Ni-rich Layer Research Articles

Microstructure and corrosion property evolution of a surface-nanostructured 15–15Ti austenitic steel during immersion in liquid LBE at 550 °C

This study investigated the compatibility of surface-nanostructured 15–15Ti austenitic steel in 550 °C LBE with an oxygen concentration of 5 × 10−7 wt.% for various exposure durations (759, 1638, 2404, and 3012 h). The results demonstrate that the grain size was reduced from 33.50 μm to the nano-scale after shot-peening (SP), achieving 17.62, 15.44, and 14.25 nm under SP pressures of 0.06, 0.15 and 0.25 MPa, respectively. The untreated steel experienced severe oxidation and dissolution corrosion, whereas the surface-nanostructured steel exhibited only mild oxidation and was resistant to dissolution corrosion. The enhanced corrosion resistance of surface-nanostructured steel is attributed to the higher protectiveness of the Cr-rich spinel layer and the less defective Ni-rich layer beneath it. Recrystallization occurred exclusively in the Ni-rich region, while the deformed steel underwent recovery during exposure. The thickness of the recrystallization layer was 2.9 μm at 759 h, increased to 8 μm at 1638 h, and remained stable thereafter. The size of recrystallized grains in SP-samples processed under pressure of 0.06 MPa and 0.15 MPa was approximately 2.92 μm, whereas it was about 1.32 μm for 0.25 MPa processed sample.

Evolution mechanism of element Ni on matrix, surface and interface during static soaking of copper-nickel alloy

This article uses XRF, WLI, SEM, EDS, XPS and EIS techniques to characterize the surface element segregation and the state of corrosion product films under different periods of artificial seawater immersion. The research results show that when the film is intact, a uniform Ni-rich layer is formed below the film due to the preferential dissolution of Cu elements, which weakens the segregation degree of Ni elements on the surface of the substrate. At the same time, Ni elements enter the film in the form of doping, which increases the resistance of the film. When the film layer is damaged, the Ni-rich layer between matrix and surface will be rapidly converted to NiO, the enrichment state of Ni element will be destroyed, and the segregation degree will be increased. However, NiO only plays a temporary protective role, and it is easy to hydrolysis into loose Ni (OH)2, resulting in the film layer fall off. After the matrix is exposed, the Cu element is preferentially dissolved again, and the nickel-rich layer is re-formed on the substrate surface.

Effect of polyacrylic acid on the corrosion behavior of Alloy 690 in pressurized water reactor secondary water

The effect of polyacrylic acid (PAA) on the corrosion behavior of Alloy 690 in simulated pressurized water reactor secondary water was investigated. The duplex oxide film structure, consisting of a Ni-rich outer layer and a Cr-rich inner layer, was maintained regardless of PAA presence. PAA inhibited the growth of outer Ni-rich particles while promoting Cr enrichment in the inner layer and inducing its amorphization, both enhancing oxidation resistance. However, excess PAA (≥ 500 ppb) suppressed protective oxide formation during initial oxidation, leading to oxygen penetration into the matrix. A PAA concentration of around 250 ppb is considered optimal for steam generators, as it provides the benefits of PAA without adverse effects on the alloy.

In Situ Thermal Interactions of Cu-Based Anti-Corrosion Coatings on Steel Implemented by Surface Alloying

Incorporating expensive alloying elements into bulk steel for corrosion protection is undesirable, considering that only the surfaces are exposed to aggressive environments. Therefore, this work focused on developing and optimizing a new surface functioning technology through in situ observation of thermal interactions between the metallic powders at elevated temperatures. The study revealed that the Cu-Ni powder mixture, with 12.5 wt% Ni, began to melt at 1099.5 °C and was fully melted at 1175 °C, significantly different from the Cu-Ni solid solution and bulk Cu or Ni. As a result of high-temperature reactions, copper penetration of up to 35 µm for pure copper and 55 µm for copper-chromium composite coatings occurred due to liquid metal corrosion. In contrast, the copper-nickel composite coating exhibited a cupronickel solution microstructure with FeNi dendrites and a nickel-rich transition layer. This cupronickel coating, with a chemical composition of 89.3 wt% Cu, 6.2 wt% Ni, and 4.5 wt% Fe, demonstrated uniform thickness, superior surface morphology, and continuous coverage on the steel substrate. Furthermore, the Ni-rich transition layer played a vital role in preventing copper penetration along the grain boundary of the steel matrix while forming a chemical binding between the coating and the substrate. The practicality of the coating was further confirmed through the hot-rolling procedure and subsequent electrochemical corrosion tests, which resulted in a 44% improvement in corrosion resistance.

Influence of thermocycling on the functional properties of the NiTi alloy produced by wire arc additive manufacturing

The influence of the thermocycling under a stress of 200 and 300 MPa on the martensitic transformation temperatures, recoverable and irreversible strain was study in the NiTi samples produced by wire arc additive manufacturing (WAAM). Two types of samples were used: the T1 sample including the Ti-rich NiTi and Ni-rich NiTi layers in the working length and the T2 sample including only the Ni-rich NiTi layers. It was found that the variation in the martensitic transformation temperatures on thermal cycling depended on the chemical composition of the layer. The transformation temperatures decreased on thermal cycling in the Ti-rich NiTi layer (in T1 sample), whereas they were constant in the Ni-rich NiTi layers (in T1 and T2 samples). The recoverable strain in both samples did not change during thermal cycling. The irreversible strain was found in the T1 sample regardless of stress acting on thermal cycling, while T2 sample showed the plastic strain only in the first cycle under 300 MPa. It was shown that the difference in a functional behavior of the T1 and T2 samples on thermocycling was due to that the T1 sample contained the Ti-rich NiTi layer, that was characterized by a low dislocation slip limit contrary to the Ni-rich layers which were hardened by the Ni4Ti3 precipitates.

Passivation and Corrosion Behavior of Modified S13Cr Stainless Steel in Ultra-high Temperature Geothermal Fluid

This research aims to investigate the passivation and corrosion behaviour of modified S13Cr stainless steel (SS) in ultra-high temperature geothermal fluids. In this study, S13Cr SS before and after modified were both immersed in a simulated geothermal fluid environment with a temperature of 210°C and CO2 pressure of 3 MPa for 120 h. The results show that the modified S13Cr SS had smaller grain size and lower reverse austenite content, and exhibited higher transpassive potential and lower passive current density in the ultra-high temperature environment. After 120 h of immersion, the passivation film of the modified 13Cr SS was completely dissolved, and a corrosion product film mainly composed of FeCO3 and FeCr2O4 formed with localized corrosion occurring. Moreover, a Ni-rich barrier layer formed at the interface between the inner layer of the product film and the substrate, which hindered the penetration of the corrosive medium. Additionally, the residual MoO2 in the product film played a stabilizing role. Overall, the corrosion resistance of the modified S13Cr SS in ultra-high temperature geothermal fluids is improved.

SURFACE QUALITY AND CORROSION RESISTANCE OF 316L STAINLESS STEEL ELECTROPOLISHED USING PHOSPHORIC – SULFURIC ACIDS

Electropolishing is an electrochemical surface finishing technique. It is commonly applied to equipment that requires a gleaming finish. This surface property is frequently required in 316L stainless steel (SS) medical implants. Electropolishing removes a thin layer from the metal's surface through electrochemical processes. This results in a very clean, smooth, and bright metal surface. The process parameters, such as electrolyte solution, electrical current, and electropolishing time, influence surface roughness and glossiness. The dissolution of metallic ions during the process may also affect the corrosion resistance of the treated material in addition to producing a shiny surface. This study investigated the surface glossiness, surface roughness, and corrosion of electropolished 316L SS. Electropolishing experiments on 316 SS were carried out using various H3PO4 (50%) and H2SO4 (32%) electrolyte solution compositions. The influences of electrolyte solution composition, electric current, and electropolishing time were studied. The results showed that increasing the H2SO4 content of the mixture and electropolishing the 316L SS for a longer period of time improved the surface roughness and glossiness. Under 10 Amp electric currents, the best surface glossiness was discovered. A corrosion test revealed that the electropolishing produced a Cr and Ni-rich layer that improved the corrosion resistance of the samples.

Ultra-strong and ductile amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate thin films

Films with a combination of high strength, large ductility, and high thermodynamic stability are always pursued for industrial applications. Here, we prepared the amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate with hardness and yield strength of 7.4 GPa and 3.8 GPa, and large deformability of ∼70%. The ductility is attributed to two aspects. One is the Ti-Zr-Hf-Nb-Ta/Co-Ni-V layer interfaces acted as barriers to obstruct the propagation of nanocracks at the heavily deformed stage. Another is that amorphous layers acted as dislocation sinks promoting the dislocations to get annihilated when undergoing plastic flow, maintaining the plastic deformability of the crystalline layers. After annealing at 873 K for 1 h, the Co-Ni-V layer changes to a V-rich amorphous layer with minor nanocrystals, while the Ti-Zr-Hf-Nb-Ta layer transforms to a Ni-rich amorphous layer, due to the diffusion of Co and Ni. This chemical partitioning and consequent amorphization lead to the enhanced hardness and yield strength of 9.4 GPa and 4.5 GPa, but low ductility. In addition, the microstructure and mechanical properties of the nanolaminate can be further optimized by adjusting substrate temperature, layer thickness, and annealing process. The findings provide a new avenue for improving the mechanical properties of nanolaminates in a controllable manner.

TEM comparative study on oxide films of 316L and T91 steel exposed to 350–500 °C steam

The oxide films of 316L and T91 exposed to 350–500 °C steam were investigated using transmission electron microscopy (TEM). Independent of the exposure temperature, a triplex oxide structure with outer magnetite, inner Cr-rich (Fe1.4Cr1.6O4), and Ni-rich layer formed on 316L, while only a duplex layer with outer magnetite and inner Cr-rich (Fe2.2Cr0.8O4) layer formed on T91. As the fast channels for oxidant and the obstacles for solid-state diffusion, nanopores are distributed evenly in the Cr-rich inner layer and are more abundant in 316L than in T91. The oxidation behavior of the materials was understood based on the microscopic characteristics of the oxide films.

Grafting a Polymer Coating Layer onto Li1.2 Ni0.13 Co0.13 Mn0.54 O2 Cathode by Benzene Diazonium Salts to Facilitate the Cycling Performance and High-Voltage Stability.

Li-rich Mn-based cathodes have been regarded as promising cathodes for lithium-ion batteries because of their low cost of raw materials (compared with Ni-rich layer structure and LiCoO2 cathodes) and high energy density. However, for practical application, it needs to solve the great drawbacks of Li-rich Mn-based cathodes like capacity degradation and operating voltage decline. Herein, an effective method of surface modification by benzene diazonium salts to build a stable interface between the cathode materials and the electrolyte is proposed. The cathodes after modification exhibit excellent cycling performance (the retention of specific capacity is 84.2% after 350 cycles at the current density of 1 C), which is mainly attributed to the better stability of the structure and interface. This work provides a novel way to design the coating layer with benzene diazonium salts for enhancing the structural stability under high voltage condition during cycling.

Study on the growth mechanism of the internal oxide layer in 9% Ni cryogenic steel

The oxidation behavior of the Ni-rich layer in the internal oxide layer (IOL) in 9% Ni cryogenic steel is investigated at 1,150°C for 0–240 min in the air atmosphere. The morphology and phase composition of the Ni—rich layer are analyzed with energy dispersive spectroscopy, scanning electron microscopy, metallographic microscopy, and X—ray diffraction. The results show that the Ni—rich layer mainly consists of gray Fe3O4/FeO and white Ni–Fe particles, with a small amount of black Fe2SiO4. The morphologies of Ni–Fe particles undergo the following changes with isothermal oxidation time: dot—like → strip—like → net-like; at the same time, layered Ni–Fe particles were formed at about 1/3 of the thickness of the Ni—rich layer. Compared with the dot-like Ni–Fe particle, the net-like and layered Ni–Fe particles provide a fast path for the diffusion of O in the Ni—rich layer. However, the experimental steel still has a much lower oxidation rate because of the hindrance of Ni–Fe particles on the out-diffusion of Fe. During the oxidation process, the Kirkendall effect induces pores/cavities in the IOL, which weakens the stability of the IOL. In the end, the spalling phenomenon of the layered Ni–Fe particle occurs at 1,150°C for 180 min.

A mechanistic study on dealloying-induced stress corrosion cracking of Alloy 800 in boiling caustic solutions

Alloy 800 (Fe-30Ni-20Cr) is used in steam generators of some nuclear power plants. In-service performance has been excellent, but stress corrosion cracking (SCC) can occur in certain off-chemistry environments. In this study, the SCC mechanism for Alloy 800 in boiling caustic solution is investigated. After exposure, a Ni-rich porous surface film is formed with a large density of cracks. Complementary electron microscopy techniques are applied to study the SCC mechanism at the nanoscale from chemical and mechanical perspectives. Results suggest SCC initiation occurs by transmission of a micro-crack from the Ni-rich layer into the substrate material via a cleavage mechanism.

Oxides Film Formed on Fe- and Ni-Based Alloys: An Ellipsometry Insight

UV-visible spectroscopic ellipsometry was used to study the thickness and composition of the oxidized zone in Fe- and Ni-based alloys as a function of oxygen partial pressure. In the case of AISI 304 stainless steel, the weathered thickness increases with oxygen partial pressure, whereas in the case of Inconel 600, it appears to be independent of oxygen pressure. This trend is confirmed by the AFM measurements. For both materials studied, the oxygen-modified zone consists of two layers as confirmed by glow discharge optical emission spectrometry (GDOES) measurements. The thicknesses of these two layers vary differently on either side of an oxygen partial pressure of 0.1 Torr. In the case of AISI 304 stainless steel, the thickness of the Fe-rich outer layer decreases in favor of the Cr-rich inner layer. In the case of Inconel 600, the trend is reversed. The Ni-rich outer layer increases significantly above this critical pressure, while the Cr-rich inner layer decreases slightly. The composition of each layer in the oxidized zone is discussed in terms of its dielectric function in relation to reference material. The use of UV-visible ellipsometry as a non-destructive tool to study the structure and composition of the oxide bilayer of absorbing systems such as the alloys under investigation is a first.

Roles of Trimethyl Borate in Constructing an Interphase on Li Anode: Angel or Demon?

Although coupling a lithium metal anode with a Ni-rich layer cathode is a promising approach for high-energy lithium metal batteries, both electrodes are plagued by their intrinsic unstable interfaces which trigger electrolyte decomposition, lithium dendritic growth, and transition metal dissolution during cycling. Making use of electrolyte additives is one of the most effective solutions to address this issue. In this paper, we explore the roles of trimethyl borate (TMB)─a common film-forming additive to protect high-nickel-ratio ternary cathodes─in suppressing lithium dendrite growth. It is found that, on the one hand, the borate-containing solid electrolyte interphase (SEI) derived from the decomposition of TMB facilitates Li+ transport, homogenizing the deposition of Li ions. On the other hand, TMB as an anion receptor provokes LiPF6 decomposition, prompting the formation of SEI with superfluous LiF. As a result, it is imperative to raise awareness of this double-edge additive when using it to be immune to lithium dendrite and cathodic degradation.

A nickel-rich oxide, Li(Ni0.90Co0.06Mn0.04)0.995Al0.005 O2, with a dual conductive coating

Nickel (Ni)-rich layered oxides have high specific capacities and are inexpensive, but their synthesis and electrochemical performance continue to present difficulties. In this study, we investigated the effect of a dual conductive compound of dot-like Nb12WO33 and film-like lithium boron oxide (Li-B-O; applied using a simple dry-coating method) on the Ni-rich oxide layer in Li batteries. The film-like Li-B-O homogeneous coating segregated the cathode from the electrolyte, which improved the initial efficiency and cycle stability, and the dot-like Nb12WO33 provided a fast Li-ion transition channel, which improved the rate performance of the Ni-rich oxide layer. The modified cathode with dual conductive coating exhibited significantly improved electrochemical performance. Its discharge capacity was 225.6 mAh g−1, with high initial efficiency of 92.73% in the voltage range of 3.0–4.3 V at 0.1 C, whereas that of the uncoated sample was 219.4 mAh g−1, with an initial efficiency of 90.4%. The modified cathode had a discharge capacity of 179.1 mAh g−1 at 5 C, compared with that of 161.1 mAh g−1 for the uncoated sample; the capacity retention of the coated sample was 92.84% at 0.5 C after 50 cycles at 25 ℃, whereas that of the uncoated sample was only 81.41%. A similar strategy could be utilized to enhance the performance of other cathode materials.

Corrosion Evaluation of Austenitic and Duplex Stainless Steels in Molten Carbonate Salts at 600 °C for Thermal Energy Storage

Next-generation concentrated solar power (CSP) plants are required to operate at temperatures as high as possible to reach a better energy efficiency. This means significant challenges for the construction materials in terms of corrosion resistance, among others. In the present work, the corrosion behavior in a molten eutectic ternary Li2CO3-Na2CO3-K2CO3 mixture at 600 °C was studied for three stainless steels: an austenitic grade AISI 301LN (SS301) and two duplex grades, namely 2205 (DS2205) and 2507 (DS2507). Corrosion tests combined with complementary microscopy, microanalysis and mechanical characterization techniques were employed to determine the corrosion kinetics of the steels and the oxide scales formed on the surface. The results showed that all three materials exhibited a corrosion kinetics close to a parabolic law, and their corrosion rates increased in the following order: DS2507 < SS301 < DS2205. The analyses of the oxide scales evidenced an arranged multilayer system with LiFeO2, LiCrO2, FeCr2O4 and NiO as the main compounds. While the Ni-rich inner layer of the scales presented a good adhesion to the metallic substrate, the outer layer formed by LiFeO2 exhibited a higher concentration of porosity and voids. Both the Cr and Ni contents at the inner layer and the defects at the outer layer were crucial for the corrosion resistance for each steel. Among the studied materials, super duplex stainless steel 2507 is found to be the most promising alternative for thermal energy storage of those structural components for CSP plants.

Realization of a high voltage Ni rich layer LiNi0.5Co0.2Mn0.3O2 single crystalline cathode for LIBs by surface modification

Single crystalline ternary cathode material LiNi0.5Co0.2Mn0.3O2(NCM523) can operate at extremely high voltages and could offer exceptional energy density. The single crystal morphology is less easy to form the cracks and could express better structure stability compared to the polycrystalline counterpart. However, irreversible parasitic side reactions in the interface during cycling may lead to rapid electrochemical degradations. Herein, a simple chemical wet method that modifies the single-crystal NCM523 particles with Al2O3 coating is proposed. The coating layer can effectively suppress the phase transformation and irreversible phase transition on the NCM surface during cycling. Furthermore, the cladding layer can prevent the erosion of by-products such as HF. As a result, the Al2O3 modified NCM523 delivers a high specific capacity of 192.5mAh g−1, excellent cycling stability and rate capability. The capacity retention was 91.7% after 50 cycles even at ultra-high cut-off voltage of 4.7 V. This surface engineering strategy paves the way to promote the development of small size single crystal NCM523 materials for next generation LIBs.

Improvement of thin-film Ni-rich ALD cathode for microbatteries

Thin-film Li-ion batteries produced by precise thickness control atomic layer deposition (ALD) method are promising, safe, and high-energy density sources for miniature devices. The paper presents a detailed analysis of the multilayer thin film cathode for microbatteries. Structures were obtained by combining several technological parameters to increase capacity, uniformity, and lifetime. The protective function of a nano-sized coating was demonstrated. The influence of coating application on cathode capacity was explained. The studied structure consists of Ni-rich cathode layer modified with an amorphous Li-Ta-O functional layer on a steel substrate with a Cr coating. The cathode and the functional layer were obtained by the ALD multilayer approach followed by heat treatment at 800 °C for a minute. According to XPS and TEM data, the composition of the cathode after annealing was LiNi0.7Co0.3O2 well-defined structure without separation into Ni-rich and Co-rich layers, with texturing of crystallite pillars and with the absence of Fe. The Li-Ta-O films have a slight chemical composition gradient from Li3Ta1.2O4 on the surface to Ta1.7O5 in bulk. The electrochemical characterization showed that combining the functional layer and cathode heat treatment preserves the electrochemical capacity (32 µAh·µm−1·cm−2) and increases Coulomb efficiency.

Enhancing Structural Stability and Electrochemical Properties of Co-Less Ni-Rich Layer Cathode Materials by Fluorine and Niobium Co Doping

A solid-state approach was used to synthesize Li(Ni0.925Co0.03Mn0.045)0.996Nb0.004O1.98F0.02 with double ion doping. The structure parameters, micromorphology, and element valence distribution of all materials were thoroughly investigated by XRD, SEM, EDS, XPS, and HR-TEM. The results show that the distribution of F and Nb is uniform both on the surface and inside the particles and that F and Nb ions have an impact on the valence state of Ni ions on the surface of the material. In addition, the lattice parameter c is raised and the (003) crystal plane spacing is widened by the introduction of both F and Nb ions. The Li(Ni0.925Co0.03Mn0.045)0.996Nb0.004O1.98F0.02 electrode shows a higher discharge specific capacity (169.12 mAh g–1) at 10C and excellent cycling performance with a capacity retention of 83.60% after 150 cycles. Comparison of CV, dV/dq, EIS, SEM, and HR-TEM after cycling for all electrodes reveals that the particles doped with F and Nb maintained intact morphology and showed varying degrees of decrease in polarization and impedance.

Microstructural evolution of early-stage oxide film on 15–15Ti austenitic stainless steel under 500 ℃ steam

The microstructural evolution with time and dissolved oxygen of the oxide film formed on 15–15Ti austenitic stainless steel during the early oxidation stage in steam at 500 ℃ was studied using multiple test instruments such as transmission electron microscopy (TEM). A triplex oxide structure with an outer Fe-rich layer, an inner Cr-rich layer, and a Ni-rich transition layer was confirmed for all samples. The relationship between corrosion resistance and oxide structure is discussed. One mechanism for pore formation in the inner oxide layer of austenitic steel is proposed based on the spatial distribution and migration behavior of Ni during oxidation.