Corrosion-resistant Elements Research Articles

Enhancement of Corrosion Resistance and Hardness for Type 420J2 Martensitic Stainless Steel Via Laser Powder Bed Fusion Process

In the field of materials engineering, physical properties such as mechanical properties are considered as the most important properties, however, chemical properties such as corrosion resistance are also critical properties that cannot be ignored. In particular, Japan is island country where metallic materials are frequently used in coastal areas. Therefore, the problems of failures and accidents caused by corrosion reaction of structural materials are more serious than in other countries.Recently, laser powder bed fusion (LPBF) process which is a type of additive manufacturing (AM), has been attracting attention as an advanced processing tool for fabrication of metallic materials in various industrial fields. The direct-forming process by AM with the applicability of intricate-structured materials is strong advantage for manufacturing value-added and relatively small products such as medical implants or aerospace assemblies.Our previous study demonstrated the excellent corrosion resistance of LPBF-processed type 316L austenitic stainless steel, focusing on its crystallographic planes and grain boundaries [1]. Therefore, in this study, we investigated the corrosion resistance of LPBF-processed type 420J2 martensitic stainless steel. Martensitic stainless steels have the lowest corrosion resistance among all kinds of stainless-steel types such as precipitation hardening, ferritic, austenitic, and duplex, because of minimum chromium content without other corrosion-resistant elements, and high content of carbon. The primary advantage of martensitic stainless steel is superior hardness, which can be achieved quenching heat treatment. In other words, corrosion resistance and hardness are conflicting properties for stainless steels, and it is difficult to realize coexistence.In this study, the electrochemical and the non-electrochemical corrosion tests were performed to evaluate the corrosion behavior of LPBF-processed and commercial 420J2 stainless steels. The microstructural characterization and hardness tests were also performed.Commercial 420J2 stainless steel powder was used as the primary material for specimen fabrication by LPBF in this study. The nominal composition of 420J2 stainless steel was Fe-12Cr-0.3C. The LPBF process was performed in an argon atmosphere using a 3D printer. To examine the evolved texture and planes of interest of the specimens, the z-axis was defined as the build direction, and the x- and y-axes were defined as the laser scanning directions. In this study, we fabricated cubic specimens with dimensions of 11 mm × 11 mm × 11 mm. The specimens were cut mechanically to expose their yz-, xz-, and xy-planes. No post-processing was performed on the LPBF specimens.Anodic polarization measurement (linear sweep voltammetry) was performed using a potentiostat (HABF-501G, Hokuto Denko, Japan) connected to a function generator (HB-111, Hokuto Denko, Japan) with an analog cable. A saturated calomel electrode (SCE) and platinum electrode were used as the reference and counter electrodes, respectively. The specimens were fixed in a polytetrafluoroethylene holder with an O-ring. The exposed area contacting the electrolyte was 0.35 cm2 (6.7 mm in diameter). After immersing the specimens in a simulated body fluid (physiological saline: 0.9 mass% NaCl aqueous solution, aerated) at 310K, their open circuit potentials (OCPs) were recorded for 10 min. Then, a gradient anodic potential was applied at a constant sweep rate of 1 mVs-1 from the initial potential of −50 mV from the OCP. The measurement was stopped when the current density limit of 1 mAcm-2 was recorded.Figure shows the polarization curves of LPBF-processed and commercial 420J2 stainless steel specimens in physiological saline. The pitting potentials of LPBF specimens were significantly higher than those of commercial specimens. These experimental results indicate that localized corrosion resistance was effectively improved as like 316L austenitic stainless steel in the previous study [1]. The results of the hardness test showed that LPBF specimens was 53.50 ± 0.25 HRC, regardless of the measuring position. The hardness of the commercial specimens varied from 54 to 27 HRC depending on the tempering treatment conditions after the primal quenching.Thus, LPBF is found to be an ideal process that can simultaneously enhance corrosion resistance and hardness of martensitic stainless steels. The experimental results of another corrosion resistance evaluation and inclusion extraction will be presented in the session.Reference:[1] Tsutsumi Y et al. Additive Manufacturing 45 (2021) 102066. Figure 1

Effects of Mo Addition on Microstructure and Corrosion Resistance of Cr25-xCo25Ni25Fe25Mox High-Entropy Alloys via Directed Energy Deposition.

Highly entropy alloys (HEAs) are novel materials that have great potential for application in aerospace and marine engineering due to their superior mechanical properties and benefits over conventional materials. NiCrCoFe, also referred to as Ni-based HEA, has exceptional low-temperature strength and microstructural stability. However, HEAs have limited corrosion resistance in some environments, such as a 3.5 wt% sodium chloride (NaCl) solution. Adding corrosion-resistant elements such as molybdenum (Mo) to HEAs is expected to increase their corrosion resistance in a variety of corrosive environments. Metal additive manufacturing reduces production times compared to casting and eliminates shrinkage issues, making it ideal for producing homogeneous HEA. This study used directed energy deposition (DED) to create Cr25-xCo25Ni25Fe25Mox (x = 0, 5, 10%) HEAs. Tensile strength and potentiodynamic polarization tests were used to assess the materials' mechanical properties and corrosion resistance. The mechanical tests revealed that adding 5% Mo increased yield strength (YS) by 20.1% and ultimate tensile strength (UTS) by 9.5% when compared to 0% Mo. Adding 10% Mo led to a 32.5% increase in YS and a 20.4% increase in UTS. Potentiodynamic polarization tests were used to assess corrosion resistance in a 3.5-weight percent NaCl solution. The results showed that adding Mo significantly increased initial corrosion resistance. The alloy with 5% Mo had a higher corrosion potential (Ecorr) and a lower current density (Icorr) than the alloy with 0% Mo, indicating improved initial corrosion resistance. The alloy containing 10% Mo had the highest corrosion potential and the lowest current density, indicating the slowest corrosion rate and the best initial corrosion resistance. Finally, Cr25-xCo25Ni25Fe25Mox (x = 0, 5, 10%) HEAs produced by DED exhibited excellent mechanical properties and corrosion resistance, which can be attributed to the presence of Mo.

Effect of Ti addition on the microstructure and corrosion behavior of laser cladding AlCoCrFeNi high-entropy alloy coatings

AlCoCrFeNi high-entropy alloys (HEAs) has higher strength and wear resistance but poorer corrosion resistance. In the present investigation, the AlCoCrFeNi HEAs containing titanium(Ti) were fabricated via laser cladding to enhance the corrosion resistance properties of the coating and the influence of the Ti content on the microstructure of the coatings was investigated. The results show that the microstructure of the coating changed from a single BCC phase to a BCC + B2 phase with the addition of Ti. The Laves phases appeared within the coating when the Ti content was beyond 0.5 mol ratio. As an excellent corrosion-resistant element, Ti promoted the formation of a passive film and enhanced the corrosion resistance of the HEAs coating. The corrosion resistance of the coating first increased and then decreased with the addition of Ti, and the AlCoCrFeNiTi0.5 coating exhibited optimal corrosion resistance.

Influence of Ultraviolet Light and Alternating Wet-Dry Environments on the Corrosion Behavior of Weathering Steels.

The corrosion behaviors of two bridge steels (Q345q and Q500q) under simulated ultraviolet irradiation and a wet-dry alternating (UVWD) environment were studied. Weight loss measurement, stereomicroscope observation, SEM, XRD, and electrochemical impedance spectroscopy (EIS) were performed to investigate the influence of the coupled environment. The results revealed that the corrosion rates of Q345q and Q500q were significantly accelerated by the synergistic effect of UV light exposure and alternating wet-dry conditions. Numerous voids and cracks could be observed throughout the thickened rust layers, enabling the corrosive substances to easily penetrate through the rust layer. Q500q exhibited better corrosion resistance than Q345q due to the addition of Mo, Cr, and Ni as corrosion-resistant elements, which tended to transform the rust layer into α-FeOOH rather than γ-FeOOH during later stages of corrosion.

Effect of ultrasonic vibration-assisted laser cladding frequency on the microstructure and properties of Fe-0.5C-15Cr alloy cladding layers

In this paper, Fe-0.5C-15Cr wear and corrosion resistant alloy coating was prepared on 3Cr13 stainless steel surface by ultrasonic vibration assisted laser cladding technology. The effects of ultrasonic vibration frequency on the microstructure, microhardness and corrosion resistance of the coating were studied. The results show that the length of the dendrites of the cladding layer decreased significantly after ultrasonic vibration is applied, the grains size is refined significantly, and the morphology of the grain boundary carbides changed from fishbone-like to short rods, when the vibration frequency is 20.2 kHz, the grain refinement is the most significant, and the orientation of the dendrites is obviously weakened. The hardness of the applied ultrasonic vibration specimens increased by 10–20 HV0.2 relative to the non-ultrasonic specimens, with the increase of vibration frequency, the hardness of the cladding layer firstly increased and then slightly decreased, and the peak appeared at 20.2 kHz. The coefficient of friction of the specimens when the ultrasonic frequency of 20.2 kHz is applied is lower than that of the specimens with non-ultrasonic frequency by 12.8 %, and the abrasive wear rate is reduced by 14.3 %. After ultrasonic vibration, the pitting potential of the cladding layer increases, the dimensional passivation current density decreased, the width of the passivation zone becomes wider, and the intergranular corrosion reactivation rate decreased, When the ultrasonic frequency is 20.2 kHz and 20.4 kHz, the pitting corrosion resistance and intergranular corrosion resistance of the cladding layer are significantly improved. This is because the cavitation effect, resonance effect and acoustic flow effect of ultrasonic vibration promote the non-uniform nucleation, refine the dendrites and intergranular carbides, and promote the redistribution of the corrosion-resistant element Cr in the in-grain martensite and grain boundary carbides, increasing the content of Cr in the matrix, and thus improving the wear resistance and corrosion resistance of the cladding layer.

Pitting corrosion mechanism of BCC+FCC dual-phase structured laser cladding FeCoCrNiAl0.5Ti0.5 HEAs coating

This work elaborated the microstructure and corrosion behaviors of laser cladding (LC) FeCoCrNiAl0.5Ti0.5 high-entropy alloys (HEAs) coating on AISI 1045 steel substrate. It revealed that the LC FeCoCrNiAl0.5Ti0.5 HEAs coatings were composed of dendritic region (DR) and interdendritic region (IR). Furthermore, DR was mainly composed of BCC phase while IR was composed of FCC phase. There was also the transformation of BCC to L21 structure detected due to the addition of Ti element. Due to the uniform microstructure and addition of corrosion-resistant elements (such as Cr), the dual-phase HEAs coatings exhibited pretty good corrosion resistance. A dense passive film would form during the corrosion process to protect the inner structure. It was demonstrated that the corrosion rate of the coating was only 32.8% of that of the substrate. However, the pores formed during the LC process on the surface might be the initial site for pitting corrosion.

Superior resistance to cavitation erosion and corrosion of a novel SiC-reinforced superaustenitic stainless steel coating fabricated by high-velocity air fuel spraying

In this work, we developed a SiC-reinforced superaustenitic stainless steel (SS) coating aimed at enhancing resistance against cavitation erosion (CE) and corrosion. Relevant results indicated that the coating exhibited a diminished mean erosion depth compared to that of 304 SS in 3.5 wt% NaCl solution. Furthermore, a pronounced inhibitory effect on the synergistic interplay between CE and corrosion was demonstrated. Electrochemical assessments underscored the superior passivation and repassivation properties of the coating during CE, contrasting markedly with the compromised passivation capacity of 304 SS, which assumed an active dissolution state characterized by a substantially elevated corrosion current density. The exceptional resistance to CE and corrosion of the coating can be attributed to its low porosity, the elevated levels of corrosion-resistant elements, and the nanoscale grain size. Consequently, this coating emerges as a highly promising candidate for the protective coating on 304 SS flow-handling components.

Effects of welding parameters on Inconel 625 coating synthesised by tungsten inert gas cladding

Inconel 625 coatings were synthesised on AISI 4130 steel substrates by tungsten inert gas welding. Optimisation of process parameters was conducted through a combination of numerical simulations and technological experiments. The welding speed has a significant effect on the width and height of the cladding layer and the welding current mainly affected the penetration. A proper decrease of welding speed with raising heat input was conductive to the decrease of coating residual stress levels and dilution rates, which promoted the solid solution of corrosion resistant elements (Mo and Nb) and favoured the improvement of coating corrosion resistance. The cladding quality and efficiency could be improved by parameter optimisations through the combination of numerical and technological methods.

Enhanced Oxygen Evolution Activity and Stability of RuO2(110) Surface by Ti Doping

Introduction Developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER) is essential for efficient hydrogen production through polymer electrolyte membrane water electrolysis (PEMWE). Although RuO2 exhibits the highest OER activity among pure transition metal oxide catalysts, its low durability hampers its practical application as an OER catalyst for PEMWE. Recent studies have shown that the incorporation of dissimilar metal elements, such as Ni, Mn, and Cu, effectively enhances the OER activity and stability of RuO2 in acidic electrolytes (1-3). In this study, we focus on Ti, a corrosion-resistant element in the PEMWE environment, and investigate the effects of doping amounts on the OER activity and stability of a RuO2(110) single crystal model catalyst surface. Experimental Non-doped rutile-type TiO2(110) single crystals were used as sample substrates. Ru and Ti, with a total thickness of 40 nm, were deposited onto the substrate at 400 ℃ under 0.5 Pa-O2 partial pressure using the arc-plasma deposition (APD) method. Subsequently, the sample was post-annealed at 400℃ for 1 hour in air using a tube furnace. Hereafter, the samples are denoted as RuO2-Tix (x represents the atomic percentage of doped Ti).Oxygen evolution activity was measured by linear sweep voltammetry (LSV) at a scan rate of 20 mV s-1 in N2-purged 0.1 M HClO4 at room temperature. Chronopotentiometry (CP) was conducted at 1 mA cm-2 for 120 min to evaluate the durability. The electrochemical impedance spectroscopy was conducted at 1.6 V vs. reversible hydrogen electrode (RHE) to measure the solution resistance. All the LSV and CP data were iR-corrected using the Rs values. Out-of-plane X-ray diffraction (XRD) analysis was carried out to evaluate the crystal structure. The dissolution amounts of Ru into the electrolyte after CP were evaluated by inductively coupled plasma mass spectrometry (ICP-MS). Results and Discussions Fig. 1(a) presents the out-of-plane XRD patterns of Ti-doped and non-doped RuO2(110) samples. The results indicate that (110)-oriented Ti-doped and non-doped RuO2 thin films were successfully obtained on TiO2 substrates. However, the peak position of RuO2(110) gradually shifts to the lower angle side, and the peak becomes less distinct with increasing Ti-doping amounts, suggesting that doped Ti is dissolved in the RuO2 crystal lattice and the crystallinity decreases with increasing doping amounts. Initial LSV curves for OER are shown in Fig. 1(b). The current density of RuO2-Ti4, 5, and 7 samples significantly increases at higher potential regions above 1.6 V vs. RHE, while RuO2-Ti2 and 10 exhibit decreased activity. The CP curves presented in (c) demonstrate that Ti doping, especially at 5 and 7 at.%, effectively suppresses the overpotential increase during CP. The dissolution amounts of Ru after 120 min of CP are summarized in (d). The dissolution amounts tend to decrease with increasing Ti-doping amounts. These results clearly show that an appropriate amount of Ti-doping effectively enhances both the OER activity and electrochemical stability of the RuO2(110) surface.AcknowledgmentsThis study was partly supported by JSPS KAKENHI Grant Number 21H01661, 22K19078 and Toyota Mobility Foundation Hydrogen Initiative. References Z. Y. Wu, F. Y. Chen, B. Li, S. W. Yu, Y. Z. Finfrock, D. M. Meira, Q. Q. Yan, P. Zhu, M. X. Chen, T. W. Song, Z. Yin, H. W. Liang, S. Zhang, G. Wang and H. Wang, Nat. Mater., 22, 100 (2023). S. Chen, H. Huang, P. Jiang, K. Yang, J. Diao, S. Gong, S. Liu, M. Huang, H. Wang and Q. Chen, ACS Catal., 10, 1152 (2020). J. Su, R. Ge, K. Jiang, Y. Dong, F. Hao, Z. Tian, G. Chen and L. Chen, Adv Mater, 30, 1801351 (2018). Figure 1

Development of a Cr-Ni-Mo alloyed stress corrosion-resistant anchor bolt steel

PurposeThe purpose of this paper is to develop new types of anchor bolt materials by adding corrosion-resistant elements for alloying and microstructure regulation.Design/methodology/approachThree new anchor bolt materials were designed around the 1Ni system. The stress corrosion cracking resistance of the new materials was characterized by microstructure observation, electrochemical testing and slow strain rate tensile testing.FindingsThe strength of the new anchor bolt materials has been improved, and the stress corrosion sensitivity has been reduced. The addition of Nb makes the material exhibit excellent stress corrosion resistance under –1,200 mV conditions, but the expected results were not achieved when Nb and Sb were coupled.Originality/valueThe new anchor bolt materials designed around 1Ni have excellent stress corrosion resistance, which is the development direction of future materials. Nb allows the material to retain its ability to extend in hydrogen-evolution environments.

Corrosion behavior of AlCoCrFeNi2.1 high entropy alloy in a simulated oilfield produced fluid environment compared to 2205 duplex stainless steel

In this study, we investigated the corrosion resistance and passive film characteristics of AlCoCrFeNi2.1 high entropy alloy (HEA) and 2205 duplex stainless steel (DSS) when exposed to a simulated oilfield produced fluid. Our findings reveal that AlCoCrFeNi2.1 HEA exhibits a nobler self-corrosion potential (−340 mVSHE) and a lower self-corrosion current density (3.6 μA/cm2), in comparison to 2205 DSS, exhibiting better overall corrosion resistance, albeit with a narrower stable passivation interval. Long-term immersion tests establish that AlCoCrFeNi2.1 HEA primarily experiences overall corrosion, while 2205 DSS mainly undergoes localized corrosion, notably characterized by pitting corrosion. The predominant elements in the passive film on AlCoCrFeNi2.1 HEA are Al (13.4 at%), supplemented by varying amounts of Fe (2.4 at%), Cr (4.8 at%), Ni (2.2 at%), and Co (1.3 at%). In contrast, the passive film formed on 2205 DSS consists solely of Fe (7.9 at%) and Cr (5.0 at%). The absence of the corrosion-resistant elements Mo and Ni in the passive film of 2205 DSS may account for its inadequate corrosion resistance.

Corrosion resistance and microstructure analysis of additively manufactured 22% chromium duplex stainless steel by laser metal deposition with wire

Microstructure characteristics and pitting corrosion of a duplex stainless steel (DSS) manufactured by laser metal deposition with wire (LMDw) were studied. The layer-by-layer LMDw process resulted in a mixed microstructure of predominantly ferrite with 2% austenite and chromium-rich nitrides, and reheated regions with ∼33% austenite. The high cooling rate of LMDw restricted the distribution of Cr, Mo, and Ni, in ferrite and austenite, while N diffuses from ferrite to austenite. Subsequent heat treatment at 1100 °C for 1 h resulted in homogenized microstructure, dissolution of nitrides, and balanced ferrite/austenite ratio. It also led to the redistribution of Cr and Mo to ferrite, and Ni and N to austenite. At room temperature, cyclic potentiodynamic polarization measurements in 1.0 M NaCl solution showed no significant differences in corrosion resistance between the as-deposited and heat-treated samples, despite the differences in terms of ferrite to austenite ratio and elemental distribution. Critical pitting temperature (CPT) was the lowest (60 °C) for the predominantly ferritic microstructure with finely dispersed chromium-rich nitrides; while reheated area with ∼33% austenite in as-deposited condition achieved higher critical temperature comparable to what was obtained after heat treatment (73 and 68 °C, respectively). At temperatures above the CPT, selective dissolution of the ferrite after deposition was observed due to depletion of N, while after heat treatment, austenite preferentially dissolved due to Cr and Mo concentrating in ferrite. In summary, results demonstrate how microstructural differences in terms of ferrite-to-austenite ratio, distribution of corrosion-resistant elements, and presence of nitrides affect corrosion resistance of LMDw DSS.

Role of segregation behavior of Cu and Sb in the region of inclusions on initial corrosion

The distribution characteristics of corrosion-resistant elements in low-alloy steel affected the initial corrosion behavior of the matrix. In this article, the segregation behaviors of elements at grain boundaries and pearlite defects in low-alloy steel Q500 and the precipitation behavior of Cu in inclusions were studied. Cu, Ni and Sb had segregation behavior at the boundary of the inclusions, which was beneficial for reducing grain boundary segregation. Cu had the ability to capture Sb and Ni. Cu and Sb involvement in local corrosion process of inclusions were observised by multi-cycle 3.5% NaCl immersion test, during which Cu and Sb were oxidized to corresponding Cu2O and Sb2O3. Under the influences of the segregation of elements at the grain boundaries, the internal part of the crystal was preferentially corroded. Cr was enriched in the pearlite cementite, formed (Cr,Fe)7C3 and contributed to the corrosion process, forming Cr2O3 and CrO3.

High-Entropy Alloy Films

High-entropy alloy films have the same excellent properties as high-entropy alloys and can better realize the practical applications of high-entropy alloys. This paper takes the high-entropy alloy films as the object of discussion. The preparation process, microstructure, hardness, wear resistance and corrosion resistance of high-entropy alloy films are mainly discussed and the influence of nitridation, sputtering power, substrate temperature, substrate bias and other factors on the phase structure of alloy films is analyzed. High-entropy alloy films can be prepared using magnetron sputtering, laser cladding, pulsed laser deposition, detonation spraying, electrochemical deposition and other processes. High-entropy alloy films tend to form a solid solution and amorphous state, and their hardness is far higher than that of traditional films. Among them, the hardness of high-entropy alloy nitride films can reach the standard of superhard films. Wear resistance is usually proportional to hardness. Due to the corrosion-resistant elements and amorphous structure, some high-entropy alloy films have better corrosion resistance than stainless steel. High-entropy alloy films have shown profound development prospects in the fields of wear-resistant coatings for tools, corrosion protection, diffusion barrier and photothermal conversion coatings.

A microscopy study of nickel-based superalloys performance in type I hot corrosion conditions

ABSTRACT Alloy material selection for sustainable, efficient, and cost-effective use in components is a key requirement for both power generation and aerospace sectors. Superalloys are manufactured using a combination of different elements, selected carefully to balance mechanical performance and environmental resistance to be used in a variety of different service conditions. Therefore, a fundamental understanding of each element is critical to alloy design. In this paper, the interaction of alloy chemistry, particularly chromium as a corrosion-resistant element along with titanium and molybdenum, and their effect on alloys performance for the relevant gas turbine industries were discussed. Based on the findings, the single-crystal alloy is found to be a better corrosion resistant alloy exhibited higher corrosion resistance in comparison to polycrystal alloys and proved that microstructure has a significant impact on alloy performance. This study also established that molybdenum level in chromia former alloys can significantly enhance the corrosion damage.

Hydrogen Embrittlement Susceptibility of Corrosion-Resistant Spring Rod Used in High-Speed Railway

The corrosion of spring steel is very important for vehicle safety. In this work, we conducted an experiment on multi-element micro-alloy composition design; the corrosion resistance of a 60Si2Mn spring was improved by adding Cr, Ni, Cu and other corrosion-resistant elements, and the corrosion resistance index (I) was increased from 3.21 to 8.62. Hydrogen embrittlement resistance was studied using a hydrogen permeation experiment and a slow strain rate tensile experiment. For this study, the following steps were performed: Firstly, the material composition was designed, and the experimental materials that met the experimental design were prepared according to the corresponding deformation and heat treatment process; secondly, the experimental materials were charged with hydrogen; and finally, conventional tensile testing, slow tensile testing and fracture morphology testing were carried out. A hydrogen permeation experiment was carried out for the materials. The result showed that, with the increase of hydrogen charging time, the hydrogen content of two steel samples increased, and the plasticity indexes such as elongation and reduction of the area appeared in three different stages which rapidly decreased, slowly declined, and then tended to balance. The uniform NbC nano precipitated phase can double the number of irreversible hydrogen traps (Nir) per unit volume, and decreased the effective hydrogen diffusion coefficient (Deff) from 1.135 × 10−10 to 6.036 × 10−11. It limited the free diffusion of hydrogen and made the immersed hydrogen harmless, thus improving the hydrogen embrittlement resistance of corrosion-resistant spring steel 60Si2Mn.

Tuning the chemical composition of binary alloy nanoparticles to prevent their dissolution.

The dissolution of nanoparticles under corrosive environments represents one of the main issues in electrochemical processes. Here, a model for alloying and protecting nanoparticles from corrosion with an anti-corrosive element (e.g. Au) is proposed based on the hypothesis that under-coordinated atoms are the first atoms to dissolve. The model considers the dissolution of atoms with coordination number ≤6 on A-B nanoparticles with different sizes, shapes, chemical compositions, and exposed crystallographic orientations. The results revealed that the nanoparticle's size and chemical composition play a key role in the dissolution, suggesting that a certain composition of an element with corrosive resistance could be used to protect nanoparticles. DFT simulations were performed to support our model on the dissolution of four types of atoms commonly found on the surface of Au0.20Pd0.80 binary alloys - terrace, edge, kink, and ad atoms. The simulations suggest that the less coordinated ad and kink Pd atoms on Au0.20Pd0.80 alloys are dissolved in a potential window between 0.26-0.56 V, while the rest of the Pd and Au atoms are protected. Furthermore, to show that a corrosion-resistant element can indeed protect nanoparticles, we experimentally investigated the electrochemical dissolution of immobilized Pd, Au0.20Pd0.80, and Au0.40Pd0.60 nanoparticles in a harsh environment. In line with the dissolution model, the experimental results show that an Au molar fraction of the nanoparticle of 0.20, i.e., Au0.20Pd0.80 binary alloy, is a good compromise between maximizing the active surface area (Pd atoms) and corrosion protection by the inactive Au.

Structure and properties of laser cladding CoCrNi multicomponent alloy coating used in rain gauge

Rain gauge is an important measuring instrument, which is widely used for rainfall measurement under various conditions. However, since the rain gauge is used in outdoor exposed environment, its shell is easily corroded by rain, especially by acid rainwater, which will affect the service life. In order to improve the corrosion resistance and prolong its service life, CoCrNi medium entropy alloy (MEA) coating was prepared on the surface of rain gauge's shell by laser cladding. The microstructure and properties of the CoCrNi coating were studied comprehensively. The results show that the coating and the substrate form a metallurgical bond. The microstructure of CoCrNi MEA coating is mainly composed of two kinds of microstructures, and mainly containing face centered cubic (FCC) structure. The coatings have excellent corrosion resistance in acid rainwater with different pH. The corrosion current density of the laser cladding CoCrNi MEA coatings are lower than that of 304 stainless steel (SS), reduced by 2 orders of magnitude, the corrosion potential increased in varying degrees, with an increase range of 0.03∼0.47 V. The pitting corrosion resistance of the coating is excellent, with the increase of pH, the pitting resistance is enhanced. The corrosion resistance of the coating is related to the phase structure, uniformity and compactness of the microstructure as well as the corrosion resistant elements in the coating. The microhardness of the coating is 703.6 HV, the specific wear rate of the alloy is 1.4×10−4 mm3/Nm, and the friction coefficient is 0.47. Experiments show that the coating have excellent corrosion resistance and mechanical properties for the rain gauge's shell, which provides a guarantee for prolonging its service life.

Stability Design Principles of Manganese-Based Oxides in Acid

The use of non-precious catalysts (e.g., transition metal oxides) in electrochemical energy technologies in acid (e.g., proton exchange membrane fuel cells and electrolyzers) has been significantly hampered by the instability of such catalysts at low pHs. While first-row late transition metal oxides based on Fe, Co, and/or Ni have been reported with comparable or higher catalytic activity for the alkaline oxygen reduction and oxygen evolution reactions than their precious-metal-based counterparts (e.g., Pt and IrO2),[1] these oxide catalysts are not stable in acid.[2] Moreover, Mn-based oxides are more acid-stable than those based on late transition metals[1] and can be potentially stabilized by reaching dissolution-deposition equilibrium at moderately acidic pHs,[3] but they still corrode and deactivate in strong acid and after long operation.[4] To tackle this challenge, extensive efforts over the past decades have been focused on combining active, yet unstable metal oxides with corrosion-resistant oxides.[5-7] Nevertheless, having a higher fraction of corrosion-resistant elements results in more acid-stable, yet less active catalysts, indicating an activity-stability trade-off.[2,5,6] To design transition metal oxide catalysts (such as Mn-based oxides) with an optimal trade-off or bypass this limitation, it is critical to establish their stability descriptors in acid. These descriptors can offer a fundamental understanding of oxide dissolution and provide guiding principles to enhance their intrinsic stability. In this work, we employed a library of Mn-based oxides with diverse structures and Mn oxidation states to identify oxide stability descriptors in acid based on intrinsic electronic structure and energetic parameters. Using time-dependent dissolution experiments and density functional theory calculations, greater amounts and faster kinetics of oxide dissolution in acid were correlated with decreased Mn oxidation states, which are accompanied by lowered Mn-O covalency, weakened Mn-O bonds, and reduced barriers for key reaction steps (such as protonation, vacancy formation, and metal ion solvation). Such design principles were shown broadly with a computational screening across a vast chemical space of ~1,000 Mn-based oxides, where an Mn oxidation state of 4+ was found to give rise to the lowest energetic driving force for the dissolution of Mn-based oxides in acid. Moreover, limiting the percentage of ionic metal substituents in oxides and using more acidic substituents were shown to stabilize Mn-based oxides in acid. These findings can provide novel insights into designing acid-stable Mn-based oxides for renewable energy storage and conversion.

CALPHAD design and high-throughput search of novel Ni-based superalloys that are reinforced by γ' + γ''

The Calculation of phase diagram (CALPHAD) is carried out to develop Ni-Al-V-Nb-Cr systems that have high temperature stable D022 γ'' precipitation. Then, a high-throughput search is performed to explore novel Ni-based superalloys that are reinforced by L12 γ' + D022 γ''. On the premise of avoiding a harmful phase, V can make the alloy system produce a stable D022 structure γ''-Ni3V and Nb can increase the solvus temperature of γ''-Ni3V. In addition, Ni-Al-V-Nb systems have excellent compatibility with corrosion-resistant element Cr; therefore, Ni-Al-V-Nb-Cr systems are regarded as the basic alloy systems for developing novel Ni-based superalloys that are reinforced by γ' + γ''. Then, the high-throughput search is accomplished based on key material criteria, including phase composition, processability, and corrosion resistance. 13 alloys are selected from 7040 alloys as potential superalloy systems, which have a sufficient precipitation strengthening phase, a small harmful phase, a high solvus temperature of γ'', excellent processability, and high corrosion resistance. Two selected alloys were experimental validated on microstructures to prove the rationality of CALPHAD design. The design methods can guide the development of novel high-strength and long-term high temperature service Ni-based superalloys that are reinforced by γ' and γ'' and reduce the experimental cost and time consumption.