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In this study, Mg-13.2Gd-4.3Ni alloys containing continuous bulk-shaped long-period stacking ordered (LPSO), lamellar LPSO, and a small amount of eutectic phase were prepared, and the evolution of microstructure at different extrusion temperatures and its influence on mechanical and degradation properties as well as corrosion mechanism were investigated. Preheating before extrusion can effectively promote the precipitation of lamellar LPSO in matrix. EX400 with higher volume fraction of non-DRXed grains exhibited higher strength, which was mainly due to strong texture, high dislocation density, and high volume fraction of lamellar LPSO. The EX420 with higher volume fraction of DRXed grains showed higher degradation rate, which was mainly due to the higher density of grain boundary. The EX400 exhibited excellent comprehensive properties with tensile yield strength (TYS) of 334 MPa, ultimate tensile strength (UTS) of 484 MPa and elongation (EL) of 7.4%, ultimate compressive strength (UCS) of 638 MPa and compressive yield strength (CYS) of 443 MPa, degradation rate of 86.1 mg/cm2/h at 93 °C in 3 wt.% KCl solution.

The effects of Er and Ni content on the microstructure evolution, corrosion mechanism of Mg–Er–Ni alloys with different orientations were investigated. With the increase of Er and Ni content, the corrosion rate of extrusion direction (ED) increases, while transverse direction (TD) is reversed, which may be due to the distinct corrosion mechanism in different orientations, where ED and TD exhibit soluble and corrosion-resistant mechanism, respectively. Moreover, high content second phase alloy with a large deformation grain fraction and low levels second phase alloy with fully recrystallized grains have larger and smaller corrosion rate differences in ED and TD, respectively.

The poor anticorrosion property of magnesium alloys is one of main concerns prior to their various applications. In this study, an anticorrosive hydrogen phosphate coating was fabricated via the ultrasound-assisted chemical conversion treatment on AZ41 Mg alloy for concrete formwork. The coatings prepared by the conventional chemical conversion and hydrothermal treatment were also obtained as a comparison. Surface characterizations and electrochemical methods were carried out. Results show that the ultrasound-assisted coating obtained possesses a thickness more than 3 μm, which is thicker than the other two coatings. Moreover, the ultrasound-assisted coating presents a more homogeneous structure on the second phases, while the surface qualities of the other two coatings were significantly reduced due to the inhomogeneous CaHPO4·2H2O (DCPD) formed on the second phases in AZ41 Mg alloy. The ultrasound-assisted chemical conversion coating exhibits a good corrosion resistance even comparable to the hydrothermal coating. It exhibits a corrosion current density on the order of magnitude of 10−7 A·cm−2 even after the embedment of 96 h in the Portland cement (PC) system containing 3.5 wt% NaCl.

An anticorrosive CaCO3/MgO coating was obtained on AZ41 Mg alloy via rapid electrochemical deposition for the application of concrete formwork. Surface characterizations were carried out to obtain the morphology and chemical composition of the coating. Afterwards, long-term anticorrosion performance was investigated via electrochemical methods in the chloride-containing Portland cement system. Results show that the electrochemical deposited coating consists of an outer CaCO3 layer and a compact inner MgO layer. Pre-immersion in the electrochemical deposition electrolyte contributed to the formation of a dense coating. The pretreatment plays an active role in the formation of an inner MgO layer, which significantly enhanced the binding between outer CaCO3 layer and Mg substrate. The electrochemical deposited CaCO3/MgO coating with pretreatment shows improved anticorrosion property than the coating without pretreatment, which could be ascribed to the formation of the dual-layer structure. Additionally, corrosion mechanism is suggested and discussed for the CaCO3/MgO coating.

The Mg–Er–Ni alloy with comparable strength and solubility was prepared by controlling the Ni content. The mechanical properties and corrosion mechanism of alloys with long-period stacking ordered (LPSO) phase, as well as those with both LPSO and γʹ phases, were investigated and clarified. This study focused on investigating the underlying reasons for the high mechanical strength and fast corrosion rate of the Mg–13Er–3Ni alloy with LPSO and γʹ phases. The highest corrosion rate of the Mg–13Er–3Ni (wt.%) alloy is not only associated with the high volume fraction of the LPSO phase, which provides a larger zone for the corrosion cathode rather than forming a corrosion barrier, but also linked to the introduction of the γʹ phase that forms new sites for galvanic corrosion and avoids the formation the Er2O3 corrosion product film with corrosion-resistant. Moreover, The high mechanical properties of Mg–13Er–3Ni alloy are mainly attributed to the texture strengthening, dislocation strengthening and the second phase reinforcement that were caused by high volume fraction of LPSO phase and the precipitation of lamellar γʹ phase in Mg matrix. Generally, Compared to the Mg–13Er-1.5Ni (wt.%) alloy, the corrosion rates and mechanical strength of Mg–13Er–3Ni (wt.%) alloy were increased significantly by 302.8% and 50.3%, respectively, by coupling the LPSO and γʹ phases. Its ultimate tensile strength of 445 MPa and corrosion rare of 128.5 mg cm−2 h−1, which provides a new high strength and rapid corrosion Mg alloy materials for fracturing tools application.

Magnesium phosphate cement (MPC) is a promising alternative cement. However, the rheological property of this new binder is still to be explored. In this study, Response Surface Methodology (RSM) was adopted with Central Composite Design (CCD) to establish mathematical models describing the rheological characteristics of MPC in terms of initial mini slump (Y1), mini-slump loss (Y2), yield stress (Y3) and plastic viscosity (Y4), as a function of three independent variables, namely, water-to-solid ratio (W/S ratio, X1), MgO to MKP ratio (M/P ratio, X2) and borax dosage (X3). The results show that the M/P ratio and borax dosage could significantly affect the yield stress and mini-slump loss of MPC, while the W/S ratio was the significant coefficient influencing plastic viscosity and initial mini slump. The numerical optimised values of X1, X2 and X3 were 0.280, 7.528 and 0.170, respectively, and an MPC paste with desirable rheological characteristics (Y1 161.858 mm, Y2 11.282, Y3 0.680 Pa, Y4 0.263 Pa·s) with the highest desirability of 0.867 can be obtained.

The fabrication of high-performance cement-based materials has benefited greatly from the extensive use of graphene and its derivatives. This paper studies the effects of graphene sulfonate nanosheets (GSNSs) on sacrificial cement paste and mortar (the tested materials) and other siliceous sacrificial materials, especially their ablation behaviors and mechanical properties. Decomposition temperatures and differential scanning calorimetry were used to examine how different contents of GSNSs determines the corresponding decomposition enthalpy of the tested materials and their ablation behaviors. Molecular dynamics was also used to clarify the mechanism how the GSNSs work in the CSH (calcium silicate hydrated)/GSNSs composite to increase the resistance to high temperature. The experimental results show that: (1) the contents of GSNSs at 0.03 wt.%, 0.1 wt.%, and 0.3 wt.% brought an increase of 10.97%, 22.21%, and 17.56%, respectively, in the flexural strength of siliceous sacrificial mortar, and an increase of 1.92%, 9.16%, and 6.70% in its compressive strength; (2) the porosity of siliceous sacrificial mortar was decreased by 5.04%, 9.91%, and 7.13%, respectively, and the threshold pore diameter of siliceous sacrificial mortar was decreased by 13.06%, 35.39%, and 24.02%, when the contents of GSNSs were 0.03 wt.%, 0.1 wt.%, and 0.3 wt.%, respectively; (3) a decline of 11.16%, 28.50%, and 61.01% was found in the ablation velocity of siliceous sacrificial mortar, when the contents of GSNSs were 0.03 wt.%, 0.1 wt.%, and 0.3 wt.%, respectively; (4) when considering the ablation velocities and mechanical properties of siliceous sacrificial materials, 0.1 wt.% GSNSs was considered to be the optimal amount; (5) the GSNSs contribute to the reinforced effect of GSNSs on CSH gel through the grab of dissociated calcium and water molecules, and the chemical reaction with silicate tetrahedron to produce S–O–Si bonds. These results are expected to promoting the development of new kinds of siliceous sacrificial materials that contain GSNSs.

Ultra-high-performance concrete (UHPC) has been used as an advanced construction material in civil engineering because of its excellent mechanical properties and durability. However, with the depletion of the raw material (river sand) used for preparing UHPC, it is imperative to find a replacement material. Recycled sand is an alternative raw material for preparing UHPC, but it degrades the performance. In this study, we investigated the use of graphene oxide (GO) as an additive for enhancing the properties of UHPC prepared from recycled sand. The primary objective was to investigate the effects of GO on the mechanical properties and durability of the UHPC at different concentrations. Additionally, the impact of the GO additive on the microstructure of the UHPC prepared from recycled sand was analysed at different mixing concentrations. The addition of GO resulted in the following: (1) The porosity of the UHPC prepared from recycled sand was reduced by 4.45–11.35%; (2) the compressive strength, flexural strength, splitting tensile strength, and elastic modulus of the UHPC prepared from recycled sand were enhanced by 8.24–16.83%, 11.26–26.62%, 15.63–29.54%, and 5.84–12.25%, respectively; (3) the resistance of the UHPC to penetration of chloride ions increased, and the freeze–thaw resistance improved; (4) the optimum mixing concentration of GO in the UHPC was determined to be 0.05 wt.%, according to a comprehensive analysis of its effects on the microstructure, mechanical properties, and durability of the UHPC. The findings of this study provide important guidance for the utilisation of recycled sand resources.

Ultra-high-performance concrete (UHPC) has received increasing attention in recent years due to its remarkable ductility, durability, and mechanical properties. However, the manufacture of UHPC can cause serious environmental issues. This work addresses the feasibility of using aeolian sand to produce UHPC, and the mix design, environmental impact, and mechanical characterization of UHPC are investigated. We designed the mix proportions of the UHPC according to the modified Andreasen and Andersen particle packing model. We studied the workability, microstructure, porosity, mechanical performance, and environmental impact of UHPC with three different water/binder ratios. The following findings were noted: (1) the compressive strength, flexural strength, and Young’s modulus of the designed UHPC samples were in the ranges of 163.9–207.0 MPa, 18.0–32.2 MPa, and 49.3–58.9 GPa, respectively; (2) the compressive strength, flexural strength, and Young’s modulus of the UHPC increased with a decrease in water/binder ratio and an increase in the steel fibre content; (3) the compressive strength–Young’s modulus correlation of the UHPC could be described by an exponential formula; (4) the environmental impact of UHPC can be improved by decreasing its water/binder ratio. These findings suggest that it is possible to use aeolian sand to manufacture UHPC, and this study promotes the application of aeolian sand for this purpose.

In this study, the pitting behaviour of a new corrosion-resistant alloy steel (CR) is compared to that of low-carbon steel (LC) in a simulated concrete pore solution with a chloride concentration of 5 mol/L. The electrochemical behaviour of the bars was characterised using linear polarisation resistance (LPR) and electrochemical impedance spectroscopy (EIS). The pitting profiles were detected by reflective digital holographic microscopy (DHM), scanning electron microscopy (SEM), and the chemical components produced in the pitting process were analysed by X-ray energy dispersive spectroscopy (EDS). The results show that the CR bars have a higher resistance to pitting corrosion than the LC bars. This is primarily because of the periodic occurrence of metastable pitting during pitting development. Compared to the pitting process in the LC bars, the pitting depth grows slowly in the CR bars, which greatly reduces the risk of pitting. The possible reason for this result is that the capability of the CR bars to heal the passivation film helps to restore the metastable pits to the passivation state.

The electrochemical behaviour for passivation of new alloy corrosion-resistant steel Cr10Mo1 immersed in alkaline solutions with different pH values (13.3, 12.0, 10.5, and 9.0) and chloride contents (0.2 M and 1.0 M), was investigated by various electrochemical techniques: linear polarization resistance, electrochemical impedance spectroscopy and capacitance measurements. The chemical composition and structure of passive films were determined by XPS. The morphological features and surface composition of the immersed steel were evaluated by SEM together with EDS chemical analysis. The results evidence that pH plays an important role in the passivation of the corrosion-resistant steel and the effect is highly dependent upon the chloride contents. In solutions with low chloride (0.2 M), the corrosion-resistant steel has notably enhanced passivity with pH falling from 13.3 to 9.0, but does conversely when in presence of high chloride (1.0 M). The passive film on the corrosion-resistant steel presents a bilayer structure: an outer layer enriched in Fe oxides and hydroxides, and an inner layer, rich in Cr species. The film composition varies with pH values and chloride contents. As the pH drops, more Cr oxides are enriched in the film while Fe oxides gradually decompose. Increasing chloride promotes Cr oxides and Fe oxides to transform into their hydroxides with little protection, and this is more significant at lower pH (10.5 and 9.0). These changes annotate passivation characteristics of the corrosion-resistant steel in the solutions of different electrolyte.

In order to prolong the service life of reinforced concrete structures in a severe marine environment, a novel alloy steel (00Cr10MoV) was developed. The passivation behavior of 00Cr10MoV steel in a simulated concrete pore solution (SCPS) was studied by electrochemical impedance spectroscopy (EIS). Furthermore, the influence of chloride concentrations and passive film on the pitting corrosion resistance of 00Cr10MoV steel was investigated using cyclic potentiodynamic polarization (CPP) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS). For comparison, conventional low-carbon steel (20MnSiV) and 2304 duplex stainless steel were also investigated. The results indicate that the pitting corrosion resistance of passivated 00Cr10MoV steel is significantly higher than that of passivated 20MnSiV steel. The formation of a protective passive film and the generation of dense Cr-bearing corrosion products of 00Cr10MoV steel are responsible for its high pitting corrosion resistance. [ABSTRACT FROM AUTHOR]

An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-resistant steel (CR steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was evaluated by various methods including open circuit potential (OCP), linear polarization resistance (LPR) measurements, and electrochemical impedance spectroscopy (EIS). Meanwhile, the 2205 duplex stainless steel (SS steel) was evaluated for comparison. Moreover, the passive film with CR steel was studied by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Atomic Force Microscope (AFM), and the Mott-Schottky approach. The results showed that the excellent passivity of CR steel could be detected in a high alkaline environment. The grain boundaries between the fine passive film particles lead to increasing Cr oxide content in the later passivation stage. The filling of cation vacancies in the later passivation stage as well as the orderly crystalized inner layer contributed to the excellent corrosion resistance of CR steel. A passive film growth model for CR steel was proposed. [ABSTRACT FROM AUTHOR]