Tungsten (W) is a prime candidate for use in plasma-facing components in fusion reactors. These components are subjected to high temperatures and displacement damages caused by fusion neutron bombardments. The displacement damages are mainly present as high concentrations of point defects and clusters. They interact with the hydrogen, helium plasma, and various other transmutation products, giving rise to unwanted consequences, such as radiation hardening, increased brittle-to-ductile transition temperature, and thermal conductivity degradation. This review focuses on the radiation-induced displacement damage in tungsten and aims to provide a systematic summary of the underlying mechanisms for the production, evolution, and thermal recovery of radiation defect, using defect microscopy techniques and materials multiscale modeling. The information uncovered, reflects statistical laws of radiation defect characteristics; serves as the basis for a quantitative description of time- and space-dependent evolution of damage microstructure; and is in great favor of material property prediction, reliability evaluation, and the future development of novel materials.
Human body can absorb and degrade Zn. Among the biodegradable metals of Mg, Zn, and Fe, the degradation rate of Zn is the most suitable for the clinical requirements of vascular stents. Zinc ion is an essential nutrient in human body; it participates in the metabolic activities of more than 200 enzymes. Zn promotes and maintains the integrity of vascular endothelium and inhibits the progress of artery atherosclerosis, making it naturally advantageous as a vascular stent material. This review systematically summarizes the research in the field of biodegradable zinc-based vascular stents based on recent studies conducted by the author's research team. In addition, this review introduces and discusses the research background, status, and challenges as well as the countermeasures of the challenges and prospects for the future development of biodegradable Zn-based vascular stents. It is expected that the comments and itemized strategies for solving the identified challenges in this review can inspire related researchers to perform research studies in associated fields in China.
Gaseous CO2 transportation pipelines are an important part of carbon capture and storage. Corrosion control of gaseous CO2 transportation pipelines containing impurities is important to the safe operation of pipelines. This paper reviews recent research progress on the corrosion of gaseous CO2 transportation pipelines containing impurities, and the impact factors of gaseous CO2 transportation pipelines are summarized. The influence of pipe impurities and environmental conditions on the mutual solubility of water and CO2, the corrosion behavior of pipelines, the characteristic of corrosion scales, and corrosion mechanism of transportation pipelines are discussed. The determination of critical water content for the corrosion of gaseous CO2 transportation pipelines is analyzed. Predictive corrosion models of gaseous CO2 transportation pipelines are also concluded. For further research on corrosion of gaseous CO2 transportation pipelines containing impurities, the following should be the focal points: the calculation of water and CO2 mutual solubility in gaseous CO2 environments containing impurities, the influence of impurities on corrosion product film characteristics and the corrosion mechanism in a gaseous CO2 environment, the determination of the critical water content of corrosion for gaseous CO2 transportation pipelines containing impurities, and the establishment of inner corrosion prediction models of gaseous CO2 transportation pipelines containing impurities.
With the rapid development and industrialization of high-end products such as flexible screens, micro-electromechanical, medical bionics, environmental protection, and energy-saving devices, there has been an increase in the market demand and quality requirements for special alloys with different materials and specifications. In high-end processes such as micro forming, micro manufacturing, and micro equipment, foils with thicknesses of less than 0.1 mm are indispensable as raw materials. However, during rolling deformation processes, the large width-thickness ratio of a foil is affected by many factors, including grains, texture, surface morphology, transient temperature, and mechanical properties. There are generally varying degrees of size effects and local instability that directly affect the annealed structure and finishing process. These render relevant processes for finished foils complicated, resulting in large differences in shape, size, and mechanical properties. These issues also lead to a surge in costs and indirectly affect the quality index as well as the added value of a final product. To fundamentally resolve the shape index of foils with large width-thickness ratios and improve the cold-rolling deformation characteristics and comprehensive performance of foils at room/low temperature, it is necessary to establish constitutive relationships from the multiple angles of microstructure and surface topography. From differences in grain, texture, heat, force, and displacement, considering the size coupling feature and synchronization; and from the perspective of detection instruments, operating condition errors, and big-data cluster evaluation, there is a need to collaboratively analyze the logical relationship and regulation between deformation and performance. Based on the above ideas and from the aspects of shape characterizations, deformation mechanism, measurement and control, testing equipment, and mathematical model, recent studies on the cold-rolling of foils are summarized and the cascade relationship among transient temperature, structure morphology, interface morphology, deformation shape, and mechanical properties is established. For novel high-end materials, the trend of the new process of electropulsing differential speed rolling and the mechanism of plasticizing and toughening at room temperature is predicted in an attempt to provide new ideas and directions for the basic theoretical research and rapid engineering application of the shape/performance collaborative measurement and control of foils with large width-thickness ratios.
Environmentally assisted fatigue is an important factor in the design, safety review, and life management of key components used in nuclear power plants. Piping systems, valves, and small-bore pipes are sensitive to fatigue damage in nuclear power plants. In this work, a kind of hollow specimen for fatigue testing was designed. High-temperature pressurized water flows through the inside of the specimen, and the outside of the specimen is exposed to air. The corrosion fatigue behavior of 316LN stainless steel was investigated in high-temperature pressurized water using the hollow specimens. The experimental results show that the fatigue strength of 316LN stainless steel was reduced in a high-temperature pressurized water environment, and its fatigue life decreased with decreasing strain rate. The fatigue lives obtained by hollow and standard round bar specimens were comparable, which indicate that it is reasonable and feasible to use the hollow specimen to study the environmentally assisted fatigue performance of nuclear-grade structural materials in a high-temperature pressurized water environment. At low strain rate conditions, the fatigue crack initiation region is a typical fan-shaped pattern with quasi-cleavage cracking characteristics. The fatigue crack growth region is characterized by fatigue striation, and the environmental effects are highly significant in the stage of fatigue crack initiation. The fatigue damage mechanism of 316LN stainless steel in a high-temperature pressurized water environment is also discussed.
Copper-nickel alloys are extensively used in precision instruments, ship building, building decorations, and currency manufacturing because of their excellent mechanical properties, good corrosion resistance, and silvery metallic luster. However, they are likely to suffer from discoloration owing to corrosion in the polluted atmosphere containing SO2. HSO3- and H+ exhibit ionization when SO2 is adsorbed and dissolved in the thin liquid film on the surface of white copper. These sulfide-containing media will accelerate the corrosion process and affect the surface gloss. Benzotriazole (C6H5N3, BTA) is a corrosion inhibitor commonly used in Cu and its alloys that forms a chemical conversion film. It mainly protects the copper-nickel alloys in solutions containing Cl- or seawater polluted by sulfides. However, some studies have investigated the chemical conversion films of BTA that are affected by atmospheric pollution in the medium, especially focusing on analyzing their failure mode. This experiment was conceptualized based on the aforementioned problem. The corrosion behavior of the copper-nickel alloys protected by BTA in a simulated urban atmospheric environment was analyzed through SEM/EDS, XRD, and electrochemical tests. The laboratory experiments were accelerated by salt deposition. Results showed the presence of prismatic salt crystals on the surface of the copper-nickel alloy treated using BTA during the early stage of corrosion, indicating that the corrosion medium could not completely penetrate the substrate. The corrosion current density of the alloy protected by BTA will decrease first and then increase with the increasing corrosion time. This can be attributed to the oxidation and the presence of BTA chemical conversion films on the surface of the alloy; corrosion was delayed because of the combined action of these two factors. When the BTA film was damaged because of continuous consumption in the local area, the corrosion area expanded, increasing the corrosion current density. Be similar to the samples without BTA treatment, the final corrosion products of the samples treated with BTA were also loose and porous, and the main components were ZnSO4·6H2O and Cu4(SO4)(OH)6. However, the degree of corrosion of the alloy protected by BTA was more slight according to the cross-section morphology observation and mass dynamic curve analysis.
Metal-dielectric coatings consist of extremely fine metal particles embedded in dielectric matrices are considered promising as materials for high-temperature spectral selective absorption coating applications owing to their excellent thermal stability and integrated optical properties. However, during long periods of annealing under high temperatures, metal particles are prone to agglomerating, coarsening, oxidizing, and diffusing across different layers, resulting in changes in composition and microstructures. Correspondingly the metal-dielectric coatings would experience irreversible degradations in optical properties. Hence, a Cr/AlCrN/AlCrON/AlCrO multilayer solar selective absorbing coating has been designed and deposited on stainless steel by cathode arc ion plating to solve the above mentioned issue. This coating exhibited excellent thermal stability as the absorptance increased to 0.922, whereas, the emittance decreased to 0.114 after annealing at 500oC for 1000 h in air. Microstructural characterization indicates that the increase in absorptance is attributed the formation of small amounts of AlN, CrN, and Cr2N nanocrystallites in the amorphous matrices of AlCrN and AlCrON, which can effectively scatter the incident light into a broadband wavelength spectrum by increasing the optical path length in the absorbing layers, resulting in a pronounced enhancement in the absorptivity. A handful of Cr2O3 and Al2O3 nanograins are embedded in the amorphous AlCrO antireflection layer, which can effectively reflect solar infrared radiation and thermal emittance from the substrate, resulting in relatively low infrared emissivity. Besides, good thermal stability is attributed to the excellent thermal stability of the dielectric amorphous matrices and slow atomic diffusion of nanoparticles, which could effectively slow down the inward diffusion of oxygen and avoid the agglomeration of nanoparticles. However, during high-temperature annealing, aluminum atoms in the nanoparticles appear to agglomerate on the surface. These aluminum atoms would oxidize in air and form a layer of Al2O3 covering these nanoparticles, preventing agglomeration and coarsening of nanoparticles.
The rapid development of high-rise buildings has increasingly brought requirements for construction steels with high strength and toughness. For high-rise building structural steels with low yield ratio, good weldability and excellent resistance to fire and corrosion are generally required. However, high grade construction steels with comprehensive properties are yet to be developed. In this study, a 690 MPa grade functionally structured fire and corrosion resistant high strength construction steel was designed based on the thermodynamic calculations of the JMatPro software and interactions among chemical elements. The chemical composition (mass fraction, %) of the designed steel was Fe-0.08C-0.3Si-1.1Mn-0.12(Nb + V + Ti)-1.6(Cr + Cu + Ni + Mo)-0.002B-0.004N. After laboratory melting and a thermomechanical controlled process (TMCP), the microstructure features, strengthening and toughening mechanisms, mechanical properties, and fire and corrosion resistances were characterized and analyzed by EPMA, EBSD, and performance testing. Results show that the microstructure of this low-carbon microalloyed steel at its TMCP state is mainly composed of bainite ferrite, granular bainite, and lath-like bainite. The yield strength, tensile strength, total elongation, and yield ratio at room temperature are 700 MPa, 878 MPa, 20%, and 0.80, respectively, and this steel possesses good low-temperature toughness. This low-carbon microalloyed steel meets requirements for fire resistance at elevated temperatures up to 600oC for 3 h. It is disclosed that the granular bainite plays a positive role in improving corrosion resistance under marine environment. A further analysis shows that the tested steel possesses excellent strength and toughness resulting from the cumulative effects of precipitation strengthening, grain refinement strengthening, dislocation strengthening, and solid solution strengthening. Moreover, after observation and analysis of crack initiation and propagation underneath the fractured surface of low-temperature impacted samples, the microvoids prefer to nucleate at high-angle boundaries containing brittle phases and grow in a Z-type to cross lath-like bainite to consume more energy. Multiple crack deflections are beneficial for toughness improvements.
AA 7055 aluminium alloy has been widely applied in aviation and aerospace applications, especially after T7751 heat treatment, owing to its excellent properties, such as high strength and good stress corrosion and fatigue resistances. For 7XXX aluminium alloys, aging hardening is the main strengthening mechanism, and the hardening effect is determined by the microstructural features of precipitates including morphology, composition, volume fraction, nucleation density, and size distribution. To further improve the property of alloy and expand the breadth of applications, establishing a precise predictive model regarding strength performance associated with the precipitates is necessary. In this work, based on the quantitative results of the precipitates obtained using small angle X-ray scattering techniques, the strengthening models of AA 7055 Al alloys aged at 120 and 160oC were investigated. Precipitation kinetics show that at the early stages of aging, the evolution of radius and the half thickness of plate-like precipitates are both linear with t1/2 (t means the aging time). Conversely, at the later stages of aging, they are linear with t1/3. The evolution of the volume fraction of the precipitates follows a JMA (Johnson-Mehl-Avrami)-type equation. Strength contributions from both GPI zones and η' precipitates are considered. Moreover, strengthening modeling considered both the modulus and coherency strain strengthening mechanisms of these two kinds of precipitates that had been built for the AA 7055 Al alloy aged at 120 and 160oC. Therefore, yield strength during aging can be predicted.
S31042 steel is a typical 25Cr-20Ni type austenitic heat-resistant steel with excellent resistance to oxidation and creep rupture strength near 600oC. This austenitic steel is widely used as a super-heater or re-heater in ultra-super critical plants with steam specifications as high as 600oC and 25 MPa. To reduce CO2 emissions and improve power generation, the application of advanced ultra-super critical plants (steam parameters 700oC and 30 MPa) can be promoted. Owing to its excellent mechanical properties as well as good corrosion resistance at elevated temperature above 650oC, GH4169 alloys have the potential to be used in advanced ultra-super critical plants. Practically, it is meaningful to investigate the welding process of GH4169/S31042 dissimilar materials. In this work, the joint between dissimilar materials (S31042/GH4169) was studied by linear friction welding, and the microstructures and mechanical properties of the joint were investigated by OM, SEM, TEM, hardness testing, tensile testing, and creep testing at 700oC. Good metallurgic bonding was obtained under the optimized welding process parameters of 25 Hz (frequency), 2 mm (amplitude), 100 MPa of frictional pressure, and 150 MPa of forging pressure. Dynamic recrystallization occurred and the secondary phase particles precipitated within the weld zone. The microhardness of the welded joint was higher than that of the base metal, and the tensile properties of the joint were higher than S31042 steel, which is attributed to both fine grain and dispersion strengthening.
Metals are widely used for heat sink and thermal management products, and their thermal conductivities are critical in determining the cooling performance. An efficient method to calculate the thermal conductivity of pure metal is proposed based on the first principles. By introducing the constant relaxation time approximation, density functional theory (DFT) and maximum localized Wannier function (MLWFs) are used to solve the electronic thermal conductivity of metal materials, the calculation procedure of electronic thermal conductivity can be simplified. Regarding the phonon thermal conductivity calculation part, the combination of Slack equation, Birch-Murnaghan equation and Debye model is capable of improving the calculation efficiency. The electrical and thermal conductivities of Al, Mg and Zn in the temperature range of 300-700 K are calculated by the up-mentioned new method. The calculated thermal conductivity was consistent with the measured values, which confirmed the accuracy of the calculation method. The calculation results show that the electronic and phonon structures were essential parameters in thermal conduction of metals. With the increase of temperature, the ratio of the electronic thermal conductivity to the total thermal conductivity increased gradually.