Schematic diagram of controlling factor the SCC process for E690 steel in different solution. (The HE and AD/pitting effect lines represent the relative contribution of these two factor, rather than ...the real values.)
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•Corrosion of E690 steel in the local confined environment in seawater is studied.•Acidification of seawater and addition of thiosulfate increase the cathodic current.•Pitting corrosion occurs in the thiosulfate-containing, acidified seawater.•Hydrogen embrittlement dominates the cracking at low content of thiosulfate.•Occurrence of corrosion pits dominates the cracking at high content of thiosulfate.
Electrochemical corrosion and stress corrosion cracking (SCC) behavior of E690 steel in the aerated, deaerated, acidified and thiosulfate-containing artificial seawater are investigated. Corrosion product is transformed from a single iron oxyhydroxide layer to a stratified structure with an additional outer mackinawite layer after long-time immersion with addition of thiosulfate. The SCC process at low thiosulfate concentration (10−4 M) is mainly dominated by hydrogen embrittlement because of the thiosulfate-induced promotion of hydrogen permeation. At high thiosulfate concentration (10−2 M), occurrence of severe pitting corrosion leads to the highest SCC susceptibility despite that the formation of continuous mackinawite inhibits hydrogen permeation.
•The addition of graphene particles could decrease the breakdown voltage.•The addition of graphene particles could promote the micro-arc oxidation reaction.•Appropriate content of graphene particles ...could improve the MAO coatings structure.•Appropriate content of graphene particles could improve the corrosion resistance.
Ceramic coatings with different concentrations of graphene particles were prepared on 6063 Al alloy by Micro-arc oxidation (MAO) technique. Effect of graphene particles on the micro-arc oxidation behaviors and coating properties was investigated. The results showed that: The addition of graphene particles reduced the breakdown voltage and promoted the reaction of MAO. The MAO coating thickness and hardness increased with graphene particles. XRD patterns confirmed that all the MAO coatings mainly contained γ-Al2O3 phase, and characteristic peaks of graphene were detected by Raman spectra. The SEM observation indicated that the coating porosity was reduced with discharge holes plugged up when the content of graphene particles was more than 0.15g/L, and cracks appeared as the concentration was 0.2g/L. Electrochemical corrosion tests (polarization curve and EIS) showed that the corrosion resistance of the composite coatings with graphene particles increased greatly, and the best corrosion resistance was found in the coating deposited with 0.15g/L graphene particles. The same results of corrosion resistance were also verified by salt-spray corrosion test.
The interest of additive manufacturing (AM) Al-base alloys for lightweight applications, especially the novel scandium modified Al-Mg alloy is growing. In this work, the selective laser melting (SLM) ...of Al-6.2 Mg-0.36Sc-0.09Zr alloy was systematically investigated, with a particular emphasis on densification, microstructure and properties. An increased laser energy density leads to a higher densification level and a better the surface finish of the SLM samples. The surface exhibits a large number of oxides at the scan track interface and microcracks owing to the high Mg content. The x-ray diffraction reveals a (200) texture due to the preferential solidification in the direction and the diffraction peaks shiftto a higher angle after the laser melting owing to the Mg loss. The horizontal plane presents equiaxed grains while the vertical plane presents columnar ones with the aggregation of orientation. The microstructure exhibits alternately coarse and fine grain that beneath the weld pool is a fine grained band while the central zone of weld pool shows coarse columnar grains epitaxial above the fine grain band, which is caused by the segregation of Al3(Sc,Zr) particles in weld pool boundary. The microhardness of the densest part is directionally independent, which is much higher than cast alloy but lower than homogenizing annealed alloy. The maximal compression strength of SLM Al-Mg-Sc-Zr alloy reaches 390.25 MPa. The electrochemical corrosion property of SLM alloy is higher than cast one. Better understanding of the metallurgical mechanisms during SLM of the present alloy will help pave the way for designing SLM suitable Al-base alloys.
The purpose of this study is to investigate the effects of Mn addition on the microstructure, mechanical properties, and electrochemical corrosion properties of Al0.3CoCrFeNiMnx (x = 0, 0.1, and 0.3) ...high-entropy alloys. All alloys are simple face-centered cubic solid solutions. After addition of Mn to the Al0.3CoCrFeNi alloy, the lattice parameter and hardness increase from 3.591 Å to 3.611 Å and from HV141 to HV156, respectively. Meanwhile, the yield stress and ultimate tensile strength increase from 119 MP to 158 MPa and from 295 MPa to 371 MPa, respectively. The increase in yield stress is due to solid solution strengthening, and the increase in ultimate tensile strength results from the increase in work hardening due to the reduction of stacking fault energy. Polarization curves of the alloys show that the corrosion resistance slightly decreases after additions of Mn.
•All of the alloys exhibit an FCC polycrystalline structure.•Addition of Mn to the alloy increases the lattice parameter, hardness, yield stress, and ultimate tensile strength.•Solid-solution strengthening and work hardening are two mechanisms behind the strengthening.•The addition of Mn to the alloy leads to a slight deterioration of corrosion resistance.
•The Ti-6Al–4V alloy is fabricated by electron beam melting (EBM) technology.•The electrochemical corrosion behaviour of EBM-produced Ti-6Al–4V is investigated.•A larger proportions of β phase and ...ultrafine-grained lamellar α/β phases are observed in the microstructure of EBM-produced Ti-6Al–4V.•EBM-produced Ti-6Al–4V possesses slightly better corrosion resistance than the traditional wrought Ti-6Al–4V.
The electrochemical corrosion behaviour of Ti-6Al–4V prepared by electron beam melting was investigated in phosphate buffered saline and compared with those of traditional wrought counterpart. Electrochemical results showed EBM-produced Ti-6Al–4V possesses slightly better corrosion resistance than the wrought Ti-6Al–4V, which is attributed to larger proportions of β phase and ultrafine-grained lamellar α/β phases in the microstructure of EBM-produced Ti-6Al–4V. The β phase enhances the resistance of charge transfer, thereby reducing the rate of metal dissolving reaction; while the α/β phases result in homogenous distribution of alloying elements in different phases thus restraining the galvanic effect between α and β phases.
Wire and arc additive manufacturing (WAAM) technology was used for the fabrication of NiTiTa (2.5 at. % Ta) shape memory alloys (SMAs) for the first time, using commercialy available NiTi wire and Ta ...foil as the feedstock materials. The addition of Ta significantly increased the phase transformation temperatures, leading to a room-temperature microstructure composed of both B19′ martensite and B2 austenite, and (Ti,Ta)2Ni precipitates distributed at the grain boundaries. Compared with the WAAM fabricated NiTi counterpart, the corrosion potential (Ecorr) of the NiTiTa material increased from − 0.55 to − 0.44 V, while the corrosion current density (Icorr) decreased from 1.90 × 10−6 to 4.2 × 10−7 A/cm2. The X-ray brightness increased from 19.6 to 56.4 %. These results indicate that the addition of Ta can enhance the corrosion resistance and X-ray visibility of NiTiTa parts. Furthermore, the WAAM fabricated NiTiTa material was able to retain a stable superelastic response under 10 loading-unloading cycles, highlighting the great potential application value in the biomedical field. Our work provides an innovative method for additively manufacturing NiTi-based multi-component SMAs through WAAM.
RuO2 is considered as the state‐of‐the‐art electrocatalyst for the oxygen evolution reaction (OER) in acidic media. However, its practical application is largely hindered by both the high reaction ...overpotential and severe electrochemical corrosion of the active centers. To overcome these limitations, innovative design strategies are necessary, which remains a great challenge. Herein, robust interface Ru centers between RuO2 and graphene, via a controllable oxidation of graphene encapsulating Ru nanoparticles, are presented to efficiently enhance both the activity and stability of the acidic OER. Through precisely controlling the reaction interface, a much lower OER overpotential of only 227 mV at 10 mA cm−2 in acidic electrolyte, compared with that of 290 mV for commercial RuO2, but a significantly higher durability than the commercial RuO2, are achieved. Density functional theory (DFT) calculations reveal that the interface Ru centers between the RuO2 and the graphene can break the classic scaling relationships between the free energies of HOO* and HO* to reduce the limiting potential, rendering an enhancement in the intrinsic OER activity and the resistance to over‐oxidation and corrosion for RuO2.
The robust interface Ru centers between RuO2 and graphene are found to boost both activity and stability for the acidic oxygen evolution reaction (OER), exhibiting a much lower OER overpotential of only 227 mV at 10 mA cm−2 compared with that of 290 mV for commercial RuO2 but a significantly higher durability than the commercial RuO2.
In order to improve the performance of the inner wall of the 316L hydraulic cylinder, FeCoNiCrMox (x = 0.2, 0.4, 0.6) high entropy alloy coatings were prepared by laser cladding. The effects of the ...Mo element on the phase, microstructure, hardness, and tribological as well as electrochemical behaviors of the coating were investigated. The results show that the coatings consist of the FCC phase. The FCC phase increases, and the grain orientation becomes more complex with increased Mo element content. The coatings are mainly composed of columnar and equiaxial crystals. Mo0.4 coating has the finest grain structure, resulting in the coating with a maximum hardness of 421.99 HV, 2.11 times that of the substrate. The nanoindentation test shows that the elastic modulus of the HEA coating increases with the increase of Mo content. The dry sliding wear test shows that adding the Mo element improves the wear performance of the coating. The wear volume loss and wear rate of Mo0.4 coating were the lowest, 12.242 mg and 2.88 × 10−4 mm3•N−1•m−1, respectively. In the 3.5 wt% NaCl solution, the polarization curves and EIS results indicated that adding the Mo element improved the corrosion resistance of the coating. The FeCoNiCrMox coatings significantly improved the hardness, tribological, and electrochemical behaviors of the 316L substrate.
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•The FeCoNiCrMox coatings on the inwall of 316 L tube were composed of FCC phase.•The addition of Mo element refines the microstructure of the HEA coating.•The addition of Mo element improves the mechanical properties of the HEA coating.•The Mo element improves the tribological and electrochemical behaviors of the HEA coating.
This paper suggests a novel method for the dynamic measurement and control of single-crystal tungsten micro-tip corrosion in order to address the problems of poor repeatability, low control ...precision, and the inability to set control tip diameters in the conventional single-crystal tungsten micro-tip electrochemical corrosion process. This technique begins by capturing experimental images using a video microscope, performing edge detection and contour searching to extract boundary information of the single-crystal tungsten micro-tip, and subsequently calculating and displaying the instantaneous tip diameter. Subsequently, a target diameter for the micro-tip is set, and when the detected value reaches this target, the software automatically cuts off the corrosion current. Experimental results demonstrate that this technique enables the production of high-quality single-crystal tungsten micro-tips with a diameter of approximately ⌀800 nm and exhibits excellent repeatability.
