In oxygen-saturated lead-bismuth eutectic(LBE),oxide films formed on ferritic/martensitic(F/M)steels directly affect their long-term corrosion resistance and mechanical integrity during service.However,a systematic and quantitative understanding of the relationship be-tween oxide-layer growth behavior and mechanical function during LBE corrosion remains limited.In this study,the microstructural characteristics and local nanomechanical responses of multilayer oxide films formed on F/M steel under static oxygen-saturated LBE conditions were systematical-ly investigated,aiming to clarify the functional differentiation among different oxide sublayers and their distinct roles in corrosion protection. F/M steel was corroded in oxygen-saturated LBE at 550 ℃ for 2 000 h and 4 000 h.After corrosion,the cross-sectional structure and composition of the oxide layers were characterized using scanning electron microscopy and energy-dispersive spectroscopy.The local mechanical parameters of each sublayer were quantitatively obtained by nanoindentation based on the Oliver-Pharr-method.The results showed that,at both corrosion durations,a four-layer structure formed on the steel surface.It consisted of an LBE-infiltrated plumboferrite layer(PFL),an outer Fe3O4 layer(OOL),an inner Fe-Cr spinel layer(IOL),and an internal oxidation zone(IOZ).After 2 000 h of corrosion,the total oxide-layer thickness was approximately 8.76 μm.The Cr content in the IOL was approximately 12.99％(atomic fraction).Its hardness and reduced modulus were 11.30 GPa and 157.30 GPa,respectively.The hardness and reduced modulus of the OOL were 10.20 GPa and 150.30 GPa,re-spectively.In contrast,the outermost region infiltrated by LBE,defined as the PFL,exhibited degraded mechanical properties.Its hardness was 9.82 GPa,and its reduced modulus was 149.70 GPa.The IOZ consisted of dispersed Cr-rich oxide particles in the ferritic matrix and showed the lowest mechanical properties.Its hardness was 8.52 GPa,and its reduced modulus was 114.40 GPa. When the corrosion time was extended to 4 000 h,the oxide-layer structure further evolved,and the mechanical differences among the sublayers became more pronounced.The total oxide-layer thickness increased to approximately 21.92 pum,corresponding to a growth exponent of n≈1.32,which deviated from the ideal parabolic law.This indicated that the oxidation process gradually changed from diffusion-controlled growth to defect-accelerated growth associated with pore coalescence and the interconnection of vacancy channels.The IOL became thicker and denser,and its Cr content increased to 18.49％(atomic fraction).Its hardness and reduced modulus increased to 12.20 GPa and 164.10 GPa,respectively.Meanwhile,the H/Er and H3/Er2 ratios also increased,indicating excellent elastic strain tolerance and resistance to plastic de-formation.The reduced modulus and hardness of the OOL remained generally stable at 149.20 GPa and 11.80 GPa,respectively.By contrast,the PFL continued to soften.Its hardness decreased to 9.35 GPa,indicating structural weakening caused by long-term LBE infiltration.The IOZ underwent significant degradation.Its hardness decreased to 5.80 GPa,and its reduced modulus decreased to 97.97 GPa.This degradation was closely related to the formation of Kirkendall voids and network-like pores caused by unbalanced cation diffusion.In addition,a continuous por-ous band formed at the IOL/IOZ interface after 4 000 h.The approximately 40.3％mismatch in reduced modulus between the two layers made this region sensitive to potential stress concentration and interfacial instability. Based on the above quantitative microstructural and nanomechanical analyses,the protective function of the oxide film formed on F/M steel in static oxygen-saturated LBE was dominated by the inner Fe-Cr spinel layer(IOL),while the contribution of the outer Fe3O4 layer to long-term protection was relatively limited.The IOL maintained its structural integrity and mechanical stability during long-term corrosion and served as the key barrier layer.In contrast,the outer layer was gradually weakened by LBE infiltration,and the IOZ and its interface with the IOL became potential weak links during long-term service.This study revealed the structural-mechanical functional differentiation of multilayer oxide films during long-term corrosion.It provided a quantitative basis for improving the service reliability of F/M steel in lead-based liquid metal environments by regulating the formation of Cr-rich spinel layers and interfacial stability.
Coalbed methane produced water is prone to severe scaling during gathering and transportation,impairing pipeline flow and the safe operation of equipment.To improve scale inhibition,ten commonly used scale inhibitors were screened through calcium carbonate deposition tests.The results showed that polyaspartic acid(PASP),2-Phosphonobutane-1,2,4-Tricarboxylic Acid(PBTCA),maleic acid/acrylic acid copolymer(MA/AA),and 1-hydroxyethylidene-1,1-diphosphonic acid(HEDP)exhibited superior scale-inhibition performance.Composite tests were then conducted and showed that a 1∶1 mass ratio of PASP to PBTCA achieved the highest scale-inhibition efficiency of 77.4％at 20 mg/L.Further orthogonal optimization of the ratio and concentration produced a scale-inhibition efficiency of 84.4％at 40 mg/L.Scanning electron microscopy(SEM)showed that the inhibitors induced the transformation of calcium carbonate crystals from regular calcite to aragonite and vaterite,confirming a synergistic mechanism involving lattice distortion and coordination-dispersion.This study provided an efficient and environmentally friendly composite scale-inhibitor formulation for coalbed methane produced-water gathering and transportation systems.It also offered a reference for engineering applications.
As an indispensable auxiliary material in electronic assembly and soldering processes,the comprehensive performance of flux direct-ly determines the forming quality,mechanical strength,and electrical properties of solder joints,thereby fundamentally affecting the long-term reliability,service life,and operational stability of electronic products.With the rapid development of the electronic information industry,elec-tronic components have evolved toward miniaturization,high density,high integration,and lead-free technologies.This trend places more strin-gent requirements on flux.Flux must therefore provide excellent soldering performance for the precise joining of fine-pitch solder joints.It must also exhibit better temperature adaptability for lead-free soldering processes,lower residue-induced corrosiveness,and compliance with envi-ronmental regulations. This paper systematically reviewed the classification,core chemical composition,and functional mechanisms of flux.According to activity level,flux can be classified into low-activity,medium-activity,and high-activity flux,each being suitable for different soldering applications and substrate requirements.Its chemical composition mainly included film formers,activators,solvents,and additives.Film formers ensured the film-forming capability and residue characteristics of flux.Activators were the key components for removing oxide films from solder and sub-strate surfaces.Solvents regulated the viscosity of flux to meet process requirements.Additives improved auxiliary properties such as wettability and defoaming performance. On this basis,the performance evaluation system and the key influencing factors of flux were discussed in detail.The evaluation system in-cluded key indicators such as wetting force,post-soldering residue,corrosiveness,and thermal stability,which together provided a comprehen-sive basis for evaluating the applicability of flux.The key influencing factors included the proportion of chemical components,soldering process parameters(such as soldering temperature and dwelling time),and substrate surface conditions.These factors interacted with one another and directly affected the performance of flux. This paper also reviewed the research status and industrial development trends of flux in conventional soldering processes and emerging electronic applications.In conventional soldering,flux was widely applied in wave soldering,reflow soldering,and manual soldering.For exam-ple,flux for wave soldering required excellent resistance to thermal decomposition and good spreading ability,whereas flux for reflow soldering must be compatible with the high melting temperature of lead-free solder.In emerging fields,the development of chip packaging toward high-density flip-chip and three-dimensional stacking required flux with low residue,high insulation,and compatibility with ultra-fine-pitch solder joints.Soldering of high-power-density devices in power electronics required flux with excellent thermal conductivity and high-temperature sta-bility.In addition,the development of low-temperature soldering technology promoted the development of flux suitable for low-temperature ap-plications.This met the requirements of flexible electronics,bioelectronics,and other special applications. Studies showed that,driven by increasingly stringent environmental regulations,the continuous improvement of electronic product perform-ance,and the expansion of emerging application scenarios,modern flux technology developed toward environmental friendliness,high perform-ance,and multifunctionality.Among current industrial technologies,halogen-free flux became a mainstream choice because it avoided the envi-ronmental hazards and equipment corrosion associated with conventional halogen-containing flux.Meanwhile,no-clean flux also became a ma-instream solution because it simplified post-soldering cleaning,reduced manufacturing costs,and minimized residue-related risks. Finally,this paper summarized the major challenges facing current flux technology.The first was reducing volatile organic compound(VOC)emissions and improving the degradability of flux while maintaining soldering performance.The second was enhancing the long-term re-liability of solder joints under harsh environments such as high temperature,high humidity,and corrosive conditions.The third was improving the versatility and process adaptability of flux for diverse soldering technologies and emerging substrate materials.Future development was ex-pected to focus on green technologies(low VOC emissions,halogen-free,and degradable),high performance(high wettability,low residue,and excellent corrosion resistance),and multifunctionality(integrating thermal conduction,electrical conduction,and packaging protection),thereby better meeting the development needs of the electronic information industry.
Water-exposed fasteners are key load-bearing connectors in hydraulic and hydropower engineering structures.During service,the combined effects of corrosive media,local contact,and preload make them susceptible to corrosion,contact damage,and even seizing failure.Conventional protective methods,such as hot-dip galvanizing and blackening,have limited long-term stability.Physical vapor deposition coat-ings,particularly transition-metal nitride coatings,exhibit high hardness and good corrosion resistance.Because fasteners differ markedly from flat specimens in morphology,stress state,and corrosion-medium transport paths,their coating performance must be evaluated directly on actual fasteners.In this study,alternately deposited TiAlN coatings were prepared on fastener surfaces.A hybrid process combining multi-arc ion plating(MAIP)and high-power impulse magnetron sputtering(HiPIMS)was used to improve corrosion resistance and anti-loosening performance. The test specimens included single-side-polished silicon wafers and M20 × 60 mm bolt-nut assemblies.Silicon wafers were used to char-acterize coating surface morphology,cross-sectional structure,and thickness,whereas stainless-steel,carbon-steel,and blackened carbon-steel fasteners were used to evaluate coating performance.Before deposition,the specimens were ultrasonically cleaned and etched with Ar plas-ma.A Ti bonding layer and a TiN transition layer were first deposited by MAIP,followed by five alternating cycles of MAIP-TiAlN and HiPIMS-TiAlN sublayers.Based on deposition rates obtained in preliminary tests,the deposition time for each TiAlN sublayer was calculated to achieve a thickness ratio close to 1:1.The final coating thickness was approximately 3.5 μm.During MAIP deposition,the fasteners revolved with the rotating holder.During HiPIMS deposition,they faced the planar target and rotated about their own axes,thereby improving thread-surface coverage at the different deposition stages. The TiAlN coating prepared on the silicon wafer exhibited a continuous and dense cross section,with a clear interface between the TiN transition layer and the TiAlN functional layer.Owing to the MAIP process,some droplet defects remained on the coating surface;however,no obvious pores or cracks were observed in the cross section.Nanoindentation results showed that the hardness values of the TiAlN coatings on stainless-steel,carbon-steel,and blackened carbon-steel substrates were approximately 32,37,35 GPa,respectively.Scratch tests showed that the critical failure load(Lc2)of the coating on the stainless-steel substrate reached 86 N,whereas no obvious failure occurred on the car-bon-steel substrate within the loading range of 0-100 N.These results indicated that the alternately deposited TiAlN coating had high adhesion strength on stainless-steel and carbon-steel fasteners. The corrosion response of the coating was tested in a 3.5％NaCl solution at a constant potential of 1 V(vs SCE).The current responses of the coated stainless-steel and carbon-steel fasteners remained low and generally stable,indicating that the alternately deposited TiAlN coat-ing provided a stable barrier.In contrast,the coated blackened carbon-steel fastener exhibited more pronounced current fluctuations,mainly because of the higher porosity of the blackened layer and insufficient stability of the composite interface.For the stainless-steel fasteners,a seg-mented 60 min potentiostatic corrosion and weighing test showed that the mass increase of the coated specimen was only 0.063 g,whereas that of the uncoated specimen reached 8.980 g.The steady-state current of the coated specimen was approximately six orders of magnitude lower than that of the uncoated specimen. After 60 d of potentiostatic corrosion,the coated stainless-steel fastener retained a relatively intact thread profile and could be disassem-bled normally using a torque wrench.In contrast,the uncoated fastener was covered with abundant corrosion products,and its threaded mating region was severely damaged and exhibited obvious seizing.Scanning electron microscopy(SEM)showed that the thread geometry of the coated specimen remained relatively clear,whereas the uncoated specimen suffered deep corrosion damage and material loss.Energy-dispersive spec-troscopy(EDS)showed that the corroded region of the uncoated specimen consisted mainly of Fe,O,and Cr,with detectable Cl enrichment.The coated specimen surface consisted mainly of Ti,Al,and O and contained relatively little Fe and Cr.Raman spectroscopy revealed distinct α-Fe2O3 and α-FeOOH signals on the uncoated specimen.The coated specimen mainly exhibited TiN/TiAlN-related signals and a TiO2-related response,indicating that its corroded surface was still dominated by the residual TiAlN coating and surface oxidation products. The transverse vibration anti-loosening test showed that the final clamping force of the coated stainless-steel fastener was 58.68 kN,with a decay rate of only 2.2％,whereas that of the uncoated specimen decreased to 50.49 kN,with a decay rate of 15.8％.This improvement was mainly attributed to the high hardness and good coating-substrate adhesion of the TiAlN coating,which reduced direct metal-to-metal contact between mating threads,limited local plastic deformation and minor damage,and thereby reduced preload loss during transverse vibration.Overall,the alternately deposited TiAlN coating simultaneously improved the corrosion resistance and anti-loosening performance of stainless-steel fasteners by forming a dense multilayer barrier and stabilizing the threaded contact interface.These results provided a reference for the sur-face-protection design of water-exposed fasteners.
To address the numerous cracks and pores that readily form in Ni-based coatings deposited on plastic molds by electrospark deposi-tion(ESD),a Ni-based coating doped with 1.00％La2O3 was prepared by ESD,and the effects of La2O3 on coating microstructure and wear resistance were investigated.Scanning electron microscopy,X-ray diffraction,microhardness testing,and friction and wear testing were used to systematically analyze the microstructure,phase constitution,hardness,and tribological properties of the coatings.The results showed that adding an appropriate amount of La2O3 significantly reduced cracks and pores in the Ni-based coating and refined its dendritic structure into ul-trafine grains.The principal phases in both the Ni-based coating and the La2O3/Ni-based coating were a(Ni,Fe)solid solution and the hard phases M7C3,Cr23C6,and CrB.The addition of La2O3 did not change the phase constitution of the Ni-based coating but increased its average hardness by 18.0 HV0.1.Friction and wear tests showed that the wear rate of the La2O3/Ni-based coating was 47.98％lower than that of the pure Ni-based coating.Material removal from the pure Ni-based coating was brittle fatigue spalling,whereas the La2O3/Ni-based coating main-ly underwent plowing and microcutting induced by abrasive wear.
