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The challenge of cavitation erosion (CE) in flow-handling components of marine engineering has promoted the development of advanced materials due to safety incidents and economic costs. High entropy alloys (HEAs), known for high hardness and corrosion resistance, emerge as promising candidates. This paper delved into the CE characteristics of CoCrFeNiMoCu0.1 HEA when subjected to the 3.5 wt% NaCl solution, elucidating the synergistic effect of CE-corrosion. The quantitative analysis revealed that CE-corrosion synergy contributed 48.02% to total CE mass loss, primarily attributed to corrosion-induced CE damage. Meanwhile, electrochemical noise (EN) was utilized to reveal the corrosion behavior of CoCrFeNiMoCu0.1 HEA in 3.5 wt% NaCl solution combined with the morphologies observation and surface roughness. Extended CE time compromised the corrosion resistance of CoCrFeNiMoCu0.1 HEA and diminished the impact of selective phase corrosion on the surface. Eventually, the CE damage mechanism of CoCrFeNiMoCu0.1 HEA was revealed based on pertinent experimental findings. The results showed that with increased CE time, the CoCrFeNiMoCu0.1 HEA transitioned from predominantly extensive exfoliation of the initial FCC phase to further damage of the intermetallic σ and µ phases.
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Due to the development and utilization of nuclear energy, the safe disposal of nuclear waste needs to be urgently addressed. In recent years, the utilization of microorganisms' adsorption capacity to dispose of radioactive waste has received increasing attention. When compared with conventional disposal methods, microbial adsorption exhibits the characteristics of high efficiency, low cost, and no secondary pollution. In the long term, microbial biomass shows significant promise as specific chemical-binding agents. Optimization of biosorption conditions, identification of rare earth element binding sites, and studies on the sorption capacities of immobilized cells provide compelling reasons to consider biosorption for industrial applications in heavy metal removal from solutions. However, the interaction mechanism between microorganisms and radioactive nuclides is very complex. This mini-review briefly provides an overview of the preparation methods, factors affecting the adsorption capacity, and the mechanisms of microbial adsorbents.
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In this work study, a comparative analysis was undertaken to investigate investigation into the cavitation erosion (CE) and corrosion behavior of laser powder bed fusion (LPBF) TC4 and as-cast TC4 in 0.6 mol/L NaCl solution. Relevant results indicated that LPBF TC4 revealed a rectangular checkerboard-like pattern with a more refined grain size compared to as-cast TC4. Meanwhile, LPBF TC4 surpassed its as-cast counterpart in CE resistance, demonstrating approximately 2.25 times lower cumulative mass loss after 8 h CE. The corrosion potential under alternating CE and quiescence conditions demonstrated that both LPBF TC4 and as-cast TC4 underwent a rapid potential decrease at the initial stages of CE, while a consistent negative shift in corrosion potential was observed with the continuously increasing CE time, indicative of a gradual decline in repassivation ability. The initial surge in corrosion potential during the early CE stages was primarily attributed to accelerated oxygen transfer. As CE progressed, the significant reduction in corrosion potential for both LPBF TC4 and as-cast TC4 was attributed to the breakdown of the passive film. The refined and uniform microstructure in LPBF TC4 effectively suppresses both crack formation and propagation, underscoring the potential of LPBF technology in enhancing the CE resistance of titanium alloys. This work can provide important insights into developing high-quality, reliable, and sustainable CE-resistant materials via LPBF technology.
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The pores and coarse lamellar Mg17Al12 that inevitably occur in the weld zone are the major challenge for laser-welded magnesium (Mg) alloys including AZ31B. In order to improve microstructure uniformity and eliminate welding defects, a new process assisted with combination of heat and cryogenic treatment was applied in this study. The results showed that after solution treatment, the number and size of precipitates decreased and the uniformity of the microstructure improved. After cryogenic treatment, the lamellar Mg17Al12 was cracked into particles, and the grain size was refined. After solution + cryogenic treatment, Al8Mn5 substituted the lamellar Mg17Al12. Through studying the changes in microhardness, precipitates, and microstructure under different treatments, it was found that the conversation of Mg17Al12 from lamellar state into particle-like state as well as the appearance of dispersed Al8Mn5 particles played a second-phase strengthening role in improving the mechanical properties of Mg alloy laser-welded joint, and the tensile strength (258.60 MPa) and elongation (10.90%) of the sample were 4.4% and 32.6% higher than those of the as-welded joint.
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This study used electrochemical noise technology to analyse the effects of surface damage induced by cavitation erosion (CE) on the pitting and passivation behaviours of TA31 Ti alloy. According to the results, TA31 Ti alloy exhibited high corrosion resistance in NaCl solutions. However, the residual tensile stress layer generated during grinding and polishing reduced its passivation ability. Subsequently, the residual tensile stress layer was eliminated after CE for 1 h, improving the passivation ability of the material. Thereafter, pitting corrosion was initiated on the material surface. Increasing the CE time from 1 h to 2 h gradually decreased the passivation ability of the alloy. A large number of CE holes promoted the transition from pitting initiation to metastable pitting growth. which gradually dominated the surface of TA31 Ti alloy. The damage mechanism of uniform thinning increased the passivation ability and stability of the alloy with the increase in CE time from 2 h to 6 h. Therefore, the surface of TA31 Ti alloy was dominated by the initiation of pitting corrosion.
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Nickel-aluminum bronze (NAB) is widely used to fabricate flow-handling components because of its good cavitation corrosion (CE) resistance and superior casting property. The existence of different phases, e.g., the α phase, ß phase and κ phase, can cause significant selective phase corrosion on NAB. However, under the action of CE with different times, the influence of these phases on the corrosion behavior of NAB, including selective phase corrosion and uniform corrosion, needs to be further studied, which can contribute to a deep understanding of the CE mechanism of NAB in corrosive media. In this work, the corrosion behavior of NAB in 3.5 wt.% NaCl solution after different CE times was evaluated by electrochemical noise (EN), combined with scanning Kelvin probe force microscopy (SKPFM) and morphology analysis. The results showed that the corrosion behavior of NAB was closely associated with the variation in its complex microstructure after different CE times. Selective phase corrosion played a crucial role in the surface damage before 0.5 h of CE. With the prolongation of CE time, the stripping of κ phases decreased the degree of selective phase corrosion of NAB. As a result, both selective phase corrosion and uniform corrosion presented equal performances after 1 h of CE. However, after CE for 2-5 h, uniform corrosion had a dominant impact on the surface damage of NAB. Eventually, the corrosion mechanism of NAB after different CE times was clarified based on the relevant experimental results.
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To retard the spread of fire in many cases with sealing materials is significant. A series of silicone rubber foam materials were prepared with room temperature vulcanization and foaming reactions. The morphology, chemical structure, cell structure, and thermal stability were investigated and results proved that the synthesis of silicone rubber was successful in a wide range of feed ratios. The fire-retardant tests were carried out to study the fire-proof property of the composite materials, and the excellent performance showed a promising prospect for wide application in sealing materials.
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To study the effect of γ' phase elements on the oxidation behavior of nanocrystalline coatings, two comparable nanocrystalline coating systems were established and prepared by magnetron sputtering. The oxidation experiments of the nanocrystalline coatings on the K38G and N5 superalloys were carried at 1050 °C for 100 h, respectively. The chemical composition of the above coatings is the same as the substrate alloy, including the γ' elements, such as Al, Ta, and Ti. After serving at a high temperature for certain periods, their oxides participated and then affected the oxidation behavior of the coatings. The Al2O3 scale can be formed on the N5 coating, which cannot be formed on the K38G coating. Tantalum and titanium oxides can be detected on the oxide scale, which ruin its purity and integrity.
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The precipitation behaviors of the topologically close-packed (TCP) phases in the bicrystal DD5 superalloy have been investigated. The results showed that the [001] crystallographic orientations are consistent with that of adjacent grains; however, the direction of the needle-like TCP phases is not consistent with that of the γ phase channels. The angle between needle-like TCP phases and γ phase channels is 45°, but the angle between the needle-like TCP phases of the adjacent grains is equal to the misorientation of the adjacent grains. Furthermore, during long-term aging, the needle-like TCP phases gradually decompose and transform into globular and short rod-like phases. The TCP phases precipitate preferentially in the dendrite. It is difficult to precipitate at the interdendrite/grain boundary, which is caused by the segregation of the constituent elements of the TCP phase to the dendrite.
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In this paper, the effect of the equal-channel-angular-pressed (ECAPed) substrate on the coating formation and anticorrosion performance of the anodized Al-11Si alloy was systematically investigated. The ECAP process dramatically refines both Al and Si phases of the alloy. The parallel anodizing circuit is designed to enable a comparative study of anodizing process between the cast and the ECAPed alloys by tracking their respective anodizing current quota. The optimum coatings of both alloys were obtained after anodization for 30 min. The ECAPed alloy attained a thicker, more compact, and more uniform coating. Energetic crystal defects in the fine Al grains of the ECAPed substrate promote the anodizing reaction and lead to the thicker coating. Fragmented and uniformly distributed fine Si particles in the ECAPed alloy effectively suppress the coating cracks, enhancing the compactness of the coating. Overall, the ECAP-coated sample exhibits the best anticorrosion performance, which is evidenced by the concurrently enhanced prevention of coating and improved corrosion resistance of the substrate.
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In this study, we report on a low-temperature sintered enamel coating with a high-strength bonding and wear-resistance that protected a grey cast iron substrate. The SiO2â»Al2O3â»B2O3 composited prescription for the enamel coating was modified by the partial substitutions of SiO2 for B2O3 and alkali metals for Li2O. The optimized enamel coating was prepared by sintering at a relatively low temperature (730 °C) for seven minutes. Due to the composition of both the amorphous and crystalline phases, the enamel coating presented sufficient hardness and excellent wear resistance. The wear volume loss and the specific wear rate of the enamel coating were obviously lower than that of the metal substrate. The enamel coating can effectively improve the service life of the grey cast iron substrate in a complex frictional environment.
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The microstructure and wear resistance of Stellite 6 alloy hardfacing layer at two different temperatures (room temperature and 300°C) were investigated by plasma arc surfacing processes on Q235 Steel. Tribological test was conducted to characterize the wear property. The microstructure of Stellite 6 alloy coating mainly consists of α-Co and (Cr, Fe)7C3 phases. The friction coefficient of Stellite 6 alloys fluctuates slightly under different loads at 300°C. The oxide layer is formed on the coating surface and serves as a special lubricant during the wear test. Abrasive wear is the dominant mechanism at room temperature, and microploughing and plasticity are the key wear mechanisms at 300°C.