boundaries and establish a pure grain boundary system. Thus, this method is an ideal analysis tool for this research. The ideal tensile test combined with ideal separation work and charge density difference of the grain boundary in nickel-based superalloy under different oxygen concentrations, was performed using the first-principle calculation method. The internal reason for the weakening of the Ni grain boundary due to oxygen is given. A similar comparative analysis of Co and NiCr grain boundaries was also performed. Further, the cause of the oxidation and weakening of the grain boundaries is explained. The results demonstrate that the high electronegativity of O atoms weakens the Ni—Ni metal bond at the grain boundary due to the lack of charge. Further, in the stretching process, when the tensile strain reaches 0.10, the strain of the oxygen-containing Ni grain boundary is entirely provided by the Ni—Ni bond present at this boundary. The presence of oxygen significantly accelerates the fracture failure process of the Ni grain boundary. In addition, Co-based alloy has higher strength after grain boundary oxidation and has better oxidation resistance weakening performance than Ni; however, the strain of fracture is small. Although the NiCr-based grain boundary strength is the weakest, the mechanical properties after oxidation are relatively stable. The reason for the weakening of the Ni grain boundary due to oxidation is attributed to structural distortion caused by oxygen atoms, whereas the weakening of Co- and NiCr-based grain boundary due to oxidation is primarily related to changes in the charge density distribution.