Chloride molten salts, endowed with excellent physicochemical properties, exhibit broad application prospects in the electrochemical separation of spent nuclear fuel (SNF) and molten salt reactors (MSRs), in which they function as electrolytes, fuel solvents and coolants. However, the high-temperature, strongly chlorinating, and oxidizing environment of molten salt systems poses severe challenges to the corrosion resistance of structural materials, which has become the key factor restricting their engineering applications. In this study, the corrosion behaviors of stainless steels and Ni-based superalloys in molten salt environments are systematically reviewed, with a focus on the effects of various factors, including alloying elements, corrosive environments, temperatures and impurities (water and oxygen). Studies have indicated that Ni-based superalloys exhibit superior corrosion resistance compared with stainless steels due to the incorporation of a large number of refractory metal elements. Molten salt purification can effectively reduce the impurity content in the system, thereby significantly mitigating material corrosion. In chloride molten salt environments, uranium (U) exerts a significant influence on the corrosion resistance of alloys. However, its radioactivity and other inherent properties impose stringent requirements on the experimental conditions for related studies. Given the similarities in physicochemical properties such as ionic radius between U and cerium (Ce), this study investigates the mechanism by which CeCl3 affects the corrosion resistance of materials in molten salt systems. These findings provide important insights into the corrosion behavior of materials induced by U in molten salts. Currently, the corrosion of metallic materials in high-temperature molten salts remains a major bottleneck in the development of SNF reprocessing technology. Future research should focus on developing commercial alloys with excellent corrosion resistance to chloride molten salts, and further exploring their corrosion mechanisms and influencing factors, thereby providing critical support for the advancement of SNF reprocessing technology.
A novel strategy for constructing a multiscale, multiple-heterogeneity heterostructure is proposed in this study to overcome the conventional strength-ductility trade-off in duplex stainless steels (DSSs). The multiscale heterogeneous microstructure, which integrates microscale phase heterogeneity, grain-size heterogeneity, and nanoscale chemical heterogeneity, was successfully constructed in super duplex stainless steel 2507 via a simple processing route involving two-step solution treatment, cold rolling, recrystallization annealing, and aging. The effects of recrystallization annealing temperature and time on grain size and phase fraction evolution were systematically investigated, and spinodal decomposition (SD) nanostructures were quantitatively characterized using small-angle neutron scattering (SANS). The formation mechanisms of the multiscale heterostructure and their effects on mechanical behavior were elucidated, thereby obtaining the optimal processing route. The results of in-situ synchrotron X-ray diffraction tensile tests reveal that the heterogeneous microstructure induces a pronounced hetero-deformation strengthening effect and promotes dynamic stress-strain partitioning between austenite and ferrite during plastic deformation. This mechanism significantly enhances the work-hardening capability of austenite while alleviating stress concentration in ferrite, thereby suppressing the initiation and propagation of microcracks. Furthermore, the SD nanostructures formed in ferrite provide additional strengthening contributions. Consequently, the heterostructured DSS exhibited an exceptional combination of strength and ductility, with a yield strength of 1056 MPa, an ultimate tensile strength of 1399 MPa, and an elongation of 25%. These results demonstrate that the multiscale heterostructures effectively break the conventional strength-ductility trade-off in DSSs. These findings not only present a novel microstructural design strategy for developing high-performance DSSs, but also offer important theoretical references and an experimental basis for the design of advanced structural metallic materials with enhanced strength-ductility synergy.
Composites of FeCoCrNiMo/Al-10Si were fabricated by laser deposition technique with mixed powder of FeCoCrNiMo and Al-10Si as raw material. The microstructure, local composition and tribological properties of the composites were characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, and UMT-3 tribometer. The results demonstrate that the α-Al grain size gradually decreases with the increasing mass fraction of FeCoCrNiMo reinforcements. The morphology of the reinforcing phase evolves from initially spherical to petal-like, and finally to a coarse fishbone structure. A distinct interfacial reaction layer with a thickness of approximately 30 nm is formed between the FeCoCrNiMo high-entropy alloy and the Al matrix, which can be identified as Al3Ni2. As the mass fraction of the FeCoCrNiMo reinforcements increases, the wear resistance of the composites was improved correspondingly. However, when the mass fraction of FeCoCrNiMo exceeds 10%, the enhancement in wear resistance becomes less pronounced. The dominant wear mechanism shifts from fatigue and adhesive wear to abrasive wear.
To tailor the microstructure and properties of Zn-Li alloy ultrafine wires for cardiovascular stent braiding, this study systematically investigates the effects of heat treatment at 70 oC, 120 oC, and 150 oC on the microstructure, mechanical properties, and electrochemical corrosion behavior of Zn-0.45Li alloy wires with a diameter of 0.14 mm. The results revealed that heat treatment at 70 oC only resulted in static recovery, whereas treatments at 120 oC and 150 oC sequentially induced partial recrystallization, full recrystallization, and grain growth as holding time increased. After heat treatment, the ultimate tensile strength of the wire increased significantly, whereas its ductility decreased. Higher treatment temperatures resulted in greater strength enhancement and a more pronounced reduction in ductility. The optimal comprehensive performance was achieved after holding at 150 oC for 30 min, with a maximum ultimate tensile strength of 706.9 MPa, approximately 90 MPa higher than that in the cold-drawn state, while the elongation after fracture remained at 38.5%. After heat treatment, the corrosion current density increased, and the corrosion rate accelerated with increasing treatment temperature, whereas the effect of holding time on corrosion behavior at the same temperature is relatively weak. The core mechanism underlying the evolution of strength and ductility is the obstruction of grain-boundary sliding by grain growth, while micro-galvanic corrosion induced by second-phase precipitation is the dominant factor contributing to accelerated degradation. These findings provide experimental evidence and theoretical support for the optimization of the heat treatment process of medical biodegradable Zn-Li alloy wires for stent applications.
To address the severe interfacial adhesion, high cutting temperatures, and rapid tool wear encountered during the machining of the nickel-based superalloy Inconel 718, four rake-face micro-textured tools were designed in this study: grooves perpendicular to the cutting edge (VT), grooves parallel to the cutting edge (PT), grooves oriented at 45° (45T), and a square-dimple array (DT). An untextured tool (NT) was employed as the reference. Turning experiments were conducted under minimum quantity lubrication (MQL) and nano-minimum quantity lubrication (NMQL) conditions at three cutting speeds. The results indicate that the main cutting force initially decreased and then increased with increasing cutting speed, and the overall cutting load reached a minimum at Vc = 80 m/min. At this cutting speed, the main cutting forces of VT, PT, DT, and 45T were 9.12%, 7.63%, 5.21%, and 3.51% lower than those of NT, respectively, thereby confirming the effectiveness of rake-face textures in reducing cutting loads. Furthermore, the cutting temperature increased with cutting speed; however, both surface textures and lubricants significantly reduced the cutting temperature. Under MQL and NMQL conditions, the temperature reduction of textured tools relative to NT ranged from 8.8% to 14.5% and from 11.4% to 18.0%, respectively, with VT showing the most pronounced cooling effect. Based on the wear characterization of the rake and flank faces, rake-face adhesion and spalling were effectively mitigated under NMQL, and the maximum flank wear width (VBmax) of NVT was the smallest, with a value of only 60.99% of that of NNT. Overall, open-groove textures combined with WS2-enhanced NMQL demonstrated a pronounced synergistic anti-friction and anti-wear effect. This synergy reduced the apparent level of interfacial friction and improved the cutting deformation conditions, thereby alleviating heat accumulation and suppressing tool wear propagation. Ultimately, this enhanced the interfacial tribological environment and the tool service conditions during turning of Inconel 718.
This study focuses on MAX phases and addresses the challenge of their decomposition during the construction of sprayed coatings. Ti, Al, and graphite powders were selected as raw materials to design and construct Ti-Al-C reinforced composite coatings, in which a portion of the MAX phase was formed in situ through centrifugal atomization drying, sintering granulation, and plasma spraying. A nine-group orthogonal experimental design was employed to systematically investigate the effects of spray parameters on the microstructure, mechanical properties, and high-temperature tribological performance of the coatings. The results revealed that, due to the presence of MAX phases and ceramic phases, such as TiC, the optimized coatings exhibit higher hardness than that of the substrate and excellent bonding strength. High-temperature friction and wear tests revealed that the coatings exhibit significantly lower wear rates than those of the substrate, and the wear resistance improves with increasing temperature. This enhancement is likely attributed to temperature-induced phase transformations or the further formation of MAX phases. At 700 oC, the wear rate of the C2 coating in the Ti-Al-C system is 98.9% lower than that of the substrate. After repeated wear, phases such as Ti x Al y and Ti2AlC in the coating undergo friction-induced sintering and oxidation, thereby forming a glazed layer on the worn surface. During sliding, material transfer occurs between the coating and the counterface. The dominant wear mechanisms of the composite coating are identified as oxidative, adhesive, and fatigue wear.
Laser powder bed fusion (L-PBF) technique demonstrates tremendous potential in application, but this process tends to generate significant residual stresses within workpieces, potentially causing deformation. Herein, the L-PBF process for a thin-walled Ti6Al4V alloy elbow component was numerically simulated by means of finite element software in terms of the effect of the variation of laser powers and the speed of laser scanning on the deformation of the prepared workpiece of Ti6Al4V alloy. The simulation accurately predicted the deformation trends and magnitudes, quantitatively revealing the influence of laser power and scanning speed on the workpiece deformation. The optimal parameter combination was determined to be 180 W laser power and 1.2 m/s scanning speed based on the numerical investigation. Through L-PBF, a thin-walled Ti6Al4V alloy elbow component was fabricated, of which the deviations of dimensions were measured using a coordinate measuring machine, revealing good consistency between the measured data and the simulation results.
