Interaction of Mechanical and Electrochemical Factors duringCorrosion Fatigue of Fe-26Cr-1Mo Stainless Steel in 1M H_2SO_4 Solution

The cyclic plastic straining electrode technique has been used to investigate the transient electrochemical behaviour of Fe-26Cr1Mo stainless steel in 1M H2SO4 solution at a passive potential.The influence of plastic strain amplitude and plastic strain rate on the dissolution current response was analysed. The experimental results showed that the transient current was dependent on the competitive process of the surface film rupture and repassivation of the new surface. The high plastic strain amplitude and the high plastic strain rate caused a change of electrochemical activity of specimen surface. In the condition of low strain amplitude and strain rate, the characteristics of current response was mainly relative tp the process of new surface repassivation.The competition kinetics has been analysed through the comparison of plastic strain rate and repassivating rate

Manipulating Film Formation Kinetics Enables Organic Photovoltaic Cells with 19.5%Efficiency

Organic photovoltaic(OPV)cells have demonstrated remarkable performance in small,spin-coated areas.Nevertheless significant challenges persist in the form of large efficiency losses due to the fact that the ideal morphology cannot be preserved in the transition of small-area cells to large-scale panels.Herein,the ternary strategy of incorporating the third component FTCC-Br into the active layer of PB2:BTP-eC9 is employed to improve absorption response,optimize morphology,and reduce charge recombination,leading to a power conversion efficiency(PCE)of 19.5%(certified as 19.1%by the National Institute of Metrology,China).Moreover,the addition of FTCC-Br can control the aggregation kinetics of the active layer during the film formation process,transferring the optimal morphology to the blade-coated large-area films.Based on the highly efficient ternary bulk heterojunction,the 50 cm^(2) OPVmodules exhibited a PCE of 15.2%with respect to the active area.Importantly,the ternary OPV cells retain 80%of its initial PCE after 4000 h under continuous illumination.Our work demonstrates that the addition of a third component has the potential to improve the efficiency and stability of large-area organic solar cells.

The value of FinTech innovations for the finance industry:Evidence from China

This paper explores the value effects of FinTech innovations on the finance industry in China,focussing on the banking system.We use a crawler-like application programme to grab patent filing information and manually identify and classify FinTech innovations based on their application fields.FinTech patents generally bring adverse value effects to various finance sectors,revealing a competitive relationship between innovators and financial firms.FinTech innovations applied to insurance and asset management cause the most harm to the industry,especially to state-owned and joint-stock commercial banks.Moreover,disruptive FinTech innovations by start-up firms appear to pose more potential threats to commercial banks.

Fretting wear behavior of Zr alloy cladding tube mated with Zr alloy dimple under mixed fretting regime in simulated primary water of PWR

The fretting wear behavior of Zr alloy cladding tube under mixed fretting regime in a high-temperature pressurized water was investigated.The main wear mechanism is adhesive wear,with characters of small-scale delamination at the center of worn area and serious delamination on the worn edge.A long crack throughout the worn area and other cracks propagated towards the substrate are observed.The cross-sectional microstructure of worn area can be divided into a thick third-body layer,thin inner oxide layer and thick tribologically transformed structure layer,and their formation mechanisms are analyzed in detail.Finally,the mixed fretting regime process and the microstructural evolution during fretting wear are discussed.

Effect of Normal Force on Fretting Wear Behavior of Zirconium Alloy Tube in Simulated Primary Water of PWR

The effect of normal force on fretting wear behavior of zirconium alloy tube mated with grid dimple in simulated primary water of pressurized water reactor nuclear power plant was investigated.Results showed that the maximum wear depth,wear volume and wear coefficient of Zr alloy tube in simulated primary water at 315℃ gradually increased with increasing normal force,while the friction coefficient gradually decreased.Fretting process could be divided into four stages according to the variation of friction coefficient during test.When normal force exceeds 30 N,the fretting regime would transition from gross slip regime to partial slip regime after 3×10^(7 )cycles.Delamination was aggravated with increasing normal force,while abrasive wear became slighter.A thicker third-body layer with monoclinic ZrO_(2) was formed by the tribo-sintering mechanism under higher normal force.In addition,the schematic evolution processes of delamination and third-body layer formation were displayed according to morphology observation.

Microstructure, Mechanical Properties and Corrosion Resistance of the Mo_(0.5)V_(0.5)NbTiZr_(x) High-Entropy Alloys with Low Thermal Neutron Sections

High-entropy alloys exhibit significant potential for application in the nuclear industry owing to their exceptional resistance to irradiation,excellent mechanical properties,and corrosion resistance.In this work,the Mo_(0.5)V_(0.5)NbTiZr_(x)(x=0-2.0)high-entropy alloys containing alloying elements with low thermal neutron absorption cross section were designed and prepared.The crystal structure,microstructure,mechanical properties and corrosion resistance of the studied alloys were investigated.All the alloys possess a body-centered cubic crystal structure,which is consistent with the CALPHAD(acronym of CALculation of PHAse Diagram)modeling results.The addition of Zr does not alter the crystal structure of the Mo_(0.5)V_(0.5)NbTiZr_(x) alloys;however,it leads to an increase in the lattice constant as Zr content increases.The addition of Zr initially enhances the yield strength,but subsequently leads to a decline as the Zr content increases further.Specifically,the corrosion resistance of the Mo_(0.5)V_(0.5)NbTiZr_(x) alloys in superheated steam at 400℃ and 10.3 MPa decreases with the increase of Zr content.The effect of Zr content on the phase formation,mechanical properties and corrosion resistance of the Mo_(0.5)V_(0.5)NbTiZr_(x) high-entropy alloys are discussed.This study has successfully developed a novel Mo_(0.5)V_(0.5)NbTiZr_(0.25) high-entropy alloy,which demonstrates exceptional properties including high yield strength,excellent ductility,and superior anti-corrosion performance.The findings of this research have significant implications for the design of high-entropy alloys in nuclear applications.

Corrosion Behavior of X52 Anti-H_2S Pipeline Steel Exposed to High H_2S Concentration Solutions at 90℃

Initial corrosion kinetics of X52 anti-H2S pipeline steel exposed to 90 ℃/1.61 MPa H2S solutions was investigated through high temperature and high pressure immersion tests. Corrosion rates were obtained based on weight loss calculation. The corrosion products were analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and electron probe micro-analysis （EPMA）. The initial corrosion kinetics was found to obey the exponential law. With increasing immersion time, the main corrosion products changed from iron-rich mackinawite to sulfur-rich pyrrhotite. The corrosion films had two layers： an inner fine-grained layer rich in iron and an outer columnar-grained layer rich in sulfur. The corrosion film formed through the combination of outward diffusion of Fe2＋ ions and inward diffusion of HS^- ions. The variation of the corrosion products and compaction of the corrosion layer resulted in a decrease in the diffusion coefficient with increasing immersion time. The double-layered corrosion film formed after long time immersion acted as an effective barrier against diffusion.

Characterization of Different Surface States and Its Effects on the Oxidation Behaviours of Alloy 690TT

Alloy 690TT samples with four kinds of surface states were prepared： 1） ground to 400 grit; 2） ground to 1500 grit; 3） mechanically polished （MP） and 4） electro-polished （EP）. The surface morphologies and the surface skin layers＇ microstructures of these samples were characterized systematically using various methods and the effects of surface states on the oxidation behaviours of Alloy 690TT were also discussed. The results showed that surface roughness and micro-hardness decreased gradually from the ground to EP surfaces. The grains in the near-surface layers of the ground and MP surfaces had been refined and the residual strains were also very high. The dislocations on the ground surfaces were mainly parallel dislocation lines. The thickness of the superficial cold-worked layers decreased gradually from the ground surfaces to polished surfaces. The oxide morphologies and oxidation rate depended greatly on the surface states of samples. Cold-working by grinding treatments could benefit the outward diffusion of metallic atoms and the nucleation of surface oxides and then accelerate the growth of surface oxide films.

Effects of Forging and Heat Treatments on the Microstructure and Oxidation Behavior of 316LN Stainless Steel in High Temperature Water

Microstructure of 316 LN stainless steel(ss),including the as-received material and samples processed by solution anneal treatment and stress relief treatment after forging,was characterized by Vickers hardness(HV) testing and electron back scattering diffraction(EBSD).The oxide film formed on samples after immersion in borated and lithiated water at 583.15 K was investigated by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS).Results showed that the grain size of samples was largely reduced after forging.Higher fraction of coincidence site lattice(CSL) boundaries and lower residual strain were observed in samples with either solution anneal treatment or stress relief treatment.The proportion of CSL boundaries was largely enhanced by solution anneal treatment after forging,due to the recrystallization occurring during solution anneal treatment.The oxide film grown on 316 LNss with solution anneal treatment after forging exhibited more strong protectiveness,as compared to the oxide film grown on samples with stress relief treatment after forging and the oxide film grown on asreceived samples without forging.The mechanisms of oxidation were then discussed.

Analysis of Surface Oxide Films Formed in Hydrogenated Primary Water on Alloy 690TT Samples With Different Surface States

Oxidation of Alloy 690 TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 10 6B and 2.3 10 6Li with 2.5 10 6dissolved H2, at 325℃ and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion： an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones.Samples of ground Alloy 690 TT showed superior resistance to intergranular attack（IGA）.

Hydrogen-assisted fracture features of a high strength ferrite-pearlite steel

Up to now, the exact reason of hydrogen-induced fracture for ferrite-pearlite(FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim to reveal the hydrogen-induced cracking initiation and propagation processes. Slow strain rate tensile(SSRT) testing shows that the FP steel is sensitive to hydrogen embrittlement(HE). Focused ion beam(FIB)was used to prepare samples for TEM observations after HE fracture. The corresponding fractographic morphologies of hydrogen charged specimen exhibit intergranular(IG) and quasi-cleavage(QC) fracture feature. Pearlite colony, ferrite/pearlite(F/P) boundary and the adjacent ferrite matrix are found to be responsible for the initial HE fracture and the subsequent propagation. With increasing of the stress intensity factor, fracture mode is found to change from mixed IG and QC to entire QC feature which only occurs at the ferrite matrix. No crack is observed at the ferrite/cementite(F/C) interface. This may be mainly due to the limited pearlite lamella size and relatively low interface energy.

Multi-scale study of ductility-dip cracking in nickel-based alloy dissimilar metal weld

A ductility-dip-cracking(DDC)-concentrated zone(DCZ) in a width of about 3 mm was observed adjacent to the AISI 316 L/52 Mw fusion boundary(FB) in 52 Mw. The morphology, microstructure, mechanical and thermal properties and corrosion behavior in simulated primary water of DDC/DCZ were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM), 3 D X-ray tomography(XRT), 3 D atom probe(3 DAP), slow strain rate tensile(SSRT) testing and thermal dilatometry. The results indicate that DDCs are random-shaped and disc-like cavities with corrugated structure of inner surface and are parallel in groups along straight high-angle boundaries of columnar grains, ranging from micrometers to millimeters in size. Large-size M_(23)C_6 carbides dominate on the grain boundaries rather than MC(M=Nb, Ti), and thus the bonding effect of carbides is absent for the straight grain boundaries.The impurity segregation of O is confirmed for the inner surfaces of DDC. The oxide film formed on the inner surface of DDC(about 50 nm) is approximately twice as thick as that on the matrix(about 25 nm)in simulated primary water. The yield strength, tensile strength and elongation to fracture of 52 MwDCZ(400 MPa, 450 MPa and 20 %, respectively) are lower than those of 52 Mw-MZ(460 MPa, 550 MPa and 28 %, respectively). The intrinsic high-restraint weld structure, the additional stress/strain caused by the thermal expansion difference between AISI 316 L and 52 Mw as well as the detrimental carbide precipitation and the resulting grain boundary structure all add up to cause the occurrence of DCZ in the dissimilar metal weld.

Effects of Surface State and Applied Stress on Stress Corrosion Cracking of Alloy 690TT in Lead-containing Caustic Solution

The effects of surface state and applied stress on the stress corrosion cracking （SCC） behaviors of thermally treated （TT） Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit （ground）, shot-peened （SP） and electro-polished （EP） and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.

A new method to determine the synergistic effects of area ratio and microstructure on the galvanic corrosion of LAS A508/309 L/308 L SS dissimilar metals weld

The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508,both locally and globally.Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents.It was revealed that in the galvanic interaction of the DMW,the grain refined region corrodes most,followed by the partial grain refined region and base metal matrix of the A508,respectively.The electrochemical localization index(LI)estimation method and AFM analysis both confirmed the presence of a mixed(localized and uniform)corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals.Finally,the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309 L/308 L SS DMW.

Understanding the galvanic corrosion of the Q-phase/Al couple using SVET and SIET

The galvanic corrosion of the Q-phase/Al couple in 0.1 M NaCl solutions has been studied using the scanning vibrating electrode technique (SVET)f the scanning ion-selective electrode technique (SIET) and energy dispersive X-ray spectroscopy (EDX). The galvanic corrosion of the Q-phase/Al couple was found to be dependent on pH and immersion time. Current density maps obtained by SVET shows that the anodic oxidation processes emerge from Al in a localized manner in pH 2 and 6 solutions but is initiated in a uniform manner in pH 13 solution, whereas, the cathodic processes are more homogeneously distributed over the Q-phase at pH 2.6 and 13. It is seen that the Q-phase remains cathodic in the Q-phase/Al couple in acidic, neutral and alkaline solutions indicating that the galvanic polarity of the Q-phase is independent of pH. The effect of the galvanic corrosion was largest at pH 2 and 13 compared to pH 6. The pH map obtained by SIET indicates that the galvanic activity of the Q-phase/Al couple proceeds via heavy alkalization of the Q-phase surface with the generation of appreciable amounts of OH~ ions. The enrichment of Cu indicated by EDX is responsible for the observed cathodic activity of the Q-phase in the Q-phase/Al couple.

Effect of cumulative gamma irradiation on microstructure and corrosion behaviour of X65 low carbon steel

X65 low carbon steel was exposed to Co-60 radiation source with 1.25 MeV gamma rays, and cumulatively absorbed gamma irradiation doses（1, 2, and 3 Mgy） were obtained after different exposure time（333, 667, and 1000 h）. The effect of cumulative gamma irradiation on microstructure and corrosion behaviour of the carbon steel in unirradiated aerobic Beishan groundwater at 25℃ was investigated by using positron annihilation, scanning vibrating electrode, and electrochemical techniques. Cumulative gamma irradiation increases vacancy intensity and decreases open circuit potential（OCP） of carbon steel. They indicate that the irradiated carbon steel is activated. Measured current density distribution above the irradiated carbon steel shows that cumulative gamma irradiation accelerates localized corrosion after 0.5 h of immersion. In contrast, the analysis of electrochemical impedance spectroscopy of the irradiated carbon steel indicates that localized corrosion is transformed into general corrosion after 12 h of immersion, which is also accelerated by cumulative gamma irradiation.

Characterization of Corrosion Behavior of Irradiated X65 Low Carbon Steel in Aerobic and Unsaturated Gaomiaozi Bentonite

2.98 kGy/h(1007 h) gamma irradiation and 90 ℃(2000 h) thermal aging were exerted to X65 grade low carbon steel buried in Gaomiaozi bentonite containing 17 wt% Beishan groundwater. The average corrosion rate of X65 low carbon steel was measured. The elemental and phase distribution on cross section was characterized by using electron probe micro-analysis, high-resolution X-ray diffraction, and micro-X-ray diffraction. The following conclusions can be made: the average aerobic corrosion rate of the carbon steel is(45.16 ± 1.53) μm/year. Taking the original surface as boundary, the corrosion scale is divided into an internal dense product layer(DPL) mainly composed of Fe_3O_4 with segregated FeCO_3 at the corrosion front and an external DPL mainly composed of Fe_3O_4 with segregated α-Fe_2O_3 and bentonite at some relics.Si, S, and Cl are concentrated at the corrosion front of the internal DPL, while Si and Al are concentrated at the external DPL.

Characterization of machined surface quality and near-surface microstructure of a high speed thrust angular contact ball bearing

Bearings are one of the most important components in modern industry.Rolling contact fatigue(RCF)initiating from surface and subsurface is the major failure mode.In this paper,a typical high speed thrust angular contact ball bearing was selected,and the machined surface quality and near-surface microstructure of the race-way and rolling ball were systematically characterized by using of a probe surface profiler,white light interferometer,optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM)combined with focused ion beam(FIB).Two kinds of precursor,probably resulting in pitting or spalling during the following rolling contact,were detected.One is the defects on the surface of either the race-way or the rolling ball,such as heavy machining marks,scratches and slag-hole.The other is nano-crystalline layer due to machining,in the outermost layer around the surface of race-way.The results may well lay foundation for our further research on RCF with the real part of such typical rolling bearings.

Effects of cutting parameter on microstructure and corrosion behavior of 304 stainless steel in simulated primary water

The influence of surface conditions on the corrosion behavior of engineering structures has been paid more attention.However,there is still a lack of systematic research on the effect of cutting parameters on material’s microstructure and performance in service.In this paper,the effect of cutting parameters on microstructure and corrosion behaviors of 304 stainless steel in simulated primary water is well investigated.The results show that different cutting parameters can cause the superficial layer a gradient microstructure with nanocrystalized layer on top and deformation band structures underneath.With the similar surface roughness,the deformation microstructure can be very different due to the different cutting parameters.The effect degree on the depth of deformation zone is feed rate>cutting depth>cutting speed.The larger feed rate,lower cutting depth,lower cutting rate may induce a deeper deformation zone.With the increasing depth away from the machined surface,the localized corrosion rate is decreased,and at the same depth the localized corrosion rate along the deformation bands is higher than that along the grain boundaries(GBs).The nanocrystalized surface has a smallest general corrosion rate due to the quick formation of Cr rich oxide film.However,once the corrosion penetrates through this nanocrystalized layer,subsequent preferential corrosion at deformation bands and GBs will dominate and may lead to the significant increase of corrosion rate of the component in high temperature pressurized water.

Effects of processing additives in non-fullerene organic bulk heterojunction solar cells with efficiency >11%

Here we investigate processing additive-dependent photovoltaic performance and charge recombination in organic bulk heterojunction(BHJ) solar cells based on a polymeric donor of PBDB-T blended with a non-fullerene acceptor m-ITIC. We find that PBDB-T:m-ITIC solar cells exhibit good compatibilities with the utilized additives(DIO, CN, DPE, and NMP) in optimal conditions, can have a high charge dissociation probability approaching 100%(with DIO), leading to ultimate efficiency >11%. Regardless of additives, we observe a dominant 1 st order monomolecular recombination with insignificant bi-molecular recombination or space-charge effects in these solar cells. Despite of impressive power conversion efficiency(PCE), it is of surprise that Shockley-Read-Hall recombination is identified to play a role in device operation. Thus, it points to the necessity to mitigate the influences of traps to further boost the efficiency in non-fullerene based organic solar cells.